How to discharge 5 terminal/blade microwave capacitor?

Discussion in 'General Electronics Chat' started by Swale, Oct 6, 2014.

  1. Swale

    Thread Starter New Member

    Oct 6, 2014
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    See photo, middle wire connected to diode & magnetron, other 2 to transformer. Also, do you remove connectors first?
    Capacitor.JPG
     
  2. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You should discharge it before disconnecting the terminals. This prevents you from accidentally coming in contact with any live parts when trying to pull the wires.

    You should use the blade of a screwdriver with an insulated handle, or better yet, a high-power, high-value resistor. I tend to use two screwdrivers, and I cross one over the other. It's much easier to touch both terminals at the same time, and then touch the screwdriver shafts together. Simply shorting the capacitor really isn't the best way, but MO capacitors are fairly rugged and should be able to take it.

    Be VERY CAREFUL! These things can be LETHAL! It wouldn't hurt to wear thick rubber gloves, just in case.

    Matt
     
  3. Swale

    Thread Starter New Member

    Oct 6, 2014
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    Thanks for answering but it's for the 5 terminal aspect that i inquired, i've only used 2 term caps & when i searched this question all i got were "touch 1 terminal to the other", meanwhile i've got 5, what do i touch to what?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Looks like 3 are common to each other and two are common on the other side, IOW only any two.
    Essentially a two terminal cap.
    In a micro wave it is very very seldom that any charge still exists.
    Max.
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    Ive been repairing microwave ovens for years now, & always short out the HV capacitor before working on them just in case. Ive only had one that still had a charge init as the internal bleed resistor had gone open circuit, you just never know & its agood habit to get into. Itreat HV electrolytics the same.
     
  6. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    This is correct. Your capacitor only has two terminals. There just happens to be multiple connectors per terminal. Shorting any connector from one terminal to any connector from the other terminal will work.

    As for no charge, I strongly disagree. Those caps can store a charge for a long time, as well as build up a nasty phantom charge over time. Don't take any chances.
     
  7. #12

    Expert

    Nov 30, 2010
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    And I don't believe they have an internal bleed-off resistor.
     
  8. DerStrom8

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    Feb 20, 2011
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    They do not. You are correct.
     
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  9. debe

    Well-Known Member

    Sep 21, 2010
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    Interesting, I have dozens of these microwave capacitors & the all show a bleed resistor. HV CAP.1.JPG HV CAP.2.JPG HV CAP.3.JPG
     
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  10. DerStrom8

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    Feb 20, 2011
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    Interesting indeed. I have never had a microwave oven capacitor with a built-in bleed resistor, at least not that I could tell. The labels certainly never showed one.

    I think we can all agree that it would be safest to short the terminals regardless, just in case.
     
  11. b1u3sf4n09

    Member

    May 23, 2014
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    Love the massive protection diodes. Only place I've seen asymmetric diodes (in microwaves).

    Given that the oil caps have a built in resistor of 10M doesn't mean you shouldn't discharge them. It will still take time for the capacitor to discharge. Better safe than dead.
     
  12. #12

    Expert

    Nov 30, 2010
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    How about that! I learn something almost every day on this site.
     
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  13. debe

    Well-Known Member

    Sep 21, 2010
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    Its amasing what ive learnt on this site aswell, I guess I stop learning when im dead. Some of the realy early ovens back in the mid 70s had external bleed resistors.
     
  14. #12

    Expert

    Nov 30, 2010
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    Maybe it's an Australian thing.

    This is what 'mericans see.
     
  15. debe

    Well-Known Member

    Sep 21, 2010
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    Yep #12 that was what was on the GE ovens I was selling in the mid 70s. The caps in my pics are only a few years old, so may be they have changed. Most of the ovens in Australia are Chinese or Korean built.
     
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  16. takao21203

    Distinguished Member

    Apr 28, 2012
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    yes discharge them two times, or you are in for a surprise.
     
  17. DerStrom8

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    Feb 20, 2011
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    Those diodes are not for protection. They are connected with the capacitor to form a voltage doubler. An MOT can generally only provide 1-2kv, whereas the magnetron requires 2-4kv.
     
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  18. b1u3sf4n09

    Member

    May 23, 2014
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    Interesting. Thank you for the correction.
     
  19. takao21203

    Distinguished Member

    Apr 28, 2012
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    Its cheaper than making a 4kv transformer, guess so?

    I played one time with a large 400v MOT but was scared how it melted electrodes, and disposed it.

    No need to play a youtube prank pulling them apart and create a large arc.
     
  20. debe

    Well-Known Member

    Sep 21, 2010
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    In post 9 the device across the capacitor is a short protector. The other device from the capacitor to the ground lug is the HV diode. The short protector is not in all microwave ovens & they will work with out them. Description of the circuit of a typical oven, & circuit of a typical oven. MICROWAVE SHORT PROTECTOR.jpg MICROWAVE TOSHIBA ER-7621.2.jpg MW.2.jpg
     
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