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Old 07-12-2002, 12:27 PM
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Post Interpreting Voltmeters

I have a question about reading voltmeters. I have a 100amp Chrysler alternator on my hot rod and at cruising speeds with no electrical equipment running I get a good strong 14v, 13v at idle. When my radiator fan comes on I still get 14v @ cruising speed but at idle it drops below 12v which seems ok. However If I turn on the air condtioning (with auxillary electric condenser fan) and/or headlights with the radiator fan running, voltage really struggles to get above 12v at any time. Granted that is a big electric load but the 100amp alternator should keep up, no sweat.

I'm thinking my 4 year old battery may be going south. Any ideas?

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Old 07-12-2002, 01:27 PM
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willy36,

i wouldn't worry about this. It is not that strange. A car can't really generate enough power at idle to run everything off the alternator, which is why you get the lower voltages. 100A for an alternator is pretty big. I wouldn't worry about replacing your battery unless it won't hold a charge. Make sure that you maintain your battery's fluid levels if it is not a sealed battery.

Later,

JB
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Old 07-12-2002, 04:23 PM
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Just topped off my battery last week. I agree, at idle I shouldn't expect over 12v but it doesn't go over 12v @ sustained 3000rpm with a few electrical systems on.
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Old 07-15-2002, 04:04 PM
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Howdy,

Al here with AutoReWire.com in beautiful downtown Galt, CA.

How big is the wire between your Alternator and your Battery and does it pass though your fuse panel??

It would take at least a number 8 AWG wire less than 10 feet in length to adequately handle a 100 amp load at 12 volts.

No matter how big the pump is - you can only get so much water through a certain sized pipe.

Food for Thought

Have you also double checked connections? Are they clean?

al

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Old 07-16-2002, 06:24 AM
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Well, I run twin #10 wires about 3' long from my alternator to the starter battery terminal, then a #1 welding cable about 7' long to my trunk mounted battery. Connections are VERY good! Went thru the bad connection drill several years ago and learned that lesson well. When I top my battery off all nite w/ my trickle charger it seems to maitain voltage for a while so I am suspecting the battery. Doesn't ever seem to go totally bad so that is why I am confused by the low volts.
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Old 07-16-2002, 08:20 AM
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Wow! you certainly have it wired well enough in my book. Possibly that 4 year old battery but I would not be surprised to find out that a bad diode in the alternator or malfunction in the regulator is causing the problem.

Please let me know the outcome. This one is interesting.


al

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Old 07-16-2002, 02:54 PM
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Yes, it may be a diode I guess. If just one goes it is hard to detect. If I get the energy in the +100 weather this weekend, I'll pull the alternator and check the diodes. I'm getting too old and tired to do this stuff!!
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