to vacuum or not to vacuum... HEI epoxy potting?

[Jim Horton]

My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum? If so, how would it be done? Single
stage pump availability, but nothing available other than a small
polycarbonate vacuum jar which wouldn't fit the junction box. I have
read of folks placing premixed epoxy itself only under vacuum for 5
minutes, then carefully pouring the nearly bubble free solution into
their circuit. Personally, I don't think a vacuum will be required as
the transformers already have a robust potting so it would just be a
matter of keeping arcing away from the core and ground sides (maybe I'm
wrong).

2) How much heat is produced by the reaction and would the junction box
be able to handle it? Since the connections into the box are already
sealed, I could place it in water during the curing process.

3) Not wanting to spend a fortune even when the funds are available,
here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the small RC
circuit I've discovered can be soldered in later. I know it's probably
overkill, but always wanted to try it and will sometime after the
holidays with spare funds. I will point out that, years ago when I was
a teen, I tried such a feat potting insects. The result was horrible as
I didn't know at the time that the insects had to be fully dried first,
lol.

Comments and suggestions welcome. Thanks in advance.

 

[Jim Horton]

On 10/31/19 5:33 PM, Rick C wrote:

I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

 

[Rick C]

On Thursday, October 31, 2019 at 3:29:16 PM UTC-4, Jim Horton wrote:

My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum? If so, how would it be done? Single
stage pump availability, but nothing available other than a small
polycarbonate vacuum jar which wouldn't fit the junction box. I have
read of folks placing premixed epoxy itself only under vacuum for 5
minutes, then carefully pouring the nearly bubble free solution into
their circuit. Personally, I don't think a vacuum will be required as
the transformers already have a robust potting so it would just be a
matter of keeping arcing away from the core and ground sides (maybe I'm
wrong).

2) How much heat is produced by the reaction and would the junction box
be able to handle it? Since the connections into the box are already
sealed, I could place it in water during the curing process.

3) Not wanting to spend a fortune even when the funds are available,
here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the small RC
circuit I've discovered can be soldered in later. I know it's probably
overkill, but always wanted to try it and will sometime after the
holidays with spare funds. I will point out that, years ago when I was
a teen, I tried such a feat potting insects. The result was horrible as
I didn't know at the time that the insects had to be fully dried first,
lol.

Comments and suggestions welcome. Thanks in advance.

I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[John Larkin]

On Thu, 31 Oct 2019 17:43:01 -0400, Jim Horton <jhorton@nospam.net>
wrote:

On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

Vacuum degassing is common. In a high voltage system, bubbles in the
potting can cause local corona that can eventually result in HV
breakdown.

Whether you need vacuum degassing depends on your voltage gradients.

Google high voltage potting bubbles

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Martin Riddle]

On Thu, 31 Oct 2019 15:29:10 -0400, Jim Horton <jhorton@nospam.net>
wrote:

My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum? If so, how would it be done? Single
stage pump availability, but nothing available other than a small
polycarbonate vacuum jar which wouldn't fit the junction box. I have
read of folks placing premixed epoxy itself only under vacuum for 5
minutes, then carefully pouring the nearly bubble free solution into
their circuit. Personally, I don't think a vacuum will be required as
the transformers already have a robust potting so it would just be a
matter of keeping arcing away from the core and ground sides (maybe I'm
wrong).

2) How much heat is produced by the reaction and would the junction box
be able to handle it? Since the connections into the box are already
sealed, I could place it in water during the curing process.

3) Not wanting to spend a fortune even when the funds are available,
here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the small RC
circuit I've discovered can be soldered in later. I know it's probably
overkill, but always wanted to try it and will sometime after the
holidays with spare funds. I will point out that, years ago when I was
a teen, I tried such a feat potting insects. The result was horrible as
I didn't know at the time that the insects had to be fully dried first,
lol.

Comments and suggestions welcome. Thanks in advance.

I'd use what Win used, Sylguard. You can dig it out if you need too.
Epoxy is pretty permament, really no chance of repair.
There is also a Sylguard thats like a jelly and clear, too lazy to
look up the part number. We used both in a 35kv power supply.
Only problem is you need to clean the Oil/wax out of your setup, and
use the sylguard primer. It does not work well with oil contamination.

Cheers

 

[John Larkin]

On Thu, 31 Oct 2019 15:29:10 -0400, Jim Horton <jhorton@nospam.net>
wrote:

My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum?

Why pot them at all?

When I was a kid, I used to discharge oil caps into the primary of an
old-fashioned oil-filled ignition coil, through a thyratron. The spark
would climb out over the insulator and back down to hit the primary
terminals. I had to make an oil-filled extension tube to stop that,
and got maybe 3" sparks.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Rick C]

On Thursday, October 31, 2019 at 5:43:09 PM UTC-4, Jim Horton wrote:

On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I think the point is to provide a limiter to the vacuum pulled. A valve opened for a tiny leak or something similar should do the trick.

