what would make a capacitor keep blowing out?

Discussion in 'The Projects Forum' started by stanman11, Jan 24, 2013.

  1. stanman11

    Thread Starter Member

    Nov 23, 2010
    I have an old whites detector that stopped working, I had a feeling it had something to do with the discrimination nob which on the inside has a 500v capacitor. I hooked a 330v the biggest i had to it and turned it on. It started working but slowly started to get quieter til eventually it stopped working again.
    would it be a resistor that also has malfuctioned that causing it to blow?
  2. K3CFC

    New Member

    Dec 4, 2012
    If it a 500 volt then put one back. you can't over voltage a cap even by ( 1 ) one volt.

  3. BReeves


    Nov 24, 2012
    I had to giggle, you replaced a 500 volt cap with a 330 volt cap then wonder why it failed ???
  4. stanman11

    Thread Starter Member

    Nov 23, 2010
    yes, as i said its the biggest one I had and it was just to test it. So since the 500v failed as well i figured there has to be another issue.
    When i put the coil next to my other detector coil it starts going off.
  5. WBahn


    Mar 31, 2012
    But think about the logic here using a similar analogy that should make the point clear:

    I have a circuit that had a 20A fuse and it blew. The biggest one I had on hand was a 10A fuse and I put it in just to test it. It blew, too. Could the problem be something else?

    Yeah, the problem "could" be something else. But the test that was done doesn't shed any light on the situation at all. The circuit may normally run at 18A and something happened, which may or may not be persistent, that caused the 20A fuse to blow. Okay. Putting an underrated fuse in it will only result in it blowing immediately even though nothing may be wrong.

    You need to put a properly rated cap into the circuit and then test to see if the circuit is operating properly -- and that means testing the key internal voltages. This may or may not be easy because you may not have a good feel for what those voltage should be. But it is pretty safe to bet that the voltage on that cap should be well under 500V at all times. If they aren't, then either the circuit is malfunctioning elsewhere or the 500V cap that was in there may not be the correct cap (do you have good reason to believe that it is the spec'ed part?).
  6. bance


    Aug 11, 2012
    I was going to say....

    This is what can happen... (video 2)


    OK not for the reason specified but......
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    caps can also blow from other factors as well as voltage. Metal film caps have a peak current rating and electrolytics used in switcher suppies have an ESR rating which causes overheating if it's too high.