350 Utility 12V Generator Questions

Hi, Folks.

Please excuse the long narrative, but I want to provide enough background information to help you help me.

I bought an International 350 Utility about five months ago. It generally runs great, but the electrical system has seemed a little squirrely right from the start.

With the battery disconnected, the ammeter pegs at full charge. Same thing with the battery reconnected. After starting the tractor, the ammeter looks normal – a reasonable charge rate. (I’ll worry about the ammeter later.)

A couple of weeks ago a generator (12-volt Delco-Remy 1100 305, two brushes) bearing seized. The previous owner had the generator belt on WAY tighter than spec, so it destroyed the fan belt instead of the generator belt.

I replaced the generator bearings; the brushes and commutator looked good.

Just for fun I had a look at the voltage regulator. (The system had been converted from 12V positive ground to negative ground, and I wanted to see if I could tell if the regulator had been replaced with a proper one for that polarity.) The regulator is basically full of rust; the points are very dirty and I can’t tell for sure if one set is welded together. I never did find any indication of polarity. (I’ll worry about that later, too.)

The thing I’ll worry about first is the generator; I want to make sure it’s putting out power. I followed John T.’s troubleshooting Step 8 to motor test the generator in a bench vise. These are the results:

12V applied to ARM post, Field post grounded: Generator runs well.

Same, but Field post disconnected: Generator stops (should speed up instead).

Arm terminal - to - ground resistance per digital ohmmeter: 0 Ohms.

Field terminal - to - ground resistance per digital ohmmeter: 0 Ohms.

Voltage per analog voltmeter at Arm terminal (with reference to generator frame) at 1,725 rpm:

+26V DC with Field terminal grounded
0V DC with Field terminal not grounded

So, I suspect some sort of problem with the field.

And finally, my questions:

1 – Does my “field problem” hunch make sense?

2 – If so, what are the likely points of failure in the field coils?

3 – Should I really care, as long as the generator is producing 26 volts at 1,725 rpm? In other words, won’t a properly functioning voltage regulator knock it down to about 14 volts anyway, or does the regulator actually control the generator’s output and therefore need a properly operating field?

Thanks in advance and, again, sorry about the length.

Mark W. in MI

Mark, I think you need to ohm out the gennys Fields because I think they have a problem, Im tired its late so im just gonan lay some theory/thoughst on you versus re reading n try to answer everything just as asked, sorry.....

Depending on your meter (Im not handy with fanchy schmancy digitals, I like my old Simpson 260 Analog) Id expect very low ohms from ARM to case cuz the armature windings are solid copper..

However from FLD to case should be the series sum of the armature (near zero) PLUS the two series Field windings which Id expect to be maybe 3 to 6 ohms (ie a few ohms at least but NOT zero) UNLESSSSSSSSSSSSSSSSSSS theres a short such as ,,,,,,,,,the Fld post insulation is broke where it passes thru the case (from overtightening),,,,,,,,,or one of the windings is shorted to the iron field poles,,,,,,,,or theres a short where the 2 field windings splice in the middle.

To test the fields (ohm out) more accurate you need to remove the armature or just insulate (or raise) the brushes so they dont contact the commutator then

There should be like 3 to 6 ohms from FLD post to ARM post and NOT open cuz thats the 2 windings (each side) in series.........if its an open (Thats BAD) circuit suspect where the two splice in the middle.

Its should be an open circuit near infinity ohms from FLD or ARM to case (with armature out of circuit) If it shows a short from FLD or ARM to case, the fields are shorted, either one of the windings to iron pooles or where they splice in the middle OR OFTEN the FLD post pass thru the case is shorted out

Id expect the open unloaded genny output (but depends on RPM) to be maybe 20 to 30 volts BUT ITS WHAT VOLTAGE WHEN COUPLED UP TO A GOOD BATTERY THAT COUNTS in which case a batt setting should read 12.6 volts but once coupled to a good charging system rise to 13 to 14 n over volts. Im saying that open un0loaded voltage on the Gennys ARM post to ground dont mean all that much

ITs NOT the VR that cuts the gennys voltage down,,,,,,,its the fact its coupled up to the battery via the VR's cutout relay that loads down teh gennys voltage.

A VR functions by regulating the gennys fields current sooooooooooooooo if the fields are bad its not gonna regulate

I will check with ya tomorrow when Im not so tired, theres more to say but Im going to the bed lol

John T

Thanks, John. I"ll print out your response and use it as a guide to do some more testing – hopefully today, maybe Monday/Tuesday.

It"s interesting the way the regulator actually changes the supply voltage coming from the generator. I tend to think of regulators as things that take a variable voltage (Vss) as an input and provide a fixed voltage as output, without affecting Vss – like a 7805 IC, for example. It never even occurred to me to regulate voltage by actually directing a change in Vss.

I tested the old regulator with 24VDC, and was unable to get either relay to actuate. I wasn"t too surprised, as there"s an awful lot of rust in there. I ran across an excerpt from “Wired for Success" by Randy Rundle, where he says “positive ground regulators will have copper-colored current and voltage regulator coils, while the negative ground regulators will have cadmium or straw-colored coils.” If he"s right, then I definitely have a positive ground regulator in a negative ground system. :-(

Anyway, thanks again for the advice. I"ll take another look and hopefully gather some more info.

Mark W. in MI

Hi, John.

Last night and tonight I revisited the generator. With the armature in, it showed a short from the field post to the case. With the armature removed, it showed an open from the field post to the case (?!) Obviously, the armature had something to do with what was going on.

I noticed that the screw holding the terminal for the brush wire to the armature post was a little loose. Lo and behold, the same loose screw had allowed the wire from the armature post to the field coil to move around enough to contact the commutator, which had worn j...u...s...t enough insulation off the wire to create a field-to-commutator short.

So I snipped off the field wire's terminal, replaced the old insulation with some 1mm i.d. heat shrink tubing, soldered on a new terminal, and carefully rerouted the wire about 1/8” from the case and far from the commutator.

Now the field reads 5.5 Ohms. The generator motors fine, and speeds up when the field isn't grounded – just like it should!

Next (after payday) will be a new U.S.-made regulator of the correct polarity, a complete check of all the wiring, and likely a new ammeter.

I just want to say thanks a ton for your help and explanations. It's also good to know this issue will hang out in the archives just in case the same problem bites someone else in the future.

Mark W. in MI