The AM Forum

Notice how fast the standard UPS (uninterrupible power supply) dies during a power failure? Mine lasts about 5 minutes at most and then the computer dies.

I have several needs if the power goes out - my SDR receiver, the computer and other assorted low power 120 VAC uses.  This is for low power stuff, not for running the house.

I've been thinking of how to inexpensively assemble a UPS (battery and AC inverter) to extend the range by maybe a day or two during a power outage. A standard computer UPS doesn't cut it due to the small internal battery. But what if we used the same UPS and one or maybe TWO large deep cycle batteries? (two in parallel) I would think we could get a day or two out of it.

Before assembling it and spending some cash, I first wanted to see what others here thought of the idea. The only issue I see is if the UPS charger can handle the charging capacity if the battery starts from a low state. It's probably current limited and would take a long time to charge, but that's OK. Also there are dangers to having a lead acid battery in an enclosed room in the event of overcharging, etc.

I did a search and eventually came up with this excellent summary of what I want to do. Check it out:

http://revision3.com/systm/hackedups

I like the idea that this UPS will allow any plugged-in 120AC system to operate - it is not just a battery designed only for a specific piece of gear.

Another downside is that the overall system efficiency is not stellar. The inverter is maybe 90% and drops lower at lower power levels - is this true?  Either way, it is just for emergencies, so OK.

Ideas?

T

Hi Tom,

Glad to see you posting here again ...  had wondered what you were up to ...  know you were/are busy.

A couple of things.  Most UPSes are Modified Square Wave inverters,  not the best,  but should be fine for computers and the like.

Running Flooded batteries to a low State Of Charge is not good,  especially if it will take a long time to recharge them.  You might want to come up with a charger that will recharge the batts in 6-8 hours not days.

Most UPSes are designed for Gelled electrolyte batts,  and so the charger voltage is lower than ideal for Flooded batteries,  but it you redid the charger for higher charge currents,  you could fix the charge voltage.

Flooded batts DO outgas Hydrogen,  and Oxygen when they are becoming fully charged,  so venting outside is a good idea.  Flooded batts are considerably less expensive than Sealed Lead Acid batts.

There are some UPSes with real manly cababilities.  Some use 192 volt battery strings,  and can supply a number of Kwh for days.  Some of these do show up on the auction sites,  BUT,  of course,  the cost to re-battery them is high.

OR,  why don't you just do a Hybrid Grid Interactive system,  where you use PV to charge your batts,  and sell the excess PV power to the Grid?

With the WX many in North Central and NE  have had this year,  seems that many,  many folks there are thinking about backups -- and not just generators.  Opinions may differ,  GL,  Vic

Hi Vic -

Good to see you around.

I've done some more reading and see there are strapping pure sine wave inverters available cheap - that will run right off a deep cycle battery. Also I see some chargers that can be set to charge to a certain voltage and then turn off.  So maybe a combination of these components will be a better choice.  I like the modular approach.

Some of my stuff requires  pure sine wave AC, so glad you mentioned this point.

Thanks for the extra info, OM.

T

Tom,

For indoor use, you'll want the AGM (absorbed glass mat) sealed batteries. No outgassing or boiling over. I've been using a pair of PowerSonic 100Ah for several years now to power my gear set up in a 12 VDC UPS configuration. They can sit right in the shack under the desk or whereever with no worried about explosion or acid damage.

ldb

Yes, I've been seeing "AGM" mentioned a lot in my web reading, but wasn't sure what it meant yet.  100Ah is a pretty good capacity too.  I did a search and see they aren't cheap - but a very FB battery.

http://www.atbatt.com/product/3617.asp?utm_source=frog&utm_medium=cpc&utm_content=textlink-sealed-lead-acid&utm_campaign=frog1&utm_term=PS-121000&gclid=CPeIyfiezbICFQJp4Aod7gcANg

I have been reading about some guys running the stnadard flooded marine deep cycle batts in their house for 15+ years with no problems, as long as they take the precautions. Like, just a trickle charge, in a strong vented box, keep on the other side of the room, etc.

Well, I just bought a 300W 12V to 120AC pure sine wave inverter and a precision 1.25A battery charger, so just need the batt and case and we're golden. 


T

So, are you going to use the UPS circuit to detect the power failure and switch in the external battery and inverter? Or will this be a manually switched system? 

Just wondering, as I've considered the same thing my self, just to run critical items during an outage. 

Hi Ed,

First, this system is mainly as emergency power backup for a medical device needed by an elderly family member.

So I will have this device on a standard computer-type UPS in case of short term power outages or quick drop-outs.

But once the outage becomes longer, I will switch over to the inverter and big battery manually. I expect the inverter system to last at least 2-3 days.  I will also be able to transfer this system over to the SDR or computer if needed.

What kind of system are you considering?    Frank sent me a message suggesting a solar panel charging system. Interesting idea, since we have had outages last 10 days here.    We do have a 5 Kw power generator, though I hate to run it more than a few hours each day.

just a note from past experence.  you may want to check the duty cycle, most ups systems are not designed to supply backup power for extended times past what could be provided by their internal battery

I am thinking that a PV panel mounted on the roof, with several (3-4 high amp hour) sealed lead acid batteries and an inverter. Enough to run say just the gas heat on during an outage.  And maybe a little radio while the 'electrical quiet period' was in effect :)

Luckily the longest outage we've had in 18yrs here is 2.5 days, which was last octobers ice storm.  I had a Kerosene heater which kept the house warm and provided hot water for cooking & personal hygene.  We cooked most stuff on the gas grill (electric range is Not So Good) and a coleman stove.  Lights were hurricane lanterns.  Very 1850's-esq.   Still we were a lot better off than most folks with no generator (and some with).  In fact my Father in law stayed with us because we were warm and eating good.

Anyway, the gas appliances don't need a heck of a lot of power to operate, and it would be nice to keep the place warm and have hot water for a 48 hr period or so.

T,
I've been considering something along the lines that Ed is suggesting. I have a couple of 90 watt panels and a genset hook up that goes to a 10 position transfer switch. I figure taking 2 inverters and connecting them to L1 and L2 to power lights and any other light devices with at least 2 1000w inverters with batteries and batteries charged by the PV panels.  I haven't bit the bullet to purchase the inverters or the batts yet.  One thing I was considering was split phased synced inverter(s).  Haven't found anything yet but syncing may not be critical since I'm not interested in powering anything that is 240VAC.  Not sure if it matters or not. But would like to take some of the watts off grid so to speak. I would like some thing that is true sinewave vice modified just because.  

The thing that kills me though is the price of some of this "green" stuff.  The green weenies are as greedy as the non-green weenies. The prices are ridiculous IMO. I was thinking of just running 12v through the system instead of an inverter just to run 12v CFLs.  The 12vCFLs are $12.00 and higher. And those the buy them from these "green" places complain about them not lasting.  Seems silly when one can purchase a 120V CFL for a $1.50.

Yep, plus they use a simulated sinewave that may not work well for certain types of gear. So I decided to use a UPS JUST for the sudden shut down and then manually connect in the inverter and big batt.


Ed:  Sounds like you've got in covered. You'll be able to charge the batt using the solar even when power is down. I'll think about the sloar later on. It sure is getting popular.

Bob:  Two 1KW inverters is "awesome."  (as the kids say)  Are you going to use the simulated sine wave for more efficiency?

I've already committed to the 300w pure sine wave unit but still need a big batt.

What is a good deal on solar panels these days to handle a 1KW inverter unit?

T

T,
No, want true sinewave is what I want to go with.  I have many CFL's in the house and figuring that modified sine wave might wreak havoc with them like alot of other digital equipment. 

I picked up a pair of panels from a guy at work for a song and dance.  They seem to be in pretty good shape and can deliver said power.  Just need to get it into a battery bank.  I haven't been to receptive to the cost of AGM batteries and inverters just yet.  But I keep looking.  I'm hoping that if I can find the right deal for both in addition to cutting the light bill by 25% or so with just eliminating lighting cost it should be worthwhile. And any reserve can be used for shack purposes.

