Re: [CAD_CAM_EDM_DRO] Declining motor torque with lower voltage.

cnc_4_me wrote:

>I found this statment googling around today.
>
>"It is common motor knowledge that motor torque declines by the
>square of the change in supply voltage."
>
>First...Is this true.
>

Not in relation to servo motors. It is mostly true with respect to
series-wound
motors, as used in vacuum cleaners and routers, for instance.

But, it is not true with respect to permanent magnet motors and
shunt-wound motors,
as long as the field winding current is held constant. In those motors,
torque is
precisely proportional to armature current, and voltage only affects the
speed.

>
>And second if true would this be the proper way to appy this.
>
>1) You have a treadmill motor rated 130VDC, 2.5HP 6700RPM, and
> 373 oz-in continuous.
>
>2) The motor is run from a 80VDC power supply.
>
>Well, the change in voltage is 130VDC - 80VDC = 50VDC.
>The square root of 50VDC is aprox 7.
>So the motor torque declines by 373 0z-in / 7 = 53 oz-in
>
>
>

I believe the treadmill motor in question is a PM motor. The torque is
proportional
to current, the speed is proportional to voltage. The speed would fall
to 61.5% or
4123 RPM. The torque available would still be 373 Oz-In.

Jon