Alternator charges but not optimum voltage output. Help

[A.J.C.]

Vehicle specs: 98 5.0 Explorer with 2 electric fans in place of centrifugal fan.

Hey guys. I replaced my alternator because the old one started to smell and within seconds stopped working.

I put a used one in from a running vehicle. Voltage output with engine running and no accessories on is at 13.0 Volts.

With engine off, the battery reads 12.3 volts.

I do have two electric fans that run all the time at the moment until I get a proper fan controller.

Should I be worried that this alternator is on its way out too or that the fans are burning up the alternator by drawing too much current?

This is where the gauge has always stayed while the engine is running even before the old alternator went out.

 

[koda2000]

electric fans draw a ton of AMPS. They should not be running all the time. Try disconnecting the fans and see what your running voltage is.

 

[SoNic67]

Was the battery drained when you started the new "old: alternator?
Because trying to charge an empty battery with an old alternator is a good receipt for burning that alternator too...
When the voltage is 13V usually it means that one or two of the 6 internal rectifier diodes are "gone".

 

[A.J.C.]

I did not charge the battery after replacing the alternator. I will charge it up and disconnect the fans to determine the issue. Thanks for the help!

 

[A.J.C.]

At this point, I think it may be a ground issue. I will be cleaning all connections and will report my findings.

 

[SoNic67]

If you didn't charge the battery, you already fried the new alternator. It says so even on the alternator installation instructions that came in the box. But... who reads those, correct?

To check for ground, measure the alternator output between the battery (-) terminal and the alternator body with engine running. It should be zero volts or very close (0.1-0.2V).

Also, because the alternator is so accessible, you could measure the voltage between alternator output (+) and alternator body. Be VERY careful so your voltmeter tip doesn't touch nothing else, if it "slips" and shorts that output bolt, you will see sparks and likely damage the alternator. That's why that rubber gourmet is there.