I have run five 92AH AGM batteries in parallel for over 9 years with no loss of performance. I charge @ C/10 and float at 13.65V for maximum lifespan. It is done with a current regulated laboratory type DC power supply. The float voltage must be related to battery temp for max. life. AGM batteries like clean DC power for charging. Throwing one in a UPS and letting that unit continually charge it to 14+ volts will ruin the battery. They are each tested once a year @100A for 30 seconds and have stayed pretty close. It is worth the extra cost to use AGM batteries for UPS. They are not designed for cranking.

I used an old ups inverter in my shack ( living space, not radio room.. :-) ) and that's all I had for AC power.
4- 110 amp-hour , 6v golf cart batts. ( 12v ) charged by 2- 55w solar panels.

I had one crucial motor that was pulse-width controlled..
The "modified sine wave" that the inverter in the ups claimed to have created havoc with that motor controller.
Was very jumpy and unstable.

I dropped a 25 watt incandescent bulb on the output, and it cleared right up, and ran smooth.
I guess a little resistive load is what it needed.

I have not done this for a few years now, but one of the local "recycler" companies around here does all electronics. They ship the stuff out by the truckload. Big machine to pull rare earth out of CRTs and bulbs... anyhow they get old computer stuff. I got a rack UPS from a server farm from them. It had two chassis. Each about 100lbs or more, about 6" high 19"w and 24"deep. One is the UPS + basic batts, the other is ALL batts!! That one is more heavy. 120vac power cord too. Some fairly large KW rating.

It ran when I tested it last, and I may have screwed the sealed batts by letting them run down... but I would check around if there are places like that around you, and schmooze a bit. Mine was like $75 bux. I figured the batts were worth the price of admission alone, even with bad ones in the pack... plus the base unit seemed to work fine... you might find them.

                   _-_-bear

As has been touched on,  to make real split-phase 240 VAC from smallish inverters,  they must be stackable,  and few are.

Current generatrion largish inverters  4-6 KW outupt can/do output 120/240 from a single unit,  and are stackable for more power.

There are a number of good True SineWave inverters on the market.  MorningStar makes a nice 300 W job, and Samlex/Cotek and several others are good units,  as I have read.

The following company (in which I have NO interest of any kind),  does a good job,  with reasonalbe prices on quality products,  and have been in the biz for a few decades supplying off-grid,  and grid connected parts/systems:

http://www.solar-electric.com/

They have a very active Forum,  with a number of reasonable and well informed fokls,  and those at all levels.

If the above link is not permitted,  just shoot me.

The only other thing that I'd add is that most battery charge controllers and all inverters,  anymore,  are SWITCHERS.  Many are LARGE switchers,  and DO generate  RFI.  For the most part CM Chokes do wonders,  as does running wires to/from them in metal conduit.

Our Grid is not very reliable,  and really cannot be,  even if well maintained,  when most of the distribution is above ground.  This is too bad, as it seems that many,  many folks are buying gensets,  fuel storage and PV/battery systems for these ever-increasing long power outages.  I would do the same ...

As has been mentioned here before,  a smallish Inverter generator can do wonders in running a refer,  TV,  AM radio and a few lights.  And could probably run weeks from fuel stolen from one's vehicle.  The little Honda EU-1000is,  here runs all of the above for a pint an hour or less of fuel.  Keeps my AM mode RX humming!  YMMV,  GL,  Vic

I had no idea that so many were using UPS or solar charged inverter systems.

Question:  How do we regulate the solar cell charging rate? Do we go into some kind of "smart" regulator?      I understand that battery charging is critical and even a trickle charge that stays on will kill a battery over time - especially the cheaper thin-plated car batt types.   

T

Hi Tom,

For smaller systems,  PWM type Charge Controllers do a very good job,  and create less RFI than MPPT CCs, which are switchers.

MorningStar probably makes the broadest line of CCs,  altho anyone wanting a large CC,  should look at the Midnite Classic.

A link to many  CCs:
http://www.solar-electric.com/chco.html

For sealed batteries like AGMs or,  especially Gell Cells,  a Battery Temperature is important,  unless the batts are in a very temperature stable environment.

Yes,  the problem with using an unregulated charger,  connected for days to months,  is as the battery becomes fully charged,  its voltage rises due to decreased charge current.  This,  is very bad over a period of time,  as this is when the water from the electrolyte is broken down into H and O2.  This is an ineficient process,  generates heat,  increases the SG of the electrolyte (which can corrode the + plate of the batt),  and in time will reduce the electrolyte level to the point where the plates are exposed to air.  These things ruin batteries.

When using sealed batts --AGM & Gel,  it is fatal to do the above,  as the water cannot (really) be replaced,  as the batt is sealed.

Flooded batts -- ones with removeable caps --  are less expensive than sealed,  and one can actually measure the Specific Gravity of each cell,  and determine how well charged the batts are.  Sealed batts are nice,  as,  normally they do not emit gasses,  and require less maintenance,  although determining charge level is more difficult.  Altho taking a sealed batt off charge and off discharge for 3-6 hours rest,   and measuring batt terminal V  is a good indication of charge state,  if batt temp is known  ...   and so on.  Yammering done,   GL,   Vic

Hi Vic,

Thanks for the precautions and extra info.  Yes, I'm learning that charging it correctly makes a big difference in longevity and even outgassing for safety.

I will most likely get an AGM battery and that shud do the trick. Put it in a vented batt box and also put a tray under it in case of spill. I've also seen it suggested to put a layer of baking soda in the tray so that in case of a spill, the acid gets neutralized. In case of an explosion, then that's a different matter... ;D

I shud have the 300w inverter and charger here in a day or so and will get the batt next. Might add some solar stuff later.

T

Back about 15 years ago I was at a hospital auction and bought a pure sine wave UPS for $5.00. It weighed about 150 lbs, lots of iron in it and it came with two 100+ lbs 96 volt battery packs which were dead. They had motorcycle sized 6 volt batteries in each 96 volt pack. This rig was good for 14 amps at 120 volts.

What I meant to do was use 4 of our expired24 volt lead acid aircraft batteries for a really big UPS. This had no switch over time, there was a 96 volt charging system which floated the battery packs and the inverter always ran the load. It sat in my basement for about 10 years and the aircraft batteries that I had went bad over time. I finally recycled the batteries and gave the inverter away.

Wish I had it back!

Hey Tom,

Am sure that you will find the 300 W TSW Inverter very useful.

The AGM battery has "all" of the electrolyte Absorbed in a Glass Mat.  So, in theory,  even if the case broke or was cracked,  no electrolyte would escape.  They are in a non-hazardous category for shipping.

It would be very rare for an AGM to outgass.  Should only occur when significantly overgharged for a period of time.

With a good,  V regulated charger it should do fine.  Most AGMs,  I believe,  have a catalyst recombiner that converts any gas back into water.  But for large overcharge events  there will be some outgassing,  as I read it.

Have never seen any of the large UPSes that run at HV.   Sure a lotta batteries,  but they can supply a lot of power for an extended time.   GL  Vic

Well, there ya go.

Went to Walmart and bought a 114 AH marine deep cycle battery for $109.  (not AGM)   The battery is pretty heavy, maybe 50-60 pounds?

The plastic container was $5.  It has baking soda at the bottom in case of acid leaks, to neutralize.  Notice the vent holes, even though this is a sealed batttery.

The inverter is a $109 300 watt pure sine wave unit and the charger is an automatic $65 "smart" type that shuts off at full charge.

I added a 20A fuse to the battery as well as a disconnect 20A standard light switch.

Tried it out for a few hours with both a light bulb and the SDR radio and all seems to work well.   I don't plan to use it often and should not see a lot of discharges, thus, should last for years.  Maybe add a solar panel charger later.

Total cost: About $290.


So, if this is a 114 AH battery and I am pulling 2A, then it shud last about 57 hours continuous, right?   114/2 = 57.  Consider the pure sine inverter efficiency of about 80% - then let's make that about 45 hours (almost 2 days) at 2A, 10-roger?   The full size computer will take more current, of course, and might last 12 hours at best.


