Alternator On Older Snapper Lawn Tractor

Hello Friends,
My question is regarding my Snapper lawn mower LT160H42CBV2, 16 hp Briggs O/H valve V-twin 42" deck. I bought it new around 1996. Problem lately is new upper-end battery won't hold full charge, doesn't want to start without a lot of cranking and if lucky it will finally start and run through lengthy mowing. But then a trickle charge is necessary for further use after a day or two sitting. Checked voltage regulator when running, puts out about 13+ DC volts which matches battery volts after a charge, checked alternator output, 17+ volts AC which is below par by my understanding. Suspecting a bad alternator I pulled the flywheel and alternator - not my idea of fun for a 68 y/o woman. Alternator looks pristine but the flywheel was dreadfully cake-filled with dirt even laminated on the magnets, not unusual for its age. Could that be the problem? Do alternators go bad even if they look good? Since it was tested under load and failed, is there another way to bench test it? Just trying to fix this without throwing money unnecessarily at it but I don't want to keep assembling/disassembling it just to troubleshoot, I'd rather be growing old helping others. All responses gratefully appreciated, I have the electrical schematic if that be useful.
Thanks,
Laurel In Oregon

I would suggest finding the Briggs model number on a sticker on the engine and going to the Briggs website and downloading a service manual which should give detailed info as to how to troubleshoot the charging system.

Thank you for your response Bob. I did do that yesterday before I pulled it apart and the fact that the alternator was pushing only 17 volts AC led me to take the flywheel off. My engine is marked model 303777 type 1150-A1(4750) code 95092211. I can't find that exact model online - close but not exact, which makes another problem that I can't even find reference to a replacement alternator. I guess I'll just go to the repair shop in town and ask them. Thank you!

I ASSUME this has a rectifier/regulator that is mounted externally to the charging coils.

Typically, that unit (IF used on your specific engine) would be a more likely cause of charging issues than the under-flywheel charging coils.

Those units need to be well grounded to work correctly, on certain engines it's advisable to run a ground wire to one of the mounting screws.

Did the shop manual mention testing the AC voltage from the charging coils, and what that voltage should be?

Also, typically, the output from the rectifier/regulator goes through a wiring harness connector or two or three, and sometimes, even the key switch on it's way to the battery. Any loose or corroded connection in all that can cause charging issues unrelated to the charging coils or rectifier/regulator, as well

Hi Bob,
Yes, the configuration is as you assumed. The recommended AC voltage from the alternator is 30 volts so 17 AC volts that I was getting falls way short. Thank you for your suggestions, I'll do some more checking around for what you have mentioned.

Don't know where you are at, but know of a couple places to get used parts.

Sorry, I missed the detail (in your original post) where you had already measured the AC voltage, I took it to be open circuit DC voltage you were measuring! Gotta learn to read all the details a little better!

Sounds like you are on the right track.

BTW, is the 30 VAC supposed to be measured "open circuit" or with the alternator connected to the rectifier/regulator?

Which way were you measuring it?

Hi Bob,
The current is to be read open circuit, disconnected from the regulator. I measured with the tip of each probe of the multi meter to the pins on the pigtail coming of of the alternator. I'm still confused, there may be a short somewhere but can't explain the low AC voltage while running. 80 dollars is a lot for the part if I don't need a new one and I'm still not clear which one I should order but the application is for 16 amp. Another thing that stymies me is that while I was pulling the flywheel off, it magnetically gravitated to the ignition coil and it sparked and smoked a bit, what was that all about? I should have disconnected the battery before disassembly but didn't think it would be a problem. I finally disconnected the battery and the sparking stopped. Thanks for your help.

Thank you for your offer ArleninOR, I'm in Corvallis.

Sort of solved problem, the idiot holding the volt meter did not have the engine running full throttle when checking alternator voltage (me). FULL throttle, now it registers around 25.25 volts after having taken it all apart, did some cleaning. That was a beast to remove the flywheel, 1 1/4 inch nut soldered on by nature over a couple of decades, my largest impact socket is 1 1/8" fortunately I have a pulley removal tool so I didn't have to buy a tool. 68 y/o 125 pounds of fighting fury, a huge crescent wrench on a cheater bar and 3 hours of my life utilized. I will concentrate on other possibilities but everything else has to be easier from here on. Thank you all for your help!!!