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