Another use I just thought of...  it could be used to charge any device that uses a 120 VAC wall wart, like cell phone, lap top, etc..

Whenever I need it, just slide it out of the closet, and plug in whatever.  I'll keep the smart trickle charger on it to keep it topped off.
Shud work out FB.


T

I'll add a note of caution: most UPS units are very finicky about the frequency of the AC at their input, so if you're going to use a genset to provide long-term survivability, you most likely will not be able to use it to recharge batteries via a UPS.

I found out about this the hard way: those who want to read the long, sad story may visit https://groups.google.com/forum/?fromgroups=#!topic/rec.radio.amateur.moderated/Gs3wr8WgV6Q (https://groups.google.com/forum/?fromgroups=#!topic/rec.radio.amateur.moderated/Gs3wr8WgV6Q).

HTH.

Bill, W1AC

Bill the units from American Power Conversion that were built in Rhode Island have a "sensitivity" toggle on the back panel.  

Frequency variance is among the parameters the APC is designed to protect against. In applications where frequency isn't critical, you can step through low-med-high sensitivity to keep the UPS within a range you consider tolerable.

I have a generator and four of the APC units, from 450VA to 2200VA. All are on "low," and all remain in charge mode when on the genset, applying the load to the generator and not kicking out until I shut down when it's time to refuel.

To get the most power efficiency, I supply 24V from two marine deep-cycle batteries (YEAH TOM, WAL MART's the deal!) to a smaller APC, the 650VA job.  All it runs is the fiber optic box for the internet and TV, and the wireless router that serves Pam and my laptops, tablet and smartphones. Only one or two "load" LEDs light up.

I put a 1500VA on the board in the Radio Lodge (3 LEDs load) have a 1000VA here on the compooter and monitor (one LED load), and have a cool little switched UPS that runs the scope and the audio gear.  You turn on any of the connected devices, and the UPS powers up.

The APC put out real sinewave.  I came across a TrippLite, new in the box, and quickly got rid of it when I realized it's either a square wave or a "modified" sine wave. Nice way of saying dirty waveform.

Sounds like a well thought out emergency system. I like the idea that the generator is always charging the APC units.  Since none of us like to run a generator 24/7, this is an efficient way to "push-pull" it.

We have a 5Kw generator here, but have yet to set up multi-Kw APC units.  Maybe the next major power outage will give the required kick-in-the-ass.


Question:  What is the overall efficiency of a 2KW pure sinewave inverter - and a 300 w unit?  Do they get less efficient the larger they are?


T

I've heard the efficiency is worse with larger capacity, Tom, without knowing why.  

Can't say I've seen a chart.

APC used to put out white papers discussing the parameters, and efficiency seemed to rank lower for consideration than run time, which I seem to recall was usually spec'd at 50-70% max load.

Just thought of this -- The practical run time estimates didn't explore much about whether a customer might have many or few short duration startup peaks. So, in our setting, the transmit-receive environment might create less of a constant load than "typical."  I bet that's more of an issue than efficiency of the conversion circuit at various prospective load capacities.

The 2200VA that I've got takes FOUR 12 volt gel cells. Trying to remember if it's series @ 48V or series-parallel @ 24V.  I wonder if a 48V supply might improve efficiency at higher load ratings.  

There are various discussions about inter-cell problems as the battery banks get older. One impression I got was that it was better to have fewer but physically larger individual cells to create capacity, rather than a higher number of smaller cells (at higher voltage) for the same capacity.

I just read Bill's generator saga (the empty 5 gallon tank made me grin), and there's a lot of good information among the replies as well.

Also check the survivalist pages in "living off the grid."

Who was the guy in Hawaii on AM who ran his entire house and station on a generator, and otherwise did without electricity.  Used to work him on 10M. I think he passed away between solar cycles.

Ed, I'm curious: did the heater come with the house, or did you add it? If the later, how much did it cost when you added it all up? Would you do it again?

We were also out for a couple of days last October (which was when I learned the lessons I alluded to earlier), and I'm preparing for the coming winter, so thanks for your help.

Bill, W1AC

Just remember, there is a difference between a Marine STARTING battery, and Marine DEEP CYCLE batt.

But since you don't plan to discharge it on a regular basis, I suppose either one will do you fine.

Yep, I wondered the same thang when I saw it at Walmart. It was the only battery marked, "deep cycle" and with the price being only $109, I bit.

Can you tell from the picture if it's the less desirable cranking type?  The box said it was for boat trolling, etc., so I figggered it shud handle discharge cycles well.  Maybe not.

I once had a $400 LARGE floor sweeper battery in my truck for a 1500w solid state mobile linear. It lasted about two weeks and went soft. What a waste of money. So I will be careful to limit the discharges.


Paul, OK on the efficiency.  I guess it is best to err on the inefficient side of calculations. I imagine these pure sine wave units are power hogs. After all, just look how fast even a "modified" UPS dies when powering a computer.  So going with a big-ass 2200w unit like yours is a good precaution.

I plan to run this system tonight for eight hours on the medical machine to see what it does. We'll see if the Walmart can stay over 12vdc. It IS a very heavy batt, I must say, for only $109.

Bill, that was quite the story. That Oct storm was really a surprise. We lost power for TEN days. It wasn't really THAT bad cuz of the generator, but got old fast.

T

I'm following your battery power project with great interest Tom. I may try to duplicate all of the Vu "Area 51" technological breakthroughs after you elaborate on the results of your finished system.

Funny how that storm last October has affected all of us. Going without power for multiple days in the winter would be disastrous for the plumbing in most homes around here. We were lucky that a sustained period of warm weather followed that storm. I just finished up my generator project here (7500w/9500w peak) to allow us to run the furnace, well pump, refrigerator, freezer, and most of the outlets throughout the house. I figure that the daily usage in my house runs just under 3 bucks a day with CL&P and when I generate my own power it would cost me around 30 bucks in gasoline (@ 4 bucks per gallon) to run the generator 24 hours straight! Not that I would run the generator that way (my plan is 1 hour run and 2 hours off) but it gives some pause for thought about how cheap electrical power actually is.

Rob W1AEX

That's an amazing comparison between hambone and commercial power, Rob.  Yep, I always thought electricity was a bargain.  Just think how much energy you'd need to handcrank out enough to power your house.... ;D


Here's the customer reviews on my "EverStart MAXX-29 Marine Walmart Battery."  Looks like a fairly good review mixed in with some bummers.  Guess it's a OK deal for the money.

http://reviews.walmart.com/1336/16795213/everstart-maxx-29-marine-battery-reviews/reviews.htm

The key appears to be to use a "smart" charger that will shut off instead of boiling the batt to death.  And don't let the batt get drained to nothing.

T

It says "EverStart".  first glimpse would tell me it's meant as a Marine starting batt....

BUT,
Generally Starting Batts would only list the CCA rating, and not AH.

and Deep Cycle would list AH, and not CCA.

Yours has both printed on the label, AND the box mentions trolling...  so you're
likely ok.

I've used Wallmart deep cycle batteries in my moterhome for ages.  I'm not sure they all came from the same manufacturer.  I have no complaints about any that I've owned.  Lots of deep discharges and neglect but still provide reasonable life.  Typically after a few years a cell shorts out and I pick up another one.

I think the key is how the battery was maintained while on the shelf at the store. Don't know what the turn around time would be on a product like that but if it sits for a long period of time as it self discharges, can't be good. 

Good point.

Here's a piece of advice I read on the web and actually applied it to the Walmart purchase...

There were about eight of these Maxx-29 marine batts on the shelf.  I grabbed the first one and then remembered to look at the manufacturer's date code and pick the most recent one.  I noticed they all read, "04/2012."    But one in the back row read, "09/2012."   It's not much, but at least I gots one made only a month ago - pretty recently.  Why should I pay the same price for one that was almost 6 months older and probably sat dormant without a boost charge?


T

The word "trolling" on your battery Tom clinches that it's a deep discharge type. Ya done good.

A starting battery can deliver high current for short bursts as a function of its plate construction. It's bad to fully discharge it.

