The AM Forum

Hi
I need to get 12 VDC neg ground out of my 6 Volt pos ground 51 GMC. Would like at least an amp but really like about 5...Anybody have a circuit, or something to sell/trade?
Thanks
Carl
/KPD

Carl, maybe this will do:

http://www.ebay.com/itm/Ford-Model-A-Flathead-V8-Converter-6-8-volt-Positive-Ground-to-12-Volt-Neg-/280846440566?pt=Car_Audio_Video&hash=item4163c09876&vxp=mtr#ht_1232wt_948

Jim
WD5JKO

Why not convert to 6V negative ground first? If its a stock truck the change is minimal.

Ground the other battery terminal
Repolarize the generator
Reverse ampmeter leads
Reverse ignition coil leads

The complete job is probably 30 minutes or less and Ive done it to many flatty Fords.

Then a power converter becomes simple.

OTOH I could run a 12V AM/FM SS radio almost a full season on one charge of a junkyard 12V battery in the trunk. No hash either.

Carl

Jim,

I am considering that. I had seen it before, just wanted to see how hard it was to build one. There is also a used RS convertor for sale there too.

Carl,
Agree it would be easy but I like to keep it stock

Carl

It would be more stock than adding a SS converter, a matter of turning the battery around.
And a lot safer too if someone tried to jumper you and bumpers touched......

My brother had an old 6v pos ground Chris Craft inboard system in his boat. The details are fuzzy, but when he tried to make it negative ground his three brush generator suddenly went up in smoke.

Jim
WD5JKO

But unplugging the convertor from the 6V positive  cigarette lighter and removing the convertor box from the seat along with the cell phone and GPS will restore it to stock in about 30 seconds ;D
Im looking for light duty

Whatever spins your crank

Interesting read about 6V + GND to 12V - GND converson on a 1955 Ford:

http://reviews.ebay.com/6-to-12-Volt-Conversion-1955-Ford?ugid=10000000001571127

Going to 12V brings in many more issues to contend with.

3-brush "self exciting" generators are a little bit of a different animal. they rely very heavily on the residual magnetism in the field iron. And........they just use a cutout only, not a full voltage regulator. You adjust the 3rd brush to limit the total charging voltage. If you wish to change the polarity of the outpoot, it is best to disconnect it from the 3rd brush, hit it with a little AC to demagnetize it, then hit it with a little DC to remagnetize it the opposite polarity.

Been many years since I have done one, but I did do a bunch of them years ago.

the standard "more modern" 2-brush type are much simpler, you just pop the cover off of the regulator, hold the cutout relay in for a few seconds before starting the engine, then do it again after it is running and let it run for a while and you're good to go.

Its even simpler than that with the later 2 brush gennies. Simply do a momentary jump between Bat and Gen terminals on the regulator. Often needed when a vehicle is long stored, battery disconnected or genny replaced.

I still have a jumper made specifically for that.

Switching to negative ground is perfectly acceptable to even the various car clubs since it is a safety and convenience issue.

 ???  ???

Years ago, I changed my '56 Jeep CJ-5 over to 12 VDC negative ground. I used a GM 10-SI alternator, left the 6 volt starter and all was well. Drove it that way for a dozen years or so before I sold it. It was part of a frame-up resto, so I did rewire it since the old cloth insulation on the factory harness was getting brittle and cracking. Only thing I'd do differently if I had it to do all over again, is keep the Jeep rather than selling it.

My standby generator at home (a 1948 U.S.Power and light 5 Kw) has a 6v Autolite starter on it. (3-bolt Ford style with the Bendix drive hanging out on the shaft). I have been cranking that thing with 12v for more than 30 years now.

Having to take the regulator cover off is a waste of time :P

My 54 F-350 has been using the stock 6V starter since the PO converted to 12V in the 70's.

