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1939 Cadillac LaSalle Coupe 50: battery not recharging after starting the car

Gentlemen and Ladies,
I recently purchased a 1939 Cadillac LaSalle 50 total frame off restoration. A beautiful car. But I am having an issue with the battery recharging after starting. After charging the battery all night with a trickle charger the car starts easily and runs well. But the problem is that after starting and driving the car at speed (55 mph) for 30 minutes to an hour, that the battery is almost dead after stopping and shutting off the car. It barely has enough juice to turn the motor over.
I have received many recommendations and suggestions. This is summarized below:

Thanks for all the advice re: the problem listed above. I followed the recommendations step by step from the battery to the voltage regulator to the generator. We accessed the battery by lifting the carpet on the driver’s side and removing the plate covering the battery. We inspected all connections for corrosion and found them all clean. The fluid level was a little low and we topped it off with distilled water. Checking the battery with a voltage meter we found that after charging all night that it showed 6.6 volts.
Next, we reversed the polarity on the voltage regulator by running a wire/cable from the positive battery terminal to the “F” terminal on the voltage regulator and brushing the terminal with the wire/cable. We got sparks.
Next, we reversed the polarity on the voltage regulator by running a wire from the “B” terminal on the voltage regulator and brushing the other end across the “A” (Armatuer or Generator ) terminal on the voltage regulator. The generator is an A type generator. We got sparks.
Then we started the car (it starts easily, usually one crank, and runs well). After allowing the car to warm up, we tested the generator with a volt meter and found after grounding one wire on the engine and touching the other to the terminal on the generator that the generator was producing 6.02 volts.
Finally, after driving the car at speed for 30 minutes (55 mph) the needle on the amp meter on the dash never crossed over the middle of the dial and never approached “c” for charging. After getting the car back into the garage, I shut the car off and then tried to restart it. The battery did not have enough juice to restart the car. The problem is still the same.

Gentlemen and ladies, any ideas. Do I need to repolarize the voltage regulator and the generator again? The voltage regulator is new. It was made in China. The guy who restored the car is sending me the old one. Maybe the issue is a bad voltage regulator even though it is new. Is there a way to test the voltage regulator? Maybe using the volt meter to check voltage across the"B" terminal to the “F” and to the “A” terminal.

Help!

John P.

To me, 6.02 volts doesn’t sound like a high enough output for your genny to keep it charged.

Perhaps it is the generator. A 12 volt system usually requires 13 volts of output to stay charged, so if you half that, you get 6.5 volts.

You did check all of the grounds? Just to be sure? However, I think that if it starts up within one turn (quickly) then it probably isn’t a grounding problem.

Please keep posting back. We would love to see a vintage automobile on the road again, probably almost as much as you would love to drive it again.

Thanks 01ksdavis. Will check generator again. Received a post on Cadillac LaSalle Club forum site that I think targets the problem. In looking at old Delco Remy voltage regulator manuels it appears the wrong voltage regulator was installed. The one installed is an after market from China. It has 4 leads and two screws holding the cover on. The original voltage regulator for a 1939 Cadillac LaSalle 50 is part #118204 for a 6 volt positive ground voltage regulator. It has 3 leads (B, A, and F) and only one screw holding the cover on. I have ordered a NOS from eBay. Hope that does the trick.

John P

Simple fix buy American next time, and just rebuild
the gen. its very simple.
Jim