A deep cycle battery can deliver a long discharge to a lower voltage without damage.  But if you try to draw high current, the plates can overheat on the discharge and warp.

There's a loose-leaf book hanging on the battery shelf at the Wal-Mart near Annapolis where lots of boaters buy the marine types.  It 'splains the differences in good detail.  The deep discharge type, says their own book, can withstand about 85 full discharges before performance starts to degrade.

The ones in our area are made by Johnson Controls, although I saw some Exides among side-terminal automotive batts they were selling.

A disgussion of characteristics is here and other places. Intressant.

http://evbatterymonitoring.com/WebHelp/Section_2.htm (http://evbatterymonitoring.com/WebHelp/Section_2.htm)

You also done good by getting the latest manufacturing date on the shelf. Consumer Reports, in its latest issue, said to avoid those that have been sitting for more than 6 months.  They tend to sulfate, a kind of scum that gets on the lead plates. Partially reversible with use.

I once had a Lucas motorcycle battery that sulfated. The local rep questioned whether my charger was any good, but since it was within warranty he replaced it with fresh stock.

Tom,

I think you'll be happy with the WallyWorld EverStart batteries. I've been using the combo start/troll batteries for years in my vehicles. They've been starting the V-6 in the Dakota for nine years now. I just put the third one in about a year ago. The radios get left on sometime for a couple days if I forget to turn 'em off. And the batteries don't grumble at all.

One tip for longevity in a deep cycle battery, more so with AGMs, but applicable to all. Don't draw 'em down to where they're completely flat. A good rule of thumb is to only use half of the Amp-hour rating. So, from a fully charged 100 Ah battery, I'll only take 50 Ah before I charge it again. That makes my two 100 Ah AGMs in parallel a functional 100 Ah battery. They're about 8 years old and still working fine. They usually do backup duty at the house charged with a West Mountain Radio Super PwrGate, but they've gone on many exercises where they were charged with PV panels while being used.

ldb

Well, looks like the Maxxxx-29 will be FB then.  Tnx for the info.

Larry, OK on the 50% discharge level precaution.   Eight years of use is amazing. We get what we pay for, especially with those AGM batts.  

Question: What is the best way to "know" how much a battery has been discharged?  

I could see if we used a power meter that created an AH record, or had a constant load for a number of hours.  But is there a simpler way like measuring its voltage to get a reasonably accurate indication when 50% discharge has occured? (without doing an acid specific gravity test)  I wonder if, say, a batt eventually dropped from a starting 13.8 to 11.5V under load, could this be a signal to stop and charge it?  

During emergencies, we tend to get sloppy and could easily push a battery too far into discharge.

Update: Whoops, I just clicked on your battery monitoring link Paul. That looks filled with info on my question. It will take some time to digest. Tnx.

T

  Tom,  An old rule of thumb used when I was in the UPS business 30 years ago was to kill the UPS when the batteries dropped to 1.75V / cell. That would be 10.5V with a 12V battery. The deep cycle lead acid batteries of that day would take that repeatedly without damage. In fact the UPS systems we designed (up to 10 KVA by paralleling 1KVA modules) were rated upon that variable, and automatically shut off.

   The UPS systems of that day were quite crude by today's standards, some examples:

We evaluated a "step sine wave" inverter from a competitor. All them TO-3 transistors on a huge heatsink was impressive. What was neat was the failure mode where the TO-3 cans in a row acted like Gatling gun as the exploding junctions would melt the metal transistor cover, and throw sparks two meters away.

Another inverter was a self commutating SCR unit rated 10KVA. It kept blowing $100 "semiconductor fuses". So what is a "semiconductor fuse"? Seemed to be a 50 cent fuse relabeled and priced 200X. Both popped after the semiconductors they were "supposed" to protect fused.  :( Anyway after we blew all the fuses, we (not me) bypassed the fuse...I still remember the 1 awg wires twitching, and the thirty series 2V, 100 AH batteries melting down in a "China Syndrome". What a mess!

We came up with a ferroresonant inverter with the first IR power fets (IRF-100) driving two power NPN transistors, making 1KVA modules that could be stacked. Took 1150 watts to make 1000, but that 150 watts loss was always there, typical of a ferroresonant transformer. This is where I learned that ferrresonance has nothing to do with resonance since the inductor in the L-C tank is a saturated reactor. The resulting "quasi-sine wave" was quite good for the day, and tolerated better by loads than today's step inverters that peak at 150 vac, and yet with a narrowed pulse width to provide 115 vac RMS.

Sorry for the rambling, but UPS systems have a colorful history,

Jim
WD5JKO

Tom,

I use a meter similar to this one:

http://www.powerwerx.com/digital-meters/dc-inline-watt-meter-power-analyzer-bare-wire.html (http://www.powerwerx.com/digital-meters/dc-inline-watt-meter-power-analyzer-bare-wire.html)

Mine was made by Medusa Research and I think they're paws up now, but "Watts Up", "Doc Wattson" and the folks above all make similar units. And all are for sale at the Powerwerx site.

ldb

The Kerosene heater I got from my Father-in-law for hauling it off.  It did need about $30 in parts and a few hours work to make it right.  it's actually a large "portable" unit that supposedly doesn't require venting, which was a plus. I did notice a slight kero smell but that was probably due to a tiny leak I later fixed. That stuff does seem to take for ever to evaporate.   My FIL had used it for years in his duplex when my wife was a girl living there.

  It did heat our small 3 bedroom ranch ok, though the furthest room was a bit chilly like low 50's while the rest of the rooms were kept mid to high 60s.  It got hot enough on the top to actually simmer water, so we put the largest pot we had up there and that was our HW "tank".  We simply filled the sinks from that with ladle.  The girls had to have a bath, so we just heated as much water as we could at once and filled the tub.  All this by the light of hurricane lanterns. All very 1850's lifestyle.

This drove the need for short term 'backup' power so we could have a little light, run the hot water heater, and a small fan to push the warm air around the house a bit better. 

3 marine 'deepcycle' batterys, 1.5KW inverter, battery charger.  Probably <$500 all told, since needs are short term based on history, this aught to be fine.  We don't loose power often or for very long (usually, but now I've jinxed that!). this won't run a large appliane alone (startup current being a problem).   I didn't know about stacking the inverters, as that would probably have been a better route instead of trying to find on large one.

All available from the local autoparts store too I might add.

PV panels would be my next Upgrade.  Looking for power vs budget vs size, and have to convince the XYL that we would actually need them up on the roof.

Vely, vely nice device, Larry.  I might just order one today.  Didn't dawn on me that these were available - thought I'd need a power meter like on the outside of the house... :o   Tnx for the tip.


Jim:  OK on 1.75v per cell or 10.5V being the rough 50% point to recharge a batt.  If I don't get one of those power meters, I'll just hook in a pair of simple volt and amp meters and use 10.5V as my guide.

Yep, you had some crazy experiences when UPS was young. Reminds me of the early days when experimenting with big class E rigs.

T

Just to expand on my post above. Anyone remember Two Guys department stores? When I was a teen I worked in the automotive department of a Two Guys department store.   We were tasked once a month to charge the batts for about 1 hour a piece.  We also had batts we "built". They came dry and had to add the electrolyte and apply a charge to get them sale-able.  I think that's a thing of the past these days. But we rarely had a battery come back as failed.

Bob the dry charged battery takes me back to early military radio days.

Came across a few Willard Exide ER-40-6 units, brand new, in their sealed foil wrap, with an outer cloth packing, and a sealed bag with a measured bottle of H₂SO₄ alongside it.  

Around Korean War vintage, I think the date code was 1953.  We filled them up 20 years later and I got at least 7 years of use out of them running wall-mounted emergency lights that our local school had thrown out.

What was cool, and I'm looking for a picture, is that the housing was clear plexiglas, so you could see the charging bubbles and the electrolyte level at any time.

(http://www.powerstream.com/1922/battery_1922_WITTE/batteryfiles/fig.178.jpg)

Closest I can find are separate cells in an outer housing.  I also had some ER-40-2 that these resemble.  I think the "40" is amp hours, and the final digit is the voltage of the cell or the pack.

