Charging system question

[saltshaker]

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Having a issue with the charging system. 100 amp 1 wire alt and using a Tauras Fan for cooling. With the fan off the volt meter is showing 13 volts but with it on lately it is showing 11 volts and with halogen headlights on it's down to 10 volts.....motor is turning 26-2800
Rpm's. The car starts every time, had it checked out and by Advance Auto....they said it's ok Wonder if the fan is ready to go
so, any idea what's going on?
Jon

[MOTORHEAD]

Double check voltage with a known good meter, such as a Fluke. You want 13.75-14.25 VDC no load.
You can also verify current draw with a clamp-on or induction ammeter and see the actual current draw of individual accessories.

[tcabece427]

I assume the voltage regulator is separate from the alternator? If the it checks out ok by Advanced Auto then it is probably the regulator. The other thing could be if you have underdrive pulleys? It's less likely because it seems to charge at idle? Without the Fan and Headlights on.

[saltshaker]

It has a 1wire alt,never had this problem before
Jon

[ffr 1137]

Weird...that's kinda what happens with a bad cell in batt...it won't take a charge. You did say it checked OK though. That's weird. Put a charger on it. Monitor before and after
voltage. I suppose it could be some excess draw. Fan on a relay though right, and fused?

Mike

[saltshaker]

No relay but fused
Jon