Charging a Capacitor

[soupey]

hi, im about to install a cap into a friends car, was wondering if charging was really necessary or optional. for example, could i just hook up the cap to the circuit, switch on the car, and let it charge up for a few minutes?, or do i need to charge it with a resistor, then attach it to the circuit?

btw its a 1Farad cap.

and IF i haf to charge it up, what can i use to check to see if its charged?, i don't have a voltmeter available to me.

any help is appreciated, thanks

[EK 2.0]

Yes do charge it...and if its a new Cap, it SHOULD have come with a little tiny bulb to tell you when it is charged...


Is it new??

[soupey]

no used, all i got was a resistor

[KoukiS14]

Use a test light.

[angierideswitme]

if you really need to know, and now one knows, you can go to x-s cargo on the 32 ne and they have caps there, and on the box it gives you instructions for charging them, I was there today And remember reading it, but don't remember exactly how to do it

[soupey]

thanks for all the info, figured everything out within 3 hrs, lol.

[Zero102]

Yeah, for what it's worth, don't install an uncharged capacitor into a 12V circuit without a charging resistor, they can explode.
There's my $0.02.

[soupey]

heh k, my friend said he did it like that, wit no probs, but meh, ill try to charge...and somehow figure out if theres 12v

[1-Bar]

Dunno if you'll get this in time but....Just hook it up to your battery + to + and - to - for about 15 secs. Then its all charged up.....Its gonna spark at the terminals, so heads up....

[soupey]

hmm k cool, i think its workin, is there any way to test once i put it on?, i jus started the car and attached it to the circuit, nuttn seemed to happen, altho my car doesn't dim at high output anymore

[1-Bar]

yeah that's pretty much the only way you can tell its working....you shouldn't "feel" any surge when the bass hits...

[Zero102]

A way to check it is to unhook a wire from it and check the voltage at the terminals of the capacitor. Though it isn't a good indication of whether or not it is working. I am not familliar of a method to test the capacitance of something if that is what you means.
1-Bar, I will warn you again, it is dangerous to just connect a capacitor to a 12V system without a charging resistor (well anything over 0.1 farads). You run the risk of it exploding, why not take the extra 20 seconds and charge it.

[Phat_Tercel_YO!]

You won't blow up a capacitor by sticking it in to a circuit properly.

You blow up capacitors by wiring them in reverse polarity.

The reason for charging a capacitor is to avoid arcing of the terminals. If you have a nice gold or silver plating on the terminals, then you are putting that at risk if you get an arc onto them.

[Zero102]

I have bought 2 capacitors beore, and both warn you that due to the high initial current draw, a charging resistor must be used. They warn the very high current may cause it to explode.
It didn't sound quite right, because aren't they designed to deliver very high current?
I dunno, after I read it, I have always charged them with a resistor, just to be safe.

[2000impreza]

you don't need a resistor to charge the capacitor. i've installed many caps in the past and never had a problem with doing the initial charge by using a car battery charger or straight to the car battery.

[sml]

All capacitors have a certain thermal rating. ie) the point at which it melts it's housing and hot acid starts flying out and hitting you in the face. When you connect a capacitor directly to a 12V supply, the capacity will want to charge up to the same potential as the supply. I = C * dv/dt, so current is equal to the capacitance times the rate at which the capacitor charges from 0 to 12V. Assuming the capacitor charges VERY fast (ie when you connect it directly to the car battery), dv/dt would be a very large number. So, a very large number times the capacitance (which is constant) equals a very large amount of current. Since current generate a lot of heat (like your toaster and hairdryer), you will risk exceeding the thermal breakdown of the capacitor's wall. So, yes it can explode, but no with today's capacitor technology, it probably can withstand a very high current charge. Rule of thumb is to use a resistor in series with the + terminal so it can limit how much current it can suck from the car battery to charge itself.

[soupey]

ok from what ive figured, it's perfectly fine to add it straight to the circuit, just gtta make sure i don't waste time after attaching it, cuz apparently if battery is weak, cap can drain it quick, so start car, drive around block once, then it should charge up to 12v on its own if the amp is on....

[soupey]

Originally posted by Phat_Tercel_YO!
You won't blow up a capacitor by sticking it in to a circuit properly.

You blow up capacitors by wiring them in reverse polarity.

The reason for charging a capacitor is to avoid arcing of the terminals. If you have a nice gold or silver plating on the terminals, then you are putting that at risk if you get an arc onto them.

arc meaning a spark?

[1-Bar]

wow...thanks for all the info, helps me out a lot. I guess I should stop charging the cap by plugging it into the battery.

[Zero102]

The cap won't kill the battery. Batteries are rated in amp-hours, and usually vary from 40-100Ah. If you rated a capacitor in terms of amp-hours, it would be like 0.05 or 0.005Ah. Your battery will hold FAR more power, but has a much higher internal resistance, and cannot respond to a varying load as quickly.