My amp gauge started jumping from zero to +30 up and down real fast for about two miles the it stopped and sat at zero, I know it is not charging but cannot tell if it is generator or cut out. I removed the cutout and with engine running tried to check any voltage coming directly from generator, I got no reading but was using a digital volt meter should I have been able to get a reading with a digital?
Sounds like you toasted the generator. The cause may be a loose connection in the battery circuit. Make sure the battery connections are clean and tight. Running the engine with the generator post not connected to the battery will burn it up in a matter of minutes.
I had a similar failure when my traditional style cut out burned up (internal failure) but I didn't notice the amp gauge until several miles had gone by and the generator was ruined. Unfortunately for me the armature shorted open and I had to rebuild the generator with a good donor armature. A fun projects voltage regulator crowned it instead of another dumb cut out. Happy generating ever since. On the plus side, I got to learn a bunch about generator rebuilding.
That's sad. I like to buy used generators at swap meets. I usually either get one which works or some parts I can swap with other generators to get one working. It's handy to have at least one spare which is working in case something like the above happens. What happens with a loose connection is that normally the battery will regulate the voltage either 6 volts or 12 volts. The charge rate is set by the third brush. When there is a loose or corroded connection between the generator it has nothing to keep the voltage level and so it charges full capicity until it burns out. Sometimes it can be fixed. Usually what happens is that the solder at the commutator gets hot and melts and the centrifugal force throws it out. Sometimes re-soldering will fix it. Otherwise send it to someone familiar with Model T generators. The Ford generators worked on the same principal for Model T, Model A, and early V8's. I'm not sure what date they changed the generator, but I know the 35 V8 had the same type.
The jumping around and then showing zero is characteristic of a brush contact failure. It can be as simple as a stuck brush or a brush that is worn out and no longer making contact. In any case, the cure is to take the generator apart and check out the brushes. See that the brushes move up and down easily in the holders. Check to see if they are long enough to make contact. See if the wires are not holding the brushes from moving freely. If the armature is black, clean it up with some solvent (WD 40 works) and polish it with some fine emery cloth or wet and dry sand paper. This is a simple fix and inexpensive. New brushes are a lot less expensive than a rebuilt generator and are usually the things that go wrong.
BTY, you should be able to read a voltage at the generator output with a digital volt meter if the generator is working. With the engine not running, try using the ohm setting to see if there is conductivity to ground. If you see an open circuit, then it confirms bad brush contact. Or it could be a broken wire. Either case is easy to fix. If there is close to zero resistance, then check for a short at the terminal, another easy fix. Only if you find melted copper should you panic.
Neil, read above I had one answer that running the engine with the cut off removed will ruin the generator which I did when I was trying to get a reading directly from the generator
Don't have to remove the cutout. While the engine is running, if there is voltage at the generator (about 7 volts at fast idle) but only battery voltage on the other side (about 6.3 volts), then the cutout is bad. If battery voltage or no voltage at the generator then the generator is bad and look for bad brush contact or broken wire first.
Running without the cutout will cause the generator voltage to be high, which may cause a fault to ground if the insulation breaks down, but there will be no current, so it shouldn't burn up anything. The insulation will only fail if bad to begin with. In sort, you shouldn't hurt the generator by running the car with the cutout removed. I must have run a Model A without the cutout at one time in my youth, and I don't remember anything bad happening. The T and A generators are very similar.
On a modern car, you should not run the car with the battery disconnected. I am not sure if the alternator would work, and if it did the electronics may get fried.
With the cutout removed (or failed open) the only current generated is being used to excite the field windings. This current is supplied by the third brush. Depending on where the third brush is set, I guess there could be a run away situation where the voltage builds up, causing more field current, causing more voltage, causing more current. If your third brush failed before you ran the generator without the cutout, then there is no possibility of any current anywhere.
It is a simple matter of taking the generator apart and checking out the different parts. First thing to do is check to see if the brushes are making contact. Look for a black armature (commutator). Check the field windings by measuring the resistance from the third brush to ground, with it not touching the commutator. Should be a few ohms. Check the armature by measuring the resistance from commutator segment to the next segment. Should be very low, not open. Chances are you just have some bad brushes.
Running without a cutout will cause failure, because of the way the generator is wound. It will still produce a current within the armature, but with nowhere to go but internally, it will get very hot very fast. This is true unless the brushes are not making contact. If they are not making contact, you might be lucky and be able to save the generator with a clean up and new brushes.
By the way, alternators have brushes too. They eventually wear out and fail. The car owner takes the car to the mechanic and gets a rebuilt alternator and a huge repair bill. New alternator brushes are about $5 and easy to install.
I should have explained to check all the commutator segments. Look for solder that has melted and flung out from the commutator. If this has happened, you can resolder the wires back, but this is a little more technical.
With all due respect you are under some wrong impressions of how adjustable 3rd brush generators work and your advice while well meaning is dangerous to the health of most any 3rd brush generator. The 3rd brush generators (used by Ford on their cars from 1919-1939) can and WILL be damaged if you spin them up with no load on them. This happens for sure when they are spun up with nothing connected. The reason they burn up is that the internal field winding derives its current by sampling the output via the 3rd brush which picks up current from the armature. If there is no load on the generator and it is working correctly then the output voltage will rise. This rise of voltage at the output will cause a rise of voltage at the 3rd brush connection which will increase the voltage across the field winding. This higher field winding voltage will cause higher field winding current. A rise in field winding current will result in an even higher armature output which then results in higher field current and this process of "building" will continue eventually resulting in the generator burning itself out by usually burning the field winding open. It is known in electrical design as a "thermal runaway" condition. It doesn't happen if the generator is already destroyed or damaged of course. This "thermal runaway" has nothing whatever to do with the condition of the insulation in the generator. Model T's arrived from the factory without a battery installed but they had a wire connecting the generator post directly to one of the cutout mounting screws to thus "short out" the generator to ground. That wire had a red tag attached to it that warned not to remove the wire until a battery was installed. I guess I have to also tell you that most if not all digital volt meters will give erroneous readings while the engine is running. This has nothing to do with the quality of the meter. I have laboratory grade Fluke digital meters as well as Harbor Freight ones that will do the same. The problem is that the unshielded ignition system used by the Model T radiates noise in all directions and that will get into the digital sampling circuits of most digital meters and thus give wildly erroneous readings. At worst they are totally off scale and at best appear to be good readings but to accurately diagnose problems one must have total faith in any reading and that precludes using a digital meter when the motor is running. Been there many times.
Thanks for the correction. Hopefully John's generator was open before he ran it without the cutout connected.
I pulled the generator apart today,brushes seem to be making contact with armature, I checked ohm between each segment of armature they read .3 or .4 each, I also checked ohm between third brush and ground and it was 23.5. I checked for a short between communicator segments and armature ribs no short, maybe new brushes?
Give me a call 11AM-3PM est.
Since you have the generator disassembled I can advise you on initial checks of the internal components, suggestions for corrections, sources for parts and final assemble and checkout.
Ron the Coilman