How to discharge 5 terminal/blade microwave capacitor?

Thread Starter

Swale

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

DerStrom8

Joined Feb 20, 2011
2,390
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
 

Thread Starter

Swale

Joined Oct 6, 2014
2
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?
 

MaxHeadRoom

Joined Jul 18, 2013
20,703
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.
 

debe

Joined Sep 21, 2010
1,167
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.
 

DerStrom8

Joined Feb 20, 2011
2,390
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.
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.
 

DerStrom8

Joined Feb 20, 2011
2,390
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.
 

b1u3sf4n09

Joined May 23, 2014
113
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.
 

debe

Joined Sep 21, 2010
1,167
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.
 

debe

Joined Sep 21, 2010
1,167
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.
 

takao21203

Joined Apr 28, 2012
3,695
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.
yes discharge them two times, or you are in for a surprise.
 

DerStrom8

Joined Feb 20, 2011
2,390
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.
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.
 

takao21203

Joined Apr 28, 2012
3,695
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.
 

debe

Joined Sep 21, 2010
1,167
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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