Not enough voltage
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=32360
Printed Date: May 18, 2025 at 5:19 AM
Topic: Not enough voltage
Posted By: KCRKustomz
Subject: Not enough voltage
Date Posted: May 18, 2004 at 7:55 PM
Newbie to the forum here. However, I have one killing me that I haven't run into before ...... please help. We have a 2002 Altima in the shop. We have 2 DD 12" subs running off from a Alphasonik PMA 1200DA. (2470 X 1@ 1 ohm) The amp is digital with 2 - 3 farad caps. We have a PPI 4125 amp running the highs. No caps on the PPI. The stereo equipment is running from an Iotima yellow top in the trunk fed by the Optima red top under the hood. We put in a 200 amp alternator on Monday and we are still only seeing 10 - 10.6 volts at the Alphasonik amp. We figured out tonight that the alternator may not be charging. However, the feed from the Red top to the Yellow top is 2 gauge. From the yellow top to the caps we have 4 gauge. Power and grounds match in gauge and the grounds are less than 2 feet in length. Would we see a obvious jump raising the gauge of the main feed to 1 gauge or higher? Also, can anyone give us any input on something we can do to raise the voltage at the amps to around 13 or better volts? We have optioned another yellow top, as the owner already has another new yellow top. However, in the trunk of the car is literally packed. There are no groceries going in this one. We have the two DD 12" subs, a yellow top, two Sting Pro 3 farad caps, 6 gallon air tank for the suspension, 2 Viair compressors for the suspension, and a PPI 4125 amp. Hell, even the Alphasonik had to go behind the rear seat. Can anyone help us with some insight to get the voltage up at the amps?
Replies:
Posted By: forbidden
Date Posted: May 18, 2004 at 8:11 PM
Have you got a multi battery regulator in this system? What is the resistance on the ground return of the back battery to the front alternator and front battery? Disconnect the compressors and see what happens to the voltage.
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Posted By: KCRKustomz
Date Posted: May 18, 2004 at 9:00 PM
We do not have a multi battery regulator in the system. I will check resistance. When checking voltage, we have the compressors off. Plus the compressors are on the main front battery with a 50 amp circuit breaker. The compressors also run on a pressure switch that only turns them on when the air tank drops to a certain pressure, then off again when refilling. Hope that helps. However, I will definitely check the resistance. thanx Forbidden
Posted By: auex
Date Posted: May 18, 2004 at 9:09 PM
If you are not getting above 13 volts when the car is running then it sounds like you got a bad alternator. By the way, adding more batteries is probably making the problem worse. I am sure that teken would be able to add more to this if he sees it.
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Posted By: DYohn
Date Posted: May 18, 2004 at 10:53 PM
Agreed. You might also try disconnecting the caps and see if the alternator can get it up. If not, sounds like alt. needs brushes or like forbidden suggested the voltage regulator can't handle the multi-battery system... ------------- Support the12volt.com
Posted By: Djmajicmark1
Date Posted: May 18, 2004 at 11:09 PM
The first thing I would check, is do you have 13 volts off of the alternator and at the red top battery. This may sound like a dumb question but if your not getting it there, what would make you think you would get it further down the line at the battery in the back. I only mention this because a lot of time people really over look something so simple. If you don't it maybe the alt or the voltage regulator. Another thing that was unclear to me is you say you don't have 13 volts at the Alphasonik amp, are you getting 13 volts to the PPI amp or the caps? Hope this helps. Mark
Posted By: haemphyst
Date Posted: May 19, 2004 at 12:06 AM
A properly functioning and installed 200 amp alternator will (not should, but WILL) have plenty of oomph to charge two batteries and two (even two 3-Farad caps) caps. Once a cap is charged, it pulls no more current from the voltage source, unless it is shorted internally. You did not say you were blowing fuses, or that the battery was going dead overnight, so this is most likely NOT the case. Did you address the power cable from the alternator? If you are using the stock charging cable (probably a #12, MAYBE #10) you do not have enough current capacity for that alternator. 200 amps will need at least a 3 gauge, but since finding #3 wire is tough at best, you will have to upgrade it to a #2. You will also need to do the same with the chassis to engine block ground cable, and from the front battery to the chassis. Charging two batteries will not be an issue, as long as they are IDENTICAL! Either two yellow tops, or two red tops, NOT one of each. (I have done it over and over... as long as you have current to keep them both charged, about 2-4 amps each when fully charged, there is no issue.) Do not try to use different batteries, they will be parasitic to one another, and you will end up needing new batteries sooner than necessary. Like Djmajicmark1 said, check the voltage at the front battery and the alternator. If you have the voltage at the alternator, but not the front battery, your charging cable is to blame... replace it. When checking the voltage at the alternator, check it to the CASE of the alternator, not chassis ground. If your voltage is OK there, then check it to the chassis. If this is where the failure is, clean all of the mounting points of the alternator with fine sandpaper, to be certain you have a proper ground. It sounds to me like you have enough power cable in the trunk, sizewise, I do not believe you will need anything bigger, but DO address the underhood wiring.
To test any of these theories, charge the batteries overnight with a 10 amp battery charger, (go ahead and leave 'em in the car, just connect to the front battery) then check your voltage at the amps in the morning... if the voltages are ok, even with the system running, (obviously the average voltage will drop as you play the system, so take that into account) then you know all of your power distribution is OK, and it is your charging system. Check into the alternator and underhood wiring issues stated above. If, when you return to the shop in the morning, and the battery charger is STILL putting out the same or more curent than it was the night before when you connected it, or if your voltage drops RAPIDLY, then one of your batteries is defective, and will need to be replaced.
Give these suggestions a shot, and let us know how it all comes out.
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