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Varnishing my secondary.

Discussion in 'Electronic Design' started by [email protected], Sep 13, 2005.

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  1. Guest

    This weekend I managed to finish winding the secondary of my smal Tesla
    coil (just over 600 turns) and now I need to varnish it. I am 14 and
    don't have a budget allowing for enough varnish to just dip a coil in.
    I am wondering if I could buy a small bottle of varnish and paint it
  2. For a second I thought you said "vanishing my secretary"...
  3. Guest

    Thanks for such an intelligent response
  4. I don't see why not. You should test your varnish on some extra wire
    and coil form material, to make sure it dried on it, without attacking
    the wire insulation (swelling, wrinkling, coming lose, etc) or the
    form material before you risk doing the winding. If you can rig up
    something like a hand turned lathe and have someone else slowly roll
    the coil over as you run a brush along it, it should turn out nice and
    smooth. The first coat (and possibly the only coat) should just
    saturate the wire, excluding air from under it, if possible. Applying
    varnish with it turning very slowly lets the varnish soak in, while
    the air gets pushed out. Once there is varnish all around a turn, the
    remaining air tends to get trapped. Fast drying varnish is not better
    than slow drying. It just gives the air less time to escape and you
    less time to get it smooth. I think I would try a urethane based
    varnish, first, maybe thinned a bit with mineral spirits (to help it
    get under the wire). If it dries very thin, you can always add
    another coat of the full bodied varnish.
  5. Pooh Bear

    Pooh Bear Guest

    Does it actually *need* varnishing ? It may be a convenient way to ensure
    it's mechanical stable of course.

  6. Dipping is not a good idea because you wind up with poor
    penetration (air bubbles) and uneven coverage.

    Sure, that's a time-tested method.
    Yes, it probably does, and not just to tie the windings down. Air
    is a Bad Thing to immerse TC secondaries in because it permits
    corona formation which encourages primary/secondary arcs. Of course
    this depends on what voltages the thing can produce, but better safe
    than sorry. Don't forget some way to hold the wire in place while
    varnishing; if nothing else drill small holes near the ends and tie
    the wires there, afterward fill the holes with something as similar
    to the form material as possible.

    A slow-drying polyurethane is best (after corona dope, but that's
    more costly and I don't think a 14-yr-old can buy it as it's
    basically just clear polystyrene dissolved in toluene) so as to
    allow any entrapped air to escape before the stuff dries.

    DO NOT shake or stir it vigorously before application because
    that'll encourage air bubbles. Also saturate the brush well for the
    same reason, and brush strokes should go along the "grain" of the
    windings (hence the suggested lathe trick). BTW, some say that it's
    best to paint the form and wind while it's drying followed with a
    finish coat; you might want to try that with your next coil.

    I've never seen polyurethane varnish in "small bottles", but
    rather in cans (you don't want to look like a dummy at the hardware
    store, do you?) and a fairly small can should allow you to apply a
    couple of coats and have enough left over for other projects.

    Mark L. Fergerson
  7. Genome

    Genome Guest

    Mum might be your GirlFreud.

    Have a look in the extremely large area where she keeps her 'make me look
    good stuff' for something called nail varnish.

    Mind you, if you're 14 then your Mum probably has some sick looking nail
    varnish with bits in it.

  8. You might want to consider the alternative method described below - but
    I suggest you discuss it first with the adult who will be responsible
    for helping you to clear it up if it goes wrong.

    If you can get hold of a thickish plastic bag without any holes, you
    could put the coil into it and add as much varnish as you can spare.
    Then seal it and by squeezing and tumbling it gently, you could spread
    the varnish all over the inside and outside of the coil. It may take
    some time to ensure that every part has been thoroughly soaked, but you
    are in no hurry because the varnish cannot begin to dry and thicken
    whilst it is sealed inside the bag.

    The tricky part will be removing the coil and hanging it up to drain and
    dry without getting everything smothered in varnish. Perhaps you can
    drill a small hole somewhere in it that doesn't matter, then you will be
    able to hook it out with a loop of stiff wire through the hole. Arrange
    a nail or hook to hang it from as it dries, with something underneath it
    to catch the drips.

    A serious problem will arise if you have any sharp edges or solder
    spikes which puncture the bag. As it is a Tesla coil, you ought to have
    carefully removed those at the outset.

    Plan ahead and assume something (perhaps everything) will go wrong. Do
    the job outdoors, keep an old washing-up bowl or bucket handy to catch
    spillage, have some rags and white spirit solvent nearby for cleaning
    up, wear old clothes and shoes.
  9. Guest

    In my case yes. Right now my coil is being held on the form with scoth
    tape, not the best choice.
  10. John  Larkin

    John Larkin Guest

    I originally read that as "varnishing my secretary" which seemed a bit

    Regular polyurethene varnish, sprayed or brushed a coat or two, should
    be fine for tesla coils or administrative assistants.

  11. Guest

    My first impression of "varnishing my secondary" put me in mind of
    something like "waxing my weasel". Coffee in the keyboard stuff.

  12. Here, I suspect even a 14-yo can buy toluene at a tiling suppliers,
    as it's commonly used to clean up tile cement. Put some in a big
    jar and feed as much polystyrene as you see fit - it's amazing how
    much polystyrene foam you can dissolve into a given jar. If you
    can't get toluene, kerosene works just as well, but will take longer
    to dry.

    In either case, make sure you are outdoors in a drafty area with
    nothing electric operating nearby!
  13. Where's "here"? In AZ USA (and most other parts of the USA)
    toluene got a bad rep as the solvent in model cement that produces
    the "buzz" so many kids killed brain cells with. Me, I couldn't
    stand the odor so I worked with open windows and a fan going.
    Yup. I'd be careful with poly foam though. I spec'd clear
    polystyrene because using the clear solid sprue (from model car
    parts trees AKA sprues) pretty much guaranteed there were no
    conductive inclusions, which is important when making your own
    corona dope. I know this from the days I was transitioning from
    building model cars to doing electronics, and wanted to put all
    those saved sprues to good use. Dope made from the sprues that
    windshields came off had much better holdoff than say black car body
    parts; the black was probably carbon black.

    I understand that nowadays in model kits polystyrene has given
    way to some kind of resin which probably won't work at all, so
    perhaps say pure white (no potentially conductive colorants) packing
    peanuts are a decent alternative source of poly.
    getting old.
    Absolutely, and obviously stay the hell away from open flames,
    small kids, pets, etc.

    Mark L. Fergerson
  14. Guest

    You and Ross Merchant
  15. Rich Grise

    Rich Grise Guest

  16. Australia. I suspect toluene has been removed from model aircraft
    dope here also, the only place I know it's used is in tiling.
    If it's plain white, I doubt there's anything conductive in it.
    I wouldn't go with peanuts, just break up the moldings from your
    last monitor, TV or other household appliance. Certainly it seems
    to generate enough static electricity.
  17. Ian Stirling

    Ian Stirling Guest

    It is possible to simply immerse the secondary in oil.
  18. Mike

    Mike Guest

    Watch out for the ones made out of edible(ish) corn products. They
    don't contain much polystyrene. If they dissolve in water, they're not
    polystyrene :)
  19. Ian Stirling

    Ian Stirling Guest

    Or if they look just like popcorn...
    (got a computer packed in popcorn once. Mother started eating it.)
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