The AM Forum

Ive seen a discussion somewhere in the past but cant locate it.

Anyway, I have a virgin 5 gallon jug plus a partial one of genuine PCB and started thinking about extending xfmr ratings. Is there any particular formula to use, transformer prep, etc?

What about the sealed ones and also the oldies with cast iron end bells?

Carl
KM1H

Well, there are several limitations on the power a transformer can put out.

1. Heat dissipation.

2. Core saturation.

3. Poor voltage regulation due to high winding resistance and voltage drop under load.

Putting a transformer in oil only helps with number 1 -- heat dissipation.

It would be interesting to see if anyone can come up with a useful rule of thumb.

An oil bath can also greatly improve the dielectric strength of the windings, especially on modulation units.

I would not bank on dielectric but it will help for pulling heat out. Amateur service you have to ask yourself if that is really an issue. That is unless you make super old buzzard transmissions. 

while I have no direct experience or text to follow, I do think that the oil bath will improve the dielectric breakdown in some cases and to some extent. Certainly in the case where there is a breakdown through an air path, the oil will be more or less "self healing" whereas the air path will tend to oxidize and create a carbon track to follow... at least that is what i am thinking... but if the breakdown path is contact to contact, no benefit. Otoh, if the "fish paper" in the unit - if it has fish paper - is oil impregnated that is better than just plain fish paper, or fish paper with atmospheric water absorption?

I have been wondering though, in a sealed unit do they fill 99.99% with oil or do they leave a few percent air for thermal expansion??

How about a "blow out plug"??

            _-_-bear

I once used a pole pig that had been drained of oil and removed from the housing can in an amplifier power supply.  It eventually broke down and zorched in a very alarming way with a loud bang.  An autopsy (transopsy ?)revealed that the secondary (orig primary) broke down between winding layers.

Some pole-pigs run fine "dry", but this particular one relied upon the additional insulating properties of the cooling oil to operate at the rated voltage.  Perhaps, also the oil kept moisture out of the transformer internals. 

73,  Jack, W9GT

don't want to trap water in transformer that may already be there (hygroscopic adsorption) .... be sure to bake it out as described in other threads and while still warm to hot, plunk it in the oil that has also been dehydrated ... this should seal out h2o ... if oil used is flammable (a VERY bad idea ) be sure to mind flash points ...be careful ...73 ...John

Jack,

Probably there is more heat cycling in the on/off amateur service than is typical for a pole pig and the lack of oil probably aged the insulating material between windings at a faster rate.

Exploding poles pigs are impressive!  Long ago when I was in high school I was headed for a Boston concert during a thunderstorm and lightning struck nearby sending a pole pig off its pole nearly missing a passing car.  It left a most impressive mushroom cloud as it sailed to earth and was louder than any part of the later concert.

I would imagine the main benefit of oil would be allowing a trasnformer's ICAS ratings to be utilized for CCS service with probably a slight increases in ICAS current capability before core saturation and voltage drop across the windings becomes an issue.

There was an article in HR or 73 in the 60's about de-rating a pole pig used dry but I don't recall seeing any articles for the reverse situation.

Carl, are you going to go really old school and immerse some of early transmitting triodes in oil also  :)

Don't blow your lid. This happened near KE1GF's place a few years ago. I don't remember what caused it but it may have been his class E rig.  ;)

The transformer I want to protect was bult around 1946 and was in my detached garage for 20 years and received the benefits of condensation cycles many times.

Its 6000/7000V CT @ 1A CCS and is way too big for the oven or the pressurized varnish pot I built. So I did the old heat from the inside trick by shorting the secondary, watching meters in the primary and secondary and running the Variac up a bit over 4-5 days until the core was nice and warm but not too hot to hold and then holding there for another day,  Then running it normal with a 1000W resistive load for another day. That made the meter spin.

Now I just want to preserve it long term in case there is minor insulation damage. The oil is the genuine PCB Cool Aid that was fresh poured in the jug in the late 60's. Ive used the partial jug to refill dummy loads and still have the untouched full 5 gal jug. Im not worried about flash points with that stuff.

Ive no immediate plans to push the xfmr ratings but if a couple of 750TL's come along things could change ;D

As far as a pressure relief, there is none on the modulation transformer which is twice the size of this other one.

