2020 alternator?

   / 2020 alternator? #1  

DogT

Silver Member
Joined
May 30, 2016
Messages
207
Location
Hume, VA
Tractor
JD2020
Last August the front bearing on the Moto alternator started screaming, so I bought one of those $90 chinese wonders from ebay. Well yesterday, after I started it the red light stayed on. Tried couple more times and revving it too, nothing changed still red. Well after I backed the tractor out of the barn the light went out, so I thought fine. Not much later it came back on and is still on. Put the voltmeter on the thing today after charging it overnight with the smart charger. Solid 13+ volts on battery until I turn on the ignition and it starts dropping but not quickly. Start it and voltage drops to 12.3 or so and keeps dropping. Is this a good indication the alternator has gone bad or could it still be the regulator? I've got the Tech book, but reading about testing the alternator is pretty confusing and I don't have a resistor pile, but for sure the battery is not charging, but how to know if it's the alternator or regulator. I do have a 1yr warranty on the new alternator and I still have the Moto but haven't gotten the center race off the shaft yet. The outer race just fell off. I thought I may just buy some brushes for the Moto and a new bearing. It was working when I took it off. I don't know how the warranty works if the guy is going to make me send the old one back yet. So I want to know for sure it's the alternator before I do.
 
   / 2020 alternator? #2  
We'll play the music soft and slow for ya! ;)
 
   / 2020 alternator?
  • Thread Starter
#3  
Thanks, that helps.
 
   / 2020 alternator?
  • Thread Starter
#4  
I found the test voltages in the back of the electrical section, so now the tech manual makes more sense to me. I have something to work to. I'll go check things this morning and see if I can figure out what the real problem is.
 
   / 2020 alternator?
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#5  
Went through the tests in the TM for testing the alternator and regulator. First test, Fig2, reads below 1.5V indicates Defective Regulator, Shorted field windings, or Open-circuited indicator lamp circuit. I think I can discount the open circuit lamp, the lamp is good, but not sure. Still all open.

Since I don't have a field resistor I didn't do the figure 3 test.

Using fig4, jumper wire (field to output terminals) and voltmeter connections, disconnect regulator. Reads below 15V at around 12.6 or whatever the battery is. So that's low.

BUT, at this point now the indicator lamp will not light with ignition in run, start or engine running position. Not sure what that means.

Since I don't have a carbon pile, I can't do the next test.

I pulled the alternator off tractor and checked it on the bench. The isolation diode appears good, as do all six diodes on the diode assembly. Checked very low ohms between the slip rings, like 3-4 ohms (pulled the brushes out). Couldn't see anything obviously wrong, not sure how to check for open windings.

So I'm back where I started only now the charge indicator lamp is not working and still not charging. Plus I don't have the isolation diode for the Moto alternator. I suppose I could still buy a bearing install it and use the isolation diode from the new alternator and if that doesn't work try a new regulator.

Otherwise I'll have to get someone to fix it for me. Right when I need to start using it for the spring.
 
   / 2020 alternator? #6  
Probably the easiest way is to put a gm one wire on it. It will have a terminal on it to turn the dash light off as you probably burned out the bulb. I've done a few Tractors like this but it's been a while. If I remember correctly the alternator terminal illuminates the light with the key on. Once it's charging the terminal goes to ground.
 
   / 2020 alternator?
  • Thread Starter
#7  
Been playing with this thing for a few days now. Got it charging today, but then it quit. Kind of wondering if putting 12V on the field winding didn't do something that got it started but then it gave out. Tried a new (aftermarket) regulator. Nothing different. I did like the book said, remove the regulator, remove the field connection at the alternator, and shorted the out (battery) to the field, started the tractor and still no charging. That's a pretty good indication something's wrong with the alternator. I may try to clean the brushes and see if that does anything, but I've got a note to the guy I bought it from less than a year ago that I think the alternator has gone south. I've got parts coming to fix the old original Moto alternator that just had a bad bearing. I'll try that when I get the parts.

No I never burned out the bulb. It was good until today when I tried to put it back in and broke it. I put the oil pressure lamp in place of it. So that circuit is still good. I did go through and clean all the charging circuit connections and make sure there are no broken/open wires or bad connections.
 
   / 2020 alternator?
  • Thread Starter
#8  
I pulled the 4 pin regulator to harness connector apart and hooked up all the wires singly. Bingo it works. Undoubtedly it was a connection issue all along. At least I have a spare alternator and regulator now. I'm going to leave it like that and tape it up.
 
   / 2020 alternator? #9  
I pulled the 4 pin regulator to harness connector apart and hooked up all the wires singly. Bingo it works. Undoubtedly it was a connection issue all along. At least I have a spare alternator and regulator now. I'm going to leave it like that and tape it up.
I got to admit your tenacious. I'd of went gm 1 wire when it first quit. Good job.
 
   / 2020 alternator?
  • Thread Starter
#10  
Well, that doesn't appear to be the end of it. While checking the charging voltage, the idiot light went off, on, then off, on several times. I revved it way up and then it appeared to stay charging. Both regulators seem to work, but with somewhat high V, like 15.2. But I'll take that if it works, both regulators seem to show that. I'll just have to see how it goes. If it gives me problems I'm going to a single wire alternator in a heartbeat. Or re-wire the alternator to regulator. Gremlins. Must be the moon. Thinking about putting a permanent voltmeter on the thing.
 
 
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