Re: (ET) one blade not cutting well

[David C Robie <mycroftxx1 juno com>]

Well if you're going to just throw it away,  throw it in the trash in
Weymouth MA.  I'll take it.

How about just doing a bit of mowing and feeling all 3 motors for
temperature?  If the bad one is hotter or cooler than the others it'll
tell you something.

I've seen a lot of motors with cracked field magnets.  Crack  can be
fixed with JB weld.  They still work but got a bit less power if it's a
bad crack.

Dave
Weymouth MA


On Wed, 26 Jul 2006 16:36:34 -0400 "Konstanty, Walter \(GE Indust,
ConsInd\)" <Walter Konstanty ge com> writes:
> This thread is getting so long I can't remember the key points 
> anymore...
> - Blades are turning all same way?
> - Switch motors around may isolate the motor
> - Switch blades around may isolate a heavy/bad blade
> - Armatures really don't "get tired"....current flows to maintain 
> terminal volts/speed 
>     and if shorted, they blow up  (go to ground, melt, etc)...if the 
> permanent magnets get weakened, speed increases
> but torque decreases.  Magnets get weak from removing the rotor too 
> many times or
> external demagnetization.
> - Measuring motor currents lets you know load between 
> motors...measuring speed also
> would be "neat".
> - Rear or side discharge may affect the right-most motor more if all 
> grass thrown that way.
> - Friction or bad bearings show up quickly.
> 
>   Maybe we all need PLC upgrades to monitor motor temperatures, 
> load, speed, amount of
> grass cut/snow plowed...that would be real neat.
> 
> ....Walt
> 
> -----Original Message-----
> From: elec-trak-bounces cosmos phy tufts edu
> [mailto:elec-trak-bounces cosmos phy tufts edu]On Behalf Of Michael 
> S
> Briggs
> Sent: Wednesday, July 26, 2006 3:35 PM
> To: Klein Robert W NPRI
> Cc: Elec-trak cosmos phy tufts edu
> Subject: Re: (ET) one blade not cutting well
> 
> 
> 
> On Wed, 26 Jul 2006, Klein Robert W NPRI wrote:
> 
> > That's what your doing with an ammeter which has an internal shunt 
> to 
> > the meter.
> 
> Using a voltmeter to measure the voltage across a shunt isn't quite 
> the 
> same as what I'm saying (although of course most common ammeters do 
> work 
> that way). The main difference being that with the voltmeter and 
> shunt 
> approach I'd need to go out and buy some low resistance shunt to put 
> in 
> series with the motor, whereas I already have multimeters that can 
> measure 
> currents up to 10A. Me being cheap, I'd prefer an approach that 
> doesn't 
> involve buying anything new if possible. :)
>       Whether installing a shunt or just using an ammeter, the 
> same 
> thing is going on electrically (since most ammeters just measre V 
> across a 
> shunt), but from the pocketbook perspective, they're different. :-)
>       But, the ammeter approach wouldn't work if the current 
> through the 
> motors is typically >10A. It will just blow the fuse in the meters, 
> which 
> I have plenty of, but it would mean I couldn't use that approach, 
> and 
> would have to go buy a shunt.
>       I think you mentioned previously that it sounds like a bad 
> armature - I don't see how the armature could be bad really. The 
> armature 
> is just a winding of coils for current to flow through, for the 
> field to 
> make a torque on to spin the motor. Isn't the only way the armature 
> could 
> be bad when there is some break in the coil circuit, such that 
> current 
> couldn't flow through the armature at all? (which would mean the 
> motor 
> wouldn't spin)
>       Or perhaps some of the wires in the coil could short if the 
> 
> coating is worn off?
> 
> Thanks,
> Mike
> 
> 
> 
> >
> > -----Original Message-----
> > From: Michael S Briggs [mailto:msbriggs alberti unh edu]
> > Sent: Wednesday, July 26, 2006 1:04 PM
> > To: Klein Robert W NPRI
> > Cc: 'steves'; Elec-trak cosmos phy tufts edu
> > Subject: Re: (ET) one blade not cutting well
> >
> >
> >
> > Why not just put an ammeter in series? How much current do these 
> mower
> > deck motors normally pull? As long as it's <10A, I have some nice
> > multimeters that can measure currents up that high. I can just pop 
> the
> > lid, disconnect the leads, and put the multimeter (in ammeter 
> mode) in
> > series with the motor.
> >     Or is the current >10A normally?
> >
> > Thanks,
> > Mike
> >
> >
> 
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