Easiest way to test capacitors. (excluding electrolytics)

Discussion in 'Amp Tech Center' started by DucDone, Feb 3, 2021.

  1. DucDone

    DucDone Tele-Meister

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    Hi. I have some vintage Astron caps that I would have liked to tes for leakage(?). I there an easy way to do that? And is it probable that they are faulty?
     
  2. goldguitarguy

    goldguitarguy Tele-Meister

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    You would need an ESR meter. There is no advantage to using older caps over newer ones.
     
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  3. Jon Snell

    Jon Snell Tele-Holic

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    If you construct a circuit to feed the device under test with a voltage equal to its rated voltage and measure the voltage drop across a suitable feed resistor, if there is voltage drop after a few minures, the device is leaky.
    Screenshot 2021-02-03 at 15.31.59.png
     
  4. fidopunk

    fidopunk Tele-Holic Gold Supporter

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  5. BelairPlayer

    BelairPlayer Tele-Afflicted

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    Time is the enemy of all capacitors.
     
  6. Jon Snell

    Jon Snell Tele-Holic

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  7. DADGAD

    DADGAD Friend of Leo's

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    An easy way to test them in circuit is with an NE2 neon bulb. Lift one leg of the capacitor and wire the NE2 in series with the capacitor. Apply power. If the capacitor is leaking, the NE2 bulb will glow.
     
  8. Engine Swap

    Engine Swap Tele-Afflicted

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    This. You'll also want to ramp up the voltage slowly to allow the capacitor to charge.
     
  9. Boreas

    Boreas Poster Extraordinaire Silver Supporter

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    While it would be interesting to test them, I wouldn't use them. They may test fine today and fail spectacularly tomorrow. Sell them as "vintage" on eBay or trash them.
     
    Last edited: Feb 3, 2021
  10. fidopunk

    fidopunk Tele-Holic Gold Supporter

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    shoot, I wasn't paying attention that he was looking to test leakage. My fault.
     
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  11. Jon Snell

    Jon Snell Tele-Holic

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    That is the function of the Charge Resistor.
    If testing a 1uF 400v capacitor, use a 10M 1/2W Charge resistor and a 400volt source. The voltage drop, across the Charge Resistor, should read zero when charged. Any reading after a few seconds and there is a leak.
    If testing a 0.02uF 350v, use a 22M 1/2W Charge Resistor and a 350volt source. The voltage drop across the Charge Resistor, should read zero when charged. Any reading after a few seconds and there is a leak.
    If you are precise, the CR charge time will indicate the capacitance value and that should equal approximately the value of capacitor, if way out, you have a leaky capacitor.
     
  12. mrriggs

    mrriggs Tele-Meister

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    Remember that most DMMs have a ~10 MOhm input. If you use a 10 MOhm resistor then hook a DMM across it, your load will be ~5 MOhm.
     
  13. DucDone

    DucDone Tele-Meister

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    Thanks, lot of good info here...
     
  14. Jon Snell

    Jon Snell Tele-Holic

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    Simply place a 10k resistor in series with the Charge Resistor and measure across it. Can't get simpler than that.
     
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  15. tubelectron

    tubelectron Tele-Afflicted

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    I still have an old / recalibrated French Army Wien RLC% bridge from LEA (= Laboratoire d'Electroacoustique Appliquée), able to check/measure capacitors under external voltage :

    [​IMG]

    But yes, I more often go for @Jon Snell test method, sometimes adding a DC µA meter in serie with the capacitor, to cross-check... ;)

    -tbln.
     
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  16. MrCoolGuy

    MrCoolGuy Tele-Holic Silver Supporter

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    What exactly does this tell you?
    I understand that this will show leaking DC...
    But what kind of readings would you see?
    How much leakage?
     
    Last edited: May 11, 2021
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