Alternator question

[bubbanm]

My alternator was not charging and the parts house said it was good. They said the pulley was the old generator pulley and was too big and that I needed to put a smaller pulley on it. So I did and I put a small pulley on so it would turn much faster. So I put the alternator back on my MF150 and the volt meter shows nothing. I check with a multimeter and I have 12.45 volts at the battery. I start the tractor and check at the one wire post with the motor running wide open and I still only have 12.45 volts. I checked at the R1 post and I am getting 1.45 volts. I don't think this alternator is charging. Am I right?

 

[c.oawright]

No it is not charging.. The voltage should go up to 13.8 to 14 volts.
Some of the alternators have a excite wire that applies battery voltage to excite the field winding. Sometimes it is an oil pressure switch. Terminal one is the excite lead. It needs to tie to the plus terminal through the ignition switch or oil pressure switch and should go up to 13.8 when the engine is running.
Look up Delco wiring diagram.

 

[old]

What brand and type of alternator there not all the same. internal or external V.R. Maybe you have a bad wire or it is wired wrong

 

[Jim.ME]

A photo might help ID it if you don't know.

How did the parts house test it to say it was good? Did they hook it up and run it on a test bench to check the output? Did they hook more than one wire to it to make it charge? Was it charging and it stopped, or it hasn't charged since you got the tractor?

 

[bubbanm]

It turns out Autozone had sold me the wrong alternator. It was suppose to be a one wire alternator with the self exciter but it was just a regular alternator. The correct one should be
here today. Thanks for the help everyone.

 

[Jim.ME]

(quoted from post at 13:36:01 03/02/20) It turns out Autozone had sold me the wrong alternator. It was suppose to be a one wire alternator with the self exciter but it was just a regular alternator. The correct one should be
here today. Thanks for the help everyone.

Thanks for letting us know. Hope the next one works properly for you. If your tractor sets for extended periods you may want to disconnect a battery cable, or install a disconnect switch, due to possible parasitic drain by the alternator. Some bother, some don't.

So when you said they told you it was good, they didn't test it, they just said it was good, as in what you wanted? Just for future reference a one wire alternator will energize and charge with a generator pulley on it. You just need to speed the rpms of the engine up to get it started with the larger pulley. The advantage of the smaller pulley is it makes the alternator turn faster so the engine doesn't have to be revved as high. So if they said the generator pulley was stopping it from charging they were wrong there as well.