Re: Question for Mariss

--- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> Dom,
>
> The voltage rating on a step motor simply means if you apply 3VDC
> across that motor's coil, 4 amps of current will flow. In other
words
> it has 0.75 ohms resistance.
>
> The step motor coil is an inductor (L). Inductance has a property
> called inductive reactance in the same way as a resistor has a
> property called resistance. Both are measured in Ohms.
>
> What makes inductive reactance different from a resistor is
> its "resistance" is proportional to frequency. This means every
time
> you double frequency (steps per second), the "ohms" double as well.
>
> According to Ohm's Law (I=V/R), it means current is the inverse of
> speed. Torque being proportional to current, becomes the inverse
of
> speed as well.
>
> Going the other way, as speed approaches zero, the inductive
> reactance "ohms" also approach zero and current would become
> unlimited. This cannot be permitted.
>
> What actually happens is the drive limits current to a programmed
> value (4A in this case) and can be considered a "current source".
> That simply means it will not permit more than the programmed
current
> to flow into the motor.
>
> When the motor is stopped, this 4 amps produces an effective
voltage
> of 3V across the motor. As its speed increases, the effective
voltage
> across the motor increases as well so as to keep that 4A of
current
> flowing.
>
> Eventually a speed is reached where this voltage equals the supply
> voltage. Beyond this speed the motor's increasing inductive
reactance
> limits current to less than 4A and torque begins to drop as a
result.
>
> At no time does more than the programmed current ever flow thru
the
> motor. All that happens is the effective voltage across the motor
> increases with speed. That voltage times current is the power
> absorbed by the motor to be converted into mechanical energy.
>
> Hope that helps you see more clearly what happens.
>
> Mariss
>
> >--- In CAD_CAM_EDM_DRO@y..., NCS <ncs@n...> wrote:
> >
> >
> > 10A x 60 V = 600W or 200W per motor.
> > 200W / 3V = 66.6 A per motor.
> >
> > Uh-oh, somethings not right!
> >
> >
> >
> >
> >
> >
> >
> >
> > - Dom