EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: gkmaia on July 30, 2019, 01:53:57 am
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I need to take an iron core transformer apart. And the less damaging method I found was boiling it in water till the rosin/epoxy that hold the laminates gets soft enough.
I want to keep the primary winding intact and just rewind the secondaries.
My main concern is. Will the water at boiling temperature be enough to melt the enamel and then short the windings I leave untouched?
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Some use boiling water and other advise against it due to the loss of any sealing waxes.
In a second Googling of this: Dismantling transformer laminations
Found this:
http://www.tronola.com/Rewinding_a_Power_Transformer.pdf (http://www.tronola.com/Rewinding_a_Power_Transformer.pdf)
I also often refer to this for guidance:
https://ludens.cl/Electron/trafos/trafos.html (https://ludens.cl/Electron/trafos/trafos.html)
Once you break the shellac and get a couple of laminations out the rest should be fairly easy.
A solder pot is the traditional way to remove copper wire enamel and also tins the wire but there are several different heat ratings of enamel so some might be more easily compromised than others.
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I need to take an iron core transformer apart. And the less damaging method I found was boiling it in water till the rosin/epoxy that hold the laminates gets soft enough.
I want to keep the primary winding intact and just rewind the secondaries.
My main concern is. Will the water at boiling temperature be enough to melt the enamel and then short the windings I leave untouched?
The lowest temperature to melt enamel wire I have found is 155 C (for easy prototype wiring). It would seem that this leaves a 50% safety margin for that kind of wire which you probably won't find in a transformer anyway.
You could remove a winding or 2 and see how it fares in boiling water, or wrapped around a soldering iron tip ?
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Thanks for the feedback guys. And thanks for those notes. Pretty good guidance.
Have you happen to know where to buy the EI laminates?
A bit hard to find these.
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Thanks for the feedback guys. And thanks for those notes. Pretty good guidance.
Have you happen to know where to buy the EI laminates?
A bit hard to find these.
I can find out as a small family business just down the road rolls their own transformers for specialist walwarts.
Gimme a couple of days to catch up with them as I need to see them on another matter.
Remind me if I forget to post again.....got a fair bit on.
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Boiling water cannot reach more than 100C (unless pressurised.)
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Not sure I understand - why boiling water as opposed to heating the transformer up in an oven, for example?
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Boiling water cannot reach more than 100C (unless pressurised.)
Boiling oil would reach a higher temperature and would probably work better. But it would be a hell of a fire hazard. Even a common house hold deep fryer would reach 400F.
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I may have to deal with a similar situation soon. Subscribed with interest.
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Not sure I understand - why boiling water as opposed to heating the transformer up in an oven, for example?
Boiling liquid would have a lot more thermal mass and you could heat the x-fomer faster and more evenly. Also you could control the maximum temperature much better. OTOH it might be a PITA to clean everything after you got it apart.
In my experience, modern transformers are PRESSED together in large presses and it's virtually impossible to get them apart without destroying them. At that's true for high quality American made ones, the cheap imported ones might be different.
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I did manage to take it apart without heating. Just mechanical force. It is a well built Tecktronix transformer. A bit hard to put apart.
I was hoping I could keep the primaries intact and that is why I was reluctant to heat the transformer entirely.
Now with the secondaries all removed and measured I will re test the primaries insulation. May leave them there.
Thanks Tautech for the guides you attached. Pretty useful stuff.
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It is a well built Tecktronix transformer.
Out of what model ?
Tek Pt # ?
Nice windings table. :-+
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Not sure I understand - why boiling water as opposed to heating the transformer up in an oven, for example?
I'm just guessing here, but overheating the laminar e-cores has been known to cause biphasic dipthon regression when used in Turbo Encabulators.
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Out of what model ?
Tek Pt # ?
Nice windings table. :-+
It is a T912 with storage. Really cool vintage scope.
The table is a Lorch watchmaker lathe I restored a while ago. Has been really useful to restore pots, knobs and all sorts of things.
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What would be better to insulate between layers?
Polyimide or polyester tape?
The original was paper crepe tape.
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OK, feedback from my graybeard friend that's been winding transformers for decades.
Getting them apart.
Knife around the laminations one at a time to break the shellac and loosen them.
Extract tough laminations with carpenters pincers using the mechanical levering advantage they offer.
Reassembly.
You will likely not get all laminations back. As they are each sealed to isolate eddy currents cleaning them of shellac can compromise lamination insulation that minimises eddy currents. Not recommended.
A single missing lamination is unlikely to affect the ordinary transformer unduly that it shouldn't work as intended however they can run a little warmer.
To source replacement laminations exact internal measurements must be known, the width and length of the middle leg of the E lam are what the industry needs for suitable replacement laminations and best practice is to replace the complete stack for which the stack thickness needs also be known.
I now have some NZ contacts for these sorts of transformer parts but supply is normally only in bulk whereas for just a lam or 2 or a single stack my friend has offered his services if needed.
He's in Taupaki not far from me and I can arrange a hookup if required.