The BIG question....discharging filter caps.

[chcjunior]

I'm getting ready to run a check on my amp circuit I just built. I've purchased two insulated alligator clips and attached a piece of 14 guage wire between them. From what I've read discharging the filter cap should be as easy as one clip on the positive terminal of the cap and the other clip to the chassis. I'll confirm the charge has been dissipated by using the multimeter....red to positive and black to ground.

If any of the above info is incorrect, please let me know.

Now, it appears as though I have a cascade of filter caps...three in a row marked respectively: 22uF 450V, 10uF 450V and 10uF 450V. It appears there is a smaller cap fourth in line marked 22uF 25-50V. Do I have to discharge all four?

Thanks.

 

[Danglin' Fury]

Re: The BIG question....discharging filter caps.

They have cap dischargers at electronics stores but if you don't want to get one, I would recommend at least a 1 Meg-ohm resistor along with that wire. That should be large enough.
I'm an electronics student and I've tried it the way you described and had a "shocking" experience.

 

[chcjunior]

Re: The BIG question....discharging filter caps.

They have cap dischargers at electronics stores but if you don't want to get one, I would recommend at least a 1 Meg-ohm resistor. That should be large enough.

What's the advantage of the resistor? Or is it a necessity?

And I like the sound of the cap discharger.

 

[DWVINKY]

Re: The BIG question....discharging filter caps.

What's the advantage of the resistor? Or is it a necessity?

And I like the sound of the cap discharger.

The resistor will act as a load and will help to dissipate some of the current draw. Its not a very good idea to discharge a filter cap through a piece of wire straight to chassis ground. Theres probably in the area of 400 volts on those filter caps and if you don't use a resistor, at the very least you'll get a very loud "pop" when you touch the wire to chassis. At the worst, you'll get one hell of a shock.

 

[flank]

Re: The BIG question....discharging filter caps.

im not sure what the resistor value is, but i've ALWAYS read that there is a resistor as part of that process to drain the caps

 

[Scott_F]

Re: The BIG question....discharging filter caps.

I've done it both ways. I prefer the resistor. 1 megaohm should be plenty, but look it up with google.

Just make sure you take it off again before you fire the amp up. Melting plastic smells pretty bad.

Some guys use a long screwdriver with an insulated handle. Just touch the tip of the screwdriver to the positive end of the cap and then lean the screwdriver to the chassis somewhere. You might get some sparks though.

In any case, use your multimeter to check them to make sure you did it right.

 

[chcjunior]

Re: The BIG question....discharging filter caps.

im not sure what the resistor value is, but i've ALWAYS read that there is a resistor as part of that process to drain the caps

I'm going to hold off until I find something more definitive. Most of what I've found online is dictating a resistor....but the electrician I talked to at Home Depot didn't mention anything about it.

Screw it, Scott showed up. I'm going to carefully use the method without the resistor.

 

[Scott_F]

Re: The BIG question....discharging filter caps.

http://www.ehow.com/how_16749_discharge-capacitor.html

This link recommends a 20k 2 watt wirewound resistor. I think I use a 1 meg, but I can't remember.

 

[Scott_F]

Re: The BIG question....discharging filter caps.

http://www.electronicsforu.com/efylinux/efyhome/cover/Nov2000/capacitors.htm

 

[Scott_F]

Re: The BIG question....discharging filter caps.

http://www.dreamtone.org/PJ.htm

 

[Scott_F]

Re: The BIG question....discharging filter caps.

http://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

 

[Scott_F]

Re: The BIG question....discharging filter caps.

the answers are all over the place... good luck, wear rubber gloves the first time or two you do it.

 

[chcjunior]

Re: The BIG question....discharging filter caps.

Thanks to all!

 

[the guy who invented fire]

Re: The BIG question....discharging filter caps.

You guys are too fancy...I always used the screw driver method!

Just becareful...if your finger touches the metal it hurts like hell...for a good long while

 

[DWVINKY]

Re: The BIG question....discharging filter caps.

Regardless of what those articles say, i still say use a resistor. 400 volts straight to ground is one hell of a current draw and i'd rather the current draw be through a resistor rather than my fingertips. Better to be safe than sorry.