Inside a Capacitor Can

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This shows what it looks like inside a metal can capacitor. They're used a lot as motor start/run capacitors and in microwaves.

 

This one is a Magnetek 24uF 400VAC unit from some sort of HID lamp ballast. I opened it up with the intention of removing the internal bleeder resistor. It turned out that there was no obvious bleeder resistor anywhere. The capacitor itself has 5-10 megohms of leakage resistance. This is probably from doped dielectric or more likely the core it's rolled on.

 

This one was opened with a sawsall which is the messiest way of doing this. The oil and metal shavings fly everywhere. This was the first one I opened so I learned my lesson.

 

I took this picture after the oil was poured out. What you'll probably notice immediately is that the can is oval shaped but the capacitor itself is actually a cylinder. The reason for this is because if the capacitor were to overheat, the pressure that builds up inside has to have somewhere to go. When a little pressure builds up, it bends the can outward which pulls the seam apart and lets it vent to the atmosphere. They used to make them cylindrical and because they didn't expand, a lot of pressure would build up before the can ruptured and they would often explode.

 

I also posted a picture of the capacitor after it was removed from the can.

Done