Hi all, I recently had my alternator go out on me and replaced it with a used unit. Before the other one went, it usually read a hair under 14v but now it is showing quite a bit lower. I haven't any problems with it being a little lower yet but I was wondering... What should it read?

Thanks,
Taylor

 

Depending on many factors the operating voltage of a vehicle can vary... ideally with no other electrical demand the charging voltage would be about 14V but typically 13.5v - 14.8v is acceptable...

The thing you don't want to see is the voltage dropping radically with more electrical load. Turn on the high beams and blower on max. Observe the voltage gauge. It should drop a little. If it drops a lot then you likely have a sick alternator or bad connection. It is possible for an alternator to kind of fail... where it will read like it's charging but it doesn't actually output significant amps to recharge the battery and provide power for all of your electrical demands.

 

Stick a DVM across the battery and see what your voltage actually is. The dash meters are iffy at best. 13.3-14.5 is an acceptable range with the alternator charging.

 

Thank you for the detailed post. I really appreciate it. I checked today and at idle using the dash gauge, I am at about 13.16 without anything turned on and 12.33 with the blower on high and the high beams on. This is only if the gauge uses a linear scale where the distance between each line is equal to the next, which I am unsure of. I'm at school so I don't have access to my voltmeter but will grab it when I go home this weekend and get a more accurate reading.

Thanks,
Taylor

 

Taylor, yes get a DVM on it. The dash gauge can be inaccurate.

 

I consider a "used" alternator to be a weapon of last resort - if I'm buying one, it's because I need a core to rebuild.

However, any suspect IP readings (especially voltage) are to be verified independently before any other troubleshooting is undertaken - break out your DMM.

Also, you can find a writeup I've done on this board (and six or eight others - it's a copypasta, I got tired of typing it out) that will tell you how you can test your primary electrical in the driveway with a helper and a DMM in about 15-20 minutes. It's not a quantitative test, but it's a good qualitative test - and doing it has saved me lots of troubleshooting time over the last 30 years or so!