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tgranthamfd

Best Way to check stator

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tgranthamfd

Title says it all. Mowed with my 80 model black-hood for about 2 to 3 hours yesterday, when I got done and shut it down to refill and blow the grass off, it wouldn't start back up without a jump. No broken / frayed visible wiring and everything was tight connection wise. I pretty sure I read it on here or in my brothers books, but figured it would be quicker to ask the resident experts how to check the stator with a multimeter? Thanks guys.

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tgranthamfd

Can I, when not running, ohm between the plug contacts to see if I have a broken path?? Thanks Terry.

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tgranthamfd

Well, I turned the ringer on, on the multimeter, and touched to the plug where the stator wires go to the rectifier and got a tone. Does that mean I don't have any broken wires or windings in the stator? Or are the connection point in the plug connected inside the plug? :omg: Any ideas?

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Save Old Iron

With the stator still on the tractor

to check AC voltage output

statoracvoltcheck.png

if that fails then make some resistance checks

statorwindingcheck.png

statorwiringshorttocore.png

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Save Old Iron

Terry,

for the purpose of checking stator windings, the "ringer" is useless. The ringer generally is set up to ring at anything under a couple hundred ohms resistance.

A good stator winding will be a near short - but not shorted.

The resistance of the coil of wire in the stator is generally less than 1 ohm resistance.

A shorted stator is near or at 0 ohms.

Use the multimeter on low ohms scale - short the meter leads together - you will probably get a "residual" reading of the resistance of the meter leads and meter contacts for the leads. Lets say its 0.4 ohms.

That means when you connect the meter to the stator wires, 0.4 ohms of the final reading you see will actually be in your meter leads and not the stator. So if you see a 1.0 ohm reading when connected to the stator, your stator is actually (1.0 - 0.4 ohms) or 0.6 ohms - which would be good.

ALL OHMS READINGS SHOULD BE TAKEN WITH THE TRACTOR OFF AND NO BATTERY VOLTAGE PRESENT ON THE STATOR LEADS _ DISCONNECT THEM FROM THE RECTIFIER REGULATOR ASSY.

Let me know if you have any other questions.

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tgranthamfd

Thanks Chuck, was hoping you would see this. It might be a day, or so, before I can get back out to the tractor. Got to go back to work for a day or three, always take my vacation days during spring turkey season here in Oklahoma. I was, kind of, on the right track, your illustrations are the bomb. If I run into any snags I will let you know. Thanks Terry

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Kelly

I really need to get a good test meter and learn to use it, instead of just a test light.

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Save Old Iron

Terry,

for the purpose of checking stator windings, the "ringer" is useless. The ringer generally is set up to ring at anything under a couple hundred ohms resistance.

I should rephrase that statement.

A "ringer" would be useless to check the actual resistive ohm value of the stator wire.

A ringer could tell if the stator wire was open - no ringing because the wire's resistance would be over the trip point for the ringer to see continuity.

A ringer would be able to tell if the stator wire was shorted to the metal core of the stator - it would "ring" if the wire insulation were worn or burned off and the wire was now in contact or grounded to the stator metal core.

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tgranthamfd

Iron,

My meter has only 1 ohm setting on the scale, I can set the range to either M or K. when I set it to K and touched my Leeds together I got a 0.004. Does that sound about right, as far as the example you gave? (That means when you connect the meter to the stator wires, 0.4 ohms of the final reading you see will actually be in your meter leads and not the stator. So if you see a 1.0 ohm reading when connected to the stator, your stator is actually (1.0 - 0.4 ohms) or 0.6 ohms

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Save Old Iron

Interesting Terry.

your meter probably displays values up to 1999. Looks like you have an auto ranging meter. Good meters, but may not able to get down into the tenths of an ohm territory.

The 0.004 reading you see might be 0.004 x 1000 (K scale) or 4 ohms. So we are not seeing the tenths of an ohm display. You may also want to try to twist the meter lead connections around where they connect to the meter. This may also lower the "residual" meter lead reading closer to zero. Then try the 2 measurements again - meter leads shorted and then across the stator leads. Subtract the meter lead reading from the stator leads reading.

If you know the brand and model of the meter - let me know. I'll try to look up the instructions to see if it can display tenths of an ohm.

You can however check other functions.

If you place the meter (on the K scale) across the disconnected stator leads - you should get a low reading and not an over-range or infinite reading - a low reading means the stator winding is probably good an not an open circuit.

If you place one lead on one stator wire and the other lead on the stator metal core - you should get and over-range or infinite reading - that verifies the stator wires are not shorted to the stator core.

