MTFCA Forum

A question about the null point:

Last month I rebuilt several starters for my son and me. This month is generators. One of the generators I shelved had bad third brush insulation which ultimately grounded both ends of the field windings. I took a photo of the brush plate as a reference. After replacing the bearings and installing the NOS Fun Project insulators I purchased years ago, I reset the brush plate to its original position and reassembled the generator using my photo. Powering it up on two brushes showed me I had the null point set pretty close within a few thousandths.

This got me to thinking. I’m wondering if Ford knew the spot where the brushes should be set so that bench adjustment would not be required? As evidence I have worked on the later Powerhouse generators as well as the cylindrical design which replaced them. In both cases, the large brushes are fixed and unadjustable so the null point is effectively preset. So I’m wondering what changed so that Ford could delete the brush plate adjustment in 1928.

Tom
The radial location of the three brushes on the brushplate was changed with respect to the armature commutator on the Model A generator.
Ron Patterson

Thanks Ron.

I waited until it was a good day to get to my workshop and look at my other generators. What I found is one large brush is always near a specific screw hole. I also know there are three wrong ways to install the brush plate.

I am guessing that Ford dealing with sub-assemblers with questionable language skills, must of had a fixture that referenced the brush plate to the terminal slot.

What I was wondering was... Was that fixture accurate enough that little or no null point adjustment at final assembly was required. And then, did someone come up with an idea to fix that location permanently when the next design came up?

I wonder if anything is mentioned in "Ford Methods in the Ford Shops" about generator production. Can we imagine there was a person on the generator assembly line known as the "Null Setter"? Or, more to your point, was there a quick way index the brush plate without needing the finesse of skilled hands?

Jerry VanOoteghem wrote: ↑

Fri Feb 07, 2025 10:14 am

I wonder if anything is mentioned in "Ford Methods in the Ford Shops" about generator production.

“Ford Methods and the Ford Shops” was written in 1914 well before generators were available on Fords…

Adam wrote: ↑

Fri Feb 07, 2025 10:22 am

Jerry VanOoteghem wrote: ↑

Fri Feb 07, 2025 10:14 am

I wonder if anything is mentioned in "Ford Methods in the Ford Shops" about generator production.

“Ford Methods and the Ford Shops” was written in 1914 well before generators were available on Fords…

So, the answer is "no", I guess...

Right you are! When an answer seems too easy, it's usually because it's the wrong one.

Thanks!!

I can assure you there was a "null setter" on the Model T Generator production/test line. This setting was made after assembly and prior to operating and setting the current draw of the completed generator that would ultimately be installed on a production Model T. No doubt they knew what I learned.
Ford service literature broadly explains how to do this, but it is a trap for logical people. By that I mean the explanation can lead to non-working results.
I used to rebuild Model T generators, completed over 500 of them and in many cases I too had trouble with "null point setting” and soon looked for a easier solution. I found that using 12 volts for null point settings (only) made it somewhat easier to get the results the explanation describes but not always.
The problem is the correct null point "window" on a Model T generator is extremely narrow and getting it correct is tricky. I will probably regret including this next passage. This problem is due to the radial location of the brushes on the brush plate as opposed to a Model A generator. I have attached a very (read; almost incomprehensively complex explanation unless you have extensive knowledge of electromechanical generator design) of the third brush regulation which gives "some"?? insight to this issue. If your eyes don't cross after reading that do not be surprised.
I quickly learned to completely forget the goofy Ford null point setting procedure and do it another way when initially dynamically testing a rebuilt generator (which is probably happened in the Ford factory) and soon realized it was also extremely helpful when helping owners troubleshoot a non-operating or overcharging generator on a drivable Model T. In many of these cases the problems were due to incorrect null point setting.
That procedure is attached below.
Attached is a copy of that procedure.
I hope this helps and.... now you know why I gave my easy answer to the original poster of this thread. Sorry
Ron Patterson

The article above can also be useful when testing the generator on a dynamic as shown below.

Sorry wrong photo.

Now you all have a electrical schemetic of the Allen Electrric generator tester.
Go for it an make one.
Here is a photo of one I built copying the Allen Electric design.....................
If anyone has questions about it I have many other photos of the mechanical details.
Ron Patterson

Ron,

Your attachment for setting the null point on the car was excellent. Heck I could even understand it. Opening the next attachment about the 3rd brush made me glad there are people who understand it so I don't have to. Thanks You for being one of those who does.

Walt

Ron, Thanks for the detailed explanations. I now realize the A-generator is a much simpler task.

I suspect now that some of my armatures may have problems. So after I tackle that issue, I will probably build a copy of your Allen tester. I also see I need to make sure I have a good old mechanical cutout instead of a voltage regulator. While it was fun firing up my car inside the shop, I can see where electricity has an advantage.

Thanks to all who replied to my question.

Tom
If you are planning to build a generator test stand, I suggest you use a trouble free diode type "cutout"
Relay type generator cutouts are nothing but trouble you don't need.
Ron Patterson