I installed this in 1999, preparing for Y2K. The batteries are 6v 340ah, 4 ea for 28vdc. The inverters are Trace DR1524 1500W with battery chargers . The two are connected to supply 110/220vac,  needed to be able to run the deep submersible water pump. The original batteries are still doing okay. I had a second set of Trojan 6v 350ah, but they only lasted about 7 years. They were wet when I got them, which as mentioned, you really do not know how long they were sitting. The set in service now were dry when I got them, and cost less than the Trojans. The wind generator is a Bergey 1.5kw, 10' blade diameter. Three phase ac at about 150 to 180 volts with no load. The run from the wind generator is approximately 500'. A three phase transformer supplies about 28volts to the charge controller.

We have had three close lightning strikes in the last three months.  Two TV's, two Directv dvr's, modem/wireless router, the wind generator charger controller and maybe one inverter. The wind generator is okay, and no radio damage. I can't really complain, as this is the first lightning damage to the wind generator system.

Ken
w3kmp
SW PA

Pretty nice wind set up, there, Ken.

I've looked into a few 5-10kw systems myself, but always stopped short when I found out the initial investment - but even more importantly, the cost of replacing the batteries, the lifetime of the generator itself and possible weather damage.  It always made the power grid look cheaper. Of course, yours being a smaller 1500 watt  emergency system, that is a big consideration too.  How do your system expenses calculate out if run continuously?  



**  TEST UPDATE **

Well, I did some test trials on the 114 AH battery inverter system.  Added a current and voltmeter.  Last night I ran the medical machine plugged into the 120VAC inverter. The 13.8 vdc battery draw was  5 amps, 10 amps peak. This is about 96 watts or 7.5AH.

After 9 hours, (68 AH total) the machine continued to run FB and the battery voltage had dropped about 1.8 volts to 12.0 VDC. This is quite acceptable considering our estimate of 10.5vdc for a 50% discharge.

The battery is now recharging at a 1.25A trickle, so should take maybe 54 hours to recharge itself at that slow rate.

I would say the system works as expected and maybe slightly better.

T

Tom,

Seems that your back-up power system is working well.

(Made a post a few days ago which disappered,  so ...)

A couple of things.  The battery voltage reading is a poor way of determining Sate Of Charge of a battery.  This voltage varies  a large amount depending on any currents into/out of the battery.  Personally,  I'd never,  ever discharge any 12 V lead-acid battery to 10.5 V.  At that point it is DEAD .. errr,  fully discharged.  But this depends upon the discharge current.  Some of the pro level inverters have a Low Voltage Disconnect menu setting.  Normally  the inverter would wait a certain amount of time before shutting off at the set voltage.  Generally the "standard" 10.5-ish LVD on many inverters is really to protect them from excessive currents,  as,  as the DC V in is reduced,  the current increases to maintain the AC output voltage.

The common wisdom about the best value in batteries is the Golf Cart (GC-2)   batteries.  These are 6V @ 225 AH nominal,  and it has been mentioned elsewhere that one can find them at Sam's Club for example for less than $100,  with any core trade in.  I do not go there,  but other similar stores could have a similar value.  These are tough,  real Deep Cycle batts.

RE  TSW inverters vs standby (tare) power.  The large-ish TSW in use here consume 20 watts with no load,  but,  in 24 hours,  the pair burn 1 KWH,  so it does add up.

And something,  believe  VJB Paul mentioned is very true.  Try to run only a single string of batts.  If more capacity is needed,  find larger capacity batts.  This can seem to be more expensive than a number of batts in parallel,  but is it almost impossible to get the batts to share charge/discharge currents well,  and one bad batt can drag the rest of the bank to its knees.  More Pills is not more better.
Just opinions,  GL,  Vic

Tom,

In the summer of 1999 the cost for the complete project was about $5000. The system has been trouble free, with the exception of the 1 amp fuse in the charge controller, that has been replaced probably 30 or so times.
This was due to lightning induced transits. With the cost spread over almost 12 years, I feel that at $400 a year it has been acceptable. As far as electrical utility cost savings, no clue. I am amazed that the original set of batteries are still holding up. The generator only has three tapered roller bearings, one for the generator to swivel on, and two for the generator itself. The bearings should be repacked, and the blades inspected. One inverter has gone inop, and the generator charger unit took a good lick from the last lightning surge. The generator 3 phase output is fine. Actually I thought that the generator would have had a lightning strike by now. The terminal strip for the generator feed wires on the step down transformer had actually arced over, but only the 1 amp fuse blew. Batteries are around $300 ea, and the charge controller is unavailable from Beregy. Repair to the one inverter is most likely high. There is a lot of inverters and charge controllers available from China. About three years ago in February we had the power out for 7 days. We have a 5000 watt gas generator, and I would run it during the day, which supplied the house and charged the batteries, and used the batteries and inverters during the night. I had 3 55 gallon drums of gas from 1999, and probably used close to 40 gallons for the week. I am thinking about getting a natural gas conversion for the gas generator. If the SHTF, the natural gas supply would most likely be one of the last things to go. We are surrounded by new Marcellus  gas wells.

The other problem, I am getting too old for climbing towers, and moving 125 pound batteries around.  Had five neck vertebra fused in March, and I am still not back to work. Hopefully, I should be good to go by the end of the month.

I can confirm Vic's comment about not paralleling batteries. I finally just used one bank or the other. The golf cart batteries may be the way to go.

Ken
w3kmp
SW PA

Hi Vic,

OK on 10.5vdc being too low.  Good to know.   Looks like I'll be able to get away with a min 12.0 volts based on last night's test.

The golf cart batteries sound interesting. They would have been X2 the AH of my present batt, but in series. Maybe next time.

OK on the big inverters idling at 1KW per day. Guess the smaller choice was correct for this system. Then again, we usually don't keep the inverter idling when not in use.


Ken,

$5K is not too bad for your whole system, especially since yours has lasted 12 years with few minor problems.  Yep, the lightning strikes wud concern me too.  


BTW, I've been seeing a lot of talk about switching over to natural gas cuz it's so cheap. Even the CT governer is talking about it. What some don't realize is price has come down to very low levels over the last year.  It had peaks over 600% higher only two years ago. Those users at the time were hurting bad.

It's like switching over to oil when it was $10/ barrel and freaking out when it rose 1500% later on. Maybe  the best way to play it is have a few fuel combos to draw on when price is best.  

I use coal here every winter and go thru only about  200 gallons of oil per season.  Coal has been slowly creeping up, however, but BTU value still better than oil.

T

12v vs. 24v vs. 48v inverters.  What's the advantage/ disadvantage.

Each time you double the input voltage, the input current is halved. Thereby giving more runtime from a battery bank of the same Amphour rating. Assuming equal loads and efficiencies.

Generally,  the more power that the inverter system needs to supply, a higher  battery voltage is chosen.   Higher battery voltage yields higher system efficiency --  less current from the the battery.  This yields lower IR drops.  Also,  the battery charging system runs at lower current on higher battery V,  so the charging system is also more efficient.

For Solar battery chargers,  the maximum charging current is fixed,  so doubling battery V can allow twice the charging power for the same charger output current (within limits).

A 1000 watt 12 volt inverter could easily demand more than 100 DC Amps from the battery.  Many high power 12 V inverters are specmanship hype IMHO.

But for Tom Vu-san's backup system, he does not need tons of power,  and 12 V is perfectly reasonable.

The off-grid power system,  under construction, for AM sloop (not Tall Ship) power levels,  below,  FWIW.  Vic

The lower voltage systems have higher currents, and as already pointed out, this creates power loss from conductor resistance. Another factor is the semiconductor transistors used where the "ON' voltage needs to be a very small percentage of the applied DC voltage. If the on voltage is more than a few % of the applied DC voltage, then the overall system efficiency suffers.

So these days you can get FET's with < 10 milli-ohm on resistance. But consider 100 amps at .01 ohm and we get 1 volt "on" voltage. This approaches 10% of a 12V battery that is near low voltage cutoff. The other choices sometime used is the IGBT where the zitter has FET input and transistor output. Here these can be sized to the application, and get approximately 1/2 volt VCE SAT ("ON" voltage).

