On 22 Jun 2017 at 7:30, Robert Laird wrote:
> You are only using a small portion of the total area available to
> dissipate the heat.
Ah, thanks for the clarification, NOW I see what you're getting at, a heat
dissipation problem. You don't want your rheostat acting like a fuse. I'll
agree that you need to check the rheostat manufacturer's datasheet to make
sure its current rating is >= the load's full current.
That's one big advantage to using fixed field resistors as GE did -- you can
calculate the power rating required for each fixed step, and set the steps
so that it's low enough to keep the component costs down.
Or you can take the modern route (paved) and use a low power PWM controller
to drive the field. I see several 36v / ~350W DC brush motor controllers
offered on Ebay in the $20-30 range. Disclaimers: I haven't presonally
tried this, and I know nothing about the quality or reliability of these
little silver no-doubt-Chinese boxes.