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Username Post: how to check amp output from alternator        (Topic#356985)
Bruces 57 
Frequent Contributor
Posts: 2435

Reg: 01-03-07
06-26-19 12:31 PM - Post#2769307    

Ben away for a bit but back at it again. I purchased a (crappy/cheap) serpentine kit for my 57 chevy. Included was a bright new alternator which came with the wrong pulley (v Belt) but supplied in the kit was a serpentine pulley. When I went to the alternator shop (yeah I got one near my house) the guy changed my pulley but said that the alternator was "nothing coming close" to 135 amps! (advertised output of the alternator) Of course the shop told me they could make it the right output amps for about $150!!
So now I am in quest of how I can test this alternator to see just what it is putting out.
I have an old Craftsman Digital but don't know how to set it to measure amps!. (or should I just pull the darn thing and take it to a parts store for testing?
If someone knows just how to do this I would appreciate any helpful suggestions!



Very Senior Member
Posts: 4545

Reg: 12-29-02
06-26-19 12:38 PM - Post#2769309    
    In response to Bruces 57

You would need a DC clamp-on ammeter and a variable load.

Easier would be to install it and turn-on all your loads. Them measure the battery voltage. You're OK if the battery voltage still measures around 14V, regardless of the current rating of the alternator.

Super Senior Member
Posts: 5694

Loc: paradise
Reg: 09-05-03
07-04-19 10:16 AM - Post#2769925    
    In response to Bruces 57

parts store probly wont be able to understand how to do it. around here i have to get my own part numbers cause most of the parts guys we deal with are not able to. last week i wrote the number down and the guy couldnt get it right. as noted, turn all electrical stuff on at 1000 rpms you should have about 14 volts. i use 13.8 as the low limit.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


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