Hey Gang...

The 64 Ninety Eight CSC build continues...I have a voltage conundrum that has me scratchin' my head

When the engine is running, the battery reads 14.8v at idle and 15.5v when I increase the RPM.
At the same time, the alternator shows 9.5v at idle and 10.5v under increased RPM.

I have a new voltage regulator on the way, but the situation doesn't make sense. If the alternator was weak, wouldn't the flow to the battery be much less?

Any ideas?

Thanks! Ty

 

i think the reading at the battery is the important one here, and it looks fine,

 

Yeah, I thought so too, but 15.5v is a little high. Don't want to boil the battery or start popping lightbulbs. Guess I need to put a multimeter on a light terminal.

 

15.5v is too high.

 

How many butt connectors are on the battery charge wire?

Put the positive probe of your meter on the alternator charging wire stud, put the negative probe of the meter on the POSITIVE post of the battery. Start the engine, turn on every electrical item, then read the meter. Whatever the meter reads is how much voltage is lost in the charge wire.


Ideally, you shouldn’t see more than a couple tenths of a volt. You can do the same thing at the fuse box, just keep the negative probe on the positive post of the battery. Keep moving the positive probe around, hopefully you find a questionable wire.

 

Impossible. Please explain how and where the voltage tests were made. What leads went where?

 

Sure!

on the battery test I did a lead on the positive of negative terminals of the battery.

On the alternator, the positive went to the positive post and negative to ground.

Did I screw that up? Let me know if I did that incorrectly

 

Your discrepancy is a ground issue. Going to guess you didn't have a clean ground when testing the alternator.

 

Ah...okay! I will try again next time I'm out there. What if I run the negative lead right to the negative post on the battery? If I get a good reading, then I know it's a ground issue

 

If you get a good reading that way it is a ground issue with the neg voltmeter connection, and not necessarily a vehicle ground issue.

 

^^^THIS^^^

Make sure you leave the NEGATIVE lead on the negative post of the battery when measuring voltage.

​​​​

 

Also make certain the positive wire from the alternator to the battery is in good shape with good connections and is large enough.
The battery ground should have a large connection going straight to the engine and a small connection to the body (fender or core support). Those connections also need to be clean.

 

Since he is getting voltage from the alternator to the battery, that wire is probably good.

 

If you measured the alternator voltage with the negative lead to the body of the alternator, you may have a poor ground path on the alternator body itself. It is quite common and may need a secondary ground lead. That may even resolve the regulator issue.

 

Hello Gang!

Once again, the fantastic members and wealth of knowledge in this form has helped me out!

I did some sleuthin' and found that the ground strap going from the alternator negative to the frame had snapped off at some point. So, I ran a new wire to the frame.

AND PRESTO! Alternator now make 15v at idle
and the battery has 14.2-14-4v at idle.

 

wonderful. What are the readings at increased RPM?

 

15.2v at alternator, and the battery fluctuates between 14.2 and 14.4v

when I turn on the headlights, the voltage dipped for a second into the high 13s, and then comes back up

 

Sounds like you got it back to specs. Good job.