I described the Model T generator “building up” process in my other post entitled “How the Model T Ford Generator, Cutout and Battery Charging System Interoperates”.
When the 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 reaches 20+ 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 filed winding can simply burn out or the solder in the commutator segments where the winding connects melts. 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.
Another example of all of us benefiting from knowledge of our fellow Model T people. Where would we be with out the knowledge so often shared by others. Thank you Thank you
Here is a photo of what you usually find in the brush cap of a generator that has slung all the solder out of the commutator segments wire connections.
I am not having a great deal of luck posting picture this morning $@#$&^*
Ron : I know where you was looking for .
So...... You can't disconnect the battery? I've always disconnected the battery on all my old cars and then placed them on a battery tender.
Great description Ron. I used to tinker with ancient Splitdorf generators for old motorcycles. I've seen a few that had the solder splatter from overheating.
You cannot disconnect the battery and drive the car or this will happen..
Thanks Ron. I won't do that. I just disconnect the battery whenever I'm away from my cars. Not good when things go up in smoke.
I've been told by old timers (in relation to a similar charging system in a Cat 35 that I used to plow snow with) that if the battery is out of the vehicle the generator output stud should be grounded before the engine is run, and that the generator cannot burn out with the output grounded because it is a constant current device. Is this true for Model Ts as well? My T is non-electric so I've not had the chance to try this advice myself...
Yes, that is absolutely true with any third brush regulation generator.
Hey Ron, do you recommend the voltage regulator that Langs sells for $69 for the generator? Doug
just saw your other post about the regulator Ron
When you test a generator on the bench it will produce up to 40 volts (for a short time)
Open charging circuit and grounding the generator to avoid burning it out is covered in paragraph 1107 and figure 520 in the Ford Service manual.
Additional info for Robert G.: It's perfectly OK and in fact a good idea to disconnect the battery when you're away. It's just that you must re-connect it before starting the engine, or risk burning up the generator. Of course, unless you hand-crank it on Magneto, you'll have to reconnect the battery in order to start it anyway.
Back in the day, when a Model A, which also has a third brush generator, was just an old car, I would put a voltage regulator on the generator. The regulator would be from a later car and have the cutout, voltage regulator, and current limiter, all under one cover. They were all mechanical components as this was way before electronic anything. The regulator could be mounted on the firewall or hidden somewhere. All that was needed was to run the field wire from the regulator to the lead in the generator that would normally go from the third brush to the field windings and remove the third brush. The wire that would normally go to the cutout on top of the generator would go to the generator terminal on the regulator and the battery terminal would be hooked up to the battery. The cutout could be left for looks.