electrical problem.aka I screwed up

[Chris142]

The alternator in my truck stopped charging the batteries. I got home and started my diagnosis.

I unplugged the external voltage regulator. I then put 12v to the field wire. The lights got bright and my meter showed 14.xx volts and it changed pitch. This tells me that the alt works, using my basic knowledge anyway.

OK cool. The regulator quit. Easy enough. Went and bought one, put it on. No charge still. Got 12v @ the back of the alt and all other connections look good.

I have a spare alt I picked up and I put that on. Its charging now. So I had a bad alt that still put out volts and amps when full fielded.

 

[The_Eric]

If you full field an alternator, it should put out max volts, right? Around 16-18?

So if you full fielded your old alternator and it only out out 14, then maybe it tested bad and you didn't realize it.

 

[Colt45ws]

Originally Posted By: The_Eric
If you full field an alternator, it should put out max volts, right? Around 16-18?

So if you full fielded your old alternator and it only out out 14, then maybe it tested bad and you didn't realize it.

The amount of voltage it would put out with full field will depend on its watt output capability at that RPM vs. load. In this case, at idle, its capability is pretty close to the load he had on it at the time so it was only 14V.
At least, thats my understanding. A regulator controls voltage by adjusting field voltage to get the right voltage on the output. What its really controlling though is the wattage generated by the alternator.

 

[Chris142]

I took it in to a shop today. One of the brushes got hung up in the brush holder.I assume that maybe it was contacting the armature during my test. I only full fielded it a couple of seconds,didnt want to overcharge something and blow it up.

Shop didnt charge me a thing!!!