Re: Declining motor torque with lower voltage.

I think you hit the nail on the head...That formula probably deals
with AC motors...

I googled around some more looking for answers on the torque verses
voltage question for DC motors. I found about a half a dozen torque
verses voltage curves on the bodine-electric site. Every curve was
the same...

If you half the voltage, you half the torque...Direct relationship...


Wally


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@y...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" <cnc4me@g...>
> 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.
> >
> > 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
> >
> > ???? Is this right ????
> >
> > Wally
>
>
> I have a similar dead spot in my thinking.
>
> It would seem a motor as above at 24VDC spinning at the percentage
> speed. (ie: 50% voltage and 50% of max speed) that the current

would

> drop and you would get half the power. but then at 1/100th power,
> or a very slow feed, there would be no power at all. Obviously,

the

> driver increases the amps to compensate. Or we would use much
> simplier drivers. Since we use these in CNC applications, there is
> something going on besides simple arithimitic.
>
> It may be that the reference above is for AC motors ? or motors
> without the driver circuit ? I seem to remember that AC motors

have

> a 4:1 (or there about) volts to hertz ratio. that is key in the
> variable speed drives operation.
>
> Dave