Generator

Negative to the A post, positive to the generator frame. What you do with the F post depends on the make and model of the generator. The generator will motor with the field open and run fastest. With the field connected it will run slower. You want the field connected to polarize the generator. Normally on the tractor, the regulator or light switch does that job. A test lamp or volt meter can show what the field connection is. Typical for an AC the field internal connection is to the A post so the F post is grounded for maximum field. When the field is connected that way and the battery is connected to A and the frame, there will be battery voltage between F and the frame. if the generator has the other connection there will be no voltage between F and the frame. The test light should be rather sensitive for such a test.

Or one can experimentally connect F. If its the typical AC generator connection, grounding the F post to the frame will cause the generator motoring to significantly run slower. If that doesn't happen connecting the F post to the A post should cause that speed slowing.

Gerald J.

So for the Delco, as Gerald says, + on the frame and - on the A (armature).

Well it motors. Any way to identify the model as it is missing the tag. I can't find any numbers on the outside other than 152 stamped.

Battery has 12.4 v non running. Running it drops to 12.2 v.
F to frame volts is 1.25 v

ahhhh, yes I had it connected. Will do that later.

well I noticed the internal wire to F has a scorch mark where it looked like it arched to the retained bolt. The insulated covering was torn at a spot there.

The motoring test can be extended to give more information without test equipment.

The first test is without the field connected, the speed can be fairly fast but the torque low. The speed can't be predicted because it depends on the residual magnetism in the field poles and the frame. Same thing for torque which also depends on the residual magnetism. The more the magnetic field strength the slower the armature will spin but the more torque it will have. Torque can be tested relatively by working the edge of a board into the pulley groove. A test for a complete armature would look for variations in torque each revolution. A good armature will have little detectable variation in torque. An armature with an open winding or commutator bar connection will have a significant drop in torque when the brush passes that winding or commutator bar. In very fine detail there will be a little ripple in current AND torque for each armature winding/commutator bar, but the variation is small and takes good test equipment to detect.

The next test in motoring is to connect the field, to ground for many AC, but to the A pole for other brands. When the field is excited with the full rated voltage the armature speed will be considerably slower than with the field open and the motor torque with the board dragging in the pulley groove will be considerably higher.

While the motoring test is independent of polarity, it should be performed with the same polarity as the tractor battery so the residual field is the right polarity and then it won't have to be flashed.

The next step is generation which requires some power source to spin the generator in its normal direction. Spin it up with the field open and it should generate a few volts. Connect the field and if its turning fast enough it should generate more than the battery voltage. With self field excitation the voltage will be a strong function of the shaft speed squared. So doubling the shaft speed should quaruple the voltage until the field poles get saturated. Once the field poles are saturated (or the field is supplied by a fixed voltage or current source independent of the armature) the armature voltage will be a direct function of the shaft speed, a phenomena that is used to make an electrical tachometer sender.

If it passes the generation test its good. That test needs a working voltmeter.

If the field connection open gives a terminal voltage not zero or the armature voltage during the motoring test, there definitely is a field winding problem. 1.25 volts isn't a option for a good generator set of windings in the motoring test. It might be viable for a generator in generator mode and minimal residual field. The field terminal voltage when open on the typical AC connections should be the same as the armature terminal voltage. If not there's problems inside that probably can't be fixed without replacing wiring and field coils.

Gerald J.