A remaining question is how much oil? Is there a gallon per kva spec or how is it figured?

Beware flammable oils. A transformer fire in it can make a huge mess that you will never clean out of the transmitter. I may have some PCB oil for you but you have to come get it in DFW area, TX. 5-10 gallons maybe. It is in pole pig cans where the core was removed. I do not think it has been disposed of yet. An alternative is a non flammable silicon based transformer oil, but it is costly. The PCB is free.. so I can say "PCB Free"

With such a large high capacity transformer is this effort really worthwhile?

It seems like you have already done what is needed to dry it out and it didn't arc over or anything.

Putting it in oil seems like a lot of effort and mess for not much benefit.

Lots of people use old transformer successfully without going to all this trouble.

Just my humble opinion.

I have used 7200 volt pole pigs dry and never had any problem with insulation breakdown.

Also, I once used an open-frame filter choke removed from an old 48 volt telephone exchange tungar rectifier power supply, by placing it in a gallon can and pouring in enough transformer oil (undoubtedly PCB) to completely submerge it.  I used it for several years at 2500 volts DC with no problem. Luckily, I never managed to kick over the open can of oil or start a fire.  At that time the rig was in an upstairs bedroom in the house, so that would have made a big mess.

I bow to Don's wisdom in this matter.

I have used, do use, two pole pig cores. They are only 4160V, but when the 'variac' on each one is turned to 140VAC, then the voltage becomes 4853V.
This has been run for hours at a time, and there have been further abuses such as drawing 1 amp continuously from each of them for testing the power supply.

The pigs have two windings of 2080V and I have put them in series using FWCT.
In the past, they were run with one side grounded and the other at HV AC.

The pigs are at least 50 years old as the rig was built in 1957 and they were likely in used condition at that time because Col. Tucker got them from the power company. I credit the long life of these parts to USA manufacture.

In the 1947 article we have all enjoyed because it may hold the record for the number of MV rectifiers in one set, "Deluxe Amateur Transmitter", by James N. Whitaker W2BFB, Eng. Dept., Hammarlung Mfg. Co., T12 is a "Pole Trans. 220V to 2200V 2KVA" It is used in a 4)872 bridge rectifier configuration and dual section LC filter to supply a pair of 833's with up to 3000V by means of a 'variac' on its primary.
http://www.bunkerofdoom.com/lit/deluxeam/deluxe_amateur_transmitter.pdf

No one knows where this trnsmitter is today. I hope it is still in one peice.

I keep a 4800/6000/7000 VCT 1A transformer around just in case, but there has been no indication of issues, and the pigs do not even get warm.

.

I have had 2 transformer crapouts lately with my 4X1 rig. Both times it was while in standby. (I grid block the final rather than switch the primary on and off) One looked like it had had bad storage (rather rusty) and the other one looked almost new. (believe it or not the nastier looking one lasted the longest, 2 months and the pretty one lasted 2 1/2 hours) Neither one even got warm in operation.

Both were between 6500 and 7200vct 2KVA units. They were the open frame / non potted types. One had tin endbells (a Kenyon) and the other had nice cast iron end bells (American transforner co) Both died from insulation breakdown problems. These were rather old vintage transformers. They MAY have survived if they were immersed in oil. I am finding this is a commom problem with old buzzardly transformers that operate at that high of a voltage. The high voltage vs the age seems to be the issue as the lower voltage ones have a much higher survival rate.
I have since come to have little faith in these type of older transformers. These 150+ lb man-killers are also way too big to fit into my varnish bath tank. 

The insulating materials they used "back in the day" just dont seem to stand the test of time (and moisture). After having several discussions with my boss here at work (He has degrees in electrical engineering) He seems to think it is caused by corona at that high of a voltage, and agrees with mi that that is causing the old insulating materials to break down. But I have come to having little faith in transformers at that high of a voltage and age to be any good or worth fooling with unless they are well potted.

The submerging in oil would probably really help the corona breakdown.

                                                                 The Slab Bacon

http://www.foxriverwatch.com/human_health_pcb.html

Nasty stuff, I would not have it around.
While you might not mind taking the risk, you might want to make sure you live alone, never have visitors, and make plans to  have the place cleaned up after you move or die.

