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Re: [TCML] Insulating a MOT
More comments interspersed.
----- Original Message -----
From: "Jon Danniken" <danniken@xxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, November 08, 2012 5:07 AM
Subject: Re: [TCML] Insulating a MOT
On 11/07/2012 04:56 PM, mrapol@xxxxxxxxxxxx wrote:
. Has anyone ever tried spray-on rubber undercoating as
I have not used undercoating as a high voltage insulator, but glancing at
the MSDS of one particular product, "Rustoleum Undercoating"
reveals that the product contains bitumen.
Turns out this is the stuff I have on hand. I have also used CDC's spray on
Checking the wikipedia page for bitumen
(http://en.wikipedia.org/wiki/Asphalt), we learn that, "Most natural
bitumens contain sulfur and several heavy metals, such as nickel,
vanadium, lead, chromium, mercury, arsenic, selenium...."
I would expect a commercial product like Rustoleum would be refined to
remove any heavy metals, to meet any EPA requirements, but I don't know for
So the bitumen in this particular brand of undercoating might have a
metallic content, but whether or not it might be a problem in a MOT
running at 60Hz will be the question (I do not know the answer to this).
I have half a dozen MOTs lying around. I think I'll coat one with the
Rustoleum and see what happens--taking due care, of course.
Now here is another brand of undercoating (Tectyl 127cg -
which actually is an insulator, with a dielectric strength of 800V per dry
mil (0.001 inch).
So, it might depend upon exactly which undercoating product you end up
using; the Tectyl product is certainly rated as an insulator, while the
Rustoleum product will require you to run an experiment to see if it will
I'll see if I can come across any of this. Not familiar with it.
Personally, I would try to source another MOT with better insulation, or,
barring that, I would pot the one you have in paraffin (I have my NSTs
potted in wax, as it has a dielectric strength of between 200V to 300V per
mil). Paraffin has a very low viscosity at the temperature of boiling
water, which gives it the ability to penetrate pretty well; not as well as
oil, obviously, but it might be good enough depending on how deep in you
have to go (you can also preheat the MOT core to help keep the wax liquid
while it penetrates).
I have some experience with paraffin, castor oil, glycerin, and epoxy as
potting compounds. (The Cockroft Walton VM I use is potted in epoxy, and two
others I have are imbedded in paraffin). I was just curious if this
rubberized product, spray undercoating, had any hobby uses. I didn't want to
have to remake my MOT power supply in order to stop the arcing, though
that's probably the most effective thing to do.
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