Generator test

[compyello]

I have my generator off of the auto and would like to test it. Do I need to polarize it? How do I do that? I have seen motoring the generator, How do I do that? I am not sure what my generator came off of but it has two posts on the side and one on the rear. On the side the top terminal says B FIELD. I don't want to test it and end up damaging something. Thank you

[Art Newland]

A picture of the generator is probably a good idea. There are a ba-zillion different kinds.

B=battery, Field=Field, the one on the back is probably a ground.

[Ken/Alabama]

The one on the back is Armature. The one marked field on the side is field and the other is a ground post.

[JSeery]

You really need to post a photo to sort out what you have. What year engine was it on?

[compyello]

Here it is

[compyello]

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The generator is off of my 38

[koates]

You can motor the generator by connecting it to a 6 volt battery. This is not a sure way to test that the generator is going to charge when driven at speed. Connect the field wire on the side of the case ( the one with the black plastic insulator under the terminal nut ) to the rear armature terminal on the end housing with a jumper wire and also connect the battery negative terminal here with a jumper wire. Connect the battery positive terminal to the other terminal on the side of the case which is the ground terminal. The generator should motor at some speed. The only real and correct way to test it is in a generator test bench which your local auto electrical shop would have. Otherwise mount it on a car engine and run it at speed to test actual output. Regards, Kevin.

[Mart]

I have been playing with generators recently and found that while they all charge at speed, the speed at which they start to charge varies. I have one that motors quite nicely, but wont charge at normal road speeds, rendering it useless.

I have one that I was able to improve by making sure the brushes are bedded well to the armature.

Mart.

[rotorwrench]

Any test off the vehicle will just be kind of a core test to see if the unit has basic function. As Kevin states, it has to be put into a generator test stand to evaluate complete function. A thorough check can be done on the separate components when disassembled but a person needs a growler set and a multi meter to do the check of the field coils & armature/commutator. Flashing the field should be done on the car to insure a good procedure. On Fords, just disconnect the field wire at the regulator and touch it to the battery terminal also on the regulator then reconnect. The field pole shoes should be magnetized in no more than a 3 second flash. This is OK for Fords but not so much for GM set ups since most are wired differently so there is no set procedure for all the different types.

When a generator is installed and the regulator is working normally under operational testing, the output voltage should be a tad bit over 7-volts at the battery (7.3-volts on most Fords of the 6-volt era). If it just reads battery voltage then it's either not coming on line at all or the regulator unit isn't working. Regulators in the earlier era of pre-war and immediate post-war with late P/N 8A-10505 or earlier actually had adjustment provisions but the later ones of the 8BA era not as much. They are still adjustable if you know what to tweek but just not as easy as the older units. The on voltage can be set on cut outs that need a specific voltage to come on line, if the pole shoes will generate the amount necessary. If not, there is likely another problem with field or armature. Some applications use different size pulleys to insure that the generator comes on at lower engine rpms. Alternators are a lot more finicky in this respect that generators for the most part. Fords had to generate around 6.3-volts from residual magnetism to close the cut out points & bring the system on line.

[compyello]

Thank you!