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Old 10-08-2007, 02:39 PM
DavidA DavidA is offline
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Join Date: Apr 2004
Location: NJ
Age: 61
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Default Alternator Question

Hi

Have a 1970 383 Challenger. I noticed that I have just about 13.0 Volts across the Battery terminal at idle. I seem remember I used to have closer to 14 Volts. Checked at higher rpm and it stays pretty much constant at 13 volts. If the engine is cold and the weather is a little cooler then have closer to 13.5 volts but this goes down after the engine warms up.

Checked the voltage at the Alternator terminals and have 15.5 Volts cold, and then this goes down to 14.8 or less volts when engine is warm.

My battery is fairly new but often if I don't disconnect it when leaving the car for several weeks without starting it the battery hasn't got enough power to start the car. I checked for shorts and don't seem to have any external drain on the the battery.

The only change to the electrical system is about 6 months ago I installed an MSD Ignition (6AL) and MSD Coil. I still have the dual post balast resistor in place. Also tried a new Voltage regulator but this had no affect.

Questions

1. Is my Alternator not charging the battery enough ? Only do fairly short runs. The alternator was a rebuilt one from a local Auto store that I put in 7 years ago .. don't know what Amps it is. Has a dual pulley.

2. If I'm going to replace the Alternator what Amps should I aim for as I see 50, 60, 75 and higher advertised. Any recomemended supplier ?

Thanks
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Old 10-08-2007, 08:52 PM
moparmarc moparmarc is offline
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Join Date: Mar 2001
Location: Chelmsford MA
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Default

You can take the car to your local parts store - they can hook up to your alt. and see if anything is up with the charging system.

The local Autozone guy found a bad diode inside my alternator and I got the thing rebuilt. They also tested the battery to make sure it was holding a charge under load.
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