Electrical Help - Voltage / Amp

[KJThaDon 10+ year member]

So I installed my 300 amp alternator in about 2 months ago and have noticed it considerably drops while idle about 1 volt to 1.5 volts and never wants to go back up where it started at. I just figured out why my amp was cutting in and out going into protection, because there is a short in the amp or something. Could this have killed my new alternator?

I have a optima under the hood and that's all

2500 watt amp, pushing maybe 2k at the most. I don't see any reason why I keep having issues with alternators. Could it be something else??

All power and ground are secured perfect with 0 gauge wiring, everywhere.

I just went and had the alt 'tested' at oreillys. The battery tested good and he said the alt is only charging at 12.9 so it's failing..It's a 300 amp from quality power. I had the same issues with a previous 250 amp from another company. What could be the problems? This is driving me crazy. I was about to put a batcap 3000 in the trunk but now I don't even think it has anything to do with the battery..

Any inputs would be appreciated

Thank you!

Click to read more...

 

[audiobaun 5,000+ posts]

I think it may be a bad alt..saying this because I bought 2 new alts from Orielys, and withing 6months, and went to get a new one, and found that tested before leaving,it was bad..all in all, that day I went to 5 different Orileys, and all were bad, and finally found one that worked.The remanufacturing of more and more alts are going to Mylasia, and Mexico.These seem to be having issues..I have a 200amp alt and 2 redtops,and seem to be fair on the meter gauge in my truck that seems to be off?? Had the elect tested, and steady @13.9, and @14.3@2000rpm

 

[KJThaDon 10+ year member]

None of the alts I've got where from oreillys but they all seem to fail very fast..I just don't get it, $400 should not be gone that quick.

 

[Mitch86 5,000+ posts]

Its common for voltage to drop a little bit when the alternator warms up. I don't know about 1-1.5v though. Is the voltage drop occuring with no load present?(no system on) Also oreillys can't properly test a HO alternator because their machines don't put enough of a load on them... unless you're experiencing something different that what I'm comprehending from your post, your alt might be fine.

 

[LosIsATool 5,000+ posts]

Is the belt slipping?

 

[KJThaDon 10+ year member]

Its common for voltage to drop a little bit when the alternator warms up. I don't know about 1-1.5v though. Is the voltage drop occuring with no load present?(no system on) Also oreillys can't properly test a HO alternator because their machines don't put enough of a load on them... unless you're experiencing something different that what I'm comprehending from your post, your alt might be fine.

Yes with or without load it drops....That's what I thought but it seemed excessive. I hope their machines aren't correct because I wouldn't know what to do next. The test was done by a meter, the same one used to test my battery. Removing/replacing my alt is about a 4 hour job, so I would not want to take it out to test it..

Is the belt slipping?

No, not that I can see. I also put a new belt in when I changed the alt..

 

[Mitch86 5,000+ posts]

Whats your starting voltage and whats it drop to?

 

[KJThaDon 10+ year member]

Whats your starting voltage and whats it drop to?

Sometimes when I let it sit overnight, the starting voltage can be 14, then drop down to 12.0-12.8 after maybe 10 minutes of driving...

Most the time though it starts at around 13.0 - 13.6 and will also drop after a few minutes or so of driving..

 

[Mitch86 5,000+ posts]

Sometimes when I let it sit overnight, the starting voltage can be 14, then drop down to 12.0-12.8 after maybe 10 minutes of driving...
Most the time though it starts at around 13.0 - 13.6 and will also drop after a few minutes or so of driving..

Hm... something is not right then. Should be seein higher than normal voltage until it warms up and then it should rest at normal voltage of ~14.3-14.4. Check the belt and all of the grounds and power connection to the alt. Other than that, all I know that it could be is a bad alt. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[maylar 10+ year member]

Is the alt compatible with your car? Some vehicles have a control module external to the alt that controls its voltage. My Buick starts out at 14.2 v after starting and drops to 13.5 while running. It's normal for my car.

 

[KJThaDon 10+ year member]

Is the alt compatible with your car? Some vehicles have a control module external to the alt that controls its voltage. My Buick starts out at 14.2 v after starting and drops to 13.5 while running. It's normal for my car.

As far as I am aware it is. The regulator is internal. It's a Cadillac.

 

[NutHugger 10+ year member]

As far as I am aware it is. The regulator is internal. It's a Cadillac.

Cadillacs are a bit different. My dad ran into the same issue with his HO alt for his cadillac. It's not a 1 wire harness. I can't remember the pinout or what needs to happen, but the turn on wire is activated at engine start, but when some of the other wires in the harness are not present, it shuts that wire off I believe. I'm not 100% on this but you can verify with your multimeter. That wire in the alt harness should be ~12v when the engine is started and it's telling the alt to begin charging. At some point, I'll bet yours shuts off. So, if my guess is correct: Get a relay. In your fuse box find the accessory wire. (When the ignition is off it will read 0v. When it is on it should read ~12v.) Wire that to the coil in the relay and give it a ground. Then in the normally open portion wire one side to a 12v source and the other to your alt's turn on wire.

 

[KJThaDon 10+ year member]

Cadillacs are a bit different. My dad ran into the same issue with his HO alt for his cadillac. It's not a 1 wire harness. I can't remember the pinout or what needs to happen, but the turn on wire is activated at engine start, but when some of the other wires in the harness are not present, it shuts that wire off I believe. I'm not 100% on this but you can verify with your multimeter. That wire in the alt harness should be ~12v when the engine is started and it's telling the alt to begin charging. At some point, I'll bet yours shuts off. So, if my guess is correct: Get a relay. In your fuse box find the accessory wire. (When the ignition is off it will read 0v. When it is on it should read ~12v.) Wire that to the coil in the relay and give it a ground. Then in the normally open portion wire one side to a 12v source and the other to your alt's turn on wire.

If you are talking about the harness that plugs into the alternator, I know it is something like this picture. Then the only other thing that comes from the alternator is the power wiring.

http://cf.mp-cdn.net/83/8e/6faef0c6256e825fc4031c88fcd9.jpg

Also what relay should I be looking for to test this?

Thank you!