65 fl generator

[Rick]

Could someone explain how my stock oem Harley-Davidson 12 volt generator works, should the pole shoes be magnetic? I have an aftermarket generator on my bench and the pole shoes are magnetic, the original poles are not. Aftermarket shoes will probably hold a hack saw blade, originals will not. I don't think the stock generator worked very well because the GEN light comes on when I use the high beam light but that could be the regulator.
I took the generator off because the armature was hitting one of the poles every now and then. Generator was rebuilt about 8000 miles ago, bearings seem to be good and the armature runs true. I did find some hard tar like substance stuck to the armature and the poles, witch I think may have been a piece of insulation that came loose from the armature.
I believe it's okay to go back together but I need to know if it will work better with the stronger magnetic poles or maybe it doesn't matter?

Any help will be greatly appreciated.

Thanks,
Rick

[RvP]

The pole shoes are supposed to hold some magnetism and is required for the generator to self excite. The pole shoes get their initial magnetism when the generator is “flashed” (momentarily connecting the armature and battery connections together at the voltage regulator). Once flashed the pole shoes will retain the magnetism which is refreshed when the generator is used provided the generator and voltage regulator are operating properly.

The generator needs the residual magnetism held in the pole shoes to begin excitation. Once the generator is initially excited the current builds in armature and the field coils increasing the output which increases the current in the armature and the field coils and so on. Therefore once the generator is initially excited the output is dependent on the field coils significantly more than the residual magnetism in the pole shoes.

Roughly speaking the residual magnetism in the pole shoes will get the generator up to about 2V. Beyond that requires the field coils to boost the magnetic field. If the generator was above 2 volts then you are past the point where the residual magnetism in the pole shoes would have any effect, i.e. the residual magnetism had already done it’s job to excite the generator.

The pole shoes are not perfect magnets and will eventually lose their magnetism over time if the generator is not used or there is a defective component. Like any piece of magnetic material the pole shoes can lose their magnetism over time if the generator is unused, excessive heat or mechanical shock. The latter may have been caused by the armature striking the pole shoes.

In order to do an effective “stare and compare” about the relative magnetism between the pole shoes of the two generators it would require “flashing” both generators to refresh the magnetism of the pole shoes, especially in the weak generator since the magnetism may have been lost due to time or any of the other conditions mentioned.

If the armature were striking the pole shoes I would suspect a problem with the armature wiring, especially where the windings are attached to the commutator. Some of these are welded, some soldered and some pressed in. The mechanical shock could have broken some of them loose and may not be easy to see a fine break since they are stiff wires.

One way to do a cold bench check is put the generator back together and use an ohm-meter connected between the armature post and the case ground of the generator. Slowly spin the armature by hand and look for an open condition on the meter or a wildly varying reading (low ohm scale) as the armature is rotated.

I had a 32E that seemed to be getting weak when the headlight was on. I did not see anything suspicious until I did the above test. I found at one point in the rotation the ohm-meter indicated an open. Closer inspection of the armature where the open point was indicated revealed a broken armature winding at the commutator.