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Thread: Insulating Varnish & transformers

  1. #1
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    Post Insulating Varnish & transformers

    rewound a transformer and now need to varnish the windings. I think what i need is insulating varnish. do you guys know if this is something very different from regular varnish and what type of store one obtains it from, ie motor shop, etc? last question, do i have to be concerned about it acting as a solvent on the magnet wire and creating a short? thanks in advnace
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  2. #2
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    Glyptal is usually the preferred choice for electrical applications.Hope these links help.
    http://www.electro-wind.com/Product/inscoat.htm

    http://www.glyptal.com/Distributor.htm
    Home
    Good judgment comes from experience, and experience....well that comes from poor judgment.

  3. #3
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    Mac,
    I would stay away from the Glyptal/air-dried coatings for windings. Down within the windings where they do not get exposed to air/oxygen the varnish will remain a gooey mess. Yes, I know air dried coatings have been used for this application, and this leads to failure down the road.

    I would recommend a room temp. cure 2-part unsaturated polyester as used in body putty. It should be thin enough to penetrate the windings. The gel time can be regulated by the amount of hardener used. A 2-part epoxy could also be used if the viscosity is appropriate. The windings can also be heated which increases the penetration of the varnish and will decrease the cure time.

    MSC and Mcmaster sell these types of products.

    If you need more info, give a holler.

    Chris

  4. #4
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    Insulating varnish is similar to regular varnish but the insulating varnish has a higher heat resistance.

    Use Glyptal. It will air cure or you can heat cure it. Preheat to about 100-120 in the oven. Brush it on heavy and allow to set/soak a few minutes then apply another coat. If the winding keeps wicking up the Glyptal, keep applying coats until it stops. The moderate heating of the winding will thin the varnish and allow it to wick between the windings.

    When it's taken all it will take, let it air cure (and drip) for about 15-20 minutes. If you want to heat cure it and speed handling, bake at about 140-150 for 2 hours. Otherwise, it will take overnight to air cure.

    This is the best price I've found for Glyptal.

    http://www.caswellplating.com/aids/glyptal.html

  5. #5
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    The motor and transformer industry have developed over the years lasting and effective ways of immobilizing windings and that is a heat cured varnish or resin. Air dry insulating materials are not used escept for surface application.

    Take the assembled transformer to a motor shop and have them dip and bake it for you. It won't cost much and it ensures the windings are immobilized against relative movement under the influence of alternating current magnetic fields. There is nothing like an overnight dip in the real goods to ensure saturation.

    Because transformers are layer wound, there are few interstices for the impregnating varnish to insinuate itself into the conductors. Its common practice for each layer to get a few strokes from a varnish brush during manufacture. This ensures at least token bond between conductors and support.

    [This message has been edited by Forrest Addy (edited 03-12-2006).]

  6. #6
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    Forrest is right about having someone else do it for the best application. I often forget that some of you live in/near a large city and have the advantage of specialized suppliers at your finger tips.

    You didn't mention the size of the transformer or it's winding size. If it's the size of your fist or smaller, do it yourself. The last time I went to a motor shop, it cost me $50 to get into the door. I hope your suppliers are more cost effective for you.

  7. #7
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    thanks guys, as always this place is a font of knowledge.

    Forrest, I had a grin when i read your line about few interstices, says me to myself, he hasn't seen my windings! I'm getting the voltage I want it the new secondary is NOT the nice neat winding that the primary is...no doubt it was wound on a bobbin before the E was welded shut. Even with a extra set of hands helping i was not able to get a very neat job of the windings. I'm think that there are so many cavities with the poor winding job that maybe the dip or polyester is the way to go.

    thanks again for all the ideas and info

    ACF - any other hints as to how to find that kind of polyester? is it basically Gelcoat? i'm not having much luck googling. epoxy also sounds interesting, would i matter much what epoxy was used? iirc you control viscosity by heat, so I could apply several thin applications to get in the spaces

    good point CCW, the transformer is big, pulled it from a microwave, rewound the secondaries to give me about 28 rms and 8 rms, higher voltage will be at max 6 or 7 amps driving stepper motors, low is neglible amps, fans, ttl etc.

    I'm in Toronot, there are motor shops around, but if i start spending $50 on it, i should have just bought a transformer (yeah i know, don't say it...trying to make this as much diy as i can)



    [This message has been edited by Mcgyver (edited 03-12-2006).]
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  8. #8
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    They are commonly vacuum-dipped, to get varnish everywhere. We specify that.

    The heat-cured is the best type, although others do work. The varnishes used are intended for the application, and differ by heat rating, and heat class of transformer.

    Glyptal is best used for exposed areas only, it doesn't soak-in well, although its OK as a varnish. You CAN pull it in with a vacuum, but I don't actually know about its heat resistance.....

    Get it done by a motor shop if you can, that will be best.

    The correct type varnish will not affect the winding insulation at all. But you are right to be concerned, insulating systems vary, and not everything is compatible.

    Any transformer will have used a UL insulation system, and everything will carry UL recognitions and have a file number.

    No UL file number? I wouldn't advise using it in a power transformer.

    [This message has been edited by J Tiers (edited 03-12-2006).]
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  9. #9
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    Back in the good old days (50s & 60s)I hand wound a few small motors and transformers. For lack of anything better I used regular orange shellac. (Some of the old books back then actually recommended it.) They ran for years with no problems. I air dried and then put them in a warm oven. No warranty on this. Remember that the solvent in shellac is alcohol and that it is flammable

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  10. #10
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    Mac,

    The gelcoat type of of resin is what I suggested.

    Check out www.mscdirect.com and look at part number 00001958.

    A commercial shop that can bake a specialized coating would be ideal, as baked coatings are just about always better than room temp. cured products as others have mentioned.

    JT,
    If you don't mind me asking, what type of apparatus are you having VPI'ed (vacuum pressure impregnation)? The VPI process is the best way to go as it fills and penetrates even coils with layers of tape. You're probably using a P.D. George resin system as they are just about the only big insulating resin supplier left in the country.

    Chris

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