ideas on wire feedthrough sealing of oil filled HV device?

[Jim Horton]

So I decided to use mineral oil once again for my HV transformer device
after debating and even trying paraffin. However, this time I want to
be sure my wires passing through the PVC junction box are sealed
correctly so no oil leaks through.

The transformers will be inside a 6x6x6 PVC junction box (which takes up
about 50% less volume than the prior box I used) and four connections
will be needed:

2 low voltage 600 V wires for driving the transformers, and
2 wires for high voltage output (around 100 KVDC)

So, these four wires will need to pass through the PVC box into the oil
and to the transformers.

In the past, I used two part epoxy to seal the solid wires on the inside
of the box with generous application of silicone around the wire outputs
on the outside of the box (I added the silicone layers because the
outside wire didn't quite have enough insulation and would jump to my
hand sometimes... a bunch of layers of silicone around the exit points
stopped this).

Wires are all thin 20 gauge solid. I was going to use the same
procedure, using the epoxy to seal around the inside of the container
where the wire feedthroughs occur with silicone layers on the outside,
but maybe there's a better way? As I said before, when all is dry, the
interior will be filled once again with mineral oil. The entire volume
of the container will be filled with oil, so all holes with wires
passing through will need sealed correctly. Thanks in advance for your
ideas.

 

[Jim Horton]

On 10/20/19 10:50 AM, jlarkin@highlandsniptechnology.com wrote:

Oil is always a mess. Why not use a plastic potting material?

What I just described I actually had for over 8 years without leaking.
However, the cause for the small amounts of oil that finally leaked into
a larger container just for the purpose remained a mystery, so I decided
to first try using paraffin to repot everything after first removing the
oil. While paraffin worked, it shrank a lot upon cooling and I didn't
like that plus the fact that any heating of the transformers might
compromise any insulating qualities he paraffin provided leading to
possible arcovers and such. Then, I had read about additives for
paraffin that increased its strength and melting point, such as EVA glue
sticks. However, I couldn't find any mixing ratios on EVA/ paraffin
mixes, so abandoned the idea. Budget is limited and this is a hobby
device, so trying to keep costs minimal. So it was back to mineral oil
like used originally, except this time in a smaller PVC junction box
housing and better feedthroughs into and out of the mineral oil filled
box so that I wouldn't have leaks in the future. Unless I read anything
more, I will probably use epoxied solid short wire lengths as
feedthroughs and then either use alligator clips to attach the
transformer wires to them, or just solder everything before applying
epoxy.

BTW, another possible DIY potting material I came across was "machinable
wax". There actually is a recipe well known that uses a mix of HDPE and
paraffin. This ends up significantly raising the wax melting point (to
240 F) and making it machinable. However, the big drawback is that 240
F is needed to melt it all together and I'm sure not going to try
potting my transformer at this temp, let alone ever trying to melt it if
there were problems. So... back to mineral oil.

 

jlarkin@highlandsniptechnology.com wrote in
news:v0toqel72vec3k01i4cdvgngt0b9p85n04@4ax.com:

On Sun, 20 Oct 2019 00:30:47 -0400, Jim Horton
jhorton@nospam.net> wrote:

So I decided to use mineral oil once again for my HV transformer
device after debating and even trying paraffin. However, this
time I want to be sure my wires passing through the PVC junction
box are sealed correctly so no oil leaks through.

The transformers will be inside a 6x6x6 PVC junction box (which
takes up about 50% less volume than the prior box I used) and four
connections will be needed:

2 low voltage 600 V wires for driving the transformers, and
2 wires for high voltage output (around 100 KVDC)

So, these four wires will need to pass through the PVC box into
the oil and to the transformers.

In the past, I used two part epoxy to seal the solid wires on the
inside of the box with generous application of silicone around the
wire outputs on the outside of the box (I added the silicone
layers because the outside wire didn't quite have enough
insulation and would jump to my hand sometimes... a bunch of
layers of silicone around the exit points stopped this).

Wires are all thin 20 gauge solid. I was going to use the same
procedure, using the epoxy to seal around the inside of the
container where the wire feedthroughs occur with silicone layers
on the outside, but maybe there's a better way? As I said before,
when all is dry, the interior will be filled once again with
mineral oil. The entire volume of the container will be filled
with oil, so all holes with wires passing through will need sealed
correctly. Thanks in advance for your ideas.

Oil is always a mess. Why not use a plastic potting material?

Plastic? Do you mean an RTV type?

Oil filled containment is typically a vertical canister, by design,
and wire ingress and egress would be in and out the top 'lid', or at
least well above the oil fill line, and on a unit never meant to be
tipped or aggitated. Usually found in permanent, hard mounted
installations.

Yet another reason RTV potting media is a far better choice
(especially if it is a small device/package volume, and even more
serviceable inasmuch as it should not have been potted unless it
worked, so it should not fail after potting unless it is a bad
design. However, potted is easier to work on as small excavations
can be easily back filled in all instances *except* HV sections.

 

On Sun, 20 Oct 2019 00:30:47 -0400, Jim Horton <jhorton@nospam.net>
wrote:

So I decided to use mineral oil once again for my HV transformer device
after debating and even trying paraffin. However, this time I want to
be sure my wires passing through the PVC junction box are sealed
correctly so no oil leaks through.