With switchmode power supplies, the rectifiers used also are a big factor. A 5V DC supply will always be less efficient than a 12V supply. A silicon diode used in the rectifier might drop around 1 volt whereas a Schotky diode will drop about half that.


Case in point, some years ago I 'updated' an old Ham DC-DC converter that took 12V and made 800, and 300v to run a tube type transceiver in a mobile enviornment. I made a drive PCB using a PWM chip, and replaced the four PNP Ge transistors with power FET's. The output was regulated (LV B+), and everything. The part I did not anticipate was with PWM, the FET 'On' state current was over 50 amps when the average DC draw was around 25 amperes (50% duty cycle) off the 12V battery. So with the FET RDS "ON" resistance, and 50 amps, my "ON" voltage was over 2 volts, or 2 X 50 = 100 watts whenever the FET's were "ON". In contrast, the old Germanium PNP's had an "ON" voltage at just under 0.5 volt. I keep meaning to update this unit with more modern FET's in the hope of getting the "ON" voltage back to where the old PNP's were at.
Jim
WD5JKO

Question:

When charging the batt using  the 1.25 A  "smart" trickle charger, the battery tops out at 14.4 vdc and then the charger shuts off.  I then disconnected the battery so that there was no external draw on it. Within a day I measured the voltage and it had dropped down about 2 volts to 12.5vdc.

I then put the trickle charger back on it and the batt charged back up to 14.4v within 3 minutes.  What's that all about?   There's obviously not much power being trained internally if it takes only 3 minutes at 1.25 A to climb 2 volts.

Does the batt's cells naturally want to be at 12.5V?  So why is the trickle charger designed to top it off at 14.4v if it cannot hold a charge there?  I would think this is overcharging - and could shorten life if I kept the charger on all the time set at 14.4v, no?


On the last inverter test, the batt dropped down to 12 vdc after a healthy night of power draw. So maybe it's really dropping only about 0.5 volts.  (12.5 - 12.0)

T

Tom,

   What you describe seems about right. A fully charged lead acid battery AFTER it has been off the charger for a while will revert to about 2.1 volts per cell, or 12.6V for a six cell battery. The charge too voltage, and float voltage are described in detail here:

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

"Lead acid batteries should be charged in three stages, which are [1] constant-current charge, [2] topping charge and [3] float charge. The constant-current chargeapplies the bulk of the charge and takes up roughly half of the required charge time; the topping charge continues at a lower charge current and provides saturation, and the float charge compensates for the loss caused by self-discharge."

Way back when on my UPS escapades, we designed the charger as above, and the  had a long CMOS timer to indicate need for a cycle test at 1 year. So after 1 year unused at the float voltage, pushing a button ran a one time discharge, and then the charger topped up the 60V battery pack to 2.5V / cell. This seemed to help keep the battery back A-H rating from declining over time. Afterward the float voltage was reduced to around 2.25 volts / cell for another year.

If you have a two stage charger where the float voltage is on the high side, then it might be best to unplug the charger after a couple of days. You could hook it to a timer to turn it on for a while every week or so.

Earlier in this thread you asked about how low to go when the batteries were at 50% capacity. I said to stop at 1.75V / cell, or 10.5V for a 6 cell pack. What I said was true when the batteries are near 100% used up. The answer to your question depends on the battery you got, and the discharge rate. Paul, in post 35 gave you a link, and I post a graph of that here. It shows 80% gone at about 1.85V / cell. Also at around 1.7V / cell the curve goes vertical, and here the battery voltage drops like a rock. Don't go there.

Sorry for the confusion,

Jim
WD5JKO

Hi Tom,

As batteries near fully charged and fully discharged the internal R increases by a considerable amount.   This higher R at the charge/discharge end-points causes the battery V to change fairly quickly with a given amount of current. This is what causes the small charger to drive the battery V up very quickly with its low current.

An exception to this is when doing an Equalization charge (EQ).  This charge for Flooded batts increases the charge V to about 15.5 V for 12 V flooded batteries,  and the current required to reach this overvoltage can be quite high -- limited by the charger's current capability.

EQing a battery is used to attempt to overcharge the good cells to try to fully charge the lower SG cells in a string of batts.

BTW,  here is some interesting info on batt V vs SOC,  and vs current for charge and discharges and so on.  It is from Home Power mag:

http://scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

At some point,  you might want to consider a charger that has more current capability,  and one that has a Remote Temp Sensor to compensate charge voltage for the measured battery temp.  There is about 5 miliivolt change in batt V per batt cell in series,  per degree C,  IIRC,  so it can be significant,  even on 12 V banks.  GL,   Vic

Back when I was in the Navy I spent a couple of years on a couple of WWII diesel/electric submarines. That was a battery system! Two 126 cell batteries @ 1 ton per cell, charged by four Fairbanks Morse 10 cylinder opposed piston two cycle diesels @ 1,600 HP each. During equalization charges you could boil the water in the rinse side of the sink with the immersion heater that was there to keep the rinse water hot. Propulsion submerged or surfaced was by two 2,600 HP electric motors. Switching for all this was by BIG multi-bladed knife switches activated by big chromed levers back in manuevering. If you forgot to turn down the motor fields during a forward to reverse manuever you go a BIG fireball, melted copper ran down into the bilges through the slag chutes and you were the known as "Fireball" from then on!

Good times!

Thanks for the extra info, guys.

The links were excellent. I see there is a lot more to charging and maintaining batts than I thought.

I will put the system in the closet and put a timer on the trickle charger  to turn on every week.   Though the trickle charger claims it shuts down and automatically maintains the batt itself. I'll have to read about this unit some more.


OK on the "FireBall."    The captain probably got very POed... :-)


Thanks again for the advice.

Later -

T

I went to a specialty marine store for two deep cycle 100Ah batts. I asked them if they were maintained while on the shelf.  They said yes.  Got them home and they were almost dead. Terminal voltage unloaded was less then 12v. Put both on 2A charger to slow charge them and it took 3 days each to bring them up. I haven't hard load tested them but they seem to be holding a nominal terminal voltage 2 days later.

Looking at the batts neither one of them had a date code but got a 1 year 100% warranty. We'll see what happens.

I think there is a federal law out there that states that a battery (lead acid) cannot be sold if it is over six months old. I doubt there is any retail facility that is equipped to trickle charge batteries on the shelf. Again that is another problem with the release of hydrogen gas without the proper ventilating equipment. While I am not an expert on batteries, I did make my living selling and servicing industrial batteries for over thirty years.

A possible deep cycle battery source for hams that are cheap like me...

I know someone who works for a business that services power wheelchairs, scooters, and the like. They cover a large service area and once they drive a few hours to a handle a customer complaint... well, they have to sell them something. How about new batteries? The old batts are taken back to the shop, put in a pile (no pun intended) in the back room, and eventually scrapped.

I have managed to get in between their back room and the scrap yard. I give my buddy $10 a piece when he's sent to get rid of the old batts. The majority of them are in very good condition, with recent mfg dates, and have many cycles left in them. The few bad ones, I can scrap myself for a "refund". Of course I'll eventually get to refund them all. Starting to sound like "free batteries".

I now have enough 12V batteries to make a "doomsday prepper" proud.  Mostly 35 AH, some 55AH, and a few 75AH (the physical size of a car battery). My source recently switched from gel cell to AGM style as they're get better pricing on them now. Great batteries, the AGM's. They're "no spill" (even if the case is broken) and that's a very good thing when the batt is in the house. Also most AGM's are the recombinant type and vent very little hydrogen gas compared to a wet cell.

So the thought here is to find your local power chair service center and pay them a visit at lunch time. Find to the youngest guy working there. He's probably the one that has to schlep the old batteries to the recycler. "Hey kid, you got any used batteries you don't need? I'll give you a few bucks to take them off your hands." It's old school ham radio part scrounging I'll admit but, as they say, it's so crazy it might just work.

For my part I'm hooking up the batts (2 at a time for 24V) to a 1000VA UPS with PV's to recharge them. The system is almost ready to go online (well, off-the-grid anyway). Just a few more wire nuts and... free power! I like the sound of that.

