John Deere A alternator conversion

Wanting to convert my 1950 JD A to a 12v alternator. Already has a 12v battery positive ground. Has a mag right now but want to get a distributor and hot coil in the future. Can it be converted using the mag system as is ? Tractor has no kill switch just idle down and pull on throttle at carb to shut down. Are there any alternators that bolt right on ?
 
Since the Mag has no connection to the battery or alternator system whatsoever YES you can convert that ignition to an Alternator MOST ALL OF WHICH ARE NEGATIVE GROUND HOWEVER so don't forget to change the battery to NEG Ground. The ammeter leads need swapped when you change ground.

John T
 
I've converted some to alternators, usually getting a 1 wire from Napa. Only wiring change is to flip the battery around and to change the ammeter leads.

This subject seems to get some on here crazy, and while generators can still work, my tractors work for a living, and I like the convienience of a battery charged all the time.

Good luck!
 

How is the hot coil going to make a difference in a 975 rpm low compression two cylinder ?
Opening the plug gap too wide will cause cross firing under the distributer cap.
The 20 amp generator from the late 1st numbered series and the 20/30 series will bolt right on.
 
My tractor runs at 1250 rpm and is bored .125 over with high
compression pistons. It pulls farm stock all year and does
occasional work duties around the house when needed. It gets
started and shut off more often then it should so the generator
isn't getting the job done.
 
Do you remember what the part number for this alternator was or what the alternator is supposed to fit on. What's involved in mounting it? Does it fit the original generator mount or are modifications needed?
 
Yes, it can be converted using the mag system as is.

Take a look at the wiring diagram below.

a172439.jpg" width="350"


Take a look at the photos below of "Old John" Nancy's 48A.

a172440.jpg" width="650"


a172441.jpg" width="650"


a172442.jpg" width="650"


Take a look at how the alternators is mounted.

a172443.jpg" width="650"


a172444.jpg" width="650"


a172445.jpg" width="650"


Hope this helps.
 
(quoted from post at 13:29:25 10/25/14) My tractor runs at 1250 rpm and is bored .125 over with high
compression pistons. It pulls farm stock all year and does
occasional work duties around the house when needed. It gets
started and shut off more often then it should so the generator
isn't getting the job done.

Fires the same number of times a minute as an idleing V8.
 
Sorry for the slow response... been out combining.

I don't recall the number. I believe it was a Delco. There aren't a whole lot of 1 wires to pick from, so they'll figure it out.

The pics posted above show some of the mount options. You'll have to be a bit creative... I've usually had to utilize some washers as spacers, etc. The net result is a much more consistantly charged battery. And the alternator won't be a whole lot more than a new regulator for the old genny.
 
Read that a one wire needs to be run at 1000- 1200 rpm before it will turn on. Anyone had any issues with them not turning on because of the engine only turning 975 ? I don't wanna have to run it full throttle when I start it up just so it will start charging. Am I better off with a 3 wire set up ?
 
The pulley supplied will not be a one to one ratio with whats on the fan shaft. I find it varies from tractor to tractor, but usually half open will get it started charging, and will then charge well at slow idle once going.
 
Exactly why I run a three wire standard set up, the run up to charging voltage will knock out the internal voltage regulator eventually, BTDT on a standard three wire. Lasted about five years and then the ammeter went full charge and stayed there. Problem was solved by using two (instead of one) trailer clearance lights in parallel to excite the number one terminal with and it's not enough back flow current to allow run on when you kill the ignition switch which you will need when going to distributor anyway. So with two bulbs, it's charging well below idle speeds and the run up voltage spike never happens.
 
Converted this 1951 A to a one wire alternator with no problems. Fan pulley is approx. 4" dia, alternator pulley 2" so the alternator runs at 2X eng RPM, charges OK. Typical car runs at 1500 RPM's on the road, which is about where the 1 wire alternator on this old tractor is running at part throttle. Amp gage shows it charges at idle. Just swapped around the wires to the gage and changed the battery to neg ground, that was it. Now...as my Ford tractor buddy says, "it's not correct".
mvphoto12374.jpg
 
(quoted from post at 15:18:39 10/25/14) Yes, it can be converted using the mag system as is.

Take a look at the wiring diagram below.


<img src="http://photos.yesterdaystractors.com/gallery/uptest/a172441.jpg" width="650" />

Hope this helps.

Using a momentary exciter button is rather tacky. Why not use a proper charge lamp or a diode ?
 
My late father-in-law rebuilt this old tractor about 35 years ago.

He did not have the benefit of the "expert" advice offered on this forum.

Guess if it works, then no sense in fixing it.

Thanks for the information.
 
(quoted from post at 15:15:14 10/25/14)
(quoted from post at 13:29:25 10/25/14) My tractor runs at 1250 rpm and is bored .125 over with high
compression pistons. It pulls farm stock all year and does
occasional work duties around the house when needed. It gets
started and shut off more often then it should so the generator
isn't getting the job done.

Fires the same number of times a minute as an idleing V8.

What does that have to do with an alternator conversion ??
 
If your doing an alternator conversion you are most likely going from 24 volt to 12,,,so you will need a 12 volt starter.....a long Nippendenso or a long Delco will not fit well because of where the fuel filters are located,, so the Iskra is a great choice...
 
Tim S - not sure we are on the same page here a JD A is only 12 volt to start with. Maybe this was supposed to be posted on another thread ?
 

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