Originally Posted by Mtn_Brewer
I previously looked into this extensively. March 809 pumps are brushless motors (see spec sheet below) and therefore need an electronic speed control (ESC), which is rather expensive. A ball valve is way cheaper and simpler, so that's what I went with.
If there is an engineer or electrician out there, further clarification would be appreciated .
Originally Posted by BetterSense
It is true that brushless motors must be controlled by modifying the electronic commutation. AC synchronous motors (probably what the March pumps use, also 'brushless') don't have any commutation and spin at mains frequency, so you would have to have an in-between complicated gizmo to change the rotation frequency.
The 110 VAC March 809 pumps (quit buying the inline, get the center inlet- there I said it) have a PSC motor, and can be controlled with a 'variable fan speed controller'. They look like old school wall dimmers with the tan knob, but are specifically for ceiling fans/PSC motors. They used to be ~$20 new, but I haven't seen a price lately. I believe they are TRIAC based. I think the typical numbers touted for use with these pumps are that speed can be safely reduced by about 50%. PWM speed controllers can also be used with PSC motors, and should provide a bit more useable range than the fan speed controller. WalterAtMarchPump has a post on the subject, and gave a blessing, of sorts, to their use.
I think I remember reading that the more common/cheaper Thyristor based wall dimmers (with the same tan knob look, but not the 'pot' based ones), will also work as a PSC motor speed controller, but with a much more limited range (due to overcurrent/undervoltage issues). I has to do with the trigger points differences (I think), of the Thyristor vs. the TRIAC
That ESC wiki link isn't applicable. It was referring to 3 phase and/or DC motors, and small RC motors at that. For 3 phase motor speed control, vector VFDs are the king of the hill.