Transformer Varnishing methods

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Hi everyone,
after some help and encouragement from CJ I started repairing and building transformers last year.

It's a hobby I like and I'm still learning and trying to improve step by step.
I'm on the varnishing topic right now, as I have to dip some transformers I have.

I would like to ask you what are the Varnishing methods and setups you're using for dipping the transformer and curing it?
If you have pictures of your setup that would be great

__________________________________________________________________________
I bought transformer varnish from a local supplier; it's Dolphs 1401 Synthite AC-43.
the specs say:

CONVEYER IMPREGNATION
1. Thin by 10 - 15%.
2. Pre-heat unit for 10 minutes at 110oC. (Not always necessary).
3. Dip for 30 seconds.
4. Drain for 10 - 20 minutes.
5. Cure in the oven as for 60 - 90 minutes at 110oC.
__________________________________________________________________________

I guess I should have first to bake also the transformer to pre-heat it before being dipped

I don't know what "Thin by 10 - 15% " means

Do any of you use Vacuum pressure impregnation?

Thanks
 
heat transformer for two hours at about 220 F (104.444 C)

make sure varnish is at room temp (70 to 80 degrees F)

dip in varnish for about ten minutes or until the tiny bubbles stop,

bake overnight or 8 hours  at about 200 F (93.333 C)

the reason for the long preheat is to

1) get all the moisture out of the windings
2) get all the moisture out of the insulating materials like Kraft Paper or Pressboard
3) get all the moisture out of the adhesive tape like glass cloth tape
4) shrink the insulation and tape to tighten the coil up and set the adhesives
5) warm up the varnish so it is more viscous which allows it into the nooks and crannies

the reason for the overnight bake is to boil off the solvent so it does not sit inside the windings for the life of the transformer. you can never get rid of all the solvent, but you can get rid of it enough so as to not cause any long term damage.

the overnight bake also shrinks the tape and insulation further and also solidifies the varnish.

vacuum impregnate is good but not really necessary unless you are dealing with ultra high voltages like 30 KV. It is also dangerous to pull a vacuum on varnish (flash point).  Usually vacuum impregnate is used on air dry epoxy or oil filled transformers.

this stuff works good, make sure you avoid the water base version>











 

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I dont want to attempt to bake my C cores ,but I guess I could impregnate and bake the windings before assembly , I initially used sellotape to wrap the outside of my coils ,but I have kapton tape in various widths on order , I used black motor paper with industrial strenght double sided tape to make a core over the former ,shiney side in ,I left tabs at the side which I closed around the coils with tape after winding , but I'm thinking maybe a slightly thicker wire would be better for current handling /voltage drop and under possible fault conditions .
It looks like many hundreds of HY's are possible with 40awg ,maybe even thousands with a very small gap , I'll  clamp up the cores with a stainless jubilee clip later on and  do another measure with two 4 kohm dc coils , for 10-12ma on the hitachi sim I get a gap of 0 ,when I push the current to 16 ma it specifies .1mm or 2x.05mm, I read somewhere theres a sweet spot on the C3g at 12 ma ,so maybe I can leave the inductor  ungapped  for maximum inductance .
Maybe I should aim for four coils of 2500 ohms each ,so it exactly matches the dc volts dropped by the current anode load resistor of 10kohm. 
I'll post illustrations later of the former ,paper core and tape wrap technique  I used ,just to check im on the right road .
Theres a gigantic tank of varnish at the motor shop for winding impregnation ,and gunky ovens too , I might just drop in varnish through the windings after the outside is taped , seeing as theres no paper apart from the core any moisture should evaporate very quickly , I might try the nomex for a core material too but the motor stuff is very stiff and its hard to get it dead flat onto the former, it also doesnt slide off the former as well as the shiney black motor paper , in any case I'll have the polyester wrap , kapton tape and a layer of paper  between any metalwork and the coils  ,so no chance of the sharp edges of the C cores breaking the wire . I need to resize my former to better accomodate the wire and wrapping etc ,but 4x10,000 turns with the 40 awg looks like it fits with  good bobbin fill .
It takes around 25 minutes solid elbow grease to wind 10,000 turns with the hand cranked winder  ;D ,but its the best fun Ive had in ages ,guiding the wire with one hand while cranking with the other takes a bit of practise to keep speed and lateral movement of the coil even . I the other thing I was thinking was one of those old foot pedal tables for a sowing machine with the big flywheel that would be cool to hook upto a hand winder, you'd be able to keep a nice even speed while concentrating on laying the cable down neatly . I didnt order the cnc yet ,but Im gearing up for it ,I found someone claiming to ship the machine from Germany ,but Im not sure if the price includes vat or not ,techinically the first time this machine could be assessed for tax is on Irish soil , ie its being shipped from a bonded warehouse in Frankfurt Hahn ,I suspect this to be the case with this seller , effectively your importing the machine from China not Germany . Then on Aliexpress they have a similar machine , slightly better running gear ,same price ,but you know its the price excluding vat ,it also roughly coincides with the total ebay price from the so called German warehouse . Does anyone have experience of Aliexpress or buying items warehoused in so called European locations on ebay ? 
 
