Re: (ET) Weak Deck Motor / Blade Spindown

["David Stensland" <electron megsinet com>]

The problem is not the blade/motor connection.  It's not the circuit
breaker, either.

Both of those were checked before I decided to run the ET out in the grass
just to see what would happen.  The motor seemed about the same as before,
but I noticed the ammeter needle was jumping up into the red then back down
as I moved along.  Against my better judgement, I continued to mow for 
about
3 minutes... then the suspect motor kicked in "full on", power returned, 
and
the needle quit jumping.

The grass was about 7" tall... I know I shouldn't have, but I continued to
mow the rest of the backyard.  I took a 2/3 cut... only using the suspect
motor to mulch the previous round's cut.  The grass was wet from last
night's rain, but it did a great job.  Everything continued to work great
for the next 18 minutes.

The problem could still be the wiring harness or, most likely, the brushes.
Had I read Steven Naugler's note better, I wouldn't have mowed at all.  He
warned of possible damage to the motor when using worn or damaged brushes.
Hopefully, I haven't hurt it too much already.

I'll let you guys know the root cause before next weekend.

-Dave
----- Original Message -----
From: Steven Naugler <snaugler earthlink net>
To: <elec-trak cosmos5 phy tufts edu>; David Stensland
<electron megsinet com>
Sent: Saturday, June 03, 2000 9:31 PM
Subject: RE: (ET) Weak Deck Motor / Blade Spindown


> 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
>
>
>