Need some help engineering a circuit

[gajopo]

The application may seem trivial, but I need to control an aquarium powerhead (pump). I'm an elevator adjuster by trade and have no problem understanding schematics and scouring datasheets but am by no means an electrical engineer.

My issue simplified, controllable powerheads cost 8-10X the cost of the same flow 120vac single speed synchronous pumps. Their ac counterparts are simple, two coils, one with a few extra turns to get the permanent magnet impeller to turn in the desired direction. Problem is with the interval timing circuit I am using the causes the pumps to "chatter" upon excitation stressing my much loved salt water inhabitants. Yes I could spend 1500$ on Tunze controllable pumps with a controller, but I like the 150$ approach better if possible.

What I would like to accomplish is a circuit that would supply 60hz during their "on" state and