Slow Charging on a 1973 Dodge Polara Police Car

[Ryan Wofford]

Hey guys (and girls), I currently am helping out my neighbor with his mint condition, 77,000 mile, actual 1973 Dodge Polara police car. The car drives fantastic and the 400ci big block chrysler will push that boat along the highway without any problem. The problem is that there seems to be a problem with the charging system to where after about a week the battery will be dead and we will have to charge it on is battery charger. however, he drive this car a lot and most of the time a night for hours at a time so I would think that if it wasn’t charging at all, the battery would be dead a lot faster than that. we checked the voltage and it said 14V at the battery. what’s going on?

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[Alex]

Have you tested the voltage with all the lights and accessories running as well?
A weak alternator can keep a battery at 14 volts with only the engine running, but once all the other loads are on, it can get dragged down. Driving at night with all the lights on could be having some effect.

How old is the battery itself? What brand/group size? What voltage does it return to when the car is shut off after driving?
Check all wires you can see going to the alternator and battery to make sure nothing is loose/corroded/burned etc. Perform the parasitic draw test to make sure there isn’t something dragging down the battery when the vehicle is off. Do a voltage drop test on the alternator wires while it is running.

Consider installing a temporary volt gauge so the driver can keep an eye on it as it goes down the road.

Sounds like a really nice car so I hope you can get this sorted.

[Ryan Wofford]

when the car is just shut off it drop to 13 but in the morning it will be about 12. I’m not sure of the brand of battery but I know it is almost brand new maybe like a month old, we did the test with the head lights, and all the police lights on as well. On this vehicle there is no volt gauge but there is an amp gauge, with everything running it reads about -10 amps and with everything off it’s around 1 amp in the positive. I’ll help him check the connections and everything later this afternoon.

just a note this is a heavy duty, standard police alternator with 2 V-belts running to it. Not the regular alternator that is usually found on the chrysler big blocks

[Alex]

A brand new battery dropping from 13 (full charge plus surface charge) to 12 (quite low) overnight suggests parasitic loads or defective battery. At most it should go down to maybe 12.5 (good charge, no surface charge) by the next morning. Certainly do the parasitic draw test.

http://www.youtube.com/watch?v=KF1gijj03_0

I think those amp readings are expected at idle with everything on. Once the engine revs up a bit that negative amp reading should go up to zero or positive, assuming the alternator, wires, etc are in good shape. If the alternator can’t offset the loads on the car even with engine running at 1500- 2000 rpm, the battery will drain as the car is driven, even more so in slower traffic.

I’m interested in what voltages you see at the battery when everything is turned on and the amp gauge is reading -10, what it goes to when the car is revved to 1500 rpm or so. Voltage drop tests on both positive and negative cables wouldn’t hurt.

[Author]

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