Alternator charger problem

[GT35065]

I'm having trouble with my battery going dead when head lights and fans are running. I have a high output alternator that seems to be working. If you measure voltage at the alternator, it is putting out 14.2 volts with fan and headlights on. If you measure voltage at the battery it is only showing 12.4 volts. I was driving at night for about 40 minutes with these things on and when I stopped for gas the battery was dead. Checked battery and it seems OK but is three years old.

Any one have a clue what to look for?

Thanks,
Rick

[Rick Parker]

Sulfated inside, possible short circuit internally, replace battery.

[GT35065]

Thanks for quick reply. I guess that would be the easy solution. I'll try a new battery first and see what happens. It is 3 1/2 years old and not driven consistently.

Rick

[Blas]

Agreed, battery could be bad. Do you put the battery on a trickle charger when not in use? A good practice. Do you have an Optima battery installed?
I see no car number is given. Check the chassis grounding point for the battery. Contact me offline if you need further instructions on how to check ground, or have questions.
Blas

[GT35065]

Thanks Blas and Rich. Car is #1108 and I've had it for 10 years. Got a new battery as the one I had was 3 1/2 years old and still had some warranty left for trade.

Did not solve the problem. Battery is fine with no accessories on, the volts go from 12.7 before running to 13.7-13.8 with engine running. If headlights alone are turned on, the battery is still charging at around 13.4 while running. When the fans are on with the headlights, volts drop to 12.4 which is discharging the battery. I can check the ground. I can see where it is grounded near the starter motor. Don't know if ground would be the issue when car starts just fine, but still worth checking. Out put at the alternator is 14.2, so it seems to be working.

Battery in regular lead acid, and I normally use trickle chargers unless driving regularly. Other thing is this may have been going on for a while because a rarely drive the car at night with fans and headlights on. This is when I had the issue when recently doing this and battery wouldn't start car after driving for 40 minutes.

Rick

[Rick Parker]

Does it restart now after night time usage?

[jhv48]

The next step is to replace the alternator/voltage regulator.

[GT35065]

Have not tried driving at night again yet, but as stated, when you have the fans and the lights on, the battery is discharging at 12.4 V. With lights only, it does OK.

[GT35065]

Alternator appears fine. It reads 14.2 volts at the alternator. It is a one wire setup, one of Randall Thomas's 100amp Reactor alternators.

[Gaz64]

Sounds like your charging wire is not big enough or has a high resistance in a joint/crimp.

[GT35065]

That could be. I think I might try running a wire from the alternator to the battery cable
block that is on the firewall and see what kind of readings I get then. That would bypass a lot of wiring. Should tell me if there is a wiring problem somewhere in between. I'll check grounding wire too.

[undy]

Check all your connections. A bad or corroded connection can cause voltage drops. What gauge wire is going from your alternator to the battery. Cobra wiring harnesses are a lot of times woefully inadequate for high power consuming accessories.

Although it's most likely not your problem, I would NEVER run a one wire alternator. They don't charge worth a crap at low RPMs. I had one... I know. After much research I rewired the same alternator for a 3 wire setup. After that, with the same alternator and under full load, my output voltage jumped over a full volt. I've never had a battery problem since.

[jhv48]

Where is the needle on your ammeter pointing when all the accessories are on?

[GT35065]

The guy that is helping me suggested converting it back to three wire too. That might be a good option. Then it would be using the regulator that came with the car instead of the one that is in the alternator.

Volt meter reads near the center until you turn on the fans and then it goes about a quarter way towards the plus side. You would think it would go to the negative side with the extra draw on the system.

[Gaz64]

So your ammeter is reading in reverse?

Does it ever read in the negative?

Which by your description of your ammeter, would be charging not discharging.

Personally, I've never liked ammeters for the extra wire etc. Like voltmeters much better.

[jhv48]

So, under normal driving, with the lights and fan off, is the ammeter needle to the right or left of the center mark? It Should be slightly to the right (the plus side). If it stays to the left of center, then your alternator/regulator is not functioning properly and you're running off the battery.

If not, and the needle goes to the right of center when the fan and lights are all on then it's wired incorrectly. It should be slightly to the left of center when all accessories are on and the engine is running.

[lovehamr]

When I put my new BDR together I started having the same problems that you are when I started adding electrical accessories. My batt was fine, all of my connections were fine but the voltage drop when everything was turned on was draining my batt. Just to clarify, I'm running 3 fans, fuel pump, crankcase vacuum, FI, MSD and of course the lights. My older powermaster just was not keeping up. Once I removed it I found black soot where it had been trying its best and was just about to fry. After a whole lot of internet snooping I went with one of these:
Chrome 170 amp S series alternator for 1963 - 1985 GM - Mechman Alternators

The difference is in the low end charging for me. These are 6 phase alternators rather than 3 phase and now I never have an issue. Even with everything on I’m getting 13.5 volts to the battery at my 1000 rpm idle.

[GT35065]

JHV48, I'm sure the wiring may be wrong on the ammeter as it goes to positive when the fans are turned on. In normal driving w/o fans it stays pretty close to the middle. More importantly, I've measured the actual voltage at the battery as stated and battery is charging fine until headlights and dual fans are on. The fans draw a fair amount. With just the headlights on I'm still in charge condition. It is when all stuff is on it goes into discharge (12.4).

lovehamr, that looks like a beastly alternator. Maybe that is the answer. I have an electric fuel pump as well, and the dual fans due seem to draw a bunch.

[jhv48]

You probably have a 100 amp (or less) alternator.

With everything on, you're over doing its capacity.

Time for a new, and more powerful, alternator.

[Blas]

You have the standard Amp Meter Right?
Switch the wires on the back of the Amp Meter should move negative when fans come on. Disconnect battery when making the wire switch.