Re: Potting compound suggestions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mike Harrison by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mike-at-whitewing.co.uk>

Paraffin wax (candle wax) probably fits most criteria, certainy cheap, and 
also re-workable.

On Tue, 22 Jul 2003 12:54:20 -0600, you wrote:

 >Original poster: "Richter, Rick by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <rick.richter-at-hp-dot-com>
 >
 >
 >
 >         Hi all,
 >
 >         I'm looking for some suggestions for relatively cheap potting
 >compounds for a couple circuits I'm putting together. I'm looking to
 >minimize corona loss and sparkover while, at the same time, increasing the
 >safety factor (insulation) for both circuits. Let me describe each circuit
 >to give you an idea what I'm dealing with.
 >
 >         The first circuit is a six-stage Cockcroft-Walton voltage
 >multiplier circuit that takes 15 kV square wave input at 20 mA with a
 >frequency of around 20 kHz from a solid-state neon sign transformer. I may
 >scale this circuit back to have it output around 60 kV instead of around 90
 >kV.
 >
 >         I know as the number of stages in a multiplier increases, the
 >actual output voltage can change significantly according to the load.
 >Therefore, I'd like to be able to measure the output voltage using a
 >combination voltage divider and digital multimeter (with about 10 Meg
 >internal resistance). I've got some 200 Meg and 10 Meg  2% high voltage
 >resistors I want to stack to form the divider, but again I want to minimize
 >corona loss and keep the exposed high voltage to a minimum.
 >
 >         I want to pot each circuit separately and I'm trying to balance
 >off several factors. Number one is cost, I want to keep things as cheap as
 >possible. I realize that submersing the circuits in mineral oil is one
 >relatively cheap way to go, but it's also pretty messy and I'd like to
 >steer clear of that method unless I have no other choice. Second, from what
 >I've read, some epoxy-based potting compounds generate significant amounts
 >of heat during curing. Also, I've heard some types of RTV release corrosive
 >chemicals while curing. So I'm looking for something that won't melt the
 >capacitors or digest the diodes in my multiplier. Third is reversibility (
 >is that a word?). If I blow a diode in the multiplier, it would be nice to
 >be able to un-pot the circuit to replace the failed component(s). By unpot,
 >I mean anything from melt under low heat (if potting in paraffin) to gently
 >chip off pieces of the potting compound. However, being able to unpot the
 >circuit is the lowest priority.
 >
 >         Does anyone know of any potting compounds that meet one or more of
 >these requirements?
 >
 >
 >         Thanks in advance,
 >
 >         Rick Richter
 >