ajrothm

Just got the engine back in the 65' and chasing the usual gremlins, checking the charging system out and it is not up to par. The alternator is a fresh built, date code correct alternator, the voltage regulator is a brand new solid state unit, battery is brand new, cables are new.

Battery
Static voltage is 12.6-12.7v

Voltage @850, 11.9v
Voltage @1500, 12.2-12.4v
Voltage @3000, 13.0-13.1v


Alternator, 42 amp

Rear post on alternator:
Voltage @850, 12.4v
Voltage @1500, 12.65-12.7v
Voltage @3000, 14.8-15.0v



Ammeter in dash

Idle its at 0
3000rpms its at +20 amps


So I am seeing two issues here, no charging at idle, and more importantly, a huge voltage drop from the alternator to the battery. When its running at 3000 rpms, I can see 14.8v at the alternator and only 13.2v at the starter post.

I don't have a wiring diagram for this car, I am about to order one so I am just diagnosing off of my experience with C3s. I assume the the charge wire from the alternator goes directly to the starter post and then the battery charges back thru the pos cable? Or does it route through the horn relay like the C3s do?

Its obvious the alternator is making great voltage at 3000 rpms, yet it is not finding its way back to the battery. It seems that something is sucking the voltage down at the starter solenoid.

Any thoughts on this? quick checks? Maybe the new voltage regulator is not working right?

Gary's '66

My first thought for "quick checks" would to double check all connections/connectors. Usually the S/S regulators are pretty reliable but it wouldn't be the first time I've seen a bad "new" part.

ajrothm

After searching the forum, it seems that the alternator charge wire goes to the horn relay first, then from the horn relay to the starter positive post/thus charging the battery thru the pos cable. So I suppose I need to measure voltage coming out of the horn relay and see if that is where the voltage drop is at.

I know I measured voltage at the "big red wire" that is going to the positive terminal on the starter solenoid right behind the distributor (just poked the lead through the wire's insulation) and I had the same 14.56v that I had at the rear post on the alternator... So that tells me that I am not getting voltage dropping across the horn relay if the "big red wire" is in fact coming from the horn relay.

What is really weird though is I measured that big red wire in the distributor area and it had 14.56v, yet following the wire down to the starter's positive terminal and measuring it there it was only 13.0v... So it is either losing 1.5v in literally less then 3' of wire (distributor area to starter solenoid), or its getting major voltage drop at the starter solenoid for some reason.

Gonna have to keep digging....

plaidside

Take a heavy jumper lead, can use a booster cable, and go from the + post of the alternator to the + post of the battery. Measure the voltage now at the + battery terminal. If the voltage is now normal then you have a high resistance from the alternator to the battery.
Your static voltage is indicating a fully charged battery.
The 0v at 850 is puzzling, also why are you charging 20A at 3000 RPM's?
With the battery fully charged and no accessories on the output should be around 5A.
If you have a 37A alternator and it is producing 20A then you are using over 50% of capacity output.
What and how are you measuring amps? Do you have an inductive or in series meter?
Joe
Check this out:

http://temp.corvetteforum.net/classi...ternator.shtml