Re: Where to buy non induction resistors

Jon,

Thanks for the input. I went ahead and used normal wire wound ceramic
power reisistors. You were right, While I got an improvement in
speed, not as great as I was hoping.

I'm using 50 Oz/in 5V 1A motors. My table setup runs at 16,000 steps
/ in. I was getting 1.3 IPM running the motors at 12 volts. I upped
the voltage to about 34 volts. and 25 watt 27 Ohm resistors with a fan
as am (slightly) over their wattage rating. I am now able to get about
3.7 IPM - a definate improvement but still slow.

Next step will be to revise gear ratio down to a more realistic level.

Roger

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> 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 seriously doubt it. Think about it - an iron core increases the
> inductance of a coil thousands of times. The resistor has no iron
> core and the windings are spread out in space. The motor has an
> iron core, and the windings are wound as tightly together as they
> can. The motor has VASTLY more inductance than the resistor.
>
> Secondly, if you use the common circuit with a resistor from the power
> supply to the center tap of each winding, and the transistors grounding
> one end of each winding, the current is always going the same way
> in the power resistor, so the inductance has even less effect.
>
> > 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?
>
> They are available, but probably not from Allied. I have gotten some
> 3 W non-inductive resistors for current sensing from Newark, but
> I don't think they have them in the 25 W size, either.
>
> R/L drives are really poor performers unless you use HUGE resistors
> and high voltages, then the power loss is also huge!
>
> Jon