12 Volt Generator Arcing

Working on a no-charge issue on a D10.  12 Volt Positive Ground.  I had the generator taken to a machine shop to test and was told it was charging correctly and pointed the blame to the Voltage Regulator (VR).  I opened up the VR and found the points were needing a clean and did so.  I made no changes to the VR.  I can go into the details of my testing, if you would like. 

I placed the VR and Generator back on the tractor, polarized it, and started the tractor.  No Charge.  When I grounded the Field connection, no charge.  Thinking the cutout portion of the VR could be bad, I closed the VR cutout circuit, it held itself shut and the generator started charging.  However, one of the brushes was arcing quite a bit.  I shut the tractor off, the cutoff circuit opened as it should.  I started the tractor again, no charge.  I closed the cutout relay in the VR and charging occurred.  I saw the arcing on the brush and performed a short experiment.  I throttled up the tractor and took it back down.  The faster the rotation of the generator, the more arcing the brush had.  The lower, the less.  Made sense to me that it would do it.  I shut the tractor off, the cutoff opened as it should.

My question is this:  What would cause arcing (white light) from the brush of the generator?  I assume that any arcing in an electrical circuit is not good.  Is my generator not as good as the shop thought it was?   Anything I can do to "fix" or remedy the arcing?

Thanks,

Kevin

TramwayGuy wrote: You might try wiring a capacitor (condenser) to the armature post and it can reduce the sparking.

Would you use a standard condenser you would use in a distributor?

I remembered that I had a spare generator recently rebuilt in my other shop, so I grabbed it, installed it, polarized it, and installed it.  I ran the tractor without the Field or Armature posts hooked up as I could not remember if it was setup for 6 or 12 volt and the tag is not on the generator.  I attached my multimeter from the armature post and the other lead to the ground.  I then grounded the Field and saw a 30+ volt charge.  I shut down the tractor, knowing that it should be good for 12 volt and hooked it up to the charging system.  Upon starting the tractor up, the voltage regulator worked as it should and the system starting charging.  I was getting high 14 volts at the battery and the armature terminal both.  Adding a load to the system by turning on the lights, the regulator kept the system charging.  The Ammeter only has markings for 0, 30, and 60, so my guess was that the generator was charging my battery around 10 amps.  When the tractor idle speed was lowered rather low I saw the cutout release and open the circuit. And when I added throttle, the cutout closed the circuit and charging commenced.  Since the tractor has been running without a charge on the battery, I imagine that it will take some time if I was running the tractor to fully bring it up to charge and cause the VR to not have to send 10 amps to the battery. 

Now that I feel like I have proved that the generator is the problem, off to the shop she goes.  The voltage regulator seems to be working.  (Now to find an OEM 30-amp gauge instead of the 60)

Excuse my ignorance, how does one size a regulator to a generator?  I have assumed (We all know what that means) that if I had a factory generator, then the prescribed regulator would be what I need.  I suppose I have not seen a spec sheet when looking at tractor regulators.  Other than the voltages (6 or 12) I assume that the sizing would also be for amperage?

Critical factors:

Voltage rating (6, 12, 24, etc.)

Field Current 

Generator Output Current

Output current of most alternators is irrelevant because alternator current is self-limiting by design so the regulator only controls the voltage level.

Most generators (Dynamos) require some form of current regulation as they will attempt to melt down if the amperage is not controlled. The simple 'Third Brush' type generators used on Model B/C  have the current output limited by adjusting the third brush so they only use a cutout relay to prevent discharging the battery when the generator output is too low.