Audio Capacitor Wiring Question

**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...

**dMand** · 03-21-2009, 09:54 PM

Originally Posted by ajscomp372

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?

You're having a classic case of charging system imbalance.

Too much power draw causes the alternator to struggle. The alternator is trying to supply power to the load, and at the same time, charge the battery.

When it can't do both, it will leave the battery undercharged / weak.

So that now, when you press the brake pedal, other things lose essential voltage, and cut off. Pressing the brake not only sends more power to supply the tail lights, it also feeds the anti-lock brake system, some have high amperage electrical motors.

As WuNgUn indicated, you should be reading high 13's to low 14V at idle at the battery. If the symptoms continue, I recommend upgrading the alternator.

**ajscomp372** · 03-21-2009, 10:22 PM

I'm reading 14.1V at the battery.

I'm not drawing that much amperage, so I don't see how there could be a charging imbalance. My alternator is around 100A output, I think, and that should be plenty.

**dMand** · 03-21-2009, 10:31 PM

Originally Posted by ajscomp372

I'm reading 14.1V at the battery.

I'm not drawing that much amperage, so I don't see how there could be a charging imbalance. My alternator is around 100A output, I think, and that should be plenty.

Stepping the brake and hearing your fans slow down, then the PC hangs, is an indication of an imbalance. Why do you need a capacitor if 100 amps is plenty? Are you sure that is what the alternator delivers?

No guessing...we need actual specs to help you troubleshoot the problem.

What's the make, model of your vehicle, list the first twelve digits of your VIN, and how many
Performance Teknique amplifiers do you have, touchscreens, etc..and what's their total fused rating?

**ajscomp372** · 03-21-2009, 10:52 PM

It's not that the PC hangs every time I push the brakes; rather, it's once maybe every few weeks. I just want the PC to be as close to 100% reliability as possible. You probably know as well as I that it really sucks when you have a GPS route set up that you can't use because the PC hangs en route.

The capacitor is part of my (probably unnecessary) attempt at reaching 100% reliability, ensuring current for the computer even if the rest of the car voltage were to drop (my original question).

My car is a 2001 Pontiac Grand Am.
I have one amplifier, a Performance Teknique ICBM-5.1 (of car audio forum notoriety) which is rated at 2000W (which I doubt I use anywhere close to) which is hooked up to two 6" subs, two tweeters, and two 6" mid-range speakers. I don't blast this thing either, in expectation of future questions.

**dMand** · 03-21-2009, 11:07 PM

2,000 watts is = to roughly 148 amps @ 13.5volts at max power output. One third of that power will require some sort of alternator upgrade if you haven't done so already. I'm only calculating a rough estimate of the amp. Throw a pc into the equation, head unit, among other accessories like the AC, tail lights, ABS, with the headlights on- the standard 100 amp alternator simply cannot keep up.

Shop around, perhaps at the local junk yard for an undersized alternator pulley, this will increase your amperage output at idle.

Ask the experts to Cross Reference your alternator with other manufacturers like GMC, Chevy, Oldsmobile, and Cadillac. These vehicles will have smaller pulleys that are compatible with your Grand AM.

Best Regards