40 Alternator/Ammeter Question

Hotflashjr

Well-known Member
Location
Western MA
I replaced the alternator on my JD 40 with a GM 1 wire. I bought a new wiring kit from Agri-Services based on this configuration as well as the alternator. They were helpful as always and I am confident everything is wired correctly; 12 volt, negative ground without cutout or relay.

I also replaced the ammeter. I bought one for a 40 but it reads from -60 to +60 while the old broken one was -30 to +30. The alternator is charging and I get a positive test light at the 1 wire post on the alternator and back at the ammeter. When starting the ammeter shows discharge to -20 and will charge back up to 0 in about 2 minutes. The ammeter never goes above 0 but will consistently sit at 0 with the tractor running. With the lights on the ammeter shows a small negative and as soon as I shut off the lights it goes back to 0.

I think the charging system is working as it does charge but my concern is the ammeter not going above 0. Do I have something wired wrong or is that just how a 1 wire 12 volt change on these tractors work?
 
if you know it is charging, maybe amp meter is wired backwards, check voltage across battery terminals when running to determine if charging, should get around 14 volts
 
I did the same thing to my 40-w. You have to rev up the engine to excite the alternator, then it will charge. If you don't rev it up it will sit on 0.
 
Check battery voltage when it is not running and while it is running. Not running you should get around 12.6 volts and running 13.5-14.5. If your gettign the 13-14 volts then you have the amp gauge wired backwards
 
That 60 amp meter does not yield as much swing and indication that a smaller unit might subject to actual current and state of battery. A volt meter on the battery when its setting stabilized and at rest versus engine running at fast RPM will give an indication of how much she's charging or not.

A full charged lead acid battery sitting and rest and stabilized engine not running should read around 12.6 volts subject to temperature. Then at fast RPM IF SUFFICIENT TO EXCITE THE ALTERNATOR I would expect the voltage to rise to at least 13 volts up to 14.4 or so SUBJECT to RPM and alternators regulation and state of charge and condition of battery. If battery voltage never rises she not charging.

If the ammeter is wired at the correct polarity when not running if you switch on lights or ignition it should swing over to - discharge but running at fast RPM iffffffff charging it will swing to + charge.

The tractor was originally POS ground but if switched to an alternator most are NEG ground so the ammeter leads would get reversed so it doesn't read backwards.

The wire that used to go to BAT on a Voltage Regulator or Cutout Relay would now wire to the big main output stud on an alternator. The ammeters other lead eventually gets the the hot ungrounded battery post.

Insure ammeter is at correct polarity and is wired correct then check battery voltage at rest and engine running at fast RPM.

John T
 
You have two comments concerning charging. "The alternator in charging -----" and "I think the charging system is working -----". What have you measured to verify charge?
 
Tester light on the wire coming from the alternator back to the ammeter lights when the tractor is running at more than an idle. At an idle the tester light will not light and when the switch and tractor is off the light will not light.
 
You said replaced the alternator, or was it the orig 6v. genny? If it was a generator, with the fan pulley I would be interested in buying it as I want to change my 40 back to 6v system. Try email, Thanks
 

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