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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Has anyone ever potted a voltage multiplier with silicone potting compound?
I've got the board ready. (As soon as I somehow get the flux residue off of it that is).
My question is, should I give the board (particularly the foil side), a coat of primer?
I know I've got short creep distances that would flash over in air, but will it suffice to just pour and vacuum encapsulate? I guess the question is: does the silicone need to actually be "bonded" to the board to prevent a surface breakdown, or will intimate contact (no air) be enough?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
My answer is no, i havent potted a multiplier with silicone.
but a advise you to do this: first get a scrap section of that very same circuit board, then etch it with some large areas exposed and some traces left behind. then conduct a practice run with your real encapsulant, in this case your silicone.
when it is fully cured, do a pull and/or scrape test and see what the bonding properties are.
Question: what do you mean by "primer" ?
EDIT: are those blue things planar HV resistors? perhaps EGB's FEX type ones?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
depends on what type of silicone you use. some kinds just can be easly removed and some kinds stick. I prefer candle wax you can easly remove it to get to components.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
This silicone stuff I have was advertised as having "primerless adhesion to many surfaces", or something like that, but I don't have enough experience with silicones to know what that really means...primarily with regard to insulating against a surface breakdown.
When I ask manufacturers for specific information regarding adhesion to certain things, I usually get an ambiguous answer and a recommendation to do a trial run and/or to use a primer "just to be sure".
Anyway, I forgot that I had a little bottle of silicone primer (which I just found), so I guess being that I have it, I'll use it on the board.
(And BTW those resistors are Ohmite 500Meg "Slim-Mox" HV resistors (being used as a bleeder for the capacitors). They're rated at 20 kv in air (apparently), so I figured that in potting compound they could work at a higher voltage of 25 kv.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
This silicone stuff I have was advertised as having "primerless adhesion to many surfaces", or something like that, but I don't have enough experience with silicones to know what that really means...primarily with regard to insulating against a surface breakdown.
When I ask manufacturers for specific information regarding adhesion to certain things, I usually get an ambiguous answer and a recommendation to do a trial run and/or to use a primer "just to be sure".
Anyway, I forgot that I had a little bottle of silicone primer (which I just found), so I guess being that I have it, I'll use it on the board.
(And BTW those resistors are Ohmite 500Meg "Slim-Mox" HV resistors (being used as a bleeder for the capacitors). They're rated at 20 kv in air (apparently), so I figured that in potting compound they could work at a higher voltage of 25 kv.
So youve been able to grab the slim mox's , hos your supplier? how much were they? and what are thier specs?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
The AC voltage applied to the multiplier will be approximately 12.5 kv peak, so the capacitors will see about 25 kv. The capacitors themselves are rated at 30 kv, but looking at the size of them (i.e., the creep distance between the leads) they apparently have to be oil immersed or encapsulated with something to work at that voltage.
BTW this multiplier construction is starting to really get on my nerves. I just can't come up with a way to lead the voltage in and out (i.e. create a practical set of mostly corona free terminals) that I'm happy with. Pretty soon I'm going to forget terminals and just put HV wire leads on it and be done with it.
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Potting A Voltage Multiplier