What are the pros and cons of recharging a deep cycle batt with a power supply vice batt charger?  Would there be any issue charging a battery with a power supply that has adjustable current limiting and adjustable voltage output?

Bob,

Just be very careful.  Many of the Linear PSes  will fry regulator guts if powered off with the battery connected,  and some might even do that if the Vout setting is much below the batt terminal V.

A series diode should protect any PS against this.  Most switchers should be immune to this frying,  but why take the chance?

Please do not ask my just how I know this issue with Linear Lab supplies.

Good Luck with the WX.   Vic

Maybe I can help here. The maximum start rate on lead acid batteries should never 25 amps per one hundred amp hours of capacity. I am talking about an 8 hour charge rate. the finish rate should not exceed 5 percent of the amp hour capacity. For example a six hundred amp hour battery would start at 152 amperes and the finish rate should be 30 amps. For batteries like trolling motor types, the start rate would be 25 amps if it is a 100 amp hour battery and the finish rate should be 5 amps.

Now for floating a battery and it doesn't matter what it's amp hour capacity is, the charge rate should be adjusted so the float voltage goes  no higher than about 2.33 volts per cell. All lead acid batteries will start gassing at 2.37 volts per cell so it's important to keep the float voltage below the gassing point otherwise you will come back at some point and see your acid level below the plate structure and exposing the plates to air. It is one real quick way to lower the amp hour capacity resulting in short life-ed battery.  It is also important to equalize your batteries at least once a month and that is done by adjusting your charger to 2.550 volts per cell for about 4-6 hours. Then you let the batteries settle down off the charger for about 24 hours and then re-adjust the charger for 2.33 volts per cell and you will be golden!

Another important note. Never add acid to a battery. Just distilled water. If you add acid to the battery you will over time be increasing the acid strength and this added strength will destroy the active materials on the plates and short life the battery. Sulfuric acid does not evaporate, only the water evaporates!. The only time acid is added is when you have had a major spill.

The few things that I would add are;

If at all possible,  use the charging/discharge recommendations of the manufacturer of the exact battery you are using.

The nature of the use of the battery also dictates charge/discharge routines.

Use a Temperature Compensated Charger that measures battery temp.

Some Gel batts need charge currents be limited to about 5% of 20 hour Capacity.  Others can  accept 25-33% of 8 hr capacity.

For Renewable Energy applications,  most Flooded battery Finishing Currents are 1-2% of 20 hr C range.

If possible,  choose a Float V that just (barely) maintains SG.

The only consistant thing that I have discovered about batteries is,  that "it all depends".  Many,  many variables,  and many intreptations of what to do,  etc.   YMMV,  GL,  Vic

I've spent some time searching for the answer to this question. But to no avail.

Assuming I have lots of time to recharge a battery, which I do, could I apply the recommended float voltage to it and eventually get a full charge? If the float voltage maintains full charge shouldn't it also provide a full charge in due time? Manufacturers I've seen don't indicate this method but always supply the way that gives the fastest recharging time.

The setup would be a voltage regulated supply with current limiting to allow a very slow rate of charge. I would imagine this to be a gentle way to recharge causing little heating or outgassing possibly extending battery life.

The benefits would be not having to monitor the process, or change settings during it. Thus, it can be done unattended and without worry of overcharging while using about the most "dumb" charger at hand... a simple regulated supply most of us already have on the bench set at the float voltage.

Also, as a battery ages, a given cell may become weaker than others. I speculate that the manufacturers high current charging routine may cause even  further damage that a "gentle" charge wouldn't.

I am using gels and AGM's but I suppose this would work for a wet cell too.

Though slow, it sounds like a simple way to charge. But the more I learn about batteries the less simple they become!

Any thoughts?

Thanks,
Don
KK4YY

Don,

   There seems to be nothing simple regarding battery chargers as there are always exceptions, or considerations. Here are a few that apply to Gel-Cels, and NIMH:

  I worked for a company that bought pallets of gel-cel batteries for use with exit signs. They 'stored' the batteries in a non-environmentally controlled warehouse in central Texas. When the batteries were needed over a year later, they were mostly dead, and many would not take a charge. We needed to make our monthly numbers, and there was no time or budget to replace those batteries. So, being in the R&D lab with 4 other hams, and an ex-ham, we scrambled for a solution.

  Many of those batteries went high impedance, and would not pull hardly any current from the chargers. We found however that a 10 ma constant current source with about 100 volts available would 'wake-up' the batteries in 1-3 days, and do so non-destructively. The ones that came back had a terminal voltage around 12 volts, and the bad ones stayed way up, sometimes over 50 volts (these were 12V batteries).

  The ones that 'woke-up' seemed to charge normally, and then hold a load. Doing an Amp-hour test showed the good ones had at least 80% of their rating left. Many, about a third had to be recycled.

  With NI-MH, and even Ni-Cads, old cells left discharged for long periods sometimes requires brief high current charging while monitoring temperature to get them going again. Ni-Cads often short out, and sometimes can be brought back by charging something like a 50,000 mfd cap to 12V, and dumping that charge across the shorted cell. Wear safety glasses and gloves when doing this as the battery might rupture!

Jim
WD5JKO

Agree with Jim ...  there are many exceptions and variations in "best"  discharge and recharge approaches for any battery that I've used.

It is my opinion,  Don,  that  most sealed batteries will not be fully recharged if the charge voltage is limited to the speced float V.   Most sealed batts seem to have a higher Float V than do Flooded batts,  and this might help the recharge progress farther than would a flooded batt at its speced Float V.

It IS possible that the sealed batts designed for Float applications,  as in UPSes,  might also be more fully charged at their Float V spec.  Will try to find that info.

There appears to nothing consistant about even a given type of battery from manufacutrer to manufacturer.  Each has its own "special"  twist on things,  and to the extent that this twist is in the Chemistry,  and not just marketing crap,   it can affect the fine detail of charge and discharge parameters.

Deka is a large,  and good supplier of SLA batteries.  Here is their battery manual,  and is a good general read:
http://www.dekabatteries.com/assets/base/0139.pdf

Flooded batteries -- ones with removeable caps -- would do poorly being recharged at the speced Float V (at least the Lead Antinomy ones),  as they would probably only get to about 50% State Of Charge.  These batteries are designed for heavy cycling,  and will only reach about 85% SOC when the charge voltage just reaches the Absorption voltage.  This voltage is about 1.75 V above the speced Float voltage for a 12 V battery.  These Lead Antinomy batteries must gas to reach full recharge.  The last Sulphates in the plates will not be removed without this last part of the charge cycle.  And not removing the sulphates over an extended time period damages the battery.  And in time,  these sulphates harden,  become impossible to remove,   and essentially insulate the plates from the electrolyte,  reducing capatity.  This last part of the recharge is very inefficient, as it is breaking down the water in the electrolyte into Hydrogen and Oxygen  ...  and so on.

Personally,  I'd use a three-stage Charger for any Sealed Lead Acid battery.  It is almost guaranteed to fully recharge the battery,  and while it is rare,  the ideal 3 stage charger should have a Temp Sensor attached to the battery being charged,  as  sealed batteries are very picky about charge voltage,  especially Gells.

Good thing that things do NOT need to be perfect when dealing with batteries.  Flooded batteries are the most forgiving of errors in charging,  BUT they really dislike sitting around mostly or fully discharged.  Opinions,  YMMV,   GL,  Vic

Looks like this thread has turned into a very valuable summary about batteries, charging and UPS tips. Good stuff for the archives.


Well, as luck would have it, I had a chance to test out the new emergency battery/inverter (110 AH) system over the last four days due to the hurricane power outage.

I pulled about 4 amps each night over a 9 hour period. (36 AH)    After each session, the battery voltage stood at about 12.5 volts.  I recharged it with 5 to 10A for a few hours when the generator came on and all was fine for the next night.

So, it did the job and I'm happy with it.


Problems during the shake-down run:  

1) One of the crimp terminal connections pulled out making an intermittent.  Soldered and fixed.

