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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Microwatt wrote ...
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?
what voltage? 2, 20, 200, 2000, 20,000 at 5mm ?
Are you using vacuum? can you fully spead the epoxy on each layer then build them up? Are they OHP transparaencies?
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
One that works pretty well is called 3M scotchcast. We used to seal the end of windings on larger transformers that were under trains. Before we sealed them up metal filings, snow, and anything else you could think of got in there. After sealing the ends with scotchcast the problem was solved.
I packed one of the transit transformers with snow and metal filings, I packed as much snow as I could get in there I even packed it with sticks and everything else we could find, I then subjected the transformer to 6KV looking for a breakdown somewhere but it never did. I believe its rated at 5KV but it also depends on how think you apply it.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Someone on another forum suggested to expose the unmixed epoxy to vacuum to debubble it, then once mixed expose it again until set. Another possible technique is to sonicate the epoxy while molten, this tends to cause any trapped bubbles to rise.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
The best epoxy i have found for HV and vacuum work, is 'Hysol 1C' by loctite.
It is the same stuff as high spec epoxies such as 'Torr seal' and others used in aerospace and electronics manufacture.
The filler is ground silica, it is high voltage resistant, radiation resistant, heat resistant, and does not out-gas significantly. NASA uses similar stuff in its space programme.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Patrick -
Two comments -
Almost all "houshold type" silicone RTV sealants release acetic acid as part of the curing cycle. These sealants cannot be reliably used for ANY type of electrical potting or sealing use, and shouldn't be used where the reaction products may become "trapped" (for instance, sealing circular baffles inside a TC secondary coilform, where the acetic acid could become trapped in the "dead space" between baffles). There are special "electronic" grades of RTV sealant (GE RTV162, etc.) that utilize a different cure system that releases alcohol instead of acetic acid. Some automotive grades of RTV sealants also use the non-acetic-acid cure system (so they don't "poison" oxygen sensors).
Also, the "Co2 pops bubbles in epoxy" theory is an urban myth. I think I first saw that suggestion in the product application guide for the Envototx Lite epoxy that I use for overcoating wound secondary coils. I did a fair amount of experimenting with flowing room-temperature Co2 (and nitrogen) over thin films of low-viscosity epoxy that were well-populated with air bubbles of various sizes. Flowing (or completely blanketing) the epoxy with either C02 or nitrogen did absolutely nothing to make the bubbles enlarge, shrink, or pop, while subjecting the same epoxy films with gentle heat from a hot-air gun instantly popped the great majority of the bubbles. The hot air reduces the viscosity of the surface of the epoxy, and the heat expands the bubbles, so they rupture almost instantly. Feeding Co2 or niitrogen into the inlet of the hot air gun gave results no different from just using straight air.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Herr Zapp wrote ...
Patrick -
Two comments -
Almost all "houshold type" silicone RTV sealants release acetic acid as part of the curing cycle. These sealants cannot be reliably used for ANY type of electrical potting or sealing use, and shouldn't be used where the reaction products maye become "trapped" (for instance, sealing circular baffles inside a TC secondary coilform). There are special "electronic" grades of RTV sealant (GE RTV162, etc.) that utilize a different cure system that releases alcohol instead of acetic acid. Some automotive grades of RTV sealants also use the non-acetic-acid cure system (so they don't "poison" oxygen sensors).
First Herr Zapp, you communist little bugger , i was tired and should have mentioned this point (and knew someone would, but i had been drinking) but ill remind all of you, the OP wanted hardware store obtainable materials, so HYSOL-C doesnt count. there are silicones available at the hardware store that are usable for our tasks witout side reactions adverse to HV'ing.
Herr Zapp wrote ...
Also, the "Co2 pops bubbles in epoxy" theory is an urban myth. I think I first saw that suggestion in the product application guide for the Envototx Lite epoxy that I use for overcoating wound secondary coils. I did a fair amount of experimenting with flowing room-temperature Co2 (and nitrogen) over thin films of low-viscosity epoxy that were well-populated with air bubbles of various sizes. Flowing (or completely blanketing) the epoxy with either C02 or nitrogen did absolutely nothing to make the bubbles enlarge, shrink, or pop, while subjecting the same epoxy films with gentle heat from a hot-air gun instantly popped the great majority of the bubbles. The hot air reduces the viscosity of the surface of the epoxy, and the heat expands the bubbles, so they rupture almost instantly. Feeding Co2 or niitrogen into the inlet of the hot air gun gave results no different from just using straight air.
