Re: (ET) one blade not cutting well

[David C Robie <mycroftxx1 juno com>]

Armatures can short by commutator bars shorting together, mechanical
damage.  Seen quite a few.

Dave
Weymouth MA
 

On Wed, 26 Jul 2006 15:34:30 -0400 (EDT) Michael S Briggs
<msbriggs alberti unh edu> writes:
> 
> 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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