RE: (ET) Weak Deck Motor / Blade Spindown

["Steven Naugler" <snaugler earthlink net>]

David,
        I'd be most suspicious of the brushes being worn or stuck.  The 
wiring to
the motor or the circuit breaker on the motor being bad  would be my second
most likely area of concern.  The motor cutting weakly and the dynamic
braking being so poor indicates high resistance somewhere.  You've
evidently checked the wiring at the motor, but wiring in the deck harness
could also be bad.  You also need to check the circuit breakers at each
motor.  
        I'd recommend first checking the easy stuff which would be the 
wiring and
circuit breaker.  You should check the wiring harness with an ohm meter
between the plug and all three motors.  You could also run the motors and
check the voltage delivered while running and the voltage during the
dynamic braking.  If the wiring is good, the motor running when not cutting
voltage should be within 1 to 3 volts of the battery voltage.  When dynamic
braking is engaged the voltage across the motor terminals at any one motor
should be 0 to 2 volts and then 0 when motors are stopped.  Low voltage
when running or high voltage when stopping indicates high resistance
somewhere.  You could also have a bad circuit breaker on that motor.  The
normal wiring harness resistance should be less than 1 ohm.
        If you measure more than 1 to 2 volts across the circuit breaker 
with the
motor running it is probably bad.  Another check is to jumper around the
circuit breaker.  If the motor then runs normally, the circuit breaker is
bad.  Do not mow with the circuit breaker disconnected or you could fry the
motor.
        If the wiring and circuit breakers are good, the motor must be the 
culprit
and so must come apart soon.  If you run with worn or stuck brushes you
will ruin the commutator and your armature will become junk.  There are
posts from me and others in the archives on repairing motors.  (I'd send
you a copy but my old e mail program became corrupted and I currently can't
access local copies of my old posts.)  Be forewarned that if one motor has
worn brushes, or even stuck brushes, the other motors are probably close to
bing bad.  You need to check and/or service all three.
        Hope this helps some.  Post any other questions you may have.

Steve Naugler


> [Original Message]
> From: David Stensland <electron megsinet com>
> To: <elec-trak cosmos5 phy tufts edu>
> Date: 6/3/00 2:04:19 PM
> Subject: (ET) Weak Deck Motor / Blade Spindown
>
> One of my E12M's blades starting cutting badly last night.  It got so bad
> that I had to stop.  It appears that the motor is weak.  There's nothing
> wrong with the blade itself... it's sharp and well balanced.
> 
> The electric braking quit on that motor at the same time.  Now when I 
> turn
> off the deck, that particular motor continues to spin down long after the
> other two have stopped.  I pulled the cover and noticed some condensation
> inside, so I tightened the terminals and tried it again, but no change.
> 
> Before I tear it apart and inspect the brushes, I'd like to hear if 
> anyone
> else has had this problem.
> 
> Any suggestions?
> 
> Thanks,
> -Dave
> 
> P.S.  For those of you who are interested, I have pictures of the tractor
> posted at http://www.corecomm.net/~electron/Elec-Trak.htm
> 



--- Steven Naugler
--- snaugler earthlink net