12V Alternator Issue

[ChrisFromCLE]

So, here is where we stand as of today - the generator shop replaced the Transpo F7078 stating the first one was defective. He also changed the pulley on the alternator (Ford G1) to a smaller size. I put it up to the Cub and the smaller pulley with the old belt did not fit up. In order to to tension the belt the alternator would need to be pulled out father than the bracket and outside the hood tin. So I went back and had the original pulley put back on. Installed the alternator and it worked - but only about 1 in 10 times.

Turns out the Transpo needs the alternator to turn more than 2000 rpm in order to self excite. Max RPM on Farmall Cub is approximately 1800. With the larger pulley on the alternator the turns ratio was close to 1:1 making the RPM just a little too low for reliable operation. So I changed the pulley back to the smaller size, installed a smaller generator belt (a true pain in the neck busting loose parts that have been moved maybe once since 1950).

Initial result has been good - tested twice and worked 2 for 2. Will check again more thoroughly at my next chance on Friday.

The reason I have worked so hard to make this set up work is that my Cub does not have a standard ignition switch. It is battery start with magneto ignition. If I were to use a standard set up utilizing an indicator light to excite the alternator I would have to install a second switch just for the indicator light circuit. So two switches to turn on, two switches to turn off. I’d can do it if I have to but would rather not if I can make this set up work.

I appreciate the thoughtful replies and suggestions. Will let you know what I find out Friday.

Thanks,
Chris from CLE

 

[Jim.ME]

You could use an oil pressure switch to excite the alternator. It turns itself on and off based on seeing oil pressure.

Was the smaller pulley was the right width for the belt on the tractor? If you ran out of adjustment to tension the belt, install a shorter belt of the correct width. You say you installed a smaller belt, does that mean width, length, or both?

 

[ChrisFromCLE]

Actually, the larger, original pulley was the wrong width (3/8 instead of the 1/2” belt width). So it was larger and the belt rode high slowing the alternator even more. I changed the belt to a shorter length and maintained the correct 1/2” width matching the smaller and the drive pulleys.

Oil switch is a great idea. Would need to figure where to plumb it on this tractor but I like it. I will remember this if I have to go to plan B.

Chris from CLE

 

[Farmalldude45]

Actually, the larger, original pulley was the wrong width (3/8 instead of the 1/2” belt width). So it was larger and the belt rode high slowing the alternator even more. I changed the belt to a shorter length and maintained the correct 1/2” width matching the smaller and the drive pulleys.

Oil switch is a great idea. Would need to figure where to plumb it on this tractor but I like it. I will remember this if I have to go to plan B.

Chris from CLE

Finally got my head out of you-know-where. I understand that you have the field excite wire wired hot(no switch in the circuit). If so, then the field coil will draw current anytime the alternator output voltage is less than battery voltage. I believe this will result in a dead battery anytime the tractor goes unused for a long period of time. The oil pressure switch is probably your easiest solution. You can install it in a tee behind the pil pressure gauge. Many oil pressure switches are single terminal, meaning they switch to ground. You can find 2 terminal pressure switches if you search. Good luck.

 

[ChrisFromCLE]

Well, it is all back together and confirmed to be working properly. The only quirky thing is that I need to rev the engine up to about mid-throttle in order for the alternator to self excite and start charging. I can live with that so this project is done.

Here are my takeaways for using a Ford G1 alternator with a Transpo F7078 regulator/converter:

• This unit must spin up to over 2000 RPM in order to self excite
• Use a small pulley on the alternator to help increase RPM
• Changing pulley may have cascade effects to belt and/or brackets.
• There are better/more reliable equipment set ups than this one. May be better and easier to change rather than fix this one.
• Take the time to make a temporary gas tank - will save hours of on/off of the hood.

Thanks to all for helping me work through this.

Chris from CLE