400 volt capacitor how to know its leckage or dam

Discussion in 'General Electronics Chat' started by newone, Jan 20, 2006.

  1. newone

    Thread Starter Member

    Dec 23, 2005
    400 volt capacitor how to know its leckage or damaged

    one day my own digital satellite reciver not working

    itry but not fix

    i went to technican and he only change the 400 volt capacitor

    my capacitor was like new one

    my question is how to know its leckage

    i have analog and digital meter

    which is best for capacitor
  2. Gadget

    Distinguished Member

    Jan 10, 2006
    A capacitance meter.
  3. beenthere

    Retired Moderator

    Apr 20, 2004

    Your capacitor was the primary filter for the power supply. The technician probably did not check it - he changed it out because he knew from experience with that satellite receiver that it was the most likely cause for the receiver to stop working.
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    The ESR was probably too high. Electrolytics dry up and their ESR increases.

    Most capacitance meters will have a leakage test. As the ESR increases, so does the current from a DC supply.

    Thirty years ago, we would hi-pot ... 20kV rated capacitors to make sure the leakage was a less than a hundred microamps. If we had ESR testers ... that job would have been alot easier, if not alot safer. Discharging a capacitor charged to greater than 20,000 Volts with a grounding wand is enlightening, and loud.

    I remember fixing a satellite receiver that had alot, and I mean alot of dried up electrolytic capacitors. I must have checked 40 or 50 of them with a cap checker. I wish I had an ESR meter that time.

    With an ESR meter, you can rapidly check the electrolytics in circuit.
  5. pebe

    AAC Fanatic!

    Oct 11, 2004
    ESR and leakage in electrolytics are not related.

    Increased ESR is due to drying out of the electrolyte that impregnates the paper separators between the cathode plate and the anodic film that constitutes the dielectric, so effectively increasing the resistance of the electrolyte.

    Leakage current is due to the decomposition of the anodic film. The thickness of the film is proportional to the voltage at which the capacitor was 'formed' during manufacture. If the capacitor is run with reduced voltage then over a period of time the anodic film is slowly absorbed into the electrolyte. This will have no effect on the capacitor in its application (other than an increase in capacitance), but if the electrolytic is tested at its rated voltage there will be a high leakage current. The effect is accelerated at increased temperatures.

    The effect can be reversed by removing the capacitor and 'reforming' it by slowly increasing the applied volts, when the film will be re-anodised. Best done with a current limited power supply.