Charging System Help

[tkmoore]

Battery died yesterday on my 83 sc 3.0 after driving for about 20 min in the rain with headlights, wipers, and a/c running. Ran fine and no charging light.

Shut her off and battery was immediately dead when I tried to restart. I cleaned and checked grounds and battery connections and all is good. Took battery to store for a test and had a dead cell so replaced that last night. Today put a volt meter on it to get some readings. Here is what I got at the battery:

Car off 12.6 volts
Car idling 13.5 volts
Car idling with a/c on 13 volts
Car idling with both a/c and headlights in 12.5 volts.

My Bently shows specs for car off and idling but not what charge rate should be under load. Considering these readings, I'm looking for input on whether my alternator looks to be charging fine, or its charging poorly under load. Thanks, Tim

[tkmoore]

Here's my 83

[E Sully]

The bad cell in your battery may have damaged the alternator. You should have @13.5-14.5 with everything on @2,000+ rpm.

[T77911S]

some parts stores will test it for free. go have the system tested

[pampadori]

Patiently waiting for you to fix it. I am having the same symptoms and my alternator tested fine.

[timmy2]

Originally Posted by E Sully

The bad cell in your battery may have damaged the alternator. You should have @13.5-14.5 with everything on @2,000+ rpm.

Test the voltage at 2000 rpm when fully loaded. Not at idle.

[tkmoore]

Ok guys checked at higher rpm.

13.6 at idle
13.6 at 2500 rpm
13.2 at 2500 rpm under load of headlights and a/c

Sound like a bad internal voltage regulator?

Thanks, Tim

[rick-l]

I'd wait and get some comparison numbers with regard to an 83 charging system.

13.6 may be just fine

[Lapkritis]

Alternator is charging fine from sounds of it. Rain makes me suspicious of belt slipping.

[mysocal911]

It seems some always forget that there is a cable from the alt. in the rear to the
battery in the front and two connections, i.e. at alt & at starter, on the path to
the battery. All it takes is a couple of bad connections dropping .25 volts each,
so now the battery is down .50 volts to 13.6 from 14.1 at the alt.

[tkmoore]

After load test with output of 13.2 volts I came to realization that alternator (with internal regulator) was bad. Replaced it this week with re-man Bosch unit and seems good as new. Thanks for everyone's input. Tim

[mhackney]

+100 to Dave - Having just gone through a charging system issue (you can find my recent thread, just got back on the road yesterday) where I replaced battery and the alt/VR I still had a problem. In my case it turned out to be the wiring post on the starter/solenoid where the feed where from the alt connects to the big black wire to the battery. We had dropped the engine the week before and it was never tighten properly. However, this turns out to be a critical junction and if there is corrosion it might cause a voltage drop. You should take a look and clean the post and lugs and tighten. It's the post with the large red wire and huge black wire into the starter. You can access it easily with the car jacked up or on a rack.

Quick test, measure the voltage at the middle fuse on the end towards the front of the car in the fuse box under the panel in the engine compartment. You should be getting full 14.x volts there as it is the feed from the alt.



If that is in the right range (14v+) and you have a new battery, then you likely have the problem I mentioned above or another wiring/corrosion issue.

[mhackney]

Oops. I see you fixed it! I started this post before you posted yours and got called away for an hour. In any event, maybe this will help others in the future.