Like others have said, epoxy is pretty much a one way street so consider that.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Jim Horton]

On 10/31/19 7:03 PM, John Larkin wrote:

When I was a kid, I used to discharge oil caps into the primary of an
old-fashioned oil-filled ignition coil, through a thyratron. The spark
would climb out over the insulator and back down to hit the primary
terminals. I had to make an oil-filled extension tube to stop that,
and got maybe 3" sparks.

One of my HEI sets I have in mineral oil now. Running in series, they
produce up to 5' sparks across the electrodes to which they are
attached. After ten years of having them in the oil, leakage developed
and I rehoused them recently. Turns out that it probably wouldn't have
been necessary. The oil was coming out through the top of the PVC
junction box cover during hot periods, like during summer. Now, even
though rehoused, I also left some elbow room under the cover, and also
placed an absorbent pad underneath.

The epoxy idea is just a fun experiment I was going to try after the
holidays using a spare set of HEI coils in one of the unused junction
boxes I have.

 

[Jim Horton]

On 10/31/19 6:21 PM, Martin Riddle wrote:

I'd use what Win used, Sylguard. You can dig it out if you need too.
Epoxy is pretty permament, really no chance of repair.
There is also a Sylguard thats like a jelly and clear, too lazy to
look up the part number. We used both in a 35kv power supply.
Only problem is you need to clean the Oil/wax out of your setup, and
use the sylguard primer. It does not work well with oil contamination.

Cheers

I plan on using a spare set of HEI's as well as a clean junction box I
have as spare to avoid any such contamination issues. Sylguard's price
about blew me away so it definitely won't be used, not for a "fun"
experiment anyway. These are spare coils and spare box, so if they quit
working after potted in epoxy, it's no loss really.

 

[Jim Horton]

On 10/31/19 6:48 PM, Rick C wrote:

Like others have said, epoxy is pretty much a one way street so consider that.

I know, that's why I'm using some old spare coils/ boxes I had lying
around. I just wanted to try it to get a feel in case I ever find that
I really need to epoxy pot something important down the road.
>

 

[Bill Sloman]

On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:

On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I left in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing.. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

--
Bill Sloman, Sydney

 

[Rick C]

On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:

On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I left in the liquid expoxy encapsulent.. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

Jim Horton <jhorton@nospam.net> wrote in
news:qpfcm7$900$1@dont-email.me:

My latest tests on paraffin itself are showing that it may not
hold up well if the environmental temperatures vary too widely.
On tests of small blocks, I have ended up with two cracked ones
after cycling in and out of the freezer a couple of times.
Granted, the HEI's won't be in those extremes and their wax
potting would probably hold up ok over long term, I still don't
like the test results I have been getting. So, just for kicks, I
am thinking about epoxy potting, something I've never before
attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after
the holidays of course).

The transformers in their junction box home would need a tad over
32 oz of epoxy. Again, these are the HEI type, a pair, and the
HEI's already appear to be potted during manufacture. I have some
questions:

1) Since the HEI's are already potted prior, would the epoxy
potting need to be done under vacuum? If so, how would it be
done? Single stage pump availability, but nothing available other
than a small polycarbonate vacuum jar which wouldn't fit the
junction box. I have read of folks placing premixed epoxy itself
only under vacuum for 5 minutes, then carefully pouring the nearly
bubble free solution into their circuit. Personally, I don't
think a vacuum will be required as the transformers already have a
robust potting so it would just be a matter of keeping arcing away
from the core and ground sides (maybe I'm wrong).

2) How much heat is produced by the reaction and would the
junction box be able to handle it? Since the connections into the
box are already sealed, I could place it in water during the
curing process.

3) Not wanting to spend a fortune even when the funds are
available, here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the
small RC circuit I've discovered can be soldered in later. I know
it's probably overkill, but always wanted to try it and will
sometime after the holidays with spare funds. I will point out
that, years ago when I was a teen, I tried such a feat potting
insects. The result was horrible as I didn't know at the time
that the insects had to be fully dried first, lol.

Comments and suggestions welcome. Thanks in advance.

There are several. Some even can have better thermal numbers with
with little silica splinters mixed in.

I would not recommend an epoxy unless you plan on zero
serviceablity. Use an RTV so you can service it if it fails. Unless
you are making a device which gets replaced upon failure and you want
permanent encapsulation.

GE makes an RTV called "RTV-11".

They make others as well, but prices vary as HV isolation strength
goes up.

DuPont makes some to and there are a few other makers.

Dolph's makes transformer varnish which is pretty thick and can
vacuum fill your voids perhaps suitably enough.

