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Old 02-01-2004, 04:18 PM
ddarnell ddarnell is offline
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Default Charging system

I have several mopar cars and trucks from 1967 to 1973 and they all seem to have the same charging malady. With lights and heater fan on, the gauge shows a negative charge at idle. What's up with this? Is the idle too low? Is the alternator amperage rating tooo low? Is it the regulator?

Any wisdom on this subject would be very helpful. Thanks
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Old 02-01-2004, 05:42 PM
GaryS GaryS is offline
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There are several things that can cause that problem and the first is age. Wiring gets old and electrical connections become corroded. Switches develop more resistance and motors wear and create a heavier load than when they were new.

Another problem is the alternator. Early units were only rated at 38 amps, which was marginal for stock equipment. If you add electrical equipment, like a sound system, the alternator is overwhelmed by the load demand at idle.

Rebuilt alternators also cause problems as some rebuilders do not change the diodes and low output is the result of a bad diode.

I guess the usual answer is; all of the above.
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Old 02-02-2004, 10:21 PM
ddarnell ddarnell is offline
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GaryS, Thank you for your insight. Do you suppose the short solution would be to check the output on my freshly rebuilt alternator to see if it putting out it's rated ampacity? Then up the alternator output to a level high enough to run the old equipment without exceeding the ampacity of the wiring?
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Old 02-02-2004, 10:59 PM
GaryS GaryS is offline
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It wouldn't hurt to know that your alternator is operating within specs. At least you would know what to eliminate.

My '73 truck came with a higher output alternator and even when I pulled a camp trailer, it would charge at idle with everything running. My '64 Valiant, with the original alternator, also charges at idle unless I have all the accessories running. Just the heater or AC on low will not make it drop below the line, nor will the headlights.

One thing I always do when I get another car, is to replace the voltage regulator. They are cheap and I just throw the old one in the trunk for a spare.

I'd be cautious going to a higher output alternator, unless you upgrade wiring also, especially the power feeds. Lots of cars have minimal size wiring the way it is.
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Old 02-04-2004, 12:39 AM
ddarnell ddarnell is offline
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GaryS, Thank you very much for your help
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Old 02-14-2004, 04:23 AM
jwenum jwenum is offline
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Default Charging

I'm the original owner of a '68 SuperBee and it's normal to show a discharge at idle with lights or heater fan running.The alternator just wasn't very high on output at idle speed. Blip it a little and the charging rate went on up to '+' side of gauge. Jeff
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Old 02-15-2004, 01:05 PM
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71_DEPUTY 71_DEPUTY is offline
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try a smaller pully on the alt.- standard ones always had this problem!!!!!
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Old 02-15-2004, 02:17 PM
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mopardave mopardave is offline
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I have had my 1975 Duster since new and it has always shown discharge at idle. I have never seen any ill effects from the condition, though.
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Old 02-15-2004, 03:05 PM
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ehostler ehostler is offline
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Ill effects... headlights dimming when stopped at night. Battery discharging when at idle. I actually had a battery go dead on me in rush hour (more stop than go) traffic several years ago, because of this problem.

The easiest fix is a high output ND alt from a newer Ram or Jeep. There is some good info about this in the Performance Talk tech archives.
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