Starter/generator flowchart question

[toehead]

I'm troubleshooting the starter/generator on my new 154 and have an issue.
It DOES start the tractor well.

My issue: The battery isn't charging when running (hovers around 12.1 v).

I polarized the generator by shorting the bat and gen terminals together for a second or two when the engine is not running.

Following the flowchart, I get no charging up through step 4 (ammeter does work however)

On step 4, when I short Bat and Gen with the field grounded, the ammeter swings strongly to discharge. I've confirmed that this is real: battery voltage decreases and lights dim when I do this.

Anybody run into this before?

[Landreo]

There are not many reasons to polarize a generator, there is no reason to polarize a starter-generator, does not hurt anything but no reason to do it. Either way, the engine should not be running when polarizing a generator. For step 4, that is to eliminate the effects of the cutout portion of the regulator but the field has to be grounded and the engine has to be running at 1/2 speed or so. Grounding the field requires a clean connection on the field terminal,even a little rust, 2 -3 ohms worth, will invalidate the test, and a clean connection to the ground. I use the SG case as the ground and clean off the rust or paint. Make sure your have a good connection between the SG case and the tractor frame but since it starts that part should be good.

If all of the above is true and still no charge then the SG is defective. The starter part of the SG does not need the field terminal so it will start with a bad shunt or charging field but will not charge. The internal wire to the "F" terminal can twist off if the "F" terminal rotates too much when tightening the nut and this will break the wire. Easy fix.

If you have a good ground on the "F" terminal and a good ground to the SG case and tractor frame then I would run the tractor at 1/2 speed or so and check the voltage at the output or "A" terminal of the SG. 13.5 volts or more would be reasonable. If less than 13.5 volts shut off the engine, then remove both the wires to the "A" and "F" terminal and check the resistance of each with an ohm meter to the case. Each should be a few ohms or less depending on the accuracy of the meter. More than a few ohms for either terminal then something is wrong. The "A" terminal should be good since the starter part works.


That generator flow chart is good but it assumes each step is done correctly and it is easy to be fooled by a bad jumper connection when doing the steps. It also assumes that the ammeter works in both directions if it is working in one direction. I have had ammeters stuck such that they would show discharge but were stuck in the other direction. That is why you should measure the output directly at the SG with a voltmeter rather than depending on the ammeter. Easy to do on a 154, harder to do on the fcubs.

The brush end cap of the SG will typically just come off, the mounts for the brushes are on the case itself not the end cap. Once the end cap is off you can look at the brushes, feel the tension from the springs, and look at the connection at the "F" terminal.

My experience is that SGs are reliable and if they start then they will charge. Still possible that the field wire is broken but more likely that the regulator is not working or is not grounded. Double check the jumper connections for clean connections. I expect the SG will generate if you jumper the field to ground with a good connection.

Don't jumper the "A" to battery on a SG, all that is going to do is burn out your jumper wire.

If the voltage at the SG is good with the engine running and the "F" terminal well grounded then double check the regulator ground. If the regulator is bad you can remove the cover and clean the 2 sets of points. Unless the coils in the regulator are burned, cleaning the points will fix the problem. No need to buy a new regulator.

[Landreo]

I'm troubleshooting the starter/generator on my new 154 and have an issue.
It DOES start the tractor well.



On step 4, when I short Bat and Gen with the field grounded, the ammeter swings strongly to discharge. I've confirmed that this is real: battery voltage decreases and lights dim when I do this.

Anybody run into this before?

I did not directly answer your question. When the BAT and GEN terminals are shorted it allowed the cutout relay to be bypassed and it will start to charge if the cutout was the problem. However, if the generator is not producing voltage at least equal to the battery voltage then current will flow from the battery through the tractor wiring through your jumper and into the generator. For a defective generator on a running engine that current flow should not be enough to damage the generator or the wiring to the generator. For a starter generator, connecting the GEN and BAT terminals on the regulator is equivalent to hitting the starter switch. At that point, in a non running engine, a few hundred amps would try to flow through both the regular wiring of the tractor and your jumper and potentially burning the tractor's wiring. That wiring was not made or sized for starting the tractor. When you did this on a running tractor, the current flow will be a lot less but still potentially damaging to the wiring. You likely placed a load of 50 amps or so on the tractor's wiring and through the ammeter which is why it showed a large discharge.

[toehead]

Thanks, that makes sense to me.

I'm certain that I didn't damage anything. I only did it for half a second at a time, just long enough to observe behavior, and there was no heating of the wiring.


I'll keep at it. The generator is missing the rear oil cup (hole is just open) so it probably makes sense to get in there in any case.


Also, edited my previous post. I wasn't trying to polarize with the engine running. Engine was off.

[toehead]

I think I may have a grounding issue. I'm going to run new grounds and will report back.

Also, looking more closely at the rear oil cup on the generator, it looks like it is actually sealed. I wonder if these didn't come with oil cups?

[Landreo]

All the numbered series that I have seen had those sealed starter generators. Looks like a hole with a missing oil cup but it is actually a small sheet metal plug.

[toehead]

I've got the SG apart. It needs new brushes (probably less than 1/4 left) and the field coil is open somewhere internally.
I'll need to source a new field coil and brushes, bearings, etc.

Can I change the rear housing to add an oil cup? The "sealed" version had what looks like grease in the back, but the bronze bushing is very sloppy.

[toehead]

Looks like to properly do this you need a pole shoe spreader.

It seems like most of the parts companies are offering those chinese repop starter/generators. Are those any good? They aren't much more expensive than the parts that I need to get to fix the one I have.

[Landreo]

I have not seen a Chinese made SG but HamiltonBob sells a SG that likely is the same or similar to those you are talking about. It requires a different adjusting bracket so they are apparently not exactly the same.

I have not had to replace the field on a SG but have done so on regular generators. No pole spreader needed. You do need one of the hammer style impact screwdriver since the pole screw is tight.

Did you measure the resistance between both ends of the field with clean connections?

[toehead]

Yes,
I have the S/G disassembled and measured resistance directly on the leads going to the field coil (once I saw the open when testing externally).

I've got one of those hammer impacts (sears) but no luck so far on the pole screw. I'll keep at it.

In the meantime I took a chance on one of those cheap replacement units. It was only 107 with free shipping. I'll try it and report back. It didn't come with a new bracket, but I can fab what I need in the shop.

[toehead]

New unit is installed. I did have to fab a new bracket; The stock one isn't nearly long enough.

The unit turns the tractor over well and charges well.