Brett

I would rather saw the dead winding off the core and wind a new one with better insulation than have tubs of PCB oil in the shack. Even if I had to wind it by hand. Oil would have to fill every void which could take years in a top finished part.
 Heck we do have gary the transformer man.

Short term exposure to the transformer oil variety of PCB's wont hurt anybody. I know several utility company workers that handled that stuff decades ago and are healthy senior citizens today.

That article contains some truths but is also full of typical nanny state, tree hugger, Sierra Clubs style of BS.

I'll bend and weld up an enclosure complete with flanged top, gasket and top cover. Built the same as my commercial mod transformer.

I'll also weld a bung in the lid to take an air fitting so I can apply a bit of positive pressure to force air bubbles out of the core. Thanks to John, K5PRO, for that idea.
Then it will be used with the NOS genuine GE 25uF Pyranol filled caps.

I'll feel a lot safer with that iron in the oil for exactly the reasons others have mentioned. If it does blow Im only out my time and labor. And the enclosure can be used over.

Carl
KM1H

Not for nothing guys, buy why even mess with old oil? Especially the PCB stuff. Hit a chemical supplier and grab a bucket or two of Shell Diala AX. It costs about 50 bucks for a 5gal bucket and it works great. The stuff smells like a dead cat, but it'll hold off 180+ kV at an inch (more than 50kV@ 0.080 inch) and it's severe duty (Type II, better thermal stability and better oxidation resistance.) When I got some on my hands, it did irritate my skin, so glove up.

I have lots of the bigassed GE Pyronol caps hangin around here which is fine since they're clean and not leaking. HOWEVER, I don't think I would be dragging buckets of the shit into the house.

The ONLY way to insure no air pockets while filling a can is to seal off the top and suck a vacuum on it while filling. During the chicken ba..., oops, did I say that?, I mean Tesla coil experimenter days, I would fill a can by mounting the trans inside the can and making all connections that were below the cover, like the secondary connections, and leave the primary wires taped to the inside right at the top. I had a piece of half inch plexi drilled and tapped 1/4"npt at 3 places. One with a small ball valve and hose barb, one for connection to my vacuum pump, and one for a vacuum gauge. I connected a piece of clear 3/8 vinyl tubing to the hose barb and drop it in the bucket. Start up the pump and pull the can down to around 15" (not much!! Don't wanna cave in the can) I would crack the ball valve and let the tube fill with oil up to the valve. Hold the can at 15" vac which I did by adding bleed air at one of the fittings on the pump, and open the oil valve and allow the oil to flow into the can. As long as the hose stays submerged, you wont get any more air in the can. My 25kVA/7600 took about 12 gallons to cover the trans with about 4" of oil and left about 6 inches of air between that and the top. The only specific is that the top HV bushings protrude into the can about 8 inches. The ends of those where the primary wires connect need to be in the oil. So measure from the gasket surface of the lid to the bottom end of the bushings, subtract a couple of inches, make a mark inside at the needed oil level, and that's how far the oil has to come up in the can. Easy

[/ buzzard post] 

Frank,
         sawing the winding off would be definately the easy way, but............ Without having the original factory specs, how are you going to know how many turns to put back on?? I guess you could figger it out mathematically, but it would sure be nice to know the exact number of turns needed. The nice thing is that today's insulating materials are much better (and thinner) and should make it somewhat easy to accomplish.

I still have some not so fond memories of the hellish mess I went through some years back rewinding 3 American Bosch magneto coils for one of my old gas engines. (We had 3 dead ones and made 3 good ones) We invented 6 or 7 new cuss words over that job. I needed one, and 2 other friends needed one also. One guy came up with 3 dead ones and said "if you can make me 1 good one, you can keep the rest", so we made 3 good ones. the biggest problem seemed to be that we couldnt get as much wire back on as we took off and we sawed the old windings off so we didnt have a clue how much we needed. I swore that I would never do that again! ! And now I'm contemplating rewinding a 150lb plate transformer.......... Go Figger! !

