Re: Ohm's law

[Richard Bies <bies@xxxxxxxxxxxxxxxx>]

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
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided