MRC DC throttle -zero setting "drift"

[gregc]

BroadwayLion

I had one locomotive that never stopped moving once it started. Welll, never is a long tim, but wat was explained to me was "Back EMF"

"Back EMF" resists the motion of a motor.

i always learn from things like this.

Electromotive Force (EMF) is simply voltage that appies a force to charged particles.   Electromagnetic induction is the relationship between a current flowing thru a conductive wire moving thru a magnetic field.

A current passing thru a wire produces a magnetic field.   That magnetic field will briefly sustain a current when the external source of the current is interrupted.  (similar to the voltage on a capacitor).

A generator uses an external source to rotate an armature of wire in a magnetic field to induce a current.

A current is forced (EMF) thru an armature in a magnetic field to turn the armature.

The only time the current thru a motor is the applied voltage over the armature resistance (Ohm law) is when the motor is not turning.   Otherwise it is something less.

If the shafts of two similar motor are connected, an induced voltage can be measure across the unpower motor.   The current thru the powered motor is the difference between the voltage applied to the motor and the induced votlage over the reistance of the armature.

 

two things are going on in a motor.  1) the current forced thru it by an external EMF creates both a magnetic field (in addition to the magnets) and a force causing the armature to turn. 

2) a current is induced in the armature wire because it is moving thru a magnetic field.    The motion of the armature in a magnetic field results in a back EMF.   It is non-zero whenever the armature turns.

So while the armature acts as an inductor to briefly sustain a current thru it causing the armature to turn, the back EMF resists this motion causing the armature to slow as long as the armature is in motion.

 

back EMF does not perpetuate the motion of a motor, it retards it.

[BroadwayLion]

Yes, but... The back EMF may affect the power supply causing it to keep its circuit active ecen with the rehostadt turned to zero.

 

Or something like that.Computers and even railroad signals take advantave of the back EMF.

 

 

Don't ask me how, I am only a LION anr I only repeat what I thought I understood.

 

ROAR