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Username Post: Alternator charging        (Topic#360541)
Posts: 727
Reg: 08-07-08
04-16-20 06:48 AM - Post#2791266    

I have a 77 C20 that the alternator charging has changed. Before the volt gauge had been reading about 13 volts or the middle of the gauge. When the electric fan came on the gauge would move up to about 14 volts and then fall back once the fan came on. Now the gauge is reading 14 volts at idle and higher rpm. I checked the voltage at the battery and its reading about 14.5 volts which matches the truck gauge reading. My question is should I be concerned that the alternator is over working its self and fail or is it just high resistance in the original wiring. Comments welcome.


Ultra Senior Member
Posts: 11393
Reg: 03-25-05
04-16-20 08:55 AM - Post#2791276    
    In response to corvesy

Your battery may be getting weak or the battery cables are corroded.

66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)

Posts: 727
Reg: 08-07-08
04-16-20 08:59 AM - Post#2791278    
    In response to acardon

Good idea. I switched out batteries from another vehicle (charged it up first) with the same result.
Battery terminals are clean. I also changed the alternator same result.

Posts: 323
Loc: seligman,arizona
Reg: 05-14-09
04-17-20 07:36 AM - Post#2791370    
    In response to corvesy

In my personal opinion I think your just fine. my car has run at 13.8 to 14.0 for a few years with no problems that I can see.

Posts: 180

Reg: 03-20-18
07-29-20 04:55 PM - Post#2799877    
    In response to pauldian

agree, think your fine. I noted that my voltage changes when turning on and off accessories while monitoring how my charging system is performing in preparations for a charging system overhaul for extreme continuous duty application of charging house batteries. .

Also the temp of the engine compartment may be affecting your regulator as well. Around here summer been cooler than normal so voltage for me been reading higher. since it does not need to step down voltage since the battery is running cooler than normal. Thermal protection sensor maybe.

The alt has to run higher than 12 volts or it won't charge the battery. AND it has to adjust for the load changes. I would only worry if it gets in the 15 volt or higher or lower than 11 Volt ranges.

When you turn on a fan that is significant draw. the regulator detects a drop in voltage telling your alt to boost output to increase voltage upwards , I believe that is what your seeing. temperature a charge state of battery is going to impact where voltage is sitting.

when asking Questions its related to van I own: 1987 GMC 3/4 ton G2500 vandura, V6, No AC, standard length. 3speed trans(no overdrive).

Edited by VanLife on 07-29-20 05:01 PM. Reason for edit: No reason given.


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