Alternator advice

[hueroloco]

if the battery is fully charged and good, that's no good.

Normally I test an alternator with amps, but it should be at least 13.5 volts at the battery. If the problem is not the battery, you might need to test amperage output of the alternator.

[DMikeM]

Originally Posted by hueroloco

if the battery is fully charged and good, that's no good.

Normally I test an alternator with amps, but it should be at least 13.5 volts at the battery. If the problem is not the battery, you might need to test amperage output of the alternator.

Is there a way to test AMPS with a digital multi meter?. I am wondering if the AMPS are low because this is the same results I had from the Napa Auto Parts Alt I returned because the Auto Repair Shop stated it was butting out 14.5 volts but not enough AMPS.

[hueroloco]

Everybody tests differently. I used an amp clamp around the negative cable, then I load the battery with a carbon pyle battery tester. That will force the alternator to go to max output.

A good amp clamp is like $300 and they don't usually come with a multimeter. The amp setting on a multimeter is usually only 20 amps max.

Weird that you have 14.5 at the alternator and 12.5 at the battery?!? Maybe try disconnecting circuits and see if it changes? I can't imagine what would have that kind of a voltage drop?

[DMikeM]

Originally Posted by hueroloco

Everybody tests differently. I used an amp clamp around the negative cable, then I load the battery with a carbon pyle battery tester. That will force the alternator to go to max output.

A good amp clamp is like $300 and they don't usually come with a multimeter. The amp setting on a multimeter is usually only 20 amps max.

Weird that you have 14.5 at the alternator and 12.5 at the battery?!? Maybe try disconnecting circuits and see if it changes? I can't imagine what would have that kind of a voltage drop?

I could try the old small battery that used to be in there. I replaced it with a big deep cell type.
When you disconnect the main harness plug near the battery (fuse relay box) and check the volts there it is over 14.5. I will see if my shop at work has an amp clamp. We have a pretty good sized vehicle maintenance shop, and the electrical department might have something.

[DMikeM]

Had an amp clamp test done and found the ALT is putting out from 45 to 70 AMPS before the battery connection and 14.5v before the battery.
Almost no AMPS at the battery cable and 12.7V at the battery. This is all under full load. Everything electrical turned on.
Today I sent an email to Denso Aftermarket tech support to ask if this was normal behavior. Waiting for a reply.

[dr_jones2u]

I had the same problem and it turns out that all the local parts house sell the 75 amp alternator. I called Isuzu with my vin and they told me I needed a 90 amp alternator (which no one here sold). Parts house had already disposed of my 90 amp alternator so I bough a used one for 35 bucks and am now on my 3rd year with it. I was told they electrical system shuts down non essential systems to get the right amount of power to more critical applications. As soon as I got the 90 amp alternator everything started working again. Hope this helps