Just one point, if you stick with the 6 Volt system and re-polarizes the Generator you DO NOT need to change the +/- on the coil, however do need to add a resistor.   While a 12 Volt upgrade may seem appealing, unless you have the starter rebuilt using a 12 volt field coils your are likely heading for some trouble with the Bendix drive.   Yes running a 6 volt starter off a 12 volt system will work, however the torque and issue with the Bendix and ring gear can be a problem.  Back in  the 70's I worked few of these conversions in DIVCO's ( the old stand up to drive milk trucks) and today still play with model T's and have seen the error in simply dropping  in a 12 Volt Battery and changing out the bulbs.. (Although a Model T is a Negative Ground to begin with) - Steve

OK- I hear all of you.

I don't want to change the voltage or polarity. All I asked was for a schematic for a 6 volt pos ground to 12 volt neg. ground convertor. I want to be able to run my GPS and charge my cell from time to time. If I can find one with enough Moxie to run a small 2 m rig, fine. If not, I'll survive.

If no one has plans, I'll go with one of the ones on eBay

Carl
/KPD

Carl,

  I did look around. Looking at switch mode typologies, the inverting "buck-boost" will do the trick. You can Google that. I did find some circuits but they were all positive input to negative output. If you want regulation, low ripple, high efficiency, then doing a ground up DIY design is a big job; except for the other Carl who could do it blindfolded in 30 minutes or less.  ;D

Jim
WD5JKO

Jim,

Appreciate it. I did try Google, but did not see that site. Agree, its amazing the way the thread evolved. If I wanted to change the voltage, polarity or add in another battery I would have done so. I thought the questions was pretty basic

Best 73
Car;l
/KPD

I had an 64 VW bug with a 6 volt neg ground system. I HB my own 6 to 12 volt DC converter that provided about 3 amps at 12 volts. I used this to power a UHF 2 way radio and the car BC radio/tape player. I had installed a 12 volt car battery under the rear seat to provide the current needed to power the 2 way radio on transmit, 20 amps or so. It worked great with no ripple problems. The converted was tied to the battery thru a diode and the loads were all connected directly to the 12 battery thru a DPST relay that also turned on the converter with the ignition switch.

These converters are available on the web.
http://www.6to12volt.com/
6 volt input pos ground no problem.

Good luck.

Steve

Not true. Not swapping the wires sometimes works but the HV is reduced as its a buck/boost winding. Having mostly worked with flathead V-8 and Y Block Fords I guarantee they need all the voltage they can get. Even more so with the V-8 and V-12 flathead Lincolns.

Slightly OT but the Dodge electronic ignition coils at least to the mid 80's are 6V and use an external resistor. They make excellent high output coils for the oldies.

Carl

Lobster Thermidor a Crevette with a mornay sauce served in a Provencale manner with shallots and aubergines garnished with truffle pate, brandy and with a fried egg on top and spam.


klc

I got a bridge for sale if ur interested  ;D  ;D   Get real, Carl 6 0r 12v difference over 20,000v is like pissing in the ocean. It will make absolutely no appreciable difference whatsoever.
You may well have me by a few years, but I have probably worked on more of that old stuff than you. I still even have ingots of babbit for pouring babbit bearings. I was the last guy in baltimore that poured babbit bearings. 

Its not as simple as that and I'll refer you to any competent vintage car forum to complete your education...this is not the place.


I seriously doubt that as Ive been at it since 1955 and as more than a hobby at times. I just sold the R&C shop 2 years ago to my manager after a 30+ year run starting as a part time thing and ending up full time with 3 employees. My speciality was hammer welding, lead work, and engine building and I still get called to help out.


 

I still help a local who does Model A engines along with a few oddballs a year. Pouring is the easy part.

