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Safe testing of a 40µF capacitor

  • 17-01-2019 12:59pm
    #1
    Zynks
    Registered Users, Registered Users 2 Posts: 1,693 ✭✭✭


    I need to test a 40µF capacitor with my multimeter. The machine it's on (an air compressor) has been disconnected from the mains for a couple of months. Can I safely assume that the capacitor is discharged? If not, any ideas on how to discharge it?
    Thanks in advance.

    s-l300.jpg


Comments

  • #2
    Cerco
    Registered Users, Registered Users 2 Posts: 2,063 ✭✭✭Cerco


    Just short out the two cables using an insulated screwdriver.
    Or carefully tip one bare cable end off the other.


  • #3
    Zynks
    Registered Users, Registered Users 2 Posts: 1,693 ✭✭✭Zynks


    Thanks!


  • #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭2011


    You could measure the voltage across it to see if it is charged.
    This would be a DC voltage of course so set your meter accordingly.


  • #5
    Zynks
    Registered Users, Registered Users 2 Posts: 1,693 ✭✭✭Zynks


    My meter is unfused. Is that not an issue?

    I need to brush up on my knowledge


  • #6
    Twenty Grand
    Closed Accounts Posts: 1,452 ✭✭✭Twenty Grand


    Months? The cap would have discarged in minutes most likely.


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  • #7
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭2011


    Zynks wrote: »
    My meter is unfused. Is that not an issue?

    I need to brush up on my knowledge

    No.


  • #8
    tomoliver
    Closed Accounts Posts: 84 ✭✭tomoliver


    Aren't you supposed to use a resistor to discharge them or does it make a difference?


  • #9
    Twenty Grand
    Closed Accounts Posts: 1,452 ✭✭✭Twenty Grand


    tomoliver wrote: »
    Aren't you supposed to use a resistor to discharge them or does it make a difference?

    Small ones are fine with a screwdriver or bit of metal.
    Larger ones need a resistor and the big ones need a special tool.


  • #10
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭2011


    Twenty Grand wrote: »
    Small ones are fine with a screwdriver or bit of metal.
    Larger ones need a resistor and the big ones need a special tool.

    I have worked with very, very large ones. We actually had over 7MJ stored in one capacitor bank :eek:
    We discharged them with resistors.


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