With the tractor running - put the meter on VAC and measure across the stator wires connected to the rectifier. You should see 25 to 50 VAC depending on stator design and speed of the engine.

let me know how that works out for you.

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tgranthamfd

I haven't made back out to my tractor, as of yet. My meter is a

Clarke CDM 50 Multimeter

Auto-Range DMM

twisted my contacts around and got a 00.6 ohm reading, .002 K ohms, and a .002 M ohm. Has hardly been used, as you can tell. I always deal with voltages at work, or fuse checking. Thanks Terry

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tgranthamfd

How about a reading of 00.2 ohms with the stator not on the tractor? Under the 0.3 ohm to 2.0 ohm range but over the 0.0 ohm reading that makes it a shorted stator. On the other check, it shows no reading to the metal ring, so the windings and insulation are good, as well. Haven't checked the rectifier voltage with the tractor running.

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Save Old Iron

Terry, how about a little more info. I don't think we actually discussed what amperage stator you have on your setup.

If its a 15 amp Kohler K setup, .2 to .3 ohms is fine.

The hard part about confirming a good stator resistance measurements is always the shortcoming of the meter we use to make the measurements.

I have an excerpt from your meter manual below. Notice the specs for your lowest resistance range are .8% (no problem) but the +/- 3 digits can be an issue here.

The 3 digit spec means a 00.2 ohms reading could be (.2 + 3 digits) or equal to .5 ohms

or (00.2 - 3 digits) or -00.1 ohms (shorted) since we cannot have negative ohms - that would make it a superconductor.

No shorts to the stator core is great news.

I'm going to place my bet on measuring the VAC output from the stator with the engine running at full throttle. If we get better than 25 - 28 VAC, I think we can ignore any confusing resistance readings if the VAC is good.

Attached Image

post-3-1271482609.gif

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Save Old Iron

Terry, here is something else to consider

statorts.png

This diagram represents the way a stator is wired. Its just a continuous length of enameled covered copper wire wound around the stator core segments, The number of segments varies according to the stator capacity ( 10 amp vs 15 amp, etc)

The segment cores are all formed from a single piece of iron so all the cores are electrically shorted to each other.

The wires wound on each core are electrically insulated from the cores by the enamel covering on the wire.

Lets say for the sake of conversation that the stator has only three windings as I show in my diagram above. Lets also say the windings are all in series (this is not true for high amp stators as some have pairs of core windings wired in parallel to increase the stator current output).

But , for our conversation about resistance checks .....

If the wires in the first stator core short out (between numbers 1 and 2) - the overall resistance of the stator will only drop to .2 ohms (.3 overall stator resistance minus the one core's resistance usually at .1, now a 0 ohms due to the short)

This is essentially 1/3 of the stator power and voltage gone. So a 15 amp stator would now only put out 10 amps max AND the AC voltage out of the stator would also drop by 1/3. So if a good stator normally puts out 30 volts AC, now the stator will only put out 20 volts AC.

But lets say we severely overheat the stator wiring and points 1 and 3 melt off the insulation on the windings and the wiring shorts to the core.

Now there is a direct short across the stator wiring because the individual stator segments are all electrically connected together. So we have what amounts to a direct short across the stator wires leading to the rectifier / regulator .

The stator is fried and voltage / current output is at zero.

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tgranthamfd

I was wondering which amperage system I had, myself. The one I was checking was one my brother had laying around in his growing pile of parts. I haven't gotten back out to my friends house, which is where my horse is at. I am almost positive the problem is the stator. On my original check with the meter, we checked the voltage with it running, but I am not sure if my brother had it on AC or DC. I had the ringer on, with engine not running, and put the leads to the 2 wires from the stator and I am pretty sure I got a tone, like it was grounded. On another note, I went to Wally World tonight and picked up a $18 digital multimeter with 4 or 5 ohm settings on the dial, so I should be able to get out there tomorrow / today, which ever it is now, to do a more exact check on it now that I know what to look for. I think I do, anyway. Oh yeah, the stator in question is on a 80 C-145 8 speed, think the engine is from an 85 model 314 something, if that helps on the system amperage. :omg: Sorry for rambling, Been working on a wiring harness for the lighting, it was all striped off when I bought it. It is coming along nicely, but I have been doing it after work so I am getting a little sleep deprived. I'll bet the stator has been weak for a while and it wouldn't hold a charge so the PO could have torn all the wiring, switch, and lights out.

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Save Old Iron

Terry,

if your stator is still on the tractor, disconnect the stator output leads from the rectifier assy and measure the AC volts coming from the stator leads.

