But when I was getting ready do mine I found very few that included how folks planned out their update, the pieces of the change that they overlooked, how well it worked after it was finished, or what they would do differently if they were to do it again.
That’s what this is about. Just trying give food for thought for folks facing this in the future.
First, a little about my background that might give some insight into my thought process. I recently retired. I spent the last 45 years developing and implementing avionics system updates and upgrades for military aircraft. So, if I take some things a little too far in some areas, I just couldn’t help it.
I really only had three objectives.
1) First, don’t make any changes that would make it difficult to revert back to the original system
2) Second, don’t make any changes to the basic tractor
3) Third, to do the change is such a way that the electrical system change was completely transparent (no special actions or “accommodations” would be required like flipping a switch or “goosing” the throttle)
These were my objectives, you’ll need to think through and develop your own.
The first thing I went through is determining whether my alternator would “self-start” on my tractor. If you purchase a new alternator, or get pre-tested alternator from a rebuild shop, you should have a set of test results that give you a good starting point. A copy the test results from my alternator is shown below:
It shows my alternator self-starts at 2,329 RPM. That’s alternator RPM (not engine RPM).
To equate that to engine RPM I had to go through an exercise to determine the size of pulley I was going to use on the alternator. I did not want to make any changes to the crankshaft pulley or the two step fan pulley, so the alternator was the only pulley size I would/could adjust.
It turns out the smallest alternator pulley I felt comfortable using (2.5 inches) was my best option. The alternator speed ratio with a 2.5 inch alternator pulley looked to be about 2.75. The calculations, and resulting alternator speeds for several engine speeds, are shown below.
That indicated that I’d need an engine RPM of ~850 to excite the alternator output. So, to make the system work the way I wanted it to I’d had to add a 12 volt line to the field input of my alternator. There would also need to be some voltage dropping device in that line. I chose a simple light over a diode or resistor.
I looked over half a dozen different farmall wiring diagrams and came up with a composite to use as a starting point. I added all the details I could (i.e. part numbers, showing connection points, etc.) and the results follow.
Don’t forget:
1) Be sure to add a good ground to the alternator case. Yes, it’s really a good idea
2) Light Switch Dimmer Resistor (resistive wire) needs to be changed
3) Use wire with high temperature insulation (125° C) for anything forward of the battery box
4) Use care to make the switch connections as shown
5) Change all light bulbs. I used #1156 bulbs instead of #1141 bullbs. #1156 bulbs produce more light, have a longer life and have a more robust filament. They also draw more current (~2.1 amps instead of 1.4 amps), but that shouldn’t be an issue.
Expect the Unexpected. Expect to find problems that need to be fixed as you work the conversion:
1) All the light seals disintegrated when I removed the lens retaining bands to change the six volt light bulbs to 12 volt versions
2) The biggest mechanical issue was getting a full size coil bracket to work properly using the smaller mounting footprint on the tractor
What would I do differently (maybe):
1) Size the alternator capacity more closely with the expected power demand. You don’t need a 60 amp alternator on a one row tractor just to charge a battery and light up 3 #1156 bulbs.
2) Install an over current protect (fuse) in-line with the main alternator output. This I will likely do in the next few weeks. A 30 amp fuse on the alternator output maybe, to eliminate the possibility of the output current exceeding the 10 gauge wire capacity.
3) Add provisions for plugging the tractor into a battery maintainer (trickle charger). If you use the tractor infrequently, it will keep the tractor “ready to go” and likely extend the life of your battery (save money in the long run).
So, there it is. I finished the change over a couple weeks ago and it’s working like a charm.
Use what you can from my experience and ignore the rest.
