Alternator output voltage is low

[rocketrod]

I am finishing up installing a LS2/4l70e out of 2008 TBSS with a new 2005
Corvette accessory drive into a 69 Camaro. When the motor is running the alternator output is only 11.6v.

- Exciter wire - I soldered in a 470 ohm resistor inline on the red exciter wire in my harness going to the alt plug.
- Grounds - I have two 2/0 cables going from the engine to the body, the engine harness is grounded directly to the body and the trunk mounted battery has a 2/0 cable grounded to the body.
- All electrical connections & wiring to the alternator, battery and grounds are secure and free of any corrosion.




Even though the alternator is new I may have it bench check , but first does anyone have any suggestions?

[astroracer]

This is the stock 3 wire? What do you have for accessories? Have you checked output with ALL of the accessories running? The 3 wire alternator will monitor system demands so, if there are no demands, it won't necessarily be putting out full voltage. The battery only needs 7 to 10 amps to maintain a surface charge and the fuel pump shouldn't be pulling more than 5 or 10 amps. The alt can do that easily at 11.6v.
Mark

[rocketrod]

This is the stock 3 wire? What do you have for accessories? Have you checked output with ALL of the accessories running? The 3 wire alternator will monitor system demands so, if there are no demands, it won't necessarily be putting out full voltage. The battery only needs 7 to 10 amps to maintain a surface charge and the fuel pump shouldn't be pulling more than 5 or 10 amps. The alt can do that easily at 11.6v.
Mark

Thanks for the quick reply.

The alternator is a stock 2005 Corvette with a 4 pin connector. The connector only has a blue and red (exciter wire) wire, the others are empty.

I just ran checked and after getting the motor up to operating temp, 180 degrees, the voltage output was initially 11.6v but gradually declined after it was warm to 9.6V. When I turned on any accessories the voltage dips lower, but bounces back when I shut them off. Overall though, the voltage output is steadily declining the longer the motor runs, which is something it hasn't done before. Guess I need to get an ammeter and do some load tests.

[astroracer]

Does the exciter wire go to the stock Camaro harness? (Just need to know how you hooked it up... )

[hifi875]

sounds like it isn't turned on. I had my exciter wire disconnected and it did this. check your voltage on exciter wire with key on. make sure your charging wire from alt to battery is sufficient. should be atleast 4 gauge. should be 13-8 to 14.4 at alternator and under load no lower than 12.5. and that would be a large load too.

[rocketrod]

Does the exciter wire go to the stock Camaro harness? (Just need to know how you hooked it up... )

I soldered in a 470 ohm resistor inline on the red exciter wire in my harness going to the alt plug and connected it to a +12v ignition power source.

sounds like it isn't turned on. I had my exciter wire disconnected and it did this. check your voltage on exciter wire with key on. make sure your charging wire from alt to battery is sufficient. should be atleast 4 gauge. should be 13-8 to 14.4 at alternator and under load no lower than 12.5. and that would be a large load too.

I agree it sounds like it isn't turned on.....I did disconnecting the alternator plug, started the motor and revved the engine but there was no change in the alternator output. I do need to upgrade the alternator wire gauge.

[astroracer]

Read this from the Mad Electrical site...
http://madelectrical.com/electricalt...esensing.shtml
Your sensing wire should go directly to the main distribution block. According to the article it shouldn't be on a switched source.

[rocketrod]

Read this from the Mad Electrical site...
http://madelectrical.com/electricalt...esensing.shtml
Your sensing wire should go directly to the main distribution block. According to the article it shouldn't be on a switched source.

Thanks.....That's a great article, but it does not apply to the newer style alternators per my conversation with Mark at Mad Electrical last night

[rocketrod]

Well this is a lesson in humility. I check the resistance on the exciter wire and noticed I had 900 ohm resistance. I removed my 470 ohm resistor and the reading drop to 400 ohm. I reconnected the wire, started the motor and like magic the alternator output jumped to 13.2v and measured 12.7v at the battery. It's a little on the low side, but it should work with no problems

When I originally got my harness from SSP Wiring, they did not label any of the wires like they said they would and they never replied to my emails about hooking up the alternator exciter wire. I was so enamored with the fact I read I needed a 470 ohm resistor I did not check to see that they had already done this and buried it in the harness......

On the plus side, I did come across a great thread showing how corvette, f-body and truck alternators should be wired, http://www.ls1tech.com/forums/conver...ml#post7748845

[astroracer]

Good Job! We were on the right track. Just throwing stuff out there when you can't see it for yourself is tuff. Glad you figured it out.
I checked the link you posted and had learned something new. Had no clue about the late model wiring method. no oppotunity to work on any of it... yet.
Mark

[rocketrod]

Good Job! We were on the right track. Just throwing stuff out there when you can't see it for yourself is tuff. Glad you figured it out.
I checked the link you posted and had learned something new. Had no clue about the late model wiring method. no oppotunity to work on any of it... yet.
Mark

Thanks again. The link you posted to MAD Electrical is for the older style alternators that had internal or external voltage regulator, which the newer style alternators do not.

[astroracer]

Right, the newer ones are all solid state. I am still in the age of diode-trios and rectifiers...