WD generator overcharging & tire replacement help

I've got a WD with Delco-Remy 3 brush generator (1101413 2c17)  with cutout relay, 6V positive ground with magneto that gets used once a year for about 8 hours to mow roads.  The good news is, it starts right up and works great.  But I noticed when I first got it about 3 years ago that it was charging at a high voltage (battery before starting is 6.4v, after starting climbs to 7.2, and after running a while is at 8.6--when measured at generator it is 9.1).  The ammeter was dead and the wiring was old, so after consulting here a couple years ago I replaced the wiring, put in a new ammeter, and refurbished the 3 way switch (although there are no lights on this machine, so that switch is simply controlling whether it goes through the resistor or straight to ground).  That hasn't fixed the high voltage problem, but I now can measure 7 amps (and 8.6v) running through the resistor and 16 amps (8.9v) going directly to ground.

Thanks for the note:  the tires are working fine at the moment and the Allis is parked in an open shed at my hunting shack--it's just that this place is WAY out in the sticks (and under 3' of snow in Wisconsin at the moment while I'm enjoying spring in NC).   Other posts seem to suggest that getting old wheels off can be quite a challenge--so I'm looking for advice as to both if these are in such bad shape that they need to be replaced, and tips on how best to manage that (I haven't checked whether they are filled with CaCl yet either--trying to avoid getting squashed like a bug).  

https://www.allischalmers.com/forum/1951-wd-9-1-volts_topic194151.html

Jack up the tractor. Since your removing the wheel for tire replacement I like making sure the eccentrics come loose and are functional first. Great time to check them. I always spray the eccentrics with some Kroil first. If you have some time, let the Kroil soak in for a half hour. Use a long bar on a socket to loosen them. I have a Milwaukee 1/2” impact gun that will spin them loose quickly. Watch the tab as they only spin 3/4 of a turn. Remove the stops on the rails also. Once they are working well tighten them back up. Then you can remove the clamps from the wheels. If time permits it’s a great time to clean up the rims after the tires are removed, bring them home and repair any damage and paint them. Much easier to do with no tires on.

Steve in NJ: So like the other recent post about generator high voltage and high current that you posted on, if it's not a ground issue (something I should again recheck) it's within the 3 brush generator.  The prior poster found that pushing on a brush decreased the voltage and his description also suggested the possibility of internal short.  Is the high voltage and amps suggestive of any specific failure (e.g. 3rd brush setting, contact, or short)?  Are there any diagnostic checks (e.g. of resistance) that I can do short of rebuild/replace or switch to alternator?  I seem to recall there exists a Remi-Delco generator troubleshooting guide (from the 40s or 50s) but can't seem to track it down at the moment and I don't recall that high volt+amps was covered there.  Given that it is generating power, can you narrow the likely failure-- brush contact, 3rd brush position, brush wire short, or brush holder problem?  I'm still hoping for something I can fix myself.  

Any chance the rear tires are matched and Firestones? If so I would guess they may be the originals.They will give service a long time if lightly used such as mowing. JMHO.

Steve in NJ-- I was drafting my note before I saw your additional reply.  So (assuming the analog ammeter is correct) that's just too many amps to be a simple brush adjustment?

Newwood wrote: ... It's unclear to me whether this might also adjust down amps (currently putting out 7 amps when going to ground through the resistor), but I'm hoping based on Steve's comment that he "sets them up around 8 -9 amps"  that moving the 3rd brush may dial both volts and amps down ?  ...

Yes, in a properly functioning system this will reduce both Volts and Amps.

Example:
Assuming a proper charging system but the battery is nearly dead (from sitting all winter, whatever) and you had to hand crank the engine to get it running. The engine starts and you let it run at high idle with the light switch nob in the High Charge position; the ammeter will show a high rate of charge but if you put a voltmeter on the battery it will read toward the low end (possibly less than 6.0 Volts) for a while until the battery gets charged up a bit; the voltage at the battery will gradually climb and the amperage will gradually reduce.

The internal resistance of a discharged battery is very low; a given Voltage will thus push more amps into the battery, as the battery charges up it will 'resist' taking in more amps, sorta like after Thanksgiving dinner and Grandma tries to get you to eat one more piece of pie, there just isn't room for any more. The pressure (Voltage, Grandma) is still high, but you (the battery) is full. The amperage (flow of food) slows down or stops completely, until there is once again room for more.

If there is a flaw inside your generator that is causing the voltage to go way too high, it is like Grandma forcing more pie down your throat; bad things may happen.