Herr Zapp
This claim however, is quite interesting. ive always been told by every epoxy maker and professional user, that it was the CO2 that did the popping (all that bothered to reply). Yet your experiments seem to indicate for sure otherwise... Hmmm i may need to investigate this further.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Interesting.
I've used the silicon acetic system on lamps before and have yet to see a failure. The trick is to expose it to a damp atmosphere for an hour then dry in low oven at <80C for a few hours, this removes any detectable acetic.
-A "Both*(&!(*$!" said Pooh, as the Basilisk virus began to take effect..
Registered Member #3282
Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224
i am doing what can be considered potting a capacitor. can you use silicone rtv even if it is trapped in plastic layers? will it still cure? the silicone will be spread very thin.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Patrick -
(Not sure what the "CLB" reference was supposed to mean, but perhaps your liver was still slightly overworked from the weekend's festivities, and was usurping oxygenated bloodflow that should have been directed to the brain.)
I'd be interested in seeing the "Co2 degasses/pops bubbles" claims from "every epoxy maker", as in 30 years of dealing with these materials the only place I've ever seen it mentioned is in the Envirotex-Lite literature. Could you provide links to ANY of the other epoxy makers who you've seen make this recommendation?
Here's the link to the Envirotex-Lite instructions that contain the "Co2" claim, under Step 4, "degassing", where it suggests that by gently "exhaling" on the freshly applied epoxy film, the Co2 in your breath will magically cause the bubbles to pop.
Given that the Co2 content in the air that humans exhale is only around 4-4.5%, the C02/epoxy interaction would have to be very strong, IF it were real.
Also, regarding the non-acetic-acid cure silicones "available at the hardware store", could you provide some specific brands or product names? I've done a pretty thorough search of hardware stores in the S. California area (Home Depot, Lowes, Crown Ace, Orchard Supply, etc) and wasn't able to find any non-acetic-acid products.
Automotive supply stores do carry some "sensor safe" RTV sealants (Permatex or Loctite "Sensor Safe Blue RTV", for example) that utilize an non-acetic-acid cure system that should be safe for electronics use, but I've personally not had any experience with them.
(Caution - ethanol imbibition can trigger swelling of delicate intracranial tissues ...)
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Herr Zapp wrote ...
Patrick -
(Not sure what the "CLB" reference was supposed to mean, but perhaps your liver was still slightly overworked from the weekend's festivities.)
Herr Zapp wrote ...
I'd be interested in seeing the "Co2 degasses/pops bubbles" claims from "every epoxy maker", as in 30 years of dealing with these materials the only place I've ever seen it mentioned is in the Envirotex-Lite literature. Could you provide links to ANY of the other epoxy makers who you've seen make this recommendation?
I said users and makers that bothered to reply have said this, not everyone... but i did first see this claimin the envirotex poroducts.
Herr Zapp wrote ...
Here's the link to the Envirotex-Lite instructions that contain the "Co2" claim, under Step 4, "degassing", where it suggests that by gently "exhaling" on the freshly applied epoxy film, the Co2 in your breath will magically cause the bubbles to pop.
Given that the Co2 content in the air that humans exhale is only around 4-4.5%, the C02/epoxy interaction would have to be very strong, IF it were real.
yes your experiments seem to indicate CO2 has no or immeasurebly small contribution to popping.
Herr Zapp wrote ...
Also, regarding the non-acetic-acid cure silicones "available at the hardware store", could you provide some specific brands or product names? I've done a pretty thorough search of hardware stores in the S. California area (Home Depot, Lowes, Crown Ace, Orchard Supply, etc) and wasn't able to find any non-acetic-acid products.
Automotive supply stores do carry some "sensor safe" RTV sealants (Permatex or Loctite "Sensor Safe Blue RTV", for example) that utilize an non-acetic-acid cure system that should be safe for electronics use, but I've personally not had any experience with them.
Herr Zapp wrote ...
(Caution - ethanol imbibition can trigger swelling of delicate intracranial tissues ...)
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epoxy high voltage strength
, i was tired and should have mentioned this point (and knew someone would, but i had been drinking) but ill remind all of you, the OP wanted hardware store obtainable materials, so HYSOL-C doesnt count. there are silicones available at the hardware store that are usable for our tasks witout side reactions adverse to HV'ing.