Re: Soft Encapsulants.
2Spoons, Mon Jan 28 2019, 12:32AM

I think urethanes are generally cheaper than silicones.

Re: Soft Encapsulants.
Patrick, Mon Jan 28 2019, 03:32AM

let me look at the urethanes.

I did find this:

Re: Soft Encapsulants.
2Spoons, Mon Jan 28 2019, 08:01PM

Ouch$! USD 200 per litre !!
Urethane casting resin - probably a rigid resin - is going for $50/gallon on ebay. Flexible resin will be a similar price probably.
One thing with urethanes though - you MUST keep the resin components dry. The isocyanate part reacts with water to form CO2 - this is how urethane foams are made. Great for
thermal insulation, terrible for potting electronics.

Re: Soft Encapsulants.
Patrick, Wed Jan 30 2019, 06:19AM

were going to start with this one :



2 are on the way. 800ml total for 20 US$ , 20kV per mm.

Re: Soft Encapsulants.
Patrick, Tue Feb 05 2019, 06:30AM

here it is, 800 mL.

it looks like its about as viscous as honey. maybe thicker. im not sure what that means for getting in between turns on the fine secondary wires.

i could vacuum pull it, then pressure it to 50 psi.

pic:

Re: Soft Encapsulants.
2Spoons, Wed Feb 06 2019, 02:54AM

The datasheet says its thixotropic, so vibration should help it flow.

Re: Soft Encapsulants.
Patrick, Wed Feb 06 2019, 05:13AM

ok, ill build a cup to hold the liquid, a magnet drop system, and then a vibrating device ? like a piezo speaker ? i have deafening ones fro home burglar alarms. what frequency would be desirable ? the container will also be able to hold 50 Psi if needed.

Re: Soft Encapsulants.
hen918, Wed Feb 06 2019, 12:41PM

A hobby motor with an off-centre weight on the shaft is a very useful source of vibration for that kind of thing.

Re: Soft Encapsulants.
the_anomaly, Wed Feb 06 2019, 07:46PM

A hobby motor with an off-centre weight on the shaft is a very useful source of vibration for that kind of thing.

I tried using a cell phone vibration motor for something similar but it was not enough. So as long as the hobby motor is larger, I think this will be a good option. Old PS2 game controllers have decent sized vibration motors.

Re: Soft Encapsulants.
2Spoons, Thu Feb 07 2019, 01:50AM

A quick search suggests higher frequencies will be better as you can achieve higher shear at lower amplitudes. I think that will be important for filling tiny spaces - maybe even go ultrasonic.
More power will always be better too. Do you have access to a sonar transducer? That would be capable of ~100W at 80kHz

Re: Soft Encapsulants.
Patrick, Thu Feb 07 2019, 05:28AM

i would have to burgle the Navy Research Lab to get one.

Re: Soft Encapsulants.
2Spoons, Thu Feb 07 2019, 09:41PM

It occurred to me an ultrasonic cleaner would be just as good - a cheap one would do.

And fyi, a lot of fish finders put out power in the 100W range - pulsed of course.

Re: Soft Encapsulants.
Patrick, Sat Feb 09 2019, 06:48AM

heres what im planning :

i can add to it later.

Re: Soft Encapsulants.
2Spoons, Sat Feb 09 2019, 08:58AM

I'm not convinced curing under pressure is a good idea. You might end up permanently embedding stress in your encapsulant, making it more prone to cracking in the future. Or worse, you trap a bubble at 50psi, which will break things when you let the pressure go.

Re: Soft Encapsulants.
Sulaiman, Sat Feb 09 2019, 09:57AM

I too think that applying pressure during setting is not a good idea;
. as above, high pressure bubbles could be trapped in the silicone
. if the vacuum was adequate there should be no air pockets to form bubbles
. pressure vessel design is more difficult

After mixing your silicone and catalyst de-gas it before introducing to the vacuumed object to be potted.

Calculate/estimate the heat generated by each potted component as silicone rubber is an incredibly poor conductor of heat and local hotspots can destroy the rubber.
VERY frustrating to have your latest work of the art encapsulated in charred/bubbled silicone :(

This is the rubber that I bought for my diy solar panels, seems ok, no idea if still available,

Re: Soft Encapsulants.
Patrick, Sat Feb 09 2019, 07:31PM

ok ill consider that. i still need a pressure vessel for other purposes.





i mostly worry about these tiny windings packed together tightly, and the honey like viscosity of the silicone. iggies and flybacks obviously do it well.

i have 24 minutes of low viscosity then after 30 minutes it gets noticeably thicker.

Re: Soft Encapsulants.
2Spoons, Sat Feb 09 2019, 11:22PM

Maybe try adding a thinner? Like
It would not only lower viscosity, it also increases cure time - both of which would be an advantage for potting. It does reduce cured strength, but for potting I don't see that as a problem.

Re: Soft Encapsulants.
Patrick, Sun Feb 10 2019, 03:17AM

here is the piping.

Re: Soft Encapsulants.
Conundrum, Sat Mar 07 2020, 09:11AM

Useful tip: The blue cure glue sold under the brand "Xtreme UV" seems to have fair to good HV performance and I've tested it here.

Re: Soft Encapsulants.
Patrick, Sat May 02 2020, 11:42PM

this "Xtreme UV", is it the kind of UV light curing type?

I worry about curing normal hard epoxy due to heating and cooling causing failure (cracking) later in life. If I'm going to the trouble of vacuum potting I want these to last.

I'm theorizing a method where we depart from the traditional flyback solid block and move to an oil/epoxy hybrid. this would mean a thin (.050) cured epoxy layer - vacuum potted to the bobbin and windings. then a small tank of oil to do the bulk insulation. But liquid tight containers that don't burst or leak are not ideal.

Re: Soft Encapsulants.
Conundrum, Tue Mar 30 2021, 07:14AM

It is!
I've also used it for LED repairs and it works well.