Just got this mower and while mowing, I noticed the volt-meter only shows 8 v. The seller said it needed a new battery, so he took a hundred bucks off the price.
My question is that even if battery is bad, it should show around 14v when running,----right?--- my sunstar 18 does, battery can be low and when I jump it the meter goes to 14 and stays.
The 20 has Kohler Magnum 20 hp motor.

Am I looking at alternator junk?,--OR could I get lucky and it be a regulator? ---Still trying to look up what sort of charge set-up they have.

Also need to know where/how to go about testing for the problem. I don't have much in the line of alternator testing meters. Any ideas??? thanks; sonny

Battery meter could read that low if battery had two shorted cells. Test is measure battery with power off. If it reads down around 8 volts there is answer. With a good battery measure voltage at battery. Should read between 13.5 and 14.3 volts at normal running RPM.
Doc

regulator/rectifiers for those are fairly cheap AND a common issue.

the A/C terminals on the Kohler are the two outside wires but the procedure is the same. the voltage regulator on the Kohler is usually hidden under a shroud somewhere so air from the flywheel blows on it to keep it cool. they tend to get fouled with dirt & grass stuff and fry out.

https://www.youtube.com/watch?v=3Qt1ykP5ddc#action=share

Thanks for the ideas!! ---I think I saw where the reg. is mounted, it's on the top towards the rear in the flywheel housing. Been raining here for 2 days/nights, so didn't get to work outside. Temps down in the 40's and 50's with cold winds making it ruff doing outside work. thanks ; sonny

Sonny those kohlers are famous for shedding all of the flywheel magnets if they came loose they are all clumped together and they will need to be reglued to the flywheel. Use 2 part epoxy, space them even let glue set up overnight you will be back in business just keep track of all the cover screws theres a pile of 'em

Thanks, guys!! ---I did get a chance between rains to do some testing on the 20, and with regulator off, the center terminal (B+), has near battery voltage in it with key on/engine off. Just barely found a speck of white paint on 1 outside wire of plug, so I used that as negative and the other outside wire as positive, then started engine and hit wide open, looked at ac output and it shows 40.5 volts!
From the video, that would be spot on, so regulator must be bad. In process of ordering a new one.

I wasn't looking forward to having to take engine out to replace the stator, or magnets, so maybe I got lucky this time.

Now if I could get the driveshaft off the gearbox on the sunstar 18 so I can replace the front oil seal in it. Have cross bolt out, tried to drive it off, ( didn't hit super hard as gearbox is luni), and no budge. There is also a keyway showing in the end of the shaft.

It also needs the electric clutch unstuck on it. Last summer it started screeching when dis-engaged , so don't know what that will take to fix.

If I get these 2 in shape, it will help a lot on having some dependable mowers to last all summer without having to work on 1 right then. The old Craftsman 19.5 hp 42" jobber is doing good so far, but I used it hard last year.

This is the "new" used sunstar 20 that I am working on.-- so far it looks like it needs gone thru and change oil in motor,--drain and change the hydro. and install new filters. --- remove the 60" deck and clean it up, ( gotta take top shields off to get cut grass out from under belt/pulleys) and sharpen the blades, then grease everything.
The new regulator is s'posed to be here Tuesday, so maybe I can get most of the service done by then. ---Did I mention that I HATE mowing grass???? It's the most expensive thing I do!!! lol!!! thanks; sonny

Got the new regulator on and still the volt meter stays at 8. --Put charging tester on the batt and ran wide open, and have 14 running volts. --- Still need to get new batt. for it and see if that makes it show or not. volt meter could be stuck. Thanks; sonny

If voltmeter is a problem you could add one of these real cheap on a pushbutton. Available on ebay or amazon too. Digital panel meter 0-30VDC
Doc

Yeah voltmeters are iffy but if your battery has a dead cell it could be spankedng the hell out of it too

Had the battery charger on it to get it started, AND when it started this time the volt meter went to a shade over 14 volts, stayed there for the 3 hour mowing time. Will see what happens the next time I start it.--Still gotta get new battery for it but hate to make a special 40 mile trip just for one.