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Potting compound

Discussion in 'General Electronics' started by Orrin Iseminger, Mar 3, 2005.

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  1. I'm re-winding an antique coil that was used in the low tension
    ignition system for a very early internal combustion engine. The
    original was embedded in a potting compound consisting of tar. It has
    aged and at room temperature more closely resembles brittle hard coal.
    There's nothing soft and "tar-ry" about it.

    I will be using a plastic bobbin for the new coil. Because the old
    tar has a fairly high temperature melting point, I'm afraid to re-use
    it for fear of melting the bobbin.

    That brings me to my questions:

    1) Where can I obtain for a reasonable price a small quantity of
    potting compound, say, a pound or two? It can be thermosetting or an
    epoxy type. I would much prefer something that can be melted and
    poured our of the cannister, should re-winding ever become necessary,

    2) Where can I obtain Glyptal, either in quart quantities or in spray
    cans? I'd like to give each layer of the coil a coat of Glyptal as
    I'm winding.

    Thank you.

    Orrin Iseminger
    Colton, Washington, USA
    So many projects. So little time.
  2. Lou

    Lou Guest


    You could use wax or paraffin; they are cheap, good insulators and are
    easy to melt. 60 years ago, before polymers were available, electronic
    components were often impregnated that way.
  3. HankG

    HankG Guest

    How about hot-melt glue?

  4. On 4 Mar 2005 07:35:46 -0600,
    Excellent idea. Thank you.

  5. Harold Ryan

    Harold Ryan Guest

    The melting point of wax is 36 deg C. Boiling pt is 342 degC. The flame temp
    is 1250C. So you might have a problem with the wax melting in the engine

    We usually use silicone as a potting material but it can't be removed.

  6. Harold --

    Thank you for the good advice. I'll re-think my plans. I certainly
    won't want melted wax running out of the cannister!

    I didn't mention this in the original post, but this is a stationary
    engine that isn't housed in a compartment. I'm not so worried about
    ambient temperature melting the potting compound, but coil heat,
    itself, might.

    On this type of ignition system there is very little resistance. Coil
    resistance is very low, so for the brief moment it is energized,
    current is quite high. I expect that coil heating will be

    I suspect there was good reason to pot the original coil in something
    with a high melting temperature.


  7. Robert Baer

    Robert Baer Guest

    General Cement has a spray Red Dielectric Sealer.; insulating dope
    with a high dielectric strength.
    Can be used instead of Glyptal if you cannot find that.
  8. Thank you for the information. I appreciate it.

    Best regards,

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