2) The inverter kept beeping whenever there was a drop in current flow. Disconnected buzzer.

3) The inverter fan kept coming on and off with minimal current flow. Noisy distraction. Disconnected. Since the inverter is rated at about 25A and I need only about 4A, there is no need for a fan for now.

Now the system is quiet and works FB. Ready for the next "adventure" ... ::)

T

Hi fellows,

Very interesting discussion, as this is what I do for a living. Just found this thread. Thought I would throw in pictures of my "manly" UPS system. It's a whole house backup, as I live in the country and power outages are frequent in the winter. I saw Vic's pics and mine is very similar. I have two Trace/Xantrex 5.5KW stacked in // for 240VAC and 12, 850 Ah 8 volt loco batteries for the battery banks. The batteries were "freebies" from a pair of locos being scrapped locally, but I had to remove them myself, by hand. That was fun itself.  :P  Once everything was installed, I made a test of the whole system, and was able to go for 3 days, whole house, on just batteries. I heat with wood and shut down the water heater and used the wood stove for hot water, but otherwise went about daily living as normal. I was pretty happy with the system. The inverters are 48VDC inputs and I used 6 batts in each bank, to allow a rest period for each while charging or using them. We had a power outage one day, and I didn't even notice. I was busy vacuuming and didn't even notice the transition to backup power as the inverters switch in less than one cycle. My neighbors called and asked why I had power and they didn't. he he I ended up running a long cord to their place for lights for the night.

Good thread!

Paul

Don't have any plans on charging batts with a PS but was just curious. I've heard those who say it's OK. I always had my doubts but never had a clear understanding why or why not.  These posts help.

I was looking for info on charging and determining when a battery reaches full charge and came across this nice little FAQ on deep cycle batteries.

http://www.windsun.com/Batteries/Battery_FAQ.htm

Tom,  great that you had the wisdom to get your battery backup system on-line when you did,  and nice that it did the job.

Paul,  great to see you here again.  Do recall a number of years ago,   that you were in the process of moving to a fairly remote site to live.  Have never seen Loco batts ... looks like a very capable system.   Here,  we run the same or similar inverters -- SW+5548s stacked,  Surrette 4KS25s@ 48V,  about 1280 AH when the specmanship is reduced.  This has been a very good system,  altho being off-grid,  it needs to do most everything.  Need to run generators on occasion.

And,  Bob,  tend to forget about the Wind-Sun FAQs.  While their Forum has a commercial sponsor,  it is  by far,  the best general site for specific info IMHO.  It appears to me to be comprehensive,  and without any hidden  bias in the answers toward the sponsor.  They seem to be very honest to deal with and have some of the best prices around on name brand RE equipment-- no off-shore crap that Ive seen ...  and so on.

Good Luck to all those affected by Sandy and her aftermath.  Very wrenching.  Having a backup power system,  genset and fuel must make this storm much easier to deal with,  in  general ... Vic

Vic,
I read some where that a wet deep cycle batt is considered fully charged when it pulls about 2% of its Ah rating, for example 2amps for a 100Ah at around 14.5v.  What's your take on that?  It seems once a batt gets around 14.1v one can here it bubble. Once it begins to bubble is it considered charged?

Hi Bob,

Again I am no expert on this.
Speaking of Flooded batteries only,  for 12 V systems,  Think you are correct about the Constant Volatge stage of charging  (the Absorption stage),  is normally is about 14.5 V at 77 degrees F.  The bubbling does begin a bit below this V,  but 14.4 or 14.5 V is good for Absorption.  But the Asbsorption  V should be held for quite some time,  and the amount of bubbling increases markedly toward the end of this stage.  The amount of time needed IS often determined by the Finishing current,  (also known as Return amps or End amps).  And normally,  this current is between 1 and 2% of 20 hour capacity.  On the batteries here,  it is almost exactly 1% at around an equiv.  V of 14.5 ish V.  This current does depend on the Abs V and the battery temps,  and the exact chemistry of the batts,  etc.

In general for flooded batts,  the first charge stage -- Bulk -- charges the batts to about 80-85% SOC.  Bulk is called Constant Current,  and ends when the target Absorption V is reached.  The Abs stage  can easily require several hours to complete,  depending on how deeply the battery was discharged prior to recharging.

The ending current value of 1-2% of 20 hr Capacity is a good rule of thumb,  but,  of course measuring the SG of the batteries is the gold standard.  SG measurements are a fairly easy way of determining just value of ending current is required.

This is just based on my experience.  ForkLift batteries behave somewhat differently,  and have different parameters for charging,  and sealed batts also have different charge voltages and ending currents,  etc.
Mileage May Vary.    GL   Vic

Jim,

My compliments to the guy who hired so many hams for your R&D lab! You all proved him right in doing so. Very interesting on waking the dead batteries. Maybe I shouldn't toss the ones I aquire that test "dead" so fast.

I've heard of the Ni-Cad "zapping" process some years ago. Burns out the "whiskers" as I recall. I've never been a big fan of Ni-Cads but when they were the best thing going, years ago, there was much talk about them and even some mis-information that lingers to this day pertaining to "memory effect".



Vic,

I'll check that Deka link, thanks.

As an aside; we use the Deka batts on some of our forklift trucks at my job, Huge, heavy, EXPENSIVE batteries in a big steel case. We had a driver of one who was disapointed with the batt performance over his 8 hr shift and took to putting the charger on equalize EVERY night for 16 hrs. I was working nights and his batt would get smokin hot! It put an irritating smell in the air from burning off electrolye. We had to dissuade him from that activity.

Yes, the sealed batts used for UPS's I was wondering about that. Didn't know they were any different in design but I had an idea they might be charged at the float voltage as it would simplify the design of a UPS and the duty cycle in that application would permit slow recharging. I've only seen gels used there to date.

As for using a 3 state charger, I may have a limitation there. Mostly I'm charging at an off-the-grid location with very limited solar power. Maybe not enough steam for all stages of that kind of charge. Also, the charge cycle has to begin again each morning when the sun rises. The charge controllers I've looked at buying vary wildly in how "smart" they are and how expensive they are. Some relatively inexpensive ones don't seem to have temperature compensation and that can be critical as my batts are not in a temperature controlled environment. They live in a shed. Plenty hot in Summer, plenty cold in Winter. With no temp comp the batts are going to be undercharged in Winter and Overcharged in Summer. Some do have ambient compensation and that's probably enough given that I don't have enough horsepower to heat up the batteries much. So the whole deal comes down to the classic engineering choices. I can spend a litte money and get good battery life or spend alot of money and get optimum battery life. Charger $ vs battery $.

Your most salient point, IMHO, you saved for the end...

"Good thing that things do NOT need to be perfect when dealing with batteries."

As usual, I'm beating myself up over the last 10% when I'm already 90% there. But let's not let this thread devolve into my psycholgical issues.

Speaking of this thread, I'm very happy to see it here on AMfone and it's popularity speaks for itself. It's about emergency power, really. Isn't there something in § 97.1 about emergency communications? Yup.

Thanks to all for their comprehensive comments.

Don
KK4YY

Hi Vic,

Yes, mine too are the SW5548 and I love them. They are heavy and just seem to keep on going with no complaints. And one heck of a charger..80 or amps I think.  Yes, moved to the country, about 20 minutes from Vernon, BC and am loving it. So quiet and peaceful, and 20 acres to play on for my son and I. He's 10 and has an ATV, motorbike, go-cart etc and we are just now awaiting first snowfall....come on snow!! :)

If anyone wants a complete dissertation on battery charging, go to the Xantrex.com site and pick any one of their inverter/chargers, or solar or battery charger owner's manuals. They have excellent battery charging theory in there and how to properly charge flooded batteries. Actually, here is a direct link to one of the products I have, which works just great. Discontinued now which is too bad.  Great battery info in it.

http://www.xantrex.com/documents/Discontinued-Products/Link20%28445-0196-01-01%29.pdf (http://www.xantrex.com/documents/Discontinued-Products/Link20%28445-0196-01-01%29.pdf)

Cheers
Paul