Batteries are happiest when they are just comfortably full, not too hungry and not overly stuffed. A piece of pie every day would be about ideal



Edited by Les Kerf - 07 Apr 2023 at 8:43am

New wood,. If you remove those tires from the tractor, be very careful. If they are full of fluid they are going to be very heavy. I owned a farm tire shop for 22 years. I can assure you the easiest way to replace tires on a farm tractor is doing it with the rims on the tractor. It's far easier than you removing the rims and tires and taking them to a tire shop.

Les re charging system: Well, it doesn't seem that my case is associated with degree of battery discharge (battery is at good voltage before starting tractor, is high during operation, and is high but not excessive after use and turning off).  At this point I'm mostly trying to educate myself on how these 3 brush systems work -- mostly I can't resist believing that this presents a solvable diagnostic puzzle if only I can fully understand thing down at the first principles level.  So the 3rd brush controls current flow through the fields to ground, and moving that brush in the direction of rotation increases field current while moving other direction decreases field current (and thus drops both voltage and amps).  I haven't tried adjusting that 3rd brush to decrease that, but Steve in NJ who has a much deeper knowledge base than me doubts that will be sufficient to correct.  If the 3rd brush wire is shorted against the casing I don't think there would be any field current.  The field to ground with and without resistor is working as it should (increasing and decreasing voltage) so shorts in the field circuit seem less likely.  This only has a cutout, so there's no voltage regulator in the mix of possibilities.  I suspect Steve would agree with an old surgeons saying: "don't let a little skin get between you and and a diagnosis" but I'm not a surgeon (and I can't lay hands on the tractor for a while yet) so puzzling through how things should work and how things could fail and give this particular result remains an interesting puzzle to me.  Grandma's cooking might certainly offer a welcome distraction!

Newwood wrote: ...  At this point I'm mostly trying to educate myself on how these 3 brush systems work -- mostly I can't resist believing that this presents a solvable diagnostic puzzle if only I can fully understand thing down at the first principles level...

As an old avionics tech I always want to know the root cause of failure, even if there is nothing I can do about it. Here is a link to the best description I have found on Third-Brush theory of operation.
https://automotiveenginemechanics.tpub.com/TM-9-8000/TM-9-80000307.htm

Newwood wrote: ...  If the 3rd brush wire is shorted against the casing I don't think there would be any field current...

No, quite the opposite in fact. The generator armature is the source of the field current which is ultimately grounded at the light switch. If the third brush wire shorts against the casing then it will effectively bypass the resistance in the light swich, causing the generator to be "full-fielded' and thus at maximum output.

Newwood wrote: ... so puzzling through how things should work and how things could fail and give this particular result remains an interesting puzzle to me...

If I were troubleshooting this system the first thing I would want to check is the field current measured at the light switch and monitor it and voltage as the system warms up.

Here are a couple more relevant links:
http://dueyschutter.freeservers.com/photo5.html
http://vias.org/kimberlyee/ee_31_02.html

Newwood wrote: ... re 3rd brush short: yes, and the other evidence against that is that going through the resistor at the light switch does indeed change the amps from lower to higher which wouldn't have an effect if there was a short.

This, the field current is the crucial measurement needed; an ammeter capable of measuring ~20 amps will be necessary.

Newwood wrote: The bit from the manual about "the generator terminals must be grounded if the 3rd brush generator is disconnected from the battery" takes some interpretation.  I imagine this also relates to a warning about running the tractor without a battery (which you could do using the crank to start) or if you disconnected the battery while it was running.  But it seems like a puzzling recommendation doesn't it?

I'm still not quite ready to deliberately ground the armature of this generator
The word "terminals" is plural; there are only two terminals, and if the field terminal is grounded the generator will attempt to produce maximum current, which would then put this amount of current directly to ground. I do not like this idea.

Newwood wrote: Removing the connection between the field terminal and ground (which is how the tractors were shipped from the factory) would seem to do the trick:  you can't set up a field current if that terminal isn't connected, so the generator can't generate anything without it.  I seem to recall from some other thread someone suggesting just such a disconnect as a temporary solution to overcharging (e.g. if resistor has burned out, you could use a simple toggle to either allow or not allow the field terminal access to ground).  Am I missing something here?  Running the tractor and generator with the field terminal disconnected would seem to put the generator at no risk.

I agree.
There will be some current generated due to the residual magnetism in the field coils, perhaps this small amount of current should be grounded?