Carl,
       I have done all of the above. I have done more than my share of hammer welding. I learned way back before the advent of small portable wire-fed machines.
I have hand pounded body panels out of flat sheetmetal. It used to amaze my wife to watch me do it. Leadwork is easy once you learn to tin the metal so it will stick. I find it easer than bondo because you can keep heating and reshaping it with a paddle til you get the shape you are looking for. I can and have run EVERY machine in an automotive machine shop. From a line boring rig to a Sunnen CK-10. I even mastered custom paint work (including metalflake) when it was done in lacquer. Long before the days of the basecoat / clearcoat finishes. Over the years I have had my hands in everything from lawnmower engines to a top alcohol funny car.
Anything automotive was what I lived for but................... I did something very stupid..... I took what I did for enjoyment and turned it into my living. I finally got so burned out with it, I walked away and never looked back. "Back in the old days" it was pretty tough to make any real money at it, and many times you were lucky just to get a cheeseburger out of the deal.

If you want to discuss cars and older automotive stuff, you are right in my comfort zone. Feel free to bring it on. We can do it by email and not snarl up this forum.

Add a small 12 V Alternator and separate 12V battery to power any toys.

Email is a waste of time. Either OTA but Ive no idea what your call is or are you coming to Nearfest?

Come on Carl just about everyone here knows my call. You obviously dont read all of threads here. My call is KB3AHE. I want to get to Nearfest but I just cant seem to make it happen. I'm usually on on Friday and Saturday evenings for the WFDN at 5:00 PM, but can be talked into other times if necessary.

But, better than that.................. 410-668-0437 any evening between 6:00 and 9:00 PM

While Carl & Frank are off to parts unknown to joust with vertical antenna sections...

Perhaps the easiest, non-invasive way to get what you want is to take a boat battery box, glue a solar charger on top of it, put a good battery like an Optima yellow top inside, and set the whole thing in the bed and run your radios off it.

No mods to your pride ride, ought to last for years.

73DG

All I want to do is run a GPS and cell phone charger.

You would think I want to install a pair of 813s modulated by a pair of 813s and rebuild the entire electrical system. using a small thermo nuclear device:o :o :o

It just occurred to me the iPhone and the Tom Tom probably use 5 V as the end voltage. I wonder if I could rig up a LM317 and get 5V neg ground from the 6 v pos ground DC to run it? Everything will be plastic and isolated anyway. I'll have to look at the specs and see.

Carl
/KPD

A small windmill under the car along with one of them bicycle generators would jump up the voltage. Spam egg sausage and spam. You don't have to rewire the car that way. Maybee even hide a small batt underneath.

klc

No, you need a LDO or low droput regulator. LM317 can't make 5V from 6, but maybe from 7 or 8.

L4940V5 only needs about 0.45V more on the input than the output so will make 5V from 6V.

A TO-220 regulator made by STMicroelectronics, avail from digikey.com

Normal "working voltage" for a 6v vehicle electrical system is around 6.5-7.1v in the real world with the engine running, and 6.3 with the engine off. That will prolly just work for a 7805.

Be sure to keep everuthing insulated / isolated from ground.

(or just change the polarity of the vehicles electrical system it's a 5-minute job)

The real world is that generators often dont start charging until 800+ engine rpm and 5.9-6.0V is rather common when off and its a cold day. The generator charging current is determined by its rpm and starts low of course. Also since the battery is in discharge with a heavy load at idle less than 6V is possible. OT's can remember the headlights dimming coming to a stop and the heater motor slowing down. Keen ears could hear the radio vibrator slow down.
There were some low drop in sytems available for public safety, ambulances, busses, etc that kicked in as low as 500-600rpm using different pulleys and electrical components.

Standard flathead Ford regulators were set at 6.7 volts to engage and 7.3V for the voltage relay to cut out. Other brands were similar.

I certainly dont, those long winded 2x3 calls are hard to remember anyway. I only read threads that interest me as life is to short to spend all day on the PC.

I guess your name is Frank after reading someone elses reply. I have GFZ down as Frank and 2 is too hard to remember ;D Maybe you should use Frank3 based on your call district. Now there are 2 Carls in this thread from the first district but Im older and better looking so the other one can be Carl1A :o ::)

After all that I need some fresh air....carry on.

