Pm 932 Capacitor Explosion

I believe it is the start capacitor, there is normally a centrifugal motor switch which disengages the start wingdings when the RPM reaches a specific speed ~90% of rated speed. As Bill mentioned, if the switch doesn't disengage the capacitor will overheat and the motor will get vey hot. Usually there is a safety plug that will vent electrolytic capacitors, but if they fail shorted, they can explode. Too frequent start/stop cycles can also overheat the capacitors and they can go south pretty quickly. I would also check the wiring, some of it looks darkened.
 
Electrolytic capacitors have gel or liquid filled paper that is called an electrolyte. When something goes wrong, the gel or liquid gets hot and turns into vapor. Therefore boom. A voltage surge could have caused this. A defective motor could draw more current than the capacitor could handle. When you buy a new capacitor, make sure the voltage is the same or higher. The capacitance should be within 10 to 15% . This is for an AC circuit, make sure it is for AC. Electrolytic capacitors are usually polarlized and show + on it. AC electrolytics are made a certain way, its like two capacitors back to back. Also electolytics have a shelf life, so if you can, get the newest one. I've worked in electronics for over 40years, so I hope this little knowledge will help.
 
They do that sometimes...looks pretty dry
 
I am more interested in finding out why it happened. If I go and just replace the capacitor then there is a good possibility that it will happen again. I need to find the root cause of it. I am sure that it is not from too many on off cycles. I am in no hurry with these projects . You know the old saying measure twice ,cut once.There's a lot of time in between cuts. And I hope that I wasn't overloading the machine milling a piece of aluminum with a 3/8 carbide endmill. Maybe it is time for that 3 phase VFD.

Jay
 
mksj said:
I believe it is the start capacitor, there is normally a centrifugal motor switch which disengages the start wingdings when the RPM reaches a specific speed ~90% of rated speed. As Bill mentioned, if the switch doesn't disengage the capacitor will overheat and the motor will get vey hot. Usually there is a safety plug that will vent electrolytic capacitors, but if they fail shorted, they can explode. Too frequent start/stop cycles can also overheat the capacitors and they can go south pretty quickly. I would also check the wiring, some of it looks darkened.
Click to expand...
You are correct with some of the wire being darkened . Seems that things got quite hot .

Jay
 
I agree with checking the centrifugal switch, I have that same machine and FYI the switch is on the bottom so you will have to remove the motor to get to it. Here's a link to a video about repairing it...
 
That video is really outstanding. I have bookmarked it for future reference.
R
 
You must log in or register to reply here.
Back
Top