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Lists two different stators depending on serial number. It looks like replacements are available. It also looks like there is no regulator, just a diode. This means there is a limit to the current that it puts out, probably 3A or 5A.

Here is something to think about on your PTO coil resistance. At 3 Ohm and 12V it will draw 4A. If your stator only outputs 3A that will drain your battery. The other thing is that the output is half wave rectified, so your measurement of the current is likely incorrect (since half the time there is no current provided, ie blocked by the diode). I would also question the measurement of the coil resistance. Accurate low value resistance measurements require very expensive equipment. The error rate of low cost equipment is very high. My expensive Fluke meter does a poor job. It has an offset of 3ish ohms and even if I subtract that it's error percentage is VERY poor until above 10-20 ohm.

I would measure the current draw of the PTO. That is likely to be reasonably accurate, even with a cheap meter.
 

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Discussion Starter · #22 ·
Thanks for the research Frogmore. Things are coming together for a potential resolution.

i’ve been using a Beckman DM25 meter with a lot of capability. I bought the meter in mid 1980s, and although old, it still makes accurate measurements. I measured the stator output current on the DC amps scale.
Resistance scales are measured to 3 significant places. So I’m pretty sure that they’re in the ballpark.

I found the attached document on the tractordata.com site. It clearly shows that the design charging current is 3.0 amps.

i also found an old B&S parts document for my installed engine. It shows the original alternator part number to be 391529.

I searched the internet for that number and found one (new) on ebay for $15 + tax and free shipping. I’ve had a lot of experience with ebay and I’m aware of the potential pitfalls. This item has a 30 day return policy so I’ve taken a chance on it. Should be here by Saturday.

i mowed for 45 minutes today. Battery voltage at start 12.71 vdc and at finish 12.21 vdc.

Stay tuned for the next episode. I think, collectively, we’re going to solve this problem.
 

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It depends on how the ammeter testing circuit in the meter is made, as typically, it is made to expect a fairly constant DC current, while the circuit on the engine is 1/2 wave A/C (the stator produces a full A/C signal, and the diode just eliminates the negative part of it). And lots of equipment display digits they have no business doing so, you need to check the documentation for the meter as to it's accuracy at a given setting...

Anyway, I hope that part does the job...
 

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Discussion Starter · #24 ·
The new stator (391529) was delivered and is now installed. The output current measures twice what the old alternator measured.

With PTO off, battery voltage increases quite a bit faster than it did with the old stator.

With the PTO on, battery voltage slowly decreases.

I mowed for about 2 hours after changing the stator and the mower didn't quit while I was working.

Im still going to trace all the wiring and look for voltage leaks as soon as I can get the unit jacked up.

The mower deck is pretty old (don't know if it was the original). I wonder if the spindles could be binding and causing a greater load on the electrical system. I might remove the main drive belt and see what the voltage measures with the unloaded PTO engaged.
 

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I don't believe the mower deck spindles binding would cause the PTO to use more current.

I would measure the PTO current draw with an ammeter. My guess is that it is more than the 3A that the stator coil can provide and that is why the battery is draining.
 

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Discussion Starter · #26 ·
Now that I think about it, I agree with you. If the spindles were binding, it would put more load on the engine, but not on the clutch current draw.

when I engage the PTO, there’s a slight slow-down, but it comes right back up to speed.

The saga continues and I’ll be back when I have more news to report.

Barry
 

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Discussion Starter · #27 ·
Sorry for the long delay getting back to my Electrical PTO issue. Too many other projects got in the way,

I think the problem is finally resolved.

After tracing all the wiring, checking for grounds in all sorts of situations, measuring voltage drop through all components, and finding nothing that seemed out of the ordinary, I went back to square ONE. I installed a digital voltmeter on the tractor, and I had the battery checked on a full load test. It failed. Starting with a full charge (all night on the charger) the battery discharged to nothing in 21 minutes. The 10.5 ampere-hour battery performed as a 1.2 ampere-hour battery.

I've replaced the battery and, starting with a full charge, I can run the mower all afternoon and the voltage never goes below 12.5 volts.

The moral of the story: When you have electrical problems, first check the $%*#@ battery!

Thanks for everyone's help on this issue.

Now I want to move on to other issues with the tractor (replacing the muffler and exhaust piping), but I'll start a new thread.
 

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You might want to check the voltage across the battery terminals when the engine is off, and then when it's running. If it's the same voltage, then the battery isn't charging. It needs to be at over the battery voltage to charge the battery.
 
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