Pm 932 Capacitor Explosion

Jay-z

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And I thought it was going to be a dull evening. Had a capacitor go bang on my PM 932 in the middle of a small project I was working on. Definitely got my attention, as if the smoke didn't. One second the motor sounded different and then it happened.

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breakdown of the dielectric / overheating induced gas buildup?
 
breakdown of the dielectric?
No idea, I'm not an electrician. I did check all of the connections and they were tight. Motor ended up screaming hot. Sounds like a phone call to Matt.

Jay
 
I had no idea those caps could explode! Crazy.
R
 
had a polarized dc cap blow after installing with the wrong polarity - like a shutgun going off.
 
I'm letting everything cool off for a while before I get under the hood.

Jay
 
No idea, I'm not an electrician. I did check all of the connections and they were tight. Motor ended up screaming hot. Sounds like a phone call to Matt.

Jay

Does sound like an overheating induced failure - it is my understanding that in these installations the capacitor is used for motor starting, the overheating may have led to the failure of the capacitor but it may only be a symptom of a larger problem that led to the overheating to begin with (bearing failure?).
 
I'm also no motor expert, but start capacitors are supposed to be 'disengaged' (for lack of a better term) after the motor reaches some rpm threshold. I have been told that if the capacitor is not disengaged, things like this can happen.
 
The more I think about it, the more likely this capacitor is being utilized as a "Run" capacitor versus a "Start" capacitor. Start capacitors typically have a relay that disconnects the capacitor from the motor after start - a Run capacitor remains connected. If the capacitor wasn't up to spec or was failing this could have led to the motor not running properly (leading to overheating).
I'm standard AC, but mostly a DC guy when it comes to electrical projects. That said, my degree was based around electronics (Microprocessor/uController design and implementation - Industrial automation, etc). Which means I mostly know enough to get myself into trouble.
 
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