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epoxy high voltage strength

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Microwatt

Fri Sept 07 2012, 04:21AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Posts: 224

I want to know what epoxies are high voltage resistant.

jb weld
2 ton epoxy
I want something sold at a hardware store.

Patrick

Fri Sept 07 2012, 04:50AM

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

Microwatt wrote ...

I want to know what epoxies are high voltage resistant.

jb weld
2 ton epoxy
I want something sold at a hardware store.

i have had this problem myself, along with insulating oils.

EDIT: internet connection crapped out...

continuing:

first, i would avoid the JB weld and all other metal filled epoxies, for the obvious reasons.

second, in table and charts i consistently see 500 V per 0.001" (which i believe) however some claim 1000 V/mil, yet i start getting suspicious when they start moving above those numbers.....

remember sharp edges enhance breakdown, so just as important as dielctric breakdown values, is preparing the surfaces to be covered, radius and smooth everything you can.

the 5 minute clear ones ive had good luck at the 400 to 500 per mil breakdown on devices of 5-10kv for 1 to 3 years at a time. 30 minute yellow-clearish ones seem to work well too. (above 20kV potentials, with short distances, i start depending on food oils and porcelain. Not epoxy)

epoxy chemistry is very similar even between different makers.

third, supposedly elmers is good too, and i know silicone tub and tile stuff is good too from first hand experience, the MMA "plastic bonders" are the best!

threads:

HV Resistors for HV measurement....

Need Advice! Insulation thickness at HF HV AC

2Spoons

Fri Sept 07 2012, 05:23AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

Pick something clear, no metal fillers. Pretty sure JB Weld has either aluminum or steel powder filler for strength.

Patrick

Fri Sept 07 2012, 05:55AM

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

Are you needing just 4 oz ?

Ash Small

Fri Sept 07 2012, 06:43AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Do you need strength as well, or just HV insulation?

The 'five minute' epoxies don't cure with the same strength as the 'slow cure' ones.

Also, you have more time to work with the slow ones before they start to harden.

Shrad

Fri Sept 07 2012, 06:57AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

I use vinyl sheet, precisely from MacTac, product Macal 9800 pro

this is 0.1mm sheet in large rolls, similar dielectric strength as epoxy, and it has a 7 years lifespan in exterior as well as fireproof homologation and excellent mechanical properties

pretty expensive, but two layers resist easily several kilovolts, and 4 layers resist racing sparks of 10cm length

HV Enthusiast

Fri Sept 07 2012, 01:09PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Be very careful with epoxies. If you use an appropriate epoxy for high voltage insulation, you must ensure it is cured properly without air bubbles, otherwise you will compromise the integrity of the epoxy. Most cheap epoxies, such as those bought in the stores and cured at room temperature will almost always have air bubbles.

Also, if you are using any epoxy or other potting material for high voltage insulation and are using it for either high speed or high bandwidth applications such as a high bandwidth divider, the dielectric constant of the epoxy must be taken into account.

This is especially important for anything high speed as some epoxies have very high dielectric constants which mean considerable stray capacitances can exist which will impact the performance of high speed circuits.

Antonio

Fri Sept 07 2012, 01:54PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

I once tried regular Araldite as high-voltage insulator. Worked for some time, but for some reason become quite conductive after some time, eventually becoming completely useless. I had to remove everything and rebuild the device using hot glue, that worked perfectly.

Patrick

Fri Sept 07 2012, 04:51PM

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

Yes, 5 minute epoxies have about 1/2 the strength of the slow ones, (1 minutes epoxies are 1/4 strength or less of a 30-60 minute one.)

bubbles have rarely been a problem, when i pour, i use my breath or a small torch to lower the viscosity and pop bubbles. (remember it the CO2 that pops bubbles more than the heat. Dont carbonize or scorch your epoxy or youll regret it.)

I forgot! dont pour more than about 1 cubic inch of epoxy in a confined space otherwise it may smoke or burn. (Ive done it)

there are casting products for the 4-8 oz range that are low in exothermic potential.

Microwatt

Fri Sept 07 2012, 10:42PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

this use is for thin films of .So i should avoid any epoxy that uses black and white mix agents. stick with clear epoxy right? the actual distance i am insulating is about 5mm between potentials do you think bubbles will be a problem at this thickness?

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