PWM question

Yes--if you're trying to reduce torsional oscillations No--if you're concerned about dynamic performance.

You might have trouble getting the motor to even run at speeds that low. Certainly you will have trouble with *keeping* it going.

You don't say what kind of motor, or what the application is, so exactly what might happen is not known. An example might be 12v fans in computers, where anything less than about 20% voltage is likely to result in a stopped fan.

Or, more specifically, the fan will not be able to start if it is stopped and anything less that 20% pulse width is applied. That in turn means that it might continue running if the power is changed from 30% to 15%, but if it stops for any reason, it will not restart (and will eventually overheat if left in that condition).

Hence if the load on the motor is dynamic, or if it is to operate for long periods, and especially if you have no way to monitor the actually speed, very low speeds are a problem.

Motor is for auto radiator fan and will be used to drive external gear pump ( 1 cu. in. per rev. ) as circulator for hydronic heating loop. It will be running steady at various speeds conntrolled by PC with some kind of tach. for feedback. The only info I have on motor is 90 watts at 1900 rpm. Motor is a Delco 5050080, but cannot find more info on it.

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With appropriate software it should be able to average just about any speed as long as it has feedback indicating the actual speed.

A fly wheel should be un-necessary and might even complicate things in a control loop. It adds interia and a resulting large time constant that most likely will complicate the control loop. The real question is can you get sufficient torque at the low speed to do the job? You gave us the equivalent of the flow rate but did not give the pressure. With these we could figure the power required and it's place on the motor's speed-torque curve. My guess is that at that flow rate and at the likely very low pressure, you will have no problem running the motor at the required low speed. No fly wheel required or desired. Give it a try and see. If it doesn't work very well, then gear the motor to the pump with a four to one reduction using a belt and pulleys. Bob

Pumping through 200 ft. Kitec XPA tubing. ( 1.8 usg. volume for 200 ft.,

6.72 psi. pressure loss for 200 ft.pressure loss is from Kitec manual )Start rate will be 1.8 usg. /min. which is 450 rpm. pump speed with 140 deg. F fluid. There will be 2 loops like this upstairs by next winter and their performance will determine the requirements for the other 5 loops downstairs. I think that you might be correct with the reduction suggestion. I have no data on motors, other than alredy posted, but they are new, surplus and only cost me $4.99 CDN each, so if they don't work, the loss is not too great.