starter/generator
 

I think I have a problem with the s/g the 'A' terminal shows a short (1 ohm) to ground. With the tractor running and the volt meter across the battery the meter jumps all over 20 - 100 volts, it should be at about 13 or so. I think the problem is from the 'A' terminal.

YUP, time to get the S/G into the repair shop.

I would be looking for a loose/bad connection, or faulty meter
No way you are going to get that kind of ACTUAL voltage reading.
The battery in the circuit will always act as a accumulator as far as voltage and a Generator unlike an alternator, is limited in it's voltage output.
You also stated "when running" if it starts the S/G most always is good. Now that is not to say it may have bad bearing/bushing or worn brushes etc.

The 'A' terminal measures 1 ohm to ground and the 'F' terminal measures 9.5 ohms to ground, this is with all wires disconnected from it. Does anyone know what the ohm reading should be across the 'A' & 'F' terminals? This is on a 147 that I just got last week to pull my 17cf wood cart. The engine starts and runs fine no smoke and the tractor is in great shape. When I got it he said that the S/G was rebuilt. I said to myself "oh I hope I don't have problems with this".

Between A and F should be 5-10 ohms approximately.

Recently my son and I rebuilt a starter generator that was on an Original. This was not the original s/g but a replacement. We marked the ends with a stratch from the case to the end plate so we would get it back together the same way. This s/g was working at the time but was making a bit of a noise. We had a repair kit so we had at the project. When we opened it several ball bearing fell out. It was very dirty inside. We used air to blow out the dust, replaced the end bearings and the brushes. We inspected the two terminal connections and cleaned where the brushes ride and reassembled it. It was that easy to do. The only problem you can have is having enough hands and fingers to hold the brushes out while reassembling the armature. It works fine and sounds good also.

Thanks Matt, I get 9 between A & F. but I don't think I should get Zero ohms between 'A' and ground. Is this right. I just don't see how the generator would work with 'A' being shorted to ground.:bigthink:

The wire in the armature is large, so it will have little resistance. Before you said 1 ohm of resistance, and now you're saying zero...which is it? 1 ohm is probably about right. If it's turning the tractor over, it's probably fine. I am suspicious of your multimeter for the same reason ol'George is.

Ok,
lets start from the beginning.
The S/G is working because the tractor is starting.
Are we to assume it is not charging? is this assumption correct?
if so, that is usually the voltage reg. or associated wiring, because it IS starting.
IIRR,There are checks for "not charging" listed in our FAQ's.

What I don't get I guess is that terminal 'A' has a reading to ground (the case of the s/r). Should it be this way?

IIRR the internal wiring causes it to SEEM Grounded.
Without going into my old books I don't have a schematic on hand to post/show you.
You have to remember the Armature has HUGE Gauge wire compared to the field wires
Does it charge/operate correctly? if so, let it be and just "believe" Ha.LOL!

If the armature was, in fact, shorted, you'd see smoke, the S/G would get hot, and it wouldn't spin the engine over.

Ohms
 

"Before you said 1 ohm of resistance, and now you're saying zero...which is it? 1 ohm is probably about right. "

Measuring very low resistances with a 2 wire measurement (like a VOM does) is pretty pointless... and generally not repeatable even with a good meter (I use a Fluke 87).

What do you measure at the battery terminals when the motor is running?

Are you sure you're not on the AC range when you're seeing the high voltage reading? There's no way I can see of getting high voltage out of a S/G operating at normal RPM range.

I'm thinking measurement error , not equipment (S/G) error.

John

Ok I checked things over and ordered a new voltage regulator and things are much better. I also found out that DVM that I always use, would spaz out when it got close to the tractor when it was running. Switched to my back up meter from radio shack, and had no problem reading the voltages. Sorry I took so long to reply but I have been busy cutting up and splitting my truck load of (9 cords) wood. Just have a little left to split. Thanks guys for all of your help!!!

Great.
 

Good to hear it came out well.

I've seen the "dancing readings" with a cheap Harbor Freight toolbox DMM too. I should drag my O'scope down to the garage and see what the charge line looks like some day.