Re: alfa-digest V9 #401

[George Graves <gmgraves@xxxxxxxxxxx>]

While all you say is true, the back EMF is CAUSED by the inductive 
nature of the motor (I.E. when each section of the coil is 
de-energized, the magnetic field it creates, collapses causing a back 
EMF to be generated). This makes it work much like a swinging choke in 
a switching power supply .

George Graves
'86 GTV-6
now with 3.0 liter 'S' engine
and Power Steering


On Thursday, April 10, 2003, at 07:02 AM, alfa-digest wrote:


> From: Richard Bies <bies@domain.elided>
> Subject: Re: Ohm's law
>
> I've read with interest, and will try a slightly different approach....
>
> That the motor is largely "inductive" makes little difference in DC
> analysis -- but the mechanical "load" on the motor is reflected as a
> seemingly <lowered> resistance.
>
> The running motor has the applied voltage on its input.  That voltage 
> both
> meets the electrical resistance -- and the mechanical load.  When 
> running
> no-load, the motor is <generating> a "back" voltage (essentially) 
> equal --
> it is, in effect, a motor and a generator at the same time -- acting 
> as if
> the electrical resistance were extremely high (little current flows).
> Then as the mechanical load is increased, current flows to supply that
> load -- the electrical resistance seeems to have dropped (when the 
> motor
> is completely stopped, to the resistance which would be measured by a
> meter on the terminals of the stationary motor) the "back" voltage has
> dropped to zero, and only the bare electrical resistance is present.
>
> As the torque of an electric motor is coupled to this current flow, 
> this
> is why it is ideal in many applications -- self-regulating:  as the
> demand (mechanical load) increases, the torque also increases, tending 
> to
> hold the speed steady (unlike an internal combustion motor, in which
> torque dropps-off sharply below a given speed, and it quits) the 
> electric
> motor will burn itself up as the limit is approached (not always a good
> thing -- why there are fuses -- but it dies trying).
>
> r.m.bies
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