If you have over 25 - 28 volts AC, connect the stator leads to the rectifier and measure for the same AC voltage across the stator leads. The voltage should be very nearly the same.

If the 25 + VAC drops down significantly, the rectifier is probably defective. Stop the tractor to prevent the stator from overheating due to trying to drive into a short circuit in the rectifier.

I think a big take away for anyone reading this post is this - There are SEVERAL ways to troubleshoot the same problem. The issue here is the low ohms range resolution of most meters does not allow the resistance of the stator to be used as a final go / no go test for the stator.

Keep in touch - apparently we are both night birds.

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tgranthamfd

Terry,

- apparently we are both night birds.

I have been accused of being that before. For now I am headed out to the tractor.

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tgranthamfd

Yes stator in junk. First, turned the ringer on and connected to the leads and got a tone, it is grounded. Second, jumped the tractor and checked the stator wires, it was really erratic but best I could tell it was only putting out 18 to 19 VAC. Plugged back into the rectifier, and the VAC was even lower. = bad stator.

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Save Old Iron

:omg:

it is so cool when theory and real life agree with each other !

great work.

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tgranthamfd

Just for everyone's information, things are not always as they seem. Got started pulling off the "bad" stator and went as far as I could, no flywheel puller. Went to do a few other things, while I was gone my brother showed up, pulled the flywheel, changed the stator, and put it all back together. The stator he took off looked to be right out of the box. He noticed that the little clip that holds the wires tight to the ring, seemed to be a little loose so he pushed it back down to where it was tight against the ring again. When I got it home, I did all the resistance checks, and it now shows all the signs of being a "good" stator per all of the resistance measurements from the above trouble shooting illustrations. I have included a couple of pictures so you can see the stator we took off and the little clip I was talking about. In working on the stator and installing new lighting and wiring I found a poor connection going from the harness to the negative post of the amp meter, this could have been part of the issues I was having, as well. The new lighting works well and was a blast to do, and I only had around $45 to $50 tied up in that, may put a post up on that later. Thanks Terry

Here is the stator that we removed.

DSC01233.jpg

And here is the little clip that wasn't very tight.

DSC01232.jpg

Once the clip was pushed down tightly, it tested to be good.

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gwgdog66

Keep that one handy. The old one I put on there is a 30 amp, I replaced it on my C-160 for some reason, several years ago. I just can't remember why :omg: I'll probably remember right in the middle of something real important.

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Save Old Iron

Somehow ... and I hope I'm wrong on this one .... I just don't think this story is over.

Terry, if you can, confirm the VAC reading again at the rectifier / stator wire connections, I still think you should be getting 25VAC or more at full throttle - probably more like 30 -40 VAC.

I have no first hand info on what the function of the clip is, but I can't believe its the root issue here. Again, I hope I'm wrong, but I would think that clip is just a strain relief for the heavy duty stator wiring.

Keep in touch.

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tgranthamfd

Somehow ... and I hope I'm wrong on this one .... I just don't think this story is over.

Terry, if you can, confirm the VAC reading again at the rectifier / stator wire connections, I still think you should be getting 25VAC or more at full throttle - probably more like 30 -40 VAC.

I have no first hand info on what the function of the clip is, but I can't believe its the root issue here. Again, I hope I'm wrong, but I would think that clip is just a strain relief for the heavy duty stator wiring.

Keep in touch.

I have the stator in question sitting right here beside me, put the other one on. The voltage readings was very erratic with the other one at the rectifier connection. I completed the head light project and drove the tractor around for about 30 to 45 minutes and it started right back up several times. I'm going to let it set overnight and go see if starts up tomorrow. Also replaced the bad connection at the amp gage, while I was there. I really hope all is well, guess time will tell. As far as I could tell with the other stator Vac was jumping in between 19 and 27 at half throttle. Don't know if it will do. If not I will probably buy a new one and try again.

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Save Old Iron

As far as I could tell with the other stator Vac was jumping in between 19 and 27 at half throttle.

The good news is , with 27VAC at half throttle, the battery will charge and power all your lights.

The jumping around part is probably due to the corrosion you may have had on the rectifier connectors. The meter lead was not piercing down thru the corrosion to get a good solid connection and the meter was "jumping". I doubt the "jumping was from the stator itself. A small wire brush to the entire rectifier connection(s) will probably rid you of any additional jumpy readings.

These were the rectifier connections on my 520 before it was rebuilt. You will get jumpy reads thru that crud for sure !

tnIMG_0474.jpg

:omg:

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tophatbufflo

If the connectons are cruddy would it cause th single post on the bottom to get hot and melt the plastic on the solderless terminal?

Sorry for hijacking your topic :omg:

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