Charge voltage drop after cap install

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=23388
Printed Date: May 10, 2025 at 5:28 AM

Topic: Charge voltage drop after cap install

Posted By: Autos4U
Subject: Charge voltage drop after cap install
Date Posted: December 26, 2003 at 8:29 PM

Am I killing the alternator? The running voltage at idle has dropped from 14.4v to 12.3 after adding a 1 farad cap to the system. The vehicle is a 2000 Chevy Silverado with a stock alternator. The amp setup did not change. As soon as the cap was added, the charge voltage changed. Do you think it overloaded the alternator since the client listens to Rap and Alternative music? (I tried to talk him out of it) He listens to transient music. I have to fix it though.

I am thinking I have to convince him to upgrade his alternator. 12.3v is not enough current to push a charge to his deep cycle gel battery. It does bump up to 13.5 when you rev it to 3000rpm BTW.

Any ideas? Am I missing something?

Thanks!

Tucker

Replies:

Posted By: Durwood
Date Posted: December 26, 2003 at 11:31 PM

Is the idle voltage down at 12.3V even with the stereo off? Once the capacitor charges, it shouldn't impose any current drain on the system until it discharges and has to be charged again. Try taking the cap out of the system and see if the voltage goes back up to 14.4V. The only thing with the capacitor I can think of would be if it had a partial short, and was constantly drawing current from the alternator to recharge itself.

How big is his system? If the stock alternator cannot handle the average power draw on its own, no amount of capacitance is going to help. If the alternator is undersized, it may be operating "full-field" nearly constantly, which might have damaged his voltage regulator. Try taking the cap out and see if the voltage goes back to normal. If it does, replace the cap.

Scott Gardner

Posted By: LAUR
Date Posted: December 27, 2003 at 5:46 PM

The capacitor doesn't need much time to charge.so with the music off you must have the same voltage.

try another capacitor.

Posted By: LAUR
Date Posted: December 27, 2003 at 5:48 PM

any voltge between 13.5 and 14.5 is enough to charge the battery

Posted By: eargasm
Date Posted: December 27, 2003 at 9:34 PM

the capacitor will not affect the voltage coming from the battery/alternator once it is initially charged. it could be faulty if it is definitely the cap draining power.

-------------
2001 Ford Fairmont
Alpine DVD, screen,
5.1surround processor,
5ch Class-T amp, TV tuner
and centre channel.
Focal 3way Utopia splits.
VDO navigation. Stinger cap.
Soundstream Exact subs.

Posted By: Autos4U
Date Posted: December 31, 2003 at 3:35 PM

I took another look at his car today. The voltage is now running at 14.4 again. I guess it had the problem as it was charging? Dunno,

Everything is working fine now.

Thanks for all the input!

Posted By: Autos4U
Date Posted: December 31, 2003 at 3:38 PM

I Had a chnace to look at this customers' car again today. It is charging at 14.4V again, like nothing was wrong.

No idea why it was showing that problem, but it seems that all is ok for now.

Thanks for all the input!