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RE: [TCML] Polyurethane Finish Questions

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Jim Mora
> Sent: Thursday, April 23, 2009 4:08 AM
> To: 'Tesla Coil Mailing List'
> Subject: RE: [TCML] Polyurethane Finish Questions
> Hi Gary,
> I like to think that the oil base poly I use does some electrical as well as
> mechanical damage protection.

I would like to think that too, but I've never seen or heard evidence that it would.  If I increase the coupling too high on any secondary, I'm going to see racing arcs, regardless of whether it has a thick coating of poly.  One can coat their coils with Dolph's or anything else and report wonderful results, but unless the reporter has an identical secondary available with a different coating to compare against under otherwise identical operating conditions, I would view the wonderful report with suspicion.  Is the benefit you're seeking just the ability to operate at a higher coupling without racing sparks? 

If racing sparks occur on both coated and uncoated coils, the coated coil is likely to suffer greater damage, as the polyurethane probably carbonizes more readily than the high-temp enamel on uncoated wire.

> Granted its not Dolph's 43 but it would be interesting to compare. Saying
> polyurethane is for coating floors strikes me a little like saying HDPE is
> for cutting boards. - No flame intended!

I was saying that for the can of Minwax polyurethane that most of us buy at Home Depot, I do not believe that the manufacturer gives any consideration to the insulative properties of the product.  All that matters to Minwax is how it behaves on floors.  It's just a fortunate coincidence that it appears to perform the required mechanical duties as a secondary coating without causing breakdown. 

> I have particular interest at the moment as I have a mongo transformer that
> I would like to encapsulate the secondary(HV) in clear 2 part or...??epoxy.
> It is supposed to be rated at 14440 which is hard to believe given its
> construction. It is meant to be run dry too.
> Also it is fair to say the coating is an issue in very HF coils. I have a
> polystyrene thin form for this purpose. Everyone's mileage and opinion will
> vary ;-^)

What is the basis for stating that HF coils are affected by coatings?  Aren't transmitting coils in ham radios (much higher in frequency than Tesla coils) typically bare?  I guess it's not clear if the benefit you're after is a reduction of losses or protection against corona or racing sparks.

Regards, Gary Lau

> Jim Mora

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