View Full Version : Most appropriate DC motor control

05-06-2009, 06:29 PM
I've got a 1hp Leeson DC motor, 1725rpm and 180 volts to mount on my lathe.
I've seen both PWM and SCR type controllers but know nothing about either.
What would you folks recommend for a controller?
I won't ever be much lower than 700-800 motor rpm.

05-06-2009, 07:30 PM
PWM for sure. SCR controllers can generate a lot of hum in a PM motor, much worse than a single phase induction motor. It was bad enough on my milling machine that I had to avoid certain rpm ranges because of sympathetic vibrations affecting the cutter. With the new universal motor geared down 6 to 1 it's smooth as silk even with the same controller. The difference is that the AC has no magnets to get in and out of time with since in a universal motor the field and rotor are timed by the commutator.

05-06-2009, 08:42 PM
Thank you!
Are they all fairly straight forward and standard or are there features I should look for?

05-06-2009, 09:11 PM
I really don't know since I build my own. Somebody else can probably help you on that question.

J Tiers
05-06-2009, 09:54 PM
At about 40% RPM minimum, either type will work OK.

The SCR types become troublesome at LOW rpm, and the PWM types are better.

PWM offers better modulated control, in good controls, with feedback, since the PWM "makes choices" as to drive power/voltage at a much higher rate, and can respond faster. This can provide a much better regulated speed.

For a control with no speed/rate feedback, at moderate speed reductions, either will almost certainly work acceptably. The old KB SCR controls work pretty well. KB also makes PWM style controls now, which I have not used, but they are a good outfit, and their controls probably work quite well.

I have made PWM motor controls with easily a 20:1 speed ratio, that worked well. I've also made, for past employers, PWM audio amplifiers of various powers up to 3+ HP, so I had an advantage as far as design and construction.

You also have the option of bagging it and going with a VFD and AC motor, which will work very well indeed, especially at the speed ratios you refer to. It may well be cheaper, VFDs are almost at commodity status.