The transformers will be inside a 6x6x6 PVC junction box (which takes up
about 50% less volume than the prior box I used) and four connections
will be needed:

2 low voltage 600 V wires for driving the transformers, and
2 wires for high voltage output (around 100 KVDC)

So, these four wires will need to pass through the PVC box into the oil
and to the transformers.

In the past, I used two part epoxy to seal the solid wires on the inside
of the box with generous application of silicone around the wire outputs
on the outside of the box (I added the silicone layers because the
outside wire didn't quite have enough insulation and would jump to my
hand sometimes... a bunch of layers of silicone around the exit points
stopped this).

Wires are all thin 20 gauge solid. I was going to use the same
procedure, using the epoxy to seal around the inside of the container
where the wire feedthroughs occur with silicone layers on the outside,
but maybe there's a better way? As I said before, when all is dry, the
interior will be filled once again with mineral oil. The entire volume
of the container will be filled with oil, so all holes with wires
passing through will need sealed correctly. Thanks in advance for your
ideas.

Oil is always a mess. Why not use a plastic potting material?



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Jim Horton]

Since a picture says a thousands words, here is what I had and now what
I want to do. I have included captions describing what you are seeing
with the last indicating my uncertainty about proper HV feedthrough set up:

https://imgur.com/a/15c4FKK

Comments and suggestions welcome. Thank you.

 

Hysol 1c off white is ceramic loaded. I've used it in lab applications at 45 KV.

CENTER your feed wire in a pvc tube, fuse or chemically weld it to your box and fill the space around the wire with some sequential layers of 1c.

It doesnt outgas either, once drt.

Steve

 

Hysol white epoxy, its ceramic loaded.
Ive used it in lab applications in excess of 45 Kv.

Steve

 

On Sun, 20 Oct 2019 15:04:01 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

jlarkin@highlandsniptechnology.com wrote in
news:v0toqel72vec3k01i4cdvgngt0b9p85n04@4ax.com:

On Sun, 20 Oct 2019 00:30:47 -0400, Jim Horton
jhorton@nospam.net> wrote:

So I decided to use mineral oil once again for my HV transformer
device after debating and even trying paraffin. However, this
time I want to be sure my wires passing through the PVC junction
box are sealed correctly so no oil leaks through.

The transformers will be inside a 6x6x6 PVC junction box (which
takes up about 50% less volume than the prior box I used) and four
connections will be needed:

2 low voltage 600 V wires for driving the transformers, and
2 wires for high voltage output (around 100 KVDC)

So, these four wires will need to pass through the PVC box into
the oil and to the transformers.

In the past, I used two part epoxy to seal the solid wires on the
inside of the box with generous application of silicone around the
wire outputs on the outside of the box (I added the silicone
layers because the outside wire didn't quite have enough
insulation and would jump to my hand sometimes... a bunch of
layers of silicone around the exit points stopped this).

Wires are all thin 20 gauge solid. I was going to use the same
procedure, using the epoxy to seal around the inside of the
container where the wire feedthroughs occur with silicone layers
on the outside, but maybe there's a better way? As I said before,
when all is dry, the interior will be filled once again with
mineral oil. The entire volume of the container will be filled
with oil, so all holes with wires passing through will need sealed
correctly. Thanks in advance for your ideas.

Oil is always a mess. Why not use a plastic potting material?




Plastic? Do you mean an RTV type?

No, polyurethane or some such. Tap Plastics and other hobby shops have
nice clear flexy casting material.

Oil filled containment is typically a vertical canister, by design,
and wire ingress and egress would be in and out the top 'lid', or at
least well above the oil fill line, and on a unit never meant to be
tipped or aggitated. Usually found in permanent, hard mounted
installations.

Yet another reason RTV potting media is a far better choice
(especially if it is a small device/package volume, and even more
serviceable inasmuch as it should not have been potted unless it
worked, so it should not fail after potting unless it is a bad
design. However, potted is easier to work on as small excavations
can be easily back filled in all instances *except* HV sections.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Rick C]

On Sunday, October 20, 2019 at 2:29:50 PM UTC-4, Jim Horton wrote:

Since a picture says a thousands words, here is what I had and now what
I want to do. I have included captions describing what you are seeing
with the last indicating my uncertainty about proper HV feedthrough set up:

https://imgur.com/a/15c4FKK

Comments and suggestions welcome. Thank you.

I still say you can mitigate the shrinkage of the paraffin by coating the devices in layers. You can still fill in the entire container if you wish, but by coating the devices in layers each one only shrinks a bit, then more is added after the shrinkage.

Or you can fill the enclosure with paraffin only an inch or so at a time and deal with the shrinkage that way. Since the molten paraffin will melt the previous hardened paraffin somewhat, the layers should not cause any issues with gaps between layers.

Oil does seem like a terrible way to do this unless your container is sealed. After seeing the RTV added as a layered insulator I think you should not try that again. Bring the leads out the top of the container above the paraffin line.

--

Rick C.

