12 Volt Conversion, Wrap-Up

Farmall Super A, AV, 100, 130, & 140 1939 - 1973

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JohnnyR
Posts: 22
Joined: Sat Aug 24, 2019 4:33 pm
Zip Code: 31088
Tractors Owned: 1952 Super A

12 Volt Conversion, Wrap-Up

Postby JohnnyR » Fri Oct 02, 2020 2:08 pm

One of the most common “updates” done to these old tractors is changing it to a 12 volt negative ground electrical system. You can find many posts and YouTube videos that talk in general terms about doing the change over.

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:

Alternator Table.jpg


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.

Pulley Ratio.jpg


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.

12 volt conversion wiring.jpg



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.

JohnnyR
Posts: 22
Joined: Sat Aug 24, 2019 4:33 pm
Zip Code: 31088
Tractors Owned: 1952 Super A

Re: 12 Volt Conversion, Wrap-Up

Postby JohnnyR » Fri Oct 02, 2020 5:47 pm

Looks like I mis-identified the battery group on the wiring diagram. While my original thought was to use a Group 35 battery, I actually used a Group 26R battery in the project. Here's an updated wiring diagram.

12 volt conversion wiring.jpg


Sorry for any confusion,
Johnny

MarkAkerman
Posts: 24
Joined: Tue Aug 25, 2020 9:40 am
Zip Code: 32340

Re: 12 Volt Conversion, Wrap-Up

Postby MarkAkerman » Mon Oct 19, 2020 11:13 am

Does the word "stock" mean that the part can stay 6 volt? I having a hard time figuring out what has to be switched to 12v and what can remain 6v.

Jim Becker
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Re: 12 Volt Conversion, Wrap-Up

Postby Jim Becker » Mon Oct 19, 2020 11:24 am

In this diagram, that is what "stock" means. You can reuse the original parts if they are in good condition or replace with ones like the originals.

MarkAkerman
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Zip Code: 32340

Re: 12 Volt Conversion, Wrap-Up

Postby MarkAkerman » Mon Oct 19, 2020 11:39 am

Thanks, I'm probably making this more complicated than it really is. I have my grandfathers 52 super A and it was converted to 12volt years ago. The lights need to be rewired because they were not converted or in use. The light switch is missing on the panel as well. Otherwise I will just replace stuff. I want my FFA students to be able to drive it in local parades.

R.D.Owens
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Joined: Tue Dec 01, 2020 10:25 pm
Zip Code: 12571

Re: 12 Volt Conversion, Wrap-Up

Postby R.D.Owens » Sat Jan 02, 2021 12:23 am

Thanks much for the time and effort you put into this post. Your explanation and wiring diagram are super helpful.

Richard

Eugene
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Re: 12 Volt Conversion, Wrap-Up

Postby Eugene » Sat Jan 02, 2021 1:23 pm

Thought I would add a couple of comments.

Pulley size. You can use the pulley from the tractor's original generator. The original pulley will be the same belt size as the tractor's pulleys. Most tractors are started at 1/2 or more throttle, sufficient rpms to excite the alternator.

The 62 amp alternator. I have them on my tractors. Upon start up the amp gauge reads 30 amps or so, shortly drops back to charge up the battery, then back to the 1 amp range. I use these tractors to jump start other machinery.

I use the Chrysler ballast resistor with the original 6 volt coil instead of purchasing a 12 volt coil with internal resistor.
I have an excuse. CRS.

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Dh2jr
Posts: 38
Joined: Fri May 08, 2020 5:04 pm
Zip Code: 49058
Tractors Owned: 1953 farmall super A
Location: Hastings MI

Re: 12 Volt Conversion, Wrap-Up

Postby Dh2jr » Sun Jan 03, 2021 6:22 am

I also want to thank you for all your time and effort you put into this. It is going to be really useful. Again Thank You
53 Super A

JohnnyR
Posts: 22
Joined: Sat Aug 24, 2019 4:33 pm
Zip Code: 31088
Tractors Owned: 1952 Super A

Re: 12 Volt Conversion, Wrap-Up

Postby JohnnyR » Sun Jan 03, 2021 7:20 pm

I'm happy there was content here that others find useful. As Eugene points out, there's more than one right way to get it done.

This was just the way that works for me.

Cheers.


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