How to test alternator

[Brandon T.]

I have a 37 amp alternator on my 68 BB. How can I verify that the ouput is correct. The gauge reads about 20 on my instrument panel and when I put a multi meter accross the battery it reads around 13-14 volts idling. When I raise the RPM the voltage goes above 14 volts. I took it to advance and had it tested and they said it is putting out too much but they didn't seem to be sure about it. Please let me know the correct way to test it. I would also like to know how to test the voltage regulator.

[Edward J.]

Re: How to test alternator

Brandon, everything on your charging system to releative to the state of charge of the battery. first take the multi meter and check standing voltage a fully charged battery is 12.66 volts , if .2 to.3 volts below, your amp meter in car will show it charging on the high side, the voltage on meter would be around 14.2-14.5 if by chance when racing engine rpms and you charging above these spec.s your overcharging. if by chance you meter has a amp reading and you have a amp clamp, you can put the clamp on the battery wire on back of alt. and turn everything on and check the amp reading this should put out about 3/4's of the alt amp output. hope this helps Ed (49497) .

[Dick W.]

Re: How to test alternator

I believe specs call for 13.6 to 14.2 volts

[Brandon T.]

Re: How to test alternator

What will cause the alternator to over charge? Could it be my valtage regulator. I noticed one of the coils on the valtage refulator never picks up.

[Gerard F.]

Re: How to test alternator

I have a 37 amp alternator on my 68 BB. How can I verify that the ouput is correct. The gauge reads about 20 on my instrument panel and when I put a multi meter accross the battery it reads around 13-14 volts idling. When I raise the RPM the voltage goes above 14 volts. I took it to advance and had it tested and they said it is putting out too much but they didn't seem to be sure about it. Please let me know the correct way to test it. I would also like to know how to test the voltage regulator.

Brandon,

Actually, that output sounds pretty good for a 37A alternator. The voltage output is adjustible through the voltage regulator, and the voltage will reduce when the regulator is warm.

I try to keep my output 14 max with a gel battery when hot. I wouldn't want to get above 14.5 even with a lead acid battery as you tend to cook them.

Here's a handy Walmart instrument to check your charging voltage, and battery state:



Also, see the second archive post below, if you are thinking about refurbing your alternator.

Cheers,