(ET) Mower motor mayhem (maybe)

[Chris Zach <czach computer org>]

Well, I drove the tractor down to the shed, dropped off the blower and 
mounted the deck. The deck has spent the winter on it's side in a nice 
dry shed.

Hooked it up and powered it up. Sounded wrong. It would pull mower deck 
current, but the needle was "spiking" every 20 seconds or so.

Checked the deck. The center motor was spinning normally while the outer 
two were not. They would start to spin for a few seconds, then shut down 
as their thermo-breakers tripped.

Tried the deck at 12 volts. All blades spun fine. Interesting. With the 
mower unplugged, turning one blade would cause the other two to turn. So 
bearings were ok.

Then I tried bypassing one of the thermo sensors, thinking they were 
bad. Plugged into 36 volts and fired it up.

Blades spun up fine but motor started to smoke in seconds. Shut down, 
wires to it were hot.

Whoah. Reconnected the breaker and tried again. Once again motor would 
spin for a few seconds then trip. Looking in the little inspection port 
I could see sparks on the commutator.

What happened over the winter? And why to two motors?

Chris