 

[Bill Sloman]

On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:

On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

--
Bill Sloman, Sydney

 

On Thursday, 31 October 2019 19:29:16 UTC, Jim Horton wrote:

My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum? If so, how would it be done? Single
stage pump availability, but nothing available other than a small
polycarbonate vacuum jar which wouldn't fit the junction box. I have
read of folks placing premixed epoxy itself only under vacuum for 5
minutes, then carefully pouring the nearly bubble free solution into
their circuit. Personally, I don't think a vacuum will be required as
the transformers already have a robust potting so it would just be a
matter of keeping arcing away from the core and ground sides (maybe I'm
wrong).

2) How much heat is produced by the reaction and would the junction box
be able to handle it? Since the connections into the box are already
sealed, I could place it in water during the curing process.

3) Not wanting to spend a fortune even when the funds are available,
here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the small RC
circuit I've discovered can be soldered in later. I know it's probably
overkill, but always wanted to try it and will sometime after the
holidays with spare funds. I will point out that, years ago when I was
a teen, I tried such a feat potting insects. The result was horrible as
I didn't know at the time that the insects had to be fully dried first,
lol.

Comments and suggestions welcome. Thanks in advance.

32oz of epoxy may get hot enough to burn. Set is exothermic. Why use 32oz when you can pack the spaces anyway? And why epoxy when you can use silicone?


NT

 

[Bill Sloman]

On Friday, November 1, 2019 at 11:55:36 PM UTC+11, tabb...@gmail.com wrote:

On Thursday, 31 October 2019 19:29:16 UTC, Jim Horton wrote:
My latest tests on paraffin itself are showing that it may not hold up
well if the environmental temperatures vary too widely. On tests of
small blocks, I have ended up with two cracked ones after cycling in and
out of the freezer a couple of times. Granted, the HEI's won't be in
those extremes and their wax potting would probably hold up ok over long
term, I still don't like the test results I have been getting. So, just
for kicks, I am thinking about epoxy potting, something I've never
before attempted on large scale. This would be just for fun whenever I
come across some spare cash again in the future (probably after the
holidays of course).

The transformers in their junction box home would need a tad over 32 oz
of epoxy. Again, these are the HEI type, a pair, and the HEI's already
appear to be potted during manufacture. I have some questions:

1) Since the HEI's are already potted prior, would the epoxy potting
need to be done under vacuum? If so, how would it be done? Single
stage pump availability, but nothing available other than a small
polycarbonate vacuum jar which wouldn't fit the junction box. I have
read of folks placing premixed epoxy itself only under vacuum for 5
minutes, then carefully pouring the nearly bubble free solution into
their circuit. Personally, I don't think a vacuum will be required as
the transformers already have a robust potting so it would just be a
matter of keeping arcing away from the core and ground sides (maybe I'm
wrong).

2) How much heat is produced by the reaction and would the junction box
be able to handle it? Since the connections into the box are already
sealed, I could place it in water during the curing process.

3) Not wanting to spend a fortune even when the funds are available,
here is what I am considering:

shorturl.at/fISZ6

Remember that this would be for a pair of HEI coils only as the small RC
circuit I've discovered can be soldered in later. I know it's probably
overkill, but always wanted to try it and will sometime after the
holidays with spare funds. I will point out that, years ago when I was
a teen, I tried such a feat potting insects. The result was horrible as
I didn't know at the time that the insects had to be fully dried first,
lol.

Comments and suggestions welcome. Thanks in advance.

32oz of epoxy may get hot enough to burn.

If it is a fast-setting epoxy. If it's under vacuum it won't have access to oxygen and can't burn.

> Set is exothermic.

Heat may be released, but the temperature rise is determined by how fast the heat is released, and the thermal resistance from the heat source to the outside world.

> Why use 32oz when you can pack the spaces anyway? And why epoxy when you can use silicone?

NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

--
Bill Sloman, Sydney

 

[Rick C]

On Friday, November 1, 2019 at 7:47:28 AM UTC-4, Bill Sloman wrote:

On Friday, November 1, 2019 at 6:18:13 PM UTC+11, Rick C wrote:
On Friday, November 1, 2019 at 2:00:50 AM UTC-4, Bill Sloman wrote:
On Friday, November 1, 2019 at 8:43:09 AM UTC+11, Jim Horton wrote:
On 10/31/19 5:33 PM, Rick C wrote:


I don't know a lot about epoxy potting, but I know you don't want a lot of vacuum. If you pull too much vacuum the epoxy will boil and you'll end up with foam as your encapsulant. I know, I did this.

I know, that was one of my concerns. That was one reason I asked about
vacuuming just the epoxy premixing container ahead of time. As I said,
because the transformers are already well potted for the autos, I don't
even think vacuum will be necessary but thought I would throw the
question out there.