Thank you so much CJ for the explanation and procedures.
I will do as you said in the next transformers

As for the varnish I'm already settled with the Dolphs AC-43 I have a 5 liters can.

Do you thin you varnish also?

The Dolphs AC-43 is already pretty liquid
 
abbey road d enfer said:
Thin=dilute. You add solvant to make the varnish more fluid (thinner), so it gets deeper into the windings.

Thank you Abbey,
I will try that, the manufacturer suggests thinning by 10-15%.

Hitchhiker suggested turpentine, any other products you might suggest to thin the varnish for this application.

Thank you so much


 
> products you might suggest to thin the varnish

Read the can. Use what the maker suggests. The varnish and the thinner must be compatible.

It used to be simple. Shellac used spirit-alcohol (in the US, denatured, a little or a lot or totally), varnish used turpentine, lacquer used lacquer-thinner (a light petroleum distillate). Then they started changing the base resins, fortifying with other resins,  also re-formulating to reduce bad vapors and of course to reduce cost.
 
CJ said:
i don't use thinner,  last time i did the neighbors called the cops thinkin there is a meth lab in the back yard,
And there was a meth lab ...  ;)

P.S  sorry for hijacking,  I couldn't resist
 
> a meth lab

That's one of the reasons you have to Read The Label.

Toluene is an old standard solvent for spray lacquer. But in some parts of the world now you can not get toluene-- it is too handy for extracting cocaine from coca leaves. I assume consumer-grade varnish in those areas uses different resins and oils for the solvents they can use.
 
gonna bake and dip and bake a few Reddi DI units,

Edcor does not clamp their E lams very well when they measure out a 12" string, so we usually get 11.5" which is a drag if you want to get 12 transformers out of a string,  they need to put a 16" C clamp on there and compress to get a good measurement, but we always have leftover I bars, so we use them to hang the transformer after the varnish dip as seen  at the top of this guy>

 

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besides putting out a beautiful sine wave, the HP 200 CD also makes a great space heater/varnish warmer as the power tubes are cranking out about 40 watts unloaded,

we usually transfer the varnish to jars as you can seal it better to avoid "skin over"'

you have to keep the lid and grooves clean other wise you need a crow bar to get the lid off. (or hot water)

 

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outdoor bug lamp really tweaks digi pics,

made some varnish tanks out of some tea cans, if you want that British sound, you have to use Twinnings cans,  :D

left can has a xfmr getting soaked, right can has one drip drying from the hook at the top,

these could be made more stable by mounting them to a wood base plate. ever try to get varnish off of concrete?

keep the wires free from varnish, otherwise they get welded together during bakeout, when you try to split them, the pvc coating rips right off the wire,  now you have a problem, taking apart a varnished transformer and soldering new leads is not fun,  a laced core might need to get trashed. gapped core is easier to take apart.

make sure you have a tight coil/core assy.  a few times we have lifted out the xfmr from the varnish only to have the I bars stay in the tank, which is not fun.  so I bars and E lams must have the same lam count. Keeper lams can help if you can get someone to sell them.  Edcor does not sell them.  Heyboer might.

having the cans about the same size as the xfmr means that the varnish gets nice and hot from the 225 degree transformer core and therefore much more viscous, so it ends up like adding thinner.

 

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old reverb tank makes a good baking dish. you do not want the transformers sitting flush in a pan, what will happen is the heat will leak varnish out of the transformer and you end up with a puddle in the bottom of the pan, when you pull out the transformers you have one side blemished with varnish,  even with tilting in the pan, the bottom still collects varnish, so we make that side to be the bottom of the transformer so the chassis hides the blem.

ceramic tiles seen in the toaster oven  keep direct heat from the elements  off the pan, and just in case you have varnish leaking out off the pan, it does not drip on the elements.   
you can use plastic microwave dishes also from TV dinners or Stouffers mac cheese as they are rated for microwave heat (boiling liquids).

 

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I just scored a pair of HP200cd gens , both power up but are untested ,33 euros +postage , Ive been wanting one of those for ages ,
are there any things such as re capping that these units needs to be done to get them working right ,the build quality looks amazing .  The 40 watts power consumption could probably heat my new winding shed as long as I do the insulation right  ;D

 
> both power up

Do you get a Sine output?

Does the big knob turn?

The last one I had, had these troubles:
Tuning knob stuck from old oil. Had to pound it out.
Large (10u?) coupling cap from the oscillator power plate was bad.
6SJ7 oscillator first stage had a cracked heater: worked sometimes. (And being a metal type, I could not just see the no-glow.)
 

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