- Get 2,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

sroberts6328@gmail.com wrote in
news:9c351d47-31c6-4622-8c91-e21ceac78713@googlegroups.com:

Hysol 1c off white is ceramic loaded. I've used it in lab
applications at 45 KV.

CENTER your feed wire in a pvc tube, fuse or chemically weld it to
your box and fill the space around the wire with some sequential
layers of 1c.

It doesnt outgas either, once drt.

Steve

Good advice. Make a hole and place a short PVC tube in it to keep
distances. Fashion and center the wire in the tube and fill with RTV
caulk or epoxy or other FIRM type potting with good adhesion. Once
that cures, the tube/wire assy can be placed in the breech in the
tank and fixtured in place by whatever means (more firm epoxy).

 

[Jim Horton]

On 10/21/19 1:21 AM, Rick C wrote:

I still say you can mitigate the shrinkage of the paraffin by coating the devices in layers. You can still fill in the entire container if you wish, but by coating the devices in layers each one only shrinks a bit, then more is added after the shrinkage.

Or you can fill the enclosure with paraffin only an inch or so at a time and deal with the shrinkage that way. Since the molten paraffin will melt the previous hardened paraffin somewhat, the layers should not cause any issues with gaps between layers.

Oil does seem like a terrible way to do this unless your container is sealed. After seeing the RTV added as a layered insulator I think you should not try that again. Bring the leads out the top of the container above the paraffin line.

My initial try with paraffin did work. There was some shrinkage in the
center, but it didn't seem to be enough to expose anything. I had two
concerns about using paraffin over the long term: 1) the device is going
to be in an area with poor climate control, so temps in the winter might
dip into the 40's, but be in the high 80's during summer so, would this
cause cracking over time, and (2) the transformers might, over a period
of time, generate enough heat to start melting the paraffin. This was a
very remote possibility, but I still addressed it.

In the end, I went with mineral oil once again, but I had a lot more
trouble fitting the transformers into the smaller junction box.
However, the project is now completed with the small junction box housed
within the larger older one. This time, for leaks, the second box will
catch the oil plus I custom trimmed an absorbent disposable bed pad
underneath it to help absorb any oil. Believe it or not, I have already
had leakage, but it is from the junction box top as that doesn't make a
good seal and I don't think I want it to either since someone else
pointed out how mineral oil can expand and contract quite a lot. Come
to think of it, I did all of this rehousing and reoiling, but I think
the problem with the original's leakage was simply from oil expanding
out of the top cover during hot weather. That's the only way it would
have ended up on the bottom of the tub in which the device was housed.
I didn't realize this at the time and thought the leaks came from within
the junction box somehow. Don't think so. I could have simply placed
an absorbent pad underneath in that case too and probably would have
gone on for many more years. Live and learn.

This revamping started to become costly because I had to figure out how
to keep the transformers stationary within the new smaller junction box,
and yet they had to be easily removable too if the time ever came. I
figured it out but it wasn't cheap.

 

[Joseph Gwinn]

On Oct 24, 2019, Jim Horton wrote
(in article <qoss9f$rih$1@dont-email.me&gt:

On 10/21/19 1:21 AM, Rick C wrote:


I still say you can mitigate the shrinkage of the paraffin by coating the
devices in layers. You can still fill in the entire container if you wish,
but by coating the devices in layers each one only shrinks a bit, then more
is added after the shrinkage.

Or you can fill the enclosure with paraffin only an inch or so at a time
and deal with the shrinkage that way. Since the molten paraffin will melt
the previous hardened paraffin somewhat, the layers should not cause any
issues with gaps between layers.

Oil does seem like a terrible way to do this unless your container is
sealed. After seeing the RTV added as a layered insulator I think you
should not try that again. Bring the leads out the top of the container
above the paraffin line.
[snip]

In the end, I went with mineral oil once again, but I had a lot more
trouble fitting the transformers into the smaller junction box.
However, the project is now completed with the small junction box housed
within the larger older one. This time, for leaks, the second box will
catch the oil plus I custom trimmed an absorbent disposable bed pad
underneath it to help absorb any oil. Believe it or not, I have already
had leakage, but it is from the junction box top as that doesn't make a
good seal and I don't think I want it to either since someone else
pointed out how mineral oil can expand and contract quite a lot. Come
to think of it, I did all of this rehousing and reoiling, but I think
the problem with the original's leakage was simply from oil expanding
out of the top cover during hot weather. That's the only way it would
have ended up on the bottom of the tub in which the device was housed.
I didn't realize this at the time and thought the leaks came from within
the junction box somehow. Don't think so. I could have simply placed
an absorbent pad underneath in that case too and probably would have
gone on for many more years. Live and learn.

The traditional approach is simply to provide some expansion space above the
top of the normal oil level.

If it must be hermetic, a metal bellows can be used. Or a long bit of
vertical pipe with a porous vent plug at the top so air pressure equalizes
with weather and thermal expansion. The maximum observed range of air
pressure variation is 26% peak to valley.

One can make hermetic seals using epoxy as the insulator, but one must match
the thermal coefficients of the materials used in the assembly, or it will
disassemble itself under thermal cycling.

Joe Gwinn