MTFCA Forum

What is the fix for a generator that needs to be polarized every time the car is run? Output is adjusted correctly everything is fine once it get polarized. Thanks!

DaveD wrote: ↑

Wed Nov 01, 2023 2:41 pm

What is the fix for a generator that needs to be polarized every time the car is run? Output is adjusted correctly everything is fine once it get polarized. Thanks!

It always helps others to start from the beginning.
-Did you do some work on the generator, was it purchased used, or did you have it sitting around for a long time.
-Don't Flash it with a voltage regulator
-No assumptions - Model T 6volt generator negative ground?

An alternator!
Sorry...couldn't resist the temptation to stir the pot!

In my experience, it usually means that the armature has a short that will not allow the build up cycle to start on its own.
It needs some battery voltage to jump start the process, which is what you’re doing by flashing the generator. It’s a delicate cycle when the generator is building up and any sort of ground ie short, will not allow the cycle to start.
I hope this helps,
Brent

I would agree with Brent. The residual magnetism is fairly weak to start with, and it's likely that the short or insulation failure is enough to prevent the process of current build up to get started. Yet, no so bad that it prevents the generator operating once that process has been started by external means.
I know of one guy driving around with such a generator, and rather than repair it, he has a light bulb connected between the positive of the coil (distributor type) and the generator terminal. When the ignition is turned on, the generator gets magnetising current through the light bulb, and as it comes up to speed, the bulb goes out.

Brent is correct.
If you work on Model T Ford third brush regulation type generators you should get boned up on the "Building Up' process. How it works and how faluts can prevent it from happening. Failure to Build Up is a very common problem.
Here is an ariclle wrote to explain in detail how building up actually works and you can easily see how a short in any of trhe armature and field control circuits can lead to a generator that will not "Build Up".
Ron Patterson

Why the Model T Ford generator destroys itself when the battery is disconnected.
I described the Model T generator “building up” process in the article entitled “Model T Ford Battery Charging System” in the technical section of the” Model T Ford Fix” website.
When the (Reverse Current Relay type) cutout fails to operate or there is otherwise no battery connected to the battery the armature and third brush” building up” process continues uncontrollably. The armature voltage increases to 30+ volts and there is no load on the armature output to pull off the current being produced. A great amount of heat is produced in the armature and field windings and it becomes a race to see which fails first stopping the building up process. The field windings can simply burn out or the solder in the commutator segments where the winding connects melts and is found thrown around the inside of the generator case. In either case the feedback loop fails and the generator ceases to function.
This is one of the biggest downside risks of the third brush regulation generator design.
Good luck guys
Ron Patterson

Ford and other automobile manufacturers used the "Third Brush Regulation" type generator in their charging and lighting systems because it was the cheapest type available.
No surprise here?

Thanks to all for the great advice!

It's nice to see you here Ron! I hadn't seen that PDF you posted before. A nice, clear description of operation!

DaveD wrote: ↑

Wed Nov 01, 2023 2:41 pm

Output is adjusted correctly

By what process? Have you also taken the generator out of the car and adjusted the brush plate properly? With the third brush lifted, applying 6v to the generator (+ to the generator terminal) should cause it to rotate just slightly clockwise as you're looking at the gear head on facing you. If it doesn't, loosen the 4 screws and rotate the brush plate until it's correct. It's possible to do it in the car, but since you're having problems, I'd take it out and do it right and make sure it's right! Since it is working "somewhat", this is worth a try.

If that doesn't solve it, Brent very well may be correct. Old armature wires have a very nasty habit of shorting out. The lacquer coating on the wire only lasts so long. I just got 10 armatures back from being newly rewound - all were hopelessly shorted out. I have 35 more that need the same thing done but my god is it expensive!! What used to cost $50 is now over $200.

Jeff

Actually adjusting the null on the bench dont work well all the time.
Ron P. has a method in car setting to a minimum output instead of a maximum.
This method has worked great for me. Partly since my vintage test unit cant take the load @ the higher amp range. The generator slows the motor down, making for setting the actual amp draw more of a guessing game.

speedytinc wrote: ↑

Thu Nov 02, 2023 8:22 am

Actually adjusting the null on the bench dont work well all the time.

Respectfully, I disagree. Of the literally 100's of generators I've rebuilt over the years, not even once has this method failed me. Get this right, and the generator engages produces charge. Different armatures put out different charge rates, but getting the generator brush plate set correctly is key.

If you can't get this set correctly and assuming all other components are ok (brushes and field coils), 99% of the time the armature is bad or has a short or open somewhere. Shorts can be verified on a growler, but most folks don't have access to one.

I dont recall how many generators I have restored exactly. I do 12-15 @ a time. Over 100, maybe not 300.
I havent kept track over the last 40 years. Starters & generators are not all I do.
I do have all the equipment & make my own insulators, as whats available is not good enough.
The last one just wouldnt adjust right with a bench set null. Ron P's method worked.
Thats all I am saying. I am always open minded to a better way. I found that better way & pass it along to help others.

That’s what mine is doing right now too. Came from Lang’s 1 1/2 - 2 years ago and I only just now got the car running and after 2 miles on it I found this problem. Flash it with the car running and it’s good, but after a short drive, or letting the car sit for a while it is not working again.

I need to get a helper here and try Ron’s method of adjusting something on it and see if that works.

I really hope it’s not bad, I’m sure Lang’s will tell me to buy another. If so it goes to the admin guys shop.

Travis

Hello Travis,

I just sent you an email.

We wont leave you with a bad produce if we shipped it to you that way.

Thank You Steve