RE: Potting compound suggestions

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

Original poster: "Mccauley, Daniel H by way of Terry Fritz <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>


Check out GE Silicones.  www.gesilicones-dot-com

You can purchase large volumes of samples for about $20.00.  They have a
variety of different types.

I order samples through them all the time.

Dan



           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
 >
 >
 >