I'd evacuate container the before I let in the liquid expoxy encapsulent. If it frothed at the time, that wouldn't matter, as long as you got in enough of the liquid to fill the container. If the process stalled before that happened (which seems unlikely - there isn't going to be much gas in those bubbles if you degassed the liquid before you poured it in - you can use a bit of atmospheric pressure to squeeze in the last of the liquid.

You've got to do this while it's still liquid and more or less free-flowing. Once it starts setting, atmospheric pressure will flatten any bubbles that remain.

Bubbles of atmospheric pressure air are much harder to get rid of.

If it froths, it will expand to many times it regular volume and spill out onto the vacuum chamber. Frothing is bad.

That's why you out-gas the liquid encapsulant in a deep beaker, and makes sure that the froth doesn't go over the top of the beaker ... and only after you have done that do you pour the outgassed liquid into box that contains the gear you want to encapsulate.

Doing all of that under vacuum (or a vacuum of sorts - you can't get the residual pressure spectacularly low) requires a proper vacuum potting setup, which isn't all that complicated, but not all that easy to improvise either - being able to tilt a beaker and get it to pour from the other side of the the vacuum wall requires a vacuum-greased rotating joint.

Why would you even suggest something so complicated? All you need to do is to fill the mold with the device, pour in the potting compound and then put it in the vacuum chamber. Apply the partial vacuum and make sure the potting compound doesn't foam by limiting the vacuum.

To prevent foaming it would be good to have a pressure gauge attached and test the encapsulant to see at what point it foams. Then you can monitor the vacuum to make sure foaming doesn't happen.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Jim Horton]

On 11/1/19 9:34 AM, Bill Sloman wrote:

NT will never know. He can ask the questions, but doesn't seem to be much good at finding answers.

No disrespect, but I don't think that's a fair statement. Almost
always, I DO research this stuff before asking here. The big problem I
have with Internet research is that there's too much information, so
trying to narrow down a specific thing for a specific task can take huge
amounts of time. I figured people here might have more experience in
many of the things I've done, or trying to do, to help me narrow it down
and save time.

Since posting here, and both with the group's help and my own, I've
found out some things about both mineral oil and wax potting:

1) Mineral oil can expand right out through the container if it can.
In this case, I wasn't aware how much it could expand/ contract with
environmental changes. The leakage I experienced with my ten year
stored spark device came from mineral oil expanding out from the
junction box cover. So, once rehoused, I took measures to both allow
for expansion and to compensate for any future leaks.

2) Paraffin wax probably isn't ideal for potting. My own experiments
cycling a block into and out of the freezer the last few days have
resulted in a block ending up with many cracks. However, now it's time
to remelt the block and repeat the same experiment cycling into and out
of the refrigerator since, after all, the device will never be stored
outside of this range. Then, I'll know for sure.

3) I better think again before I use epoxy. Item will be
non-serviceable, vacuuming could be a problem with my limited equipment
available, and there is a lot of exothermic reaction with the 32 oz I
would need. Such information can be hit and/or miss online, but the
group has been very helpful in helping me make the decision to probably
not try epoxy potting, especially for something this large. They just
helped me save $30 for the cheapest electronic epoxy I would have used.


Things inconclusive or I have not found out here (or anywhere else):

1) Ideal wax and additive mix ratios to better improve wax properties.
I did find information on wax-rosin ratios, but then controversial
performance if used in a heated circuit. Then there was machinable wax
(wax-LDPE), and wax-EVA mixes. Only information on machinable wax was
found and proper EVA ratios remain unknown.

2) I was not aware of RTV being used for anything other than small jobs
and/or automotive use. Now, if one wanted to criticize me, here is
where they could do it by the fact that I never specified an insulator
budget amount in which both the electronic RTV and most epoxy do not
fall.

So, again, I apologize if I haven't already found the answers I have
been looking for. I really enjoy reading this and the repair group's
posts especially since so much usenet has become useless.

 

[Jim Horton]

On 11/1/19 7:23 PM, whit3rd wrote:

On Friday, November 1, 2019 at 4:14:54 AM UTC-7, DecadentLinux...@decadence.org wrote:

I would not recommend an epoxy unless you plan on zero
serviceablity. Use an RTV so you can service it if it fails.

Huh? RTV is 'room temperature vulcanizing' material, it sets up just as
irreversibly as epoxy does. How is that service-friendly?

I was wondering about that, but didn't know quite enough about
electronic RTV to ask.

 

[whit3rd]

On Friday, November 1, 2019 at 4:14:54 AM UTC-7, DecadentLinux...@decadence.org wrote:

I would not recommend an epoxy unless you plan on zero
serviceablity. Use an RTV so you can service it if it fails.

Huh? RTV is 'room temperature vulcanizing' material, it sets up just as
irreversibly as epoxy does. How is that service-friendly?