re-potting options for HV sparking device?

JonIverson, Thu Oct 17 2019, 02:17AM

I'll try to keep it simple. I have a DIY high voltage demonstration sparker that uses a quadrac driving two HEI ignition coils in opposite phase. The quadrac supporting circuitry is not in any kind of insulation/ potting, but for years the two HEI coils were under mineral oil. There were never any leaks, but recently I noticed a small puddle in the quadrac container, which lies underneath the HEI oil potted coils. Not sure where the oil was coming from, plus I wanted to change potting to something other than oil, I drained and cleaned out any remaining mineral oil, then potted the HEI container, which is simply a PVC junction box, in paraffin wax after heating the wax in a double boiler on the stove. The junction box was kept in the oven at 200 F. All seemed to go well. It took several pours, but the wax stayed molten for several hours until the oven was turned off. However, after cooling today, I noticed some depression in the center of the wax. Not enough to uncover anything, but it has me a bit concerned enough that I am thinking of repotting. So, as I used only paraffin with no additives, I'm wondering what I could mix it with, upon remelting, to provide strength, no shrinkage with temperature changes, and of course insulating properties? I read here in the archives that someone added low temperature glue sticks to their paraffin for this purpose. If this indeed works, it would be the cheapest way for me to go, providing I can find out how much glue to add. There is 6 lbs of wax to remelt (the amount that the PVC box holds and surrounds the coils). That is another issue. Since I initially melted and poured everything from the stovetop double pan, which held about 2 lbs of wax each time, melting all 6 lbs within the junction box will have to be done differently, so would welcome any ideas there too (to take a guess, I suppose Id just have to place in the oven at 200 F for many hours until all the wax melted).

Thank you in advance,
Jon
Re: re-potting options for HV sparking device?
Sulaiman, Thu Oct 17 2019, 05:08AM

I guess the easiest would just be to top up with more wax.

Pouring hot wax should melt the top layer of the old wax so it should be quite homogenous when cooled,
to be sure you could melt the top layer a little with a heat source such as,
hot air gun, hairdrier, or infra red lamp ?
Re: re-potting options for HV sparking device?
JonIverson, Thu Oct 17 2019, 04:55PM

Upon examination today, the paraffin has shrunken too much and what looks like a crack around one of the transformers.

I'd really like to do as I said above, either using a mixture of beeswax/ rosin or paraffin/ beeswax and hot glue if I can find out more about mixing ratios with the hot glue and what type of hot glue?
Re: re-potting options for HV sparking device?
2Spoons, Thu Oct 17 2019, 10:14PM

Ideally you want a wax that stays pliable when cold to avoid cracking. This is what additives like glue sticks, or polyethylene are supposed to do.
Re: re-potting options for HV sparking device?
JonIverson, Sat Oct 19 2019, 03:04PM

Nice ideas, guys, but I really need to know what ratio of hot glue to paraffin I should be mixing? My previous paraffin only potting took 6.5 lbs of paraffin, so, being that the low temperature sticks are only purchased in small quantities locally for me, there'd be no way I could mix 50/50 for example. If I can't find a reliable ratio number, and I haven't so far even with Googling, then I'm going to have to either go back to all paraffin or back to oil, but I had really hoped to not have to go back to oil. So, can anyone tell me the ratio I should be using? Thank you in advance.