Frank,
Having wound a few here is what you do. Count the number of layers in the primary and secondary windings. Saw down a couple layers and expose a layer of secondary. Count the turns on that layer. Turns times secondary layers is the secondary winding. Now saw down to the primary and do the same thing. Now measure the wire size of each to see what you need to duplicate. Next measure the thickness of the insulation paper. This tells you how much room it will take.
Do some math and go buy wire, and insulation. (I like kapton 7000V/mil)
3 mil kapton is usually thinner than the old paper.
Do the math
get some mylar tape
Make or buy the bobbin.
Get some beer
Yup it takes a bit of skill to duplicate a transformer, that is why Gary has that cool winding machine.....and a crap load of talent.
Winding them in your lap is much harder.

Now Slab Bacon's comments have gotten me worried.

I also have an old "150 lb man killer" transformer I was thinking of building into a power supply. Mine is a UTC CG-308 and looks in good condition. But who knows where it has been stored during it's life?

Here in the Sacramento area we usually have low humidity and during the summer is gets hot, so that transformer (which is currently sitting in my garage) is "baked" at 90 degrees plus each day for the last four months. I could move it out to our garden shed for a week or two as inside there must get over 140 degrees this time of year.

There is no way I'm going to submerge anything in PCB oil. I'm not that worried about the health issues as, like most here, I think those are overblown.

But, as a California real estate broker, I know if I spilled even a cup full in the house I'd have to disclose it to any future buyer. And probably get some environmental firm to clean it up and certify it was clean. That would cost more than 50 new (old) transformers.

Not disclosing you had a large PCB spill in a house, and just cleaning it up yourself, could get you sued by a new owner here in California if they ever found out. Plus as a real estate broker I couldn't plead innocent and claim I didn't know I needed to disclose it. Plus I might lose my real estate license. And, on top of that, your home owner's policy may or may not cover defending you if you are sued -- most here in California will not defend you against mold law suits or pay the judgement is you lose, for example.

If I can figure out how to enclose it so it's safe and my cat won't end up a Krispy Kritter, I guess I can hook it up and run it open circuit for a month to see if it's going to short out. I hate to build a supply around it only to have it crap out after 2 1/2 hours.

Just want to add a comment here. When taking data on a transformer rewind, dont, and I mean DONT concluded that just because you got this many turns on a layer that is what they all should have for that particular winding. 99% of the time you will be wrong. PLEASE, count every turn. It may take you longer but it will be done and work they way it should. You can buy Nomex insulation of various thicknesses thru Brownell Electric out of N.J. Around 22 bucks for a 2' X 3' sheet of 10 mil.
If anyone has a question about rewinding, I would be happy to answer any questions. Just email me direct.
Thanks and all have a great weekend.
TRS
Gary...WZ1M

And because of the attitude displayed above, anyone needing xformer work should, if he wants it, steer it to Gary.

Thanks for the info.


--Shane

Dave,
        Take that transformer and put a large resistor (like a big dogbone) across the secondary. Calculate something that will give a 25-50mA draw. Put a small fuse in parallel with a big light bulb and place that in one leg of the primary. Put the whole shebang somewhere in an out of the way safe place, fire it up and let it cook. forget about it for a while and watch for the light bulb. If it shorts out, it will blow the fuse and light the bulb as a visual indicator that it crapped out. If it survives for a week or so it will most likely be good to go.


Frank,
         I can cobble together an impromptu winding machine with a crank (or motor) and a turns counter. That isn't too much of a problem. I just need to find out where to get the magnet wire and the Kapton insulation film. Does Mouser or one of them carry it? I will have to give you a telefonium call one night to discuss it. I just might get goofy enough to try it. the cost of shipping the whole transformer plus the cost of rewinding it makes it too cost prohibitive to send it out to have it done. I just may have to get froggy and leap myself on this one. It could possibly be a good "cold winter night" project.

                                                       the Slab Bacon
        

Frank, strip a couple dead transformers to get an idea how they are wound.
Take my tape tricks and Gary's coating every winding as you wind it trick and it will outlast you.

Motor rewinders or even a transformer shop will usually sell you a partial spool of wire. Calculate what you need and get plenty extra.

I'll defer to Gary for the best insulation for the wire itself these days.

I was having many transformers built at a local outfit until the owner up and dropped dead one day. The place closed and liquidated.

