# discharging a capacitor



## CJE (Oct 10, 2010)

Short across it with a screwdriver.


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## Foestauf (Jan 5, 2011)

Magnettica said:


> I have to do this tomorrow on an old and discontinued attic fan.
> 
> I've never had to do this before.
> 
> ...


Technically you just send a pole to ground. 
But on a small cap disconnect power by the time you get back to the cap it will have discharged itself.


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## CJE (Oct 10, 2010)

Foestauf said:


> Technically you just send a pole to ground.
> But on a small cap disconnect power by the time you get back to the cap it will have discharged itself.


True, but I still short them to be sure.


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## Jlarson (Jun 28, 2009)

I think pretty much everyone just shorts small caps with a screwdriver or whatever.

With larger caps you don't wanna do that, a resistor is the way to go there, plus check the voltage across them before you go touching anything.


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## dmxtothemax (Jun 15, 2010)

The safest way to discharge a capacitor is to use a light bulb,
I use my test lamp, which is just a stardard 100w GLS light bulb,
with some wires soldered on to it.
If you put some croc clips on the wires, you can leave it on,
this will stop the charge from building up again.
Highly technical stuff !!!
Shorting a capacitor might be the way most people do it,
But it is not the safest way.
NOT RECCOMMENDED.

If you have seen what I have seen with shorting caps,
You will understand.
I once accidentily shorted out a 10 farad cap bank,
(not a typo, yes 10 farads,) the result was spectaculare to say the least,
3 inchs of track instantly vaperised,
With a deafening bang. 
So much power in such a small package.
BE REAL CAREFUL.


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## brian john (Mar 11, 2007)

WIGGY or light bulb avoid the spark and damage to the terminals.


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## NolaTigaBait (Oct 19, 2008)

brian john said:


> WIGGY or light bulb avoid the spark and damage to the terminals.


Never heard about the wiggy, So you just put a lead to each pole? The last cap I did had a resistor on it already...I assume it "self-discharges"


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## micromind (Aug 11, 2007)

brian john said:


> WIGGY or light bulb avoid the spark and damage to the terminals.


Same here.

I have a solenoid type wiggy, just use it to discharge the cap. Then either measure voltage across it or if it's small, short it with a screwdriver. 

I never short them unless they've been discharged slowly first.


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## RIVETER (Sep 26, 2009)

Magnettica said:


> I have to do this tomorrow on an old and discontinued attic fan.
> 
> I've never had to do this before.
> 
> ...


Use a resistor across the terminals for a short time; It is better than causing a high current discharge via a screwdriver.


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## Jlarson (Jun 28, 2009)

brian john said:


> WIGGY or light bulb avoid the spark and damage to the terminals.


Only problem I have with my guys using a light bulb is one day they are gonna go try to discharge a big cap and they are gonna grab a bulb with a blown filament and I know lots of em unusually forget to check the voltage they are gonna end up getting knocked on their ass.


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## Mike_586 (Mar 24, 2009)

Magnettica said:


> What do I need to discharge a capacitor?


Kiss it :laughing:

Seriously though Brian and dmxtothemax had the right answers...


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## RIVETER (Sep 26, 2009)

Jlarson said:


> Only problem I have with my guys using a light bulb is one day they are gonna go try to discharge a big cap and they are gonna grab a bulb with a blown filament and I know lots of em unusually forget to check the voltage they are gonna end up getting knocked on their ass.


It may be time to teach them what you already know.:thumbsup:


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## leland (Dec 28, 2007)

brian john said:


> WIGGY or light bulb avoid the spark and damage to the terminals.



Any load. I stay away from the 'Short' method.


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## Jlarson (Jun 28, 2009)

RIVETER said:


> It may be time to teach them what you already know.:thumbsup:


That's why my guys either have to short them or use a resistor, if its something bigger than a motor start cap they have to use a resistor. No light bulbs, it's policy.


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## captkirk (Nov 21, 2007)

Cool I think im gonna make my own stun gun now....


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## Jlarson (Jun 28, 2009)

captkirk said:


> Cool I think im gonna make my own stun gun now....


I was talking to a radio shack guy the other day, one that actually knew the different between a capacitor and a resistor and he said they had a guy come in a while back and by every capacitor they had. Seems this guys dog's shock collar stopped doing its job so he wanted to give it more of a punch. 

Sounded like either a Darwin award and/or an animal cruelty charge in the making. :laughing:


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## Foestauf (Jan 5, 2011)

Jlarson said:


> I was talking to a radio shack guy the other day, one that actually knew the different between a capacitor and a resistor and he said they had a guy come in a while back and by every capacitor they had. Seems this guys dog's shock collar stopped doing its job so he wanted to give it more of a punch.
> 
> Sounded like either a Darwin award and/or an animal cruelty charge in the making. :laughing:


PETA is all over that.


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