Sealing an electrolytic capacitor in Epoxy

[saint gillis]

I had an old 4-in-1 electrolytic capacitor in a metal can to replace, and as it was more practical to keep the same kind of package to wire all the components of the device, I decided to open the can and put 4 newer capacitors inside, then sealed them in epoxy.

I was wondering if sealing them in epoxy might have any disadvantages or problems I hadn't thought of?

 

[Khron]

Well, sealing the vents might not be the best idea..(?)

 

[saint gillis]

it crossed my mind too, with the same question mark

 

[JohnRoberts]

There is typically a vent hole in the rubber bung at the bottom of radial electrolytic capacitors. This allows electrolyte to escape during extreme overheating events. Completely sealing the capacitors could make them into a DIY hand grenade, while that is probably unlikely.

Do you feel (un)lucky?

JR

 

[saint gillis]

That sounds like a real answer

 

[CJ]

I see no problem, if the caps do vent the gas will probably find an exit in the terminal plate or at the metal seam, if they explode the the cans just rupture and open up like a sardine can ask me how I know,
If by some astronomical chance the cans do explode and emit shrapnel, it will be contained by the outer can.
those caps contain electrolyte, not C4. Not even enough explosives to create a toe popper. Is that epoxy or silicone (rtv)

If it is epoxy and you sealed the whole can up tight, then













YOUR GONNA DIE!

 

[saint gillis]

Epoxy

 

[JohnRoberts]

I see no problem, if the caps do vent the gas will probably find an exit in the terminal plate or at the metal seam, if they explode the the cans just rupture and open up like a sardine can ask me how I know,
If by some astronomical chance the cans do explode and emit shrapnel, it will be contained by the outer can.
those caps contain electrolyte, not C4. Not even enough explosives to create a toe popper. Is that epoxy or silicone (rtv)

If it is epoxy and you sealed the whole can up tight, then













YOUR GONNA DIE!

I already suggested that there is a low probability of damage, but better to let the built in capacitor protection work. It's probably possible to mount the caps inside the cans without sealing the bungs, allowing them to still function.

FWIW back in the 60s as a junior technician working on a then new technology switching power supply, I had a good sized film capacitor literally explode on my work bench. The capacitor was snubbing overshoot from a huge switching spike and over heated. Luckily I was away when it happened but my bench was covered with what looked like snow flakes from the thousands of small bits of capacitor film everywhere.

JR

 

[cyrano]

Also, caps expand quite a bit when heating up. Put something flexible in there?

As a kid, I used to blow up old electrolytical caps with overvoltage. After my grandfather stopped me from making gun powder...

 

[CJ]

the worst are the Tants, hot, high velocity partcicles with eyeball seeking sensors,

correction: the worst are PCB filled caps, explosions spread dioxins and poly chlorinated biphenyls as far as a fast mover dropping agent orange,

 

[JohnRoberts]

the worst are the Tants, hot, high velocity partcicles with eyeball seeking sensors,

correction: the worst are PCB filled caps, explosions spread dioxins and poly chlorinated biphenyls as far as a fast mover dropping agent orange,

When hurricane Katrina dropped my power pole into my side yard the transformer leaked some oil. When the utility came to collect the transformer and pole remnants they also dug up a box full of dirt where the transformer leaked. They didn't say why but I will speculate that the transformer was cooled with pcbs.

JR

The protective fluid in most distribution transformers for homes and businesses is mineral oil. However, between the 1930s and 1970s, transformers were sometimes manufactured with Askarel (a group of synthetic fire-resistant chemicals used in electrical insulating fluids), which may contain 45–100% polychlorinated biphenyls (PCBs).

 

[cyrano]

Mmmmm... Never tried tantaliums. Maybe I should try those? Or maybe I'm too old for that kind of fun?

 

[ubxf]

Why do you need to seal anything? I have done similar repairs (putting new electros in the old can) but left the whole thing empty and it seems to work ok.

 

[Disco Volante]

I use a bees-wax mix like the ancestors did. It is softer than epoxy and smells nicer.

 

[saint gillis]

Why do you need to seal anything? I have done similar repairs (putting new electros in the old can) but left the whole thing empty and it seems to work ok.

I needed them not to move to avoid shortcuts, the can was quite full of capacitors, and I had this epoxy pot, it sounded as a good idea at the moment, then I wondered if it was really such a good idea..

 

[ubxf]

I see , I insulated the legs of the caps in mine. The gear is also not moving a whole lot in the studio so quite a different situation.
I hope it works out for you.

 

[AudioFurga]

I already suggested that there is a low probability of damage, but better to let the built in capacitor protection work. It's probably possible to mount the caps inside the cans without sealing the bungs, allowing them to still function.

FWIW back in the 60s as a junior technician working on a then new technology switching power supply, I had a good sized film capacitor literally explode on my work bench. The capacitor was snubbing overshoot from a huge switching spike and over heated. Luckily I was away when it happened but my bench was covered with what looked like snow flakes from the thousands of small bits of capacitor film everywhere.

JR

There are probably many of us who have experienced "similar adventures"

 

[PermO]

Test it...

Put a cap in epoxy with some wires on, take it outside and blow it up...

Make sure to film it

 

[sodderboy]

I glue the caps inside for stability, and use ptfe on the leads. If the chassis allows, I leave the old can in situ, seal the unconnected bottom with epoxy, and install the new caps below the deck.
No booms yet.
I wear reading glasses and they have protected my eyes from the epoxy shards of old polyester caps popping upon awakening from deep sleep.
Mike