Audio Capacitor Wiring Question

ajscomp372 · 11-07-2008, 10:05 PM

I have seen several different guides as to how to hook up an audio capacitor, but some say to hook it up inline on the 12V line and others say to hook it up in parallel. I thought that if it was hooked up inline, then I wouldn't have to worry about the current flowing backwards into the rest of the car if the car's voltage dropped for a moment, but then I read on wikipedia that this backwards current (reverse bias) can destroy an electrolytic capacitor. So, in conclusion, I want to hook up the capacitor so current won't flow backwards (if possible), but I want to know that if I hook it up in that way, the capacitor will not be destroyed. Are my assumptions correct? How should I connect the capacitor? Please let me know.

HyperZulu · 11-07-2008, 11:46 PM

If by "in parallel" you mean battery > cap+ | cap- > amp +

Then no. If not, then not sure what you mean, but all + power leads connect together. Power meaning non-speaker + just power distribution. Alternator + to battery + to cap + to amp +... likewise, keep power grounds together.

The other way may work, but it's not a good idea. You may kill your cap, you may brown out your amp. Your amps draw current, so you want to always put the positive lead on the positive lead of the power source. Many men have melted jumper cables assuming that car batteries were meant to be wired like a pair of Duracell AA's. =O

FPeter · 11-08-2008, 06:20 AM

there is no alternate way with cap:

if the voltage drop is too high during engine start, then the battery should be replaced. put the cap as close as possible to the amp, less than 30cm required for real effect...

IonDokk · 11-08-2008, 03:45 PM

is true only way to hook it up personally I like to keep the chassis grounds in the same place...

HyperZulu · 11-09-2008, 12:20 AM

I've actually hooked up a cap on an amp the other way to see what would happen and the amp turned on and produced power, but it would go into protection mode whenever the bass was about to hit.

ajscomp372 · 11-09-2008, 09:54 PM

It's not that the voltage drops too much when the engine starts, that's not the problem. The problem is that when I'm driving, on occasion, the voltage will drop when I'm braking (I have no idea why) which causes the PC (sorry I wasn't quite so specific before) to hang. But before you ask, yes, I've checked the alternator, and the battery is virtually brand new.

Thanks, also, for the cap wiring diagram.

HyperZulu · 11-11-2008, 12:14 PM

Does it happen just because of the brake pedal being pressed or the change in motion? Can you make it happen when the car is stopped and you press the brake pedal?

GTSparkey · 11-12-2008, 10:27 AM

Here's the real poop.

A capacitor's impedence (resistance) varies inversely (one gets bigger the other gets smaller) with the frequency of the signal. DC frequency is zero so a capacitor acts like an open circuit (connection). The whine we hear has some frequency much higher than DC or zero. The higher the frequency the less resistance to ground.

OK, all that said the capacitor should be connected between 12+ and ground for it to work as filter to pull off the whine and shunt it to ground. The reason it "sort of worked" in series is this. Most of the non zero frequency sound, cymbals, guitars vocals etc pass through the cap. The real low grequncy stuff, bass guitar and bass drum, are close to zero so the cap acts as an open circuit, thus causing protection circuit to isolate from amplifier.

Best of luck. Remember too, the bigger the cap the better.

ajscomp372 · 11-12-2008, 04:32 PM

Hmm.. I'm not sure. I'll have to hook up my multimeter and test it tonight.

HyperZulu · 11-12-2008, 06:57 PM

Quote: Originally Posted by GTSparkey

Remember too, the bigger the cap the better.

That might be taken to mean a 20F batcap is better than a standard canister cap. The canisters are quicker to react than a batcap, which is why you use them in the first place.

ameuba10 · 01-30-2009, 12:17 AM

heres my opinion on the whole situation. first question is what do you want the capacitor to do? alot of times one isnt needed. as for reverse biasing a capacitor, i wouldnt advise that. ive seen em blow in the lab being reversed. and i can tell you if you have a one farad capacitor discharge, itll be like a shotgun blast! so be careful and make sure its discharge before you handle it. ive heard from people that you are supposed to charge the cap before wiring it in by using a 100 ohm resistor in series with it to your power supply. the only solution that came into my head about stopping the current from flowing to your other car electricals would to use a diode. diodes act as a gate allowing current one way, but not the other. but i havent heard anyone use it for such high current situations as a mobile audio system. here is a sticky i wrote for a civic website on capacitors.

http://www.8thcivic.com/forums/i-c-e...ors-101-a.html

ajscomp372 · 03-21-2009, 01:19 AM

Well, sorry for dragging a thread up from the dead. But, I finally stopped procrastinating and got my multimeter into my car. The interesting thing that I have noticed is that when braking, I can hear the HVAC fans slow down, but the voltage actually only drops about 0.1V. I wonder why sometimes braking has caused the computer to hang. Maybe it's a rogue voltage drop, like a rogue wave?

WuNgUn · 03-21-2009, 08:13 AM

What PSU are you using? What gauge wire is powering it?
What does your altenator read at idle?
Is your car a standard? Are you 'coasting' to a stop with the clutch depressed?

The PSU has caps to help sustain any 'rogue' drops, as you put it...so long as they're brief...
I'm thinking your battery isn't nearly as good as you think it is...

ajscomp372 · 03-21-2009, 05:34 PM

My PSU is an M2-ATX. It is connected to a distribution block by ~4ft. of 10GA wire (oh, and a 1/2 F capacitor in parallel midway to the block) which is connected to the battery with ~12ft. of 8GA wire. I don't know how to read the voltage off of just my alternator without disconnecting it from the battery, which seems like a really bad idea for my car. My car is an automatic, so null for the question after that.

I think I got my battery less than six months ago (from Napa Auto Parts), so if it isn't good anymore then Napa has some serious problems.

WuNgUn · 03-21-2009, 06:47 PM

Maybe that .5f cap is 'eating' the power before it gets to the PSU? Get rid of it...
Keep the power wire as short and clean as possible...
And think about a different PSU.

You don't need to disconnect the battery...you should be reading high 13's to low 14V at idle at the battery...

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