Film caps in vacuum environment

The ones I've post-mortemed have barely any thickness of epoxy 0.2mm at the sides, maximum diameter of the foil roll

Vacuum impregnated types or wound in air ?

If there is any difference at all, it will not apply to the former. BTW:

Vacuums really suck -

but not near as much as tedious wankers like you.

.... Phil

That's a kinda a wimpy vacuum. And right near the minimum for the break down voltage.

So I might be more worried about the voltage level and gap length.

George H.

here's a URL for NASA information:

I used to work in vacuum around 10e-11 torr, routinely 10e-9, so slightest outgassing was a real problem.

I'm looking for the parts list for an amplifier that is mounted INSIDE the vacuum to find a list of the 'accepted' caps to use, but somewhere it's buried in the 1.2GB files/folders of archives.

Also keep in mind that MOST of the heat is dissipated hrough the air in the form of convection. Remove that heat sink and we were very surprised to watch the OpAmps desolder themselves and fall off the boards. Not that much heat, either. So allow for CONDUCTION paths to get that heat out.

That's a kinda a wimpy vacuum. And right near the minimum for the break down voltage.

So I might be more worried about the voltage level and gap length.

Thanks. A good lead I think. There have been a couple of failures.....

cheers, JB

here's a URL for NASA information:

I used to work in vacuum around 10e-11 torr, routinely 10e-9, so slightest outgassing was a real problem.

I'm looking for the parts list for an amplifier that is mounted INSIDE the vacuum to find a list of the 'accepted' caps to use, but somewhere it's buried in the 1.2GB files/folders of archives.

Also keep in mind that MOST of the heat is dissipated hrough the air in the form of convection. Remove that heat sink and we were very surprised to watch the OpAmps desolder themselves and fall off the boards. Not that much heat, either. So allow for CONDUCTION paths to get that heat out.

On reflection, I think that this problem may be thermal related after all. Will have to investigate further. Thank you for your pointers. cheers, JB

I once used some ~100V piezo's in vacuum. We had to turn off the power as it pumped down. Do you really need the vacuum or just a lack of air? Maybe you can back fill with some other inert gas? Or get a better vacuum pump and reduce the pressure.

George H.

On Thu, 13 Nov 2014 09:05:59 -0000, "JB" Gave us:

It depends on how they are packaged.

If they are epoxy dipped, they'll be OK.

Could you soft-solder the capacitor into a hermetic case? Any small bubble of air in the capacitor could be a stress and stability problem.

I once used some ~100V piezo's in vacuum. We had to turn off the power as it pumped down. Do you really need the vacuum or just a lack of air? Maybe you can back fill with some other inert gas? Or get a better vacuum pump and reduce the pressure.

The actual problem is understanding the failure mode of some of these MKP type X2 caps. They are used in a quality LED driver fitted into our light fixture used in a turbine engine test chamber [simulating high altitude flight I suppose]. We have no control over the chamber environment. Fortunately our warranty doesn't cover this either. I'm just curious as never seen this failure mode before.

cheers, JB

On Thu, 13 Nov 2014 09:05:59 -0000, "JB" Gave us:

It depends on how they are packaged.

If they are epoxy dipped, they'll be OK.

cheers, JB

Could you soft-solder the capacitor into a hermetic case? Any small bubble of air in the capacitor could be a stress and stability problem.

No, we don't make the actual module. See my reply to George above.

thanks. JB

Try asking these people, they'd know and are small enough to reply.

Look for vent holes in the cap, especially under them.

The last batch of X2 MKP type caps I got has paper wrap as part of the dielectric and they also have a hole in the case on the bottom.

I suppose a vacuum could dry them out.

Jamie