I was also having a lot of 3 phase jobs made for Shanes buddies that had some interesting alternator arrangements in their Surburbans with 454 power. ;D

Carl
KM1H

Wanna see some Doozies, check out the older Dahl catalogs....  Look for Mr.  Gilmore.

7Kv AC @ 6A xformers, etc.

6-8 dual stator, single rotor alternators (Electrodyne).  Insane stuff.

454s is an understatement.  There are engines spinning alternators that have > 25 thousand dollars in the longblocks, nitrous injected (2 or even 3 stages).  The problem a lot of guys have is they  need so much horsepower, but have to go "old school" because NO electronics can be made to withstand the RF fields the AC Sky idiots (guys) do.

Takes a lot of horsepower to create a hundred kilowatts of RF :(  Takes (away) a lot of brain cells, too, me thinks!

--Shane

Seconding the post on the old PCB based xfmr oil - don't mess with it.

A few years ago I checked with a local wholesale supplier, and I could get a new 5 gal bucket of non PCP stuff for $35... I'd go with the new, and label the new xfmr enclosure with what it in it - for future reference, etc.

W1ATR posted on vacuum filling the xfmr case - but how to seal it after the oil is in there?? I know how they seal vacuum tubes, but this isn't glass that you can melt the filler tube shut... what's the trick??

             _-_-Wbear2GCR

PS. it is friggin raining something fierce here tonight (again)

PPS. it is ok to water your lawn and wash your car...

Bear, you don't seal the trans undrr a vac. The only point to vac filling transformers is to expand the air that's in the nooks and crannies that would otherwise be trapped if the oil were just dumped in. (And yes, it is hella downpouring over here, wow.)

Shane, Gilmore was a steady customer as was many of the mid west and New England crowd. Id have a ball with them every year at Dayton. Those guys came loaded with $$ to shop there also. The NE guys would sometimes be 3-5 deep here on a weekend installing new iron, testing, and generally screwing around. The cops must of thought I was dealing ;D

Carl
KM1H

Luckily, you didn't have the "old skewl DaveMade" crew hanging around.  I've seen their shenanigans at the CB Breaks in the 90s, and I've also watched them sell everything in the SUburban just to get home.

Gilmore is a really nice guy, once you get to know him.  NOT an RF engineer, his Elmer once told me the ONLY way his tetrodes didn't take off was the rats nest inside wouldn't support ANYTHING resembling oscillation!  Funny then as it is now, but if you've ever SEEN the insides of his stuff, you'd appreciate the comment.

"Them d00dz is insane"...  I have videos of one of Gilmore's mobiles shooting the top off a top loaded antenna at 45 kilowatts carrier. That's the same mobile that when they hit the nitrous, it jumped to 75Kw, and ejected the tape from the camcorder.

I hear Arnie is the supplier of choice for those guys now:  That, and they have pretty much solidified up their own people 'acquiring' parts inside the various employs in the great lakes area :)


--Shane


--Shane

If you need need tranformer oils I can put you in touch with a the rep that supplies me with high flaspoint, high dielectric rating synthetic oil.

The only caveat is you have to buy a 5-gallon (pail) minimum.

Phil - AC0OB

Ahhh... I kinda liked the idea of sealing it under vacuum...

So, how full do we make it?
Do we have to leave some air space for heat based expansion??

                  _-_-bear

I'm sure there's some spec for each transformer, but I would say 80-90% fill. Covering the core is obviously the most important, but on those little square trannies a lot of our gear has, I'd say leave some air space anyway, otherwise when it heats up, it could pop the seals around the terminals.

IIRC, I had to drain and reseal the power trans on my r388 and when I refilled it, I remember it taking like 5oz to top it off all the way, (had to be filled with a large syringe like the kind used for filling inks btw) and I sucked out about on ounce with the needle and soldered over the hole. Been running daily now for over a year and it hasn't smoked out yet, so there must be enough in there. 

EDIT: also, I didnt have a way to put a small trans like that into a vac, so I just filled it a bit and rolled it around in my hands with a piece of tape over the fill hole on the top. Did it like that a few times and hoped for the best. I think it originally started puking it's oil because the filter caps were shot and loading it down making it overheat. I recapped the PS on this particular rx and the trans doesn't get anywhere near as warm as it used to. So heat and pressure definitely play a part with these sealed trannies.

