: Voltage question

07-26-06, 10:23 PM
Alright guys, I got a new high performance alternator installed, but I dunno if it's putting out the voltage I need/want. I remember my old one putting out right around 13.7 at idle, and never going much below or above that in any situation. Since my new one has been installed, I'll idle at around 12.3, get about 13.5 when driving down the road, and maybe occasionaly 13.8 if I'm putting my foot into it. This doesn't seem right to me. What are you guys getting for voltage read outs at idle? Cruising? Correct me if I'm wrong, but I believe the regulator is inside the alternator? And maybe mine wasn't tuned right, or something is wrong with it? Any input is appreciated.

07-27-06, 12:18 AM
What else has been done to your electrical system?

07-27-06, 10:04 PM
Besides and Optima yellow top battery, nothing else has been done to my electrical system.

07-28-06, 07:13 PM
Check voltage at battery terminals with a volt meter. Don't rely on gauges. Charging voltage should be around 14.5V

07-31-06, 05:10 PM
Mine runs 13.7 at idle, engine hot. If you want to test it the right way, go to an Advance or Autozone and have them load test the alternator. This test's the amperage output, which is what you want to know. Remember, volts = pressure, but amps = flow.

07-31-06, 08:08 PM
a high performance alternator is still gonna charge at around the same voltage. The difference is in the amperage output of the alternator. The stock unit outputs around 150 amps or so if I recall correctly. A higher performance unit can output in upwards of 2-300amps depending on application. UNless you've got some outrageous sound system requiring a high output alternator...it really isn't needed.

08-03-06, 04:50 PM
I'm putting out around 250-275 amps from the alternator, I know that much. After the guys put it in for me, they tested it, said it ran around 80 amps at idle, and after that it'd peg out their gauge at 250. I do have a sound system, heh, that's why I needed it, I'm running about 1500 watts RMS. My voltage is still all over the place though, and it's really starting to bug me. I'm on vacation, but around the beginning of next week I'm gonna take it back and see if they can do anything about it.

I already talked to them briefly about it, and they said that the alternator/regulator is computer controlled, and that maybe by changing something in the computer they can fix what voltage I'm charging at? I dunno, didn't sound very solid to me. And I have tested it at the terminals with a multimeter, not just gone by the dash reading. I was actually idling at 12.2 volts the other day, and I revved it a little and got up to 12.8. The dash read out is pretty accurate though, within a tenth or so. Any ideas?

Tommy Deville
08-03-06, 08:57 PM
with my A/C lights and radio & heated seats on at idle in drive or park its 12.4 with the lights off its 13.5 13.8

08-03-06, 10:33 PM
I've never seen mine below 13.2 with the car running......

12.2?? Car was running?? Just a battery by itself should put out around 12.8, I think.....

Sounds low. Clarkz71 is right, take it someplace and have them put the machine on it.... then you can see amps, volts, everything... how much your starter draws...how much your car is drawing when running....

You say "nothing has been done to the electrical system", and then in a later post you say "I have a big stereo, that's why I needed the alternator".... but when RedGalant asked "what have you done to the electrical system", a big stereo would definitely be a modification to the electrical system....

So, bottom line is, at idle, it's entirely possible your new alternator still can't support your stereo..... when turning 2000 rpm's or greater, it may be fine....

08-03-06, 10:50 PM
Remember, volts = pressure, but amps = flow.

and if the pressure doesn't get above approximately 12.6-12.8V, there will be no flow. :yup:

08-04-06, 07:32 AM
You don't need more alternator, you need more batteries.
With high drains on the electrical system you need more reserve capacity. Relying on your alternator to output that much current is just going to leave you sitting on the side of the road a lot. Most guys who have big audio systems like that use multiple batteries hooked in parallel to keep the power where it should be.
12.3V is too low at idle, you need to shed some loads or you'll let the smoke out of your new alternator, or give it more reserve power.
I would agree that the voltage at the battery is more critical than what the gage is showing. The car regulates it's own voltage based on lots of things. There is no set voltage that you should see, but it should stay within a 13-15 Volt window.

08-05-06, 11:38 PM
Well, I have a brand new optima yellow top, along with a Bat/cap in the trunk , which has a capacity equivalent to a roughly 400 farad capacitor. From what I was told, that should be enough?

So is there a good chance the alternator is over heating and that's dropping the voltage?

08-06-06, 04:34 PM
Anything else would be a guess, one that might waste even more of your time.
Not sure what to tell you to do, except have it tested by someone who really knows how to test it.