Re: [CAD_CAM_EDM_DRO] Re: Where to buy non induction resistors

L/R drive just uses a constant voltage and the maximum current is
set by the series resistance. Because of the motor inductance,
applying say 12V causes the current not to be maximum instantly,
but to ramp up to it. If the pulses are short, then the current
doesn't get up very high, so motor torque is less at higher speeds
when the pulses are shortest.

Constant current works by using higher voltage (like 80V) on the
windings, and no resistors. The current ramps up faster thru the
motor windings because of the higher voltage. When the current
reaches a maximum, a monitoring circuit removes the voltage.
This action is pulsing, and with various systems, the frequency
can be from 200Hz up to 50kHz or more. Maximum current and torque
is maintained at maximum motor speeds. The method uses no resistor
to limit the current, so you don't get the heating problems.

lenskeeper2000 wrote:

>
> Okay, so it sounds like I'm wasting my time worrying about resistor
> induction. Sound like I can just stick in normal power resistors and
> get about the same result. (I tried upping my voltage with what I
> had around the house and really liked the improvement but this was
> just a test was cooking the resistors)
>
> What is a constant current drive? Isn't that the same thing as a L/R
> Drive circuit? (I my have just demonstrated my ignormace)
>
> Roger
>
> --- In CAD_CAM_EDM_DRO@y..., Russell Shaw <rjshaw@i...> wrote:
> > The inductance of *any* resistor will be *much* lower than the
> > inductance of any motor. The only way is to use higher supply
> > voltage, lower inductance motors, or constant current drive.
> >
> > lenskeeper2000 wrote:
> > >
> > > Where can I buy non-induction power resistors? I'm using a simple
> > > L/R style drive circuit and want to step up my voltage but have
> found
> > > I have too much inductance to get my speed rate up. I'l thinking
> if
> > > I can reduce the effect of the wire wond reisitor's im using this
> > > will help.
> > >
> > > I've seem lots of power resistors for sale (allied etc.) but none
> > > seem to be non inducting. Looking for 25 watt in the 20-25 hom
> > > range. Any suggestions?
> > >
> > > I'm trying to keep on a budget and am trying to learn electronics
> > > while upgrading my desktop CNC mill. so holding off going to a
> > > chopper curcuit as I want to design myself (will leikely
> eventually
> > > give in and by Gecko drivers).