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Potting A Voltage Multiplier

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jpsmith123

Tue Jan 10 2012, 02:51AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Well I vacuum potted the multiplier today with the Qsil 12. (I'll try to post a picture of it tomorrow, as it should be fully cured by then).

After talking to Qsi's tech support dept., I decided to use primer on the foil side of the circuit board and on the bottom and walls of the ABS box.

It went alright I suppose, but I had to stop pumping it down when it got just under 1 torr pressure, as it thickened up quicker than I thought it would, and even small bubbles were splattering the stuff all over. I hope it's good enough as is.

Anyway, I know one thing for sure: If I ever make another multiplier, it's going to be air insulated.

Patrick

Tue Jan 10 2012, 09:32AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Why bother pulling a vacuum at all, their are no small spaces like in a dry transformer or layered cap. just slowly poor it in.

And since you did pull a vacuum, did you let the vacuum go before the Qsil setup? you should have... the atmosphere with press the fluid into the small spaces that were still at 1 torr.

jpsmith123

Tue Jan 10 2012, 02:36PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

The main issue is that there are places where the efield is high. For example there are some traces on the circuit board where I've got 20 kv separated by 0.5" or so...along with the unavoidable field enhancement.

Also: (1) the board is laying flat, which tends to trap air, and (2), you'd be amazed how much air gets trapped in the encapsulant as you're mixing it...you don't realize it until you see it come out later under vacuum.

jpsmith123

Wed Jan 11 2012, 02:27AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Here's what the finished multiplier looks like:

And here's the inside:

1326248841 1321 FT130463 Multiplier Inside

Patrick

Wed Jan 11 2012, 02:51AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I have to admit JP you do good work...

jpsmith123

Wed Jan 11 2012, 03:26AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Thanks Patrick, but that's the OCD talkin' (or in this case, workin')...not me...so I really can't take any credit for it...

Alex M

Wed Jan 11 2012, 03:44AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

jpsmith123 wrote ...

Here's what the finished multiplier looks like:

And here's the inside:

Nice job buddy ( ;

Patrick

Wed Jan 11 2012, 06:00AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

can you get those spark plug clips too? where did you snag those male spark plug tips.

in your previous devices i see you use all-thread to extend them out ofthe main device.

jpsmith123

Wed Jan 11 2012, 02:28PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Originally I was going to use banana jacks. I was plannning to make them out of modified 1/4-20 x 2" pan head brass machine screws. But then I ran into problems because the alloy used in those screws is really hard to drill and tap. I made one (after breaking a drill bit and almost breaking a tap), and I decided I'm not making any more.

So I went back to my old tried-and-true method of making some 10-24 threaded studs - with 1.5" of 10-24 thread, then a 5/16" flange, then about 0.35" of 8-32 thread (for the spark plug nut). I made these out of 5/16" brass (360 alloy) rod. The other end of the rod is also drilled and internally tapped for a 4-40 x 1/4" screw (for a ring terminal).

Simulations tell me that there won't be any corona along the insulator body, but only at the end.

Anyway, I got the spark plug nuts from a company called "BG Service" (or something like that)...which reminds me I have to see if I can get some more...if not I have to try and make some.

Lastly, I'm going to use "Beru C6" connectors (with 7mm dia. silicone insulated, copper-core spark plug wire) for the transformer-to-input side of the multiplier connections, but I think I will try to make my own connectors for the 50 kv multiplier output, so as to minimize corona and accomodate bigger wire with more insulation.

radhoo

Wed Jan 11 2012, 06:11PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

It looks very nice, very pro built.

BTW, do you know that Glassman manufactures their High Voltage power supplies using multipliers insulated by air?

They use some very nice PCB boards, and the soldering is carefully executed to avoid any sharp points.

I used a few up to 70KV with nothing but air as an insulator:

LE: It would have been wise to also add some HV low ohmic value resistors in series with those diodes to limit the current and reduce the stress they receive .

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