Wow, your R-388 has an oil filled power transformer!?

Whaddya know! Mine is open with two end bells... it probably has one or more shorted turns, because it runs rather hot and I think it let some magic smoke out last year... I put a tiny 2" square fan from a computer supply on it, running at reduced RPM to keep it quiet, seems to keep it cool enough.

I replaced the can cap by fabricating one out of aluminum tubing, an octal socket and some tubular caps plus 5-min epoxy and silicone rubber... the old one got leaky.

Would be nice to find one of the transformers in a can... I have a handful of general purpose transformers standing by in case more of the magic smoke escapes from the one in there now.

I had assumed the square ones were tar filled, not oil filled...

               _-_-bear

Nope. Factory 388 was oil filled. Here's a fast pic with my Blackberry.

Having worked in a cannery for my church, I can tell you this:

Get the oil in the box hot... REAL HOT (not flash point hot, but > normal operating temperature).  Then seal it, and let it cool.

You now have a vacuum seal.

For home canning and food storage, we did it in a double boiler.  Transformers get hotter, so maybe a heat spreader and then put the case on top of the spreader device (to keep hot spots from appearing, weakening the structural integrity), get it all HOT, and then solder / seal it up after the oil has gotten to 'greater than operating temperature'.


The trick is to do it hotter than you think it will ever be, and then you'll have more than enough expansion room.  The "other" trick is to know how much liquid product you need to keep the dry product completely immersed both when cold and hot.  It's a volume / vs product type thing.

--Shane

Any of the R-388 power transformers I have done were potted in a tar substance, not oil filled. See the picture of the transformer on this subject, now see the round circle on the top of the case. Thats a plug that is soldered on. This access hole is where the potting material was poured after the can was put together.
Regards,
Gary...WZ1M

My 388 (Its the run with the front panel Break-In switch) is as Gary says but with many production runs there may be different vendors and construction.

Carl
KM1H

Well, a pic is worth a thousand words, but this was also about a thousand pics ago. I do have them, but I' have to do some diggin to find them, but you'll see what I mean. There's a small hole on the bottom corner next to the terminals that was slobbered over and the leak was from there. When the trans would get hot, (and I mean hot enough to burn your hands hot), it would start dripping on the table and leave a nice little puddle of clear sticky crap to clean up. All I had to do was wick the slobber off, turn it upside down and put it in my vise. I got it warm with a heat gun and drained off the juice into a water glass so I could see how much to put back. It dripped out about 3-4oz of clear thick liquid, which for a minute I thought was glycerin. (Crystal clear like water and thick like motor oil.) I used one of these needles I fill my printer cartridges with and filled it back up with new oil and about twice as much, (Shell Diala AX). It's a steel case, so I used silver bearing solder and a bit of white paste flux to close the hole and it's been behaving nicely. The bottom hole worked out nice because I didn't have to deal with repainting the trans and fooling with the stencil. This RX is mint, so I try to keep it nice.

I know transformers were encapsulated with a refined version (lowered acidity) of basic pitch, or bitomen, or whatever they called it, but this defin was not that. Now I have heard of some newer trannies being done with whats called "Pale" wax, but I don't think this material was even that because it wouldn't solidify. Like I said, I thought for a while it was glycerin. I almost put that back in there, till I thought about it for a second. Glycerin expands like quite a bit with heat because some of my gauge manifolds have liquid filled gauges, and when the truck gets hot enough, a little will come pissing out of the vents. So it's gotta be some sort of oil for cooling.   

Now this RX had been on most of the day today and the trans is only warm to the touch, feels like maybe 120F. Used to get twice as hot.

73   

My big question is weather or not the oil will react with the glues or dialectic insulation materials used in an otherwise built to be a dry type transformer??

I know many of our comments sometimes get covered up by the flow of comments but would someone please answer this for little ole me  :P :P

Pies-4-U, I have never heard or read of the xfrmr oils reacting with anything... of course, that means nothing.

                        _-_-bear

Thanks Bear, now I feel better ;D ;D

Glad I could help and be didactic on this issue...

                _-_-bear

Never heard the word before. Had to look it up.