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Testing a washing machine capacitor

Discussion in 'Hobby Electronics' started by Craig, Jan 2, 2004.

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  1. Craig

    Craig Guest

    I have a 67uf 220V washing machine capacitor that I would like to see if
    it works. How can I test it without a capacitance meter?

  2. Justin Thyme

    Justin Thyme Guest

    stick it across 240V momentarily, then hold onto the connectors. if you
    light up like a christmas tree you know it works.
    Seriously... if you have a LED and a resistor of about 300-500ohms, you
    should be able to connect it across a 12V battery as follows -
    You should see the led light brightly for a short period then fairly quickly
    fade out. Then get your resistor and Led and put them across the cap
    terminals. Again it should quickly glow then fade out.
  3. Phil Allison

    Phil Allison Guest

    ** A good cap will charge - hold that charge, then let it loose with a

    Try charging the cap with a 600 volt 1 amp diode and 100 ohm 5 watt
    resistor in series off the AC - be careful and have a safety switch on the
    circuit !!!!

    Leave it for a few minutes then short the terminals with a clip lead -
    should give a nice loud bang and spark.

    ........... Phil
  4. David

    David Guest

    Good caps will NOT let loose any charge with a bang. If the cap lets
    the charge loose with a bang the cap is stuffed and probably has an
    internal short. A good cap should hold a charge for hours.
    Extremely dangerous thing to recommend Phil. If the cap is shorted the
    diode and resistor will smoke. The cap will potentially have 340V DC
    (1.4 x 240VAC) on it, which is pretty lethal. A safety switch (I assume
    you mean an RCD device) will not protect you against potential
    electrocution if you touch both terminals of the cap.
    This could destory the capacitor, and cause molten metal to fly from the
    arc you create. The current in shorting a large capacitor charged to 340V
    DC is only limited by its internal resistance and that of the clip lead,
    and could be 100 amps or more. This could also melt the internal
    connection of the cap if it was not designed for high current discharges.

    If you really want to try this, PLEASE WEAR SAFETY GLASSES to prevent bits
    of molten metal and exploding capacitor getting in your eyes.

    A much safer way of doing this, if you have access to multimeter, would be
    to charge the capacitor from a 9 Volt or 12 Volt battery, with a series
    current limiting resistor (or from a current limited power supply if you
    have one), and let the cap charge to the battery voltage. Check the
    leakage by measuring the current into the cap. It should be less than a mA
    or so after the cap has charged.

    You could then get an estimate of the capacitance by discharging the cap
    into a know resistance. The cap will discharge to approx 37% of its inital
    voltage in one time constant, which is the product of R and C. If you
    discharged it with a 100K resistor, the voltage should be 37% of the
    starting voltage after approx 6.7 seconds. You may need to take into
    account the resistance of the voltmeter. By measuring how long it takes to
    discharge you can work out its capacitance.

  5. Phil Allison

    Phil Allison Guest

    ** Try reading the whole post before going off half cocked - arsehole.

    ** Bullshit - it's done all the time with complete safety.

    ** The 5w resistor will just internally fuse with 300 watts dissipation.

    ** I can see you have never worked on any valve equipment or off line

    ** Nor if a meteorite hits you.

    ** What utter bullshit !!!!!!!!!!!!!!

    The current in shorting a large capacitor charged to 340V

    ** It will discharge in a millisecond or two.

    This could also melt the internal

    ** So you have never seen a camera flash gun or high powered strobe

    Camera flashes use electro caps of several hundred uF and discharge
    them in 1 mS.

    Strobes use caps like the one the OP's and charge and discharge them 10
    times per second.

    ** What utter rot !!!!!!

    The stored energy is only 3.5 joules !!!!!!!!!

    Snip rest of fraidy cat drivel - which will not find a defective

    ............ Phil
  6. David

    David Guest

    Recommending someone with possibly limited experience connect things
    directly to the mains is very dangerous and irresposible thing to do.
    Depends on the resistor. If the resistor is not a specially
    designed fuseable resistor, it may not fuse without a lot of arcing etc.
    There is a big difference between a fuse and a resistor.

