I have a problem with my alternator when i am at idle. when i am running the A/C and i come to a stop the voltage drops way down. when i start driving it moves back up, but it never goes back over the 13 mark. is there something i can do about the low voltage at idle? is it an alternator poblem? thanks


Steve

 

DO you have undrive pullies installed on your engine?. i will assume no, however if you do, that is the cause. It could be that your alternator has had it's day. It could also be that your a/c has a problem and it is drawing more power than it should. Have you checked out everything with your a/c system? and electrical for your heater/ac controls. I can tell you that my old firebird had the same problem and it turned out to be the fan for the heater/ a/c. it could also be a bad alternator. check them all out. test for voltage draws and compare it to a service manual to find out if your systems are drawing the proper amount of power.

hope this helps
C

 

It could all be normal too. Because the engine is moving the alternator slower (at idle), the alternator will putting out a lot less current (and thus voltage - the two are directly related to each other).

I suspect the reason that the voltmeter reads about 13 volts (or a little less) is because, when you are at idle, the alternator cannot keep up with the current demand, so the battery takes over. Then, when the alternator is putting out enough to provide the current demands of the vehicle (above idle), it now also has to charge the battery because it was being used during the time you spent at idle. Until the alternator can charge the battery back, 13 volts could be normal. Normally, the alternator provides enough current to power the factory electrical demands of a vehicle and also provide enough current to the battery to charge it. If the battery is not in too bad a state of discharge, I would expect a voltage above 13 volts (13.5 or a little higher) while it is charging. I've seen mine at about 13.0-13.2 volts when charging a battery in a very low state of charge. Once it becomes charged, it increased to 13.8 - 14.9 volts (depending upon outside temperature - remember, the alternator output is temperature sensitive to compensate for the differnece of battery resistance at differnent temperatures).

You may want to check the condition of the battery and/or alternator nevertheless. If the battery is old then it could be losing its capacity (and/or ability to accept a charge, etc.).

Just some thoughts.

[This message has been edited by Stuart Moss (edited September 18, 2000).]

 

You should check your original volt gauge first. On my formula I always thought I had charging problems with the pulleys but it turned out to be the volt gauge not working right. I found out by hooking up an autometer volt meter and the volts at idle with no accessories were at 14 and with all accessories(a/c, lights, radio) the volts went to 13 even at idle. So check your gauge first before getting into anything else.

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Erik '89 Formula 350 TPI
14.10 @ 98 on motor
12.83 @ 109 w/NOS
http://www.geocities.com/formulal98/

 

yeah check it with a meter.. gauges arent always very accurate, although the alt one is dead on in my car.

Steve

 

Thanks guys. i will check it with a volt meter and see if the problem is with my gauge.

Steve

 

Ok, I have the same exact problem, but I know it is not the meter. I know this cause the A/C doesn't work as well (if at all it feels sometimes ) when the voltage drops that low. Also, the turn signals get slower. I have a new alternator and battery, both of which check out fine. The problem seems intermittent with the A/C on, but if I put the rear defrost on, the voltage drops immediately.


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Bobby Jarvis
92 Z28 305
auto, white, t-tops