Opcom,

Thank you for the idea, like the LM317 it carries a common ground, but I am thinking that won't matter since neither item will be referencing to the vehicle ground. I just need a small piece of perf board, a input cable and cigarette lighter (wired backwards) and then a plastic case to hold the perf board and two female cigarette adapters.

Comments on the circuit idea and logic are welcome .


73

Carl

/KPD

Yea, right............ ;D  ;D You dont miss a trick and always like to get the last word in if others will let you. I also have all day seeing that I sit in front of a computer all day at work.

nothing like a good slack every now and then........................ ;D  ;D

Carl, I dont know about that device Patrick was talking about, but a 7900 series regulator is a negative lead regulator in a TO-220 case so you could just ground the mounting tab and hook one lead to the vehicles electric system and one lead would be the outpoot to whatever you want to run. IIRC, a 7905 would be a 5v negative lead regulator.

2 Carls here could make things a bit confusing................................ ;D  ;D

Frank- and others

Here is what I am thinking about. Imagine a small hard plastic case with a set of wires coming out of it attached to a male cigarette plug. Inside the magic plastic box is the regulator, heat sink and other needed components.  Mounted on the box is either two female cigarette lighter sockets or USB sockets. the entire box has no external conductivity. When I want my 5 v I just plug the cigarette lighter plug into the +6V ground lighter jack on the dashboard, and my other plugs, or USB ports for 5V neg ground. Simplified drawing would be like this. I can't see why it will not work.
Thanks and 73
Carl
/KPD

I agree no need to ground anything there.

Yes that circuit will work

The 6V discussion/hubub is why I suggested a very low drop regulator. A VLDO is just the best part for the job. The 1.5A part I mentioned will do a better job at regulating a 500mA typical USB charging current (dropout 0.25v@500mA @50 deg C.) if the input voltage is low-ish, than a 7805 or LM317 will, because those old favorites have higher dropout voltages of 1.7V (L7805, the low dropout version) and 1.75V, respectively at 500mA and 50 deg C. The datasheets will show that, so you be the judge of it. If you foresee the current being high enough to cause dropout issues, a regulator for each USB socket would help.

L4940 - input cap should be monolithic or ceramic, output can be electrolytic.
L78L05 - low ESR caps, tant. mylar or other - output can be electrolytic
LM317 -  low ESR caps, tant. mylar or other - output can be electrolytic

Modern regulators are sensitive due to improvements. Because there's no real ground, just a lot of wire, treat it like an RF IC and put the caps right at the IC.

Whichever regulator is chosen it is wise to add a transient supressor or a zener diode in front of it to eat any spikes that come from the electrical system such as when starting, load switching, etc.

Too bad Vin and Vout are so close together or a buck would work well. Maybe a buck-boost but the monolithic ICs are tiny and require reflow soldering these days.

Post up some pics of the plug, box, board, etc. when you make this. It will be good for others who have the same requirement!

IIRC, LM317 is supposed to be an adjustable + lead reulator.
       7800 series is a fixed voltage + lead regulator and
       7900 series is a fixed voltage - lead regulator.

Using a 7900 series (7905) and grounding the mounting tab just makes things a little easier to build. (less to keep floating) uses the same circuit ou have drawn, but just reverse the polarity of the in and out leads. Also being able to ground the mounting tab makes it a little easier to heatsink. No worries if the heatsink touches anything metal.

I have also made regulators for "odd" voltages by floating the center pin and stacking diodes and/or zeners under it. It gives you a little "adjustment".......

Excellent idea. A real "duh" moment for me as I was worried a bit about the current of the two devices at the same time. I'm thinking of doing three. Two with USB and one with cigarette lighter.
I have a PC to cannibalize for the USBs and I think I will take a close look at the PS components.

Really appreciate the help

Thank you Frank. I think I'll keep the sink inside the box and drill air holes. I want to keep any thought in the future of the heat sink being a ground reference for anything off the table!