Re: [TCML] re-pot

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

I've used an oven. Mine had a very accurate and fairly low heat control. I simply tried one temp, then waited half an hour. If that wasn't enough to soften it, I raised the temp 5°, then waited again. Once I got the ideal temp, I would take it to the garage and carefully dig out the potting with wooden implements. Once I dug around it below the HV wires and bushings, I unscrewed the theminals and removed the transformer. I kept heating and cleaning the transformer until I had most of it clean. I used a good gasoline soaking, followed by toothbrush cleaning. The end result was probably hours of oven heating and cleaning, followed by several days of gas cleaning. I also tried using a heat gun, but that required more attention than simply leaving it in the oven, though it was faster. Since I found the temperature in the oven where it was just getting soft, there were no fumes or odors.

I never cut away the case, which I reused on all by my last rebuild. I always used paraphen to repot. The last time I rebuilt two France 15/30's, I bolted them together and found a Rubbermaid container that held both of them, and I mounted the LV and HV terminals on the lid. I filled this with motor oil. It ran fine until I got rid of it. I now only have one NST, which is a 15/120. I primarily use 14.4 and 25 kV PT's and a 14.4 kV 25 kVA pig.

As to putting it all back together, I once had to remove several layers of the fine secondary wire. I simply resoldered the larger lead to it, then wrapped it with the same "tape" that I removed to get to it. I stripped this fine wire with an Exacto knife, then handled it carefully, until I had secured it with the tape. If you plan on using wax for potting, you can probably use any kind of tape. However, if you plan on putting it in oil, you'll need an oil resistant tape, and will also have to figure out how to secure the transformer, so it doesn't slide around in your case. I believe some folks have used ammo cases for a good, gasketed metal box.

Good luck.
Adam

--- On Wed, 6/11/08, douglas smith <eyemfedup2@xxxxxxxxx> wrote:

> From: douglas smith <eyemfedup2@xxxxxxxxx>
> Subject: [TCML] re-pot
> To: tesla@xxxxxxxxxx
> Date: Wednesday, June 11, 2008, 10:42 PM
> i have been trying to learn how to re-pot nst's with
> very poor luck.
> i hate the small secondary wires i keep breaking them
> i tried the barbecue thin it didn't work well.
> I've been soaking it in diesel for 5 days doing OK but
> very gooey.
> is kerosene best or is there something better.
> my next try is to peal off box to expose brick.
> then soak it for as long as it takes.
> i don't dear smacking it with a hammer with my luck
> 
> 
>       
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