HELP! How do you discharge a capacitor?

[rc2002]

I'm selling my car and I want to pull the system out. I know how to get everything out except for the 1 Farad capacitor. How do I discharge it?

I appreciate any help you guys can give.

[redec]

unhook from battery (pull fuse), wait


if you want you could unhook it from the battery, and keep your system on until it dies....doesn't take long to discharge...this may not be overly good for the system tho...

I've never actually done this myself, but afaik, caps won't hold a charge for very long after you remove the power source

[ryder_23]

If u take the cap out, and if u have a degarger type thing, follow those instructions and use it. When i took mine out, i accidentally hit both top ends with a wrench...cap was disconnected. got a little shock, but needless to say, it was discharged, lol. I dont recommend it.

[alloroc]

Best way is to string a 120v light bulb across the terminals.

A not so good but entertaining way is to connect some wires to it, about 10 cm. and tape it to the underside of a toilet seat with just the tip of each wire poking out each side and wait.

[BigYellowMonkey]

If you take a regular adapter cord (like you would buy to replace a frayed or broken power cord to some small appliance), strip the end of it back, and wrap and electric tape the 3 wires in the cord to a screwdriver with a steel or aluminum (steel preferably) "shaft" or whatever you wanna call it, and a plastic handle . Once it's wrapped and taped, plug the other end of the cord into a wall socket. Then touch the tip of the screwdriver to one of the the contacts, and it will discharge down and out the wall socket.

This is the process that you would use to discharge the capacitor inside a CRT monitor for your computer, and I'm sure it will work the same way for that capacitor.

-Biggie!

[kaput]

.

[ghosts-10]

Hey dawg,

Go to Radio Shack of a store that carrys resistors. Buy a 4 ohm resister and some electical tape (good tape not the cheap stuff) . Wrap about 6-8 layers of tape around the body of the resistor. Place the leads of the resistor on the posts of the cap. BECARFUL THE RESISTOR GETS HOT!!!!!! The tape is there to hold on to while placing the leads under the posts of the cap. Wait about 1 min. before disconnecting the resistor. When you got to hook up the cap again you can use the resistor to charge the cap. Hook up the neg of the cap and place one end of the resistor under the pos of the cap. Touch the pos wire to the other end of the resistor. This stops the SPARK and make it safer to work with. I am a electrician and deal with caps a lot. This is the way we charge and discharge them when we have to replace them. The capacitor banks hold 5-20 caps @ 1 farrad of bigger and haave never been hurt by this method.

[Hash_man]

Don't car audio capacitors hold enough charge to cause seriously harm to a person? I was under the impression that a fully charged cap of that size could potentially kill a person?

But lots of capacitors are mostly filled with sand.

[ghosts-10]

Hash man, Where did you hear that caps have sand in them? Does sand conduct electricity? No it doesn't. A cap is made up of a thin layer of metal wraped in a same thinkness of paper of plastic. Both layers are rolled up and placed inside a plastic tube..thats what we see.

[rc2002]

Cool, that helps a lot. It's embarassing that you guys know so much about this stuff. I've got one more year left of electrical engineering and I don't know the first thing about capacitors.

4 ohms sounds like pretty low resistance, but I guess a higher resistance would impede current flow and take longer to discharge.

Thanks for all your input guys.

[Dirty_SOHC]

Caps are mostly made of oil, look for a small relieve indenture on the top or bottom, if you reverse the leds on the cap you could potenialy explode the oil out.

[sml]

Originally posted by richardchan2002
Cool, that helps a lot. It's embarassing that you guys know so much about this stuff. I've got one more year left of electrical engineering and I don't know the first thing about capacitors.

4 ohms sounds like pretty low resistance, but I guess a higher resistance would impede current flow and take longer to discharge.

Thanks for all your input guys.

Here's what you'll learn in the last year of your EE degree:
Capacitance formula: I = C*dv/dt
Lightbulb: P = I^2*R = V^2/R

P = (C*dv/dt)^2*R

dv/dt = ((P/R)^1/2)/C, where P = lightbulb power (60W), R = series resistance (4ohms), and C = capacitance (1F)

For example, if you connected the circuit like this: cap in series with a resistor, which is in series with a lightbulb, which is connected back to the cap... you'll have:

dv/dt = ((60/4)^1/2)/1
dv/dt = 3.87

Since your cap will be charged to your battery voltage, the change in voltage (dv) will be from +14V to 0V, which is 14V delta.

So...

dt = dv/3.87
dt = 14/3.87
dt = 3.61 seconds!!!

A 1F cap charged to +14V will discharge a 60W lightbulb in 3.61 seconds. You can play with different values of resistors to see what you can find cheaply in stores. But one word of advice is that you'll be running 60W of power through this 4 ohm resistor... P=I^2/R => I =(P*R)^0.5 => I=3.87A... You better make sure you have a super high powered resistor to handle the current draw. Most cheap resistors that you can buy in radio shack probably go up to 0.25W... You're about 240 times less than the required wattage. My advice will be to go to a MUCH bigger resistor as you can probably remember that current is inversely proportional to the resistance (I=V/R), so bigger resistor, lower the current for the same power output.

Final words: If you want to wait for the cap to discharge by itself, you better have a lot of time on your hands to wait for it to self discharge... I'm guessitmating it to be in the ballpark of at least 1 week... best of luck!

[Dr. Lightspeed]

hehe just lick both fingers and grab it at the same time lol

[Hash_man]

Hash man, Where did you hear that caps have sand in them? Does sand conduct electricity? No it doesn't. A cap is made up of a thin layer of metal wraped in a same thinkness of paper of plastic. Both layers are rolled up and placed inside a plastic tube..thats what we see

I could be completely wrong, but I have heard about a report that Monster cable did.. where they cut open a bunch of capacitors, and many of them were filled largely with sand. They had the metal and whatever in the middle, but surrounding it was sand.

Again, I could be wrong, but this is what I have heard.

[spike98]

Just use a 12v autoimotive light bulb. 99 cents at crappy tire. Touch it on there and it will die out pretty fast. DONE