    ** I can see you have never had a capacitor blow up in your face.
    Over 30 people a year on average are fatally electrocuted in Australia.
    Can you tell me how many have been fatally hit by a meteorite please Phil?

    Can you tell me how this provides information that the capacitor is the
    correct value. Can you tell me how to differentiate between a 10uF and
    67uF bang please Phil?

    ** Of course I have seen a camera flash gun and strobe lights. I also
    know that photo flash capacitors are specially designed to cope with
    very rapid high discharge current. They are normally self healing

    A bit different to a motor starting capacitor. In fact some motor start
    capacitor manufacturers recommend fitting a bleed resistor to the start
    capacitor to avoid damaging the run capacitor by excess current discharge.

    BTW, fortuntely for you Phil, the Quadrantids meteor shower due 4/5th Jan
    will be in the Northern Hemisphere, you should be safe from those.
    Watch out for the alpha-Centaurids meteor shower, which begins 28th
    Jan and continues into Feb.

  7. Phil Allison

    Phil Allison Guest

    "David" <

    ** More bullshit from a stinking liar. I gave a clear warning of the
    need to use a safety switch and use care.

    Where were you when folk here were giving instructions to a novice on how
    to fix his microwave oven ????

    I got roundly abused for saying that was irresponsible.

    ** 5 w resistors are wire wound - they fuse when severely overloaded.

    ** I can see you are a fucking bullshit artist.

    ** How many of them were killed by poly caps ????

    ** The cap value is most unlikely to have changed.

    Other failures are far more likely - they would be revealed by my
    suggested test.

    ** You do not know any such thing.

    ** Electros are not self healing.

    ** We do not know exactly what the cap is - I assumed a polypropylene
    as that is what you commonly see in washing machines. Such caps are self
    healing and are used in high power (stage) strobes which I have serviced.

    Typical failures modes are going open or developing a high internal

    ........... Phil
  8. Bill Bailley

    Bill Bailley Guest

    How are you with crocodiles and babies Phil ???
  9. Rod Speed

    Rod Speed Guest

    All they're good for is croc food.
  10. Arpit

    Arpit Guest

    we are talking 60 times the rated dissipation here. diode will go
    quickly in the event of arcing anyway
    i have,twice, hurts a lot when the top hits your face, but believe me,
    no caps are gonna be exploding in phils setup, unless perhaps the
    resistor and diode are both short.
  11. Arpit

    Arpit Guest

    THe motor start caps often look very similar to pulse rated caps....
    which may or may not be relevant ;)
  12. Allan

    Allan Guest

    If your electrocuted it is FATAL...

    And Phil is again right..
    so get off his back,.
  13. Rod Speed

    Rod Speed Guest

    Not necessarily. Plenty survive.
    Heard the one about your head and a dead bear's arse ?
  14. Bob Parker

    Bob Parker Guest

    Happy New Year Rod,
    This is totally pedantic, but according to the two definitions of
    "electrocute" Google found for me, it means "Kill by electric shock".
    So by that definition, surviving electrocution would be like
    surviving being murdered!

  15. Phil Allison

    Phil Allison Guest

    ** The Rodbot has survived electrocution numerous times - someone just
    replaces his blown fuse.

    ........... Phil
  16. Rod Speed

    Rod Speed Guest

    Thanks, same to you and that cat from hell too |-)
    Thats what the Macquarie and Oxford say too.
    That was just a troll so I could admit that my original was wrong.

    The latest incarnation of a fatal virus deliverable in plain text
    usenet posts, designed to cause a fatal implosion between the
    ears of the pathetic creatures reading my posts looking to nit pick |-)
  17. Mike Harding

    Mike Harding Guest

    I have printed this in 36pt type and framed it.

    Mike Harding
  18. Bob Parker

    Bob Parker Guest

  19. Rod Speed

    Rod Speed Guest

    Yeah, certainly doesnt have the same 'why dont
    you go and **** yourself' glare the last pic had.
    Yeah, lucijet is the answer.
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