I had the generator rebuilt 3 years ago and have just got the car running. The output is very low. It seems to put out about 8 to 9 amps with the engine around 1000 rpm. The ammeter seems accurate (it was also rebuilt). with the engine not running and the ignition on with just the coil drawing current the ammeter reads -6 and if I just turn the parking lights on with the ignition off the draw is -2 amps and if I turn on the headlights the draw is -11amps, so I believe the ammeter is reading correctly. When the engine is running at about 1000 rpm with just the coil drawing current the ammeter reads about 2 amps. If I turn the parking lights on the ammeter reads 0 amps. If I turn the headlights on the ammeter reads -8 amps. So if the coil draws 6 and the headlights draw 11 for a total of 17 and the ammeter reads -8 with the engine running then the generator is putting out about 9 amps. I have tried adjusting the third brush, however, is doesn't make any improvement. What could I be missing? Supposedly the generator was load tested and calibrated. He did replace at least one field coil. So far he has not returned my first call. This is a model 943J Thanks
8-9 amps should be more than plenty. In most cases it is too much output and will boil the battery. If more than 12 amps the generator will overheat and throw the solder of the armature. Without a regulator (yes I have a '31 generator with Peterson solid state regulator that I move to my current tour vehicle) it only takes a few minutes at 8 amps to replace the starting loss in the battery. Then it is either necessary to periodically run with the parking lights or occasionally add water to the battery. I don't know any of us that drive our older Chevys long distances at night requiring a higher generator output.
Found it! thanks Steve. Chipper, my concern is that the ammeter never reads above 1 or 2 amps when running with just the ignition and reads -8 with the lights on. I have tried the third brush from one extreme to the other but the ammeter doesn't change. Should the coil draw 6 amps when the ignition is on and the engine not running? It is a new coil from TFS.
I would take the generator to a rebuilder for testing. I can only guess at best but it sounds like it is not charging correctly. With the ignition on and not running I think the battery can drain to ground thru the points or the generator or possibly both. I don't think the ignition system draws more than 2-3 amps but my electrical knowledge is not the greatest. I am sure Chipper or others can provide accurate info.
I would take the generator to a rebuilder for testing. I can only guess at best but it sounds like it is not charging correctly. With the ignition on and not running I think the battery can drain to ground thru the points or the generator or possibly both. I don't think the ignition system draws more than 2-3 amps but my electrical knowledge is not the greatest. I am sure Chipper or others can provide accurate info.
I disconnected the generator and ran the engine. The ignition seems to draw -1 to -2 amps like chipper said. I reconnected the generator and ran the engine and I can't get the ammeter to go over 1 or maybe 2 amps when I speed the engine. I am wondering if there is any testing I can do while the generator is on the car with my VOM meter. I haven't found anyone close by to bench test it yet.
Does your meter have an AMP range? Can you tell how many AMPs it is rated for? There are ways to get creative with your current meter but requires some messing around with some wires as a shunt so requires a fair amount of effort and time (and a high margin for error/frustration).
The neatest, cleanest thing you could do is buy a clamp style Ammeter with the inductive clamp that simply forms a loop around the wire like the pickup on many timing lights. These are handy even for troubleshooting things around the house so I would highly recommend your time/money is well spent going to the store to buy one.
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette
Does your meter have an AMP range? Can you tell how many AMPs it is rated for? There are ways to get creative with your current meter but requires some messing around with some wires as a shunt so requires a fair amount of effort and time (and a high margin for error/frustration).
The neatest, cleanest thing you could do is buy a clamp style Ammeter with the inductive clamp that simply forms a loop around the wire like the pickup on many timing lights. These are handy even for troubleshooting things around the house so I would highly recommend your time/money is well spent going to the store to buy one.
On my first post I said that the coil was drawing -6 amps when key is on and engine not running. This seems to be the case, however, when the engine is running with just the coil hooked up and no generator the draw is -1 to -2. I guess this is correct.
That 6 amp draw with the key on and the engine not running seems a little high.
Here are a couple of ideas.
With the key on and the ammeter showing -6 amps, slowly turn the engine by hand while someone watches the ammeter. That load should drop when the ignition points open.
Another test would be to disconnect the generator with the key off. Then turn the key on and check the ammeter reading. That will tell you if there is a partial ground or short in either of the generator coils. Or if the cutout points are not opening.
That 6 amp draw with the key on and the engine not running seems a little high.
Here are a couple of ideas.
With the key on and the ammeter showing -6 amps, slowly turn the engine by hand while someone watches the ammeter. That load should drop when the ignition points open.
Another test would be to disconnect the generator with the key off. Then turn the key on and check the ammeter reading. That will tell you if there is a partial ground or short in either of the generator coils. Or if the cutout points are not opening.
When the points are open the amps are 0. Disconnecting the generator makes no difference.
I would NOT turn on the ignition switch and then slowly rotate the engine as it might just start when unexpected. Instead have an assistant open and close the points on the distributor manually. It will be essentially the same load but with no chance of the engine starting. I guess you could also pull off the rotor or disconnect the spark plug wires or coil center wire.
I would NOT turn on the ignition switch and then slowly rotate the engine as it might just start when unexpected. Instead have an assistant open and close the points on the distributor manually. It will be essentially the same load but with no chance of the engine starting. I guess you could also pull off the rotor or disconnect the spark plug wires or coil center wire.
I opened the distributor cap and turned the engine by hand until the points opened then turned on the ignition and saw that the ammeter did not move from 0.
It appears everything is as it should be except the generator. Could be as simple as the commutator segments need polishing. Did you try repolarizing the generator? I did not go back and re-read the whole thread but remember you posting that one of the fields was replaced.
It appears everything is as it should be except the generator. Could be as simple as the commutator segments need polishing. Did you try repolarizing the generator? I did not go back and re-read the whole thread but remember you posting that one of the fields was replaced.
It is rebuilt, every thing looks like new polished and shiny. I wondered if I should repolarize it, however since it does put out a few amps I assumed it was magnetized. Do you think I should try to re-magnetize it? It said on the receipt from the re-builder that he "replaced one field" I am thinking that both coils may have been replaced they are hooked together and what I can see they both look the same.
Yes I would try re-polarizing. If that does not work then it may be time to bring it back to the rebuilder. Seeing that you said moving the third brush made no change it's possible the brush is stuck or the spring weak.
I found some old notes in my wish book of thing that field winding are about 1.44 ohms and armature 0.29 ohm . This on 943 in old Ford manual .
I seem to be getting 1.4 ohms thru the armature (measured between wire going to relay and ground) I am getting .3 ohms between the third brush wire (I isolated the brush from commutator with paper) and ground. That should be going thru the fields. This seems to be the opposite of what you said. Maybe I am not doing it correctly.
