I took my car out the other evening and noticed the gauge lights seemed dim, particularly at stoplights. The Battery gauge was indicating a substantial discharge. I took a look at the charging system last night and this is what I found:

At idle, the Battery gauge reads slightly above zero. Checking the alternator output at the battery shows 12.5 volts, which seems a little low. Turning the headlights on drops alternator output to 12 volts with the Battery gauge showing a substantial discharge - reads about halfway to the left of zero.

Increasing engine speed to normal cruising speed shows 13 volts with the headlights off (Battery gauge just above zero) and 12.5 volts with the headlights on (battery gauge showing a substantial discharge).

I have a spare alternator and swapped it out, taking the same measurements. Everything was essentially the same with voltage readings within a half-volt of the first alternator. The battery is about 2 and a half years old. While I have not put a load test on it, all other readings appear fine for the battery. The alternator is about two years old and is rated at 63 amps, which should be plenty for my car. I do not believe the alternator is the problem as both alternators had essentially the same reading. I have not tested the voltage regulator yet. Does anyone think this could be the problem or should I look elsewhere first?

Thanks.

Mike

 

ASSUMING all your connections are tight and not corroded, I would check out the regulator. I would also get the battery tested. Most places that sell batteries will do this at no charge.

 

...i'd agree that you should first check for faulty grounds...and if there's any question about the voltage regulator, don't even bother to get it tested, just replace it...if you're not over the edge on correctness, get the solid state version of the VR, case looks identical and it's reliable....$20 locally, don't know of a mailorder source

 

If the system is only reading 12.5 volts at idle the charging system is dead. Could be the alternaor, regualtor, or wiring. Trouble shooting and checkout procedures are in the shop manual.

Duke

 

I had the Vette out for a drive at lunch - nice day here in Virginia - 75 degrees and partly sunny. Now the Battery gauge is far to the right. I still had my pocket battery/alternator tester with me. I pulled over and checked it out. At idle its showing a solid 14 Volts. With headlights on it drops to 13.5 at idle. All good! I agree with you Duke, its probably the VR but perhaps swapping out the alternators resulted in a connection being re-established. I will watch the condition and if it returns, dump the VR. In the meantime, I will keep one of those portable battery units with me.

Thanks for everyone's help and I'll let you know if I see anything else that is strange.

 

.....damn near 80 up here....must be nice to have a car on the road :cry

 

I had exactly the same problem about a month ago. I found out i was my Voltage Regulator. I got that change and got one of those optimas new batteries just in case since i already neede a new battery and no problems now. I love does new optimas they are about 130 in autozone and they are well worth it.

 

A 12 volt system will usually charge at 14.4 volts. Sounds like an alternator or more likely voltage regulator problem. Does you alternator have an internal voltage regulator or the original external one? Chuck

 

Piece-a-crap VR's!! I've put 3 in my vert since new. One new one was hammered when I put it in. The last one I installed has been working for a few months now. (Knock on wood). I've heard there is a VR out there with electronics in it. Looks stock but doesn't have 3 sets of points in it. Gotta check into that for sure. :chevy

 

Thanks everyone for the advice. The car has an eternal VR. I will keep a watch and if the problem comes back, swap in a new VR. My experience with the two old Vettes I have had is if it isn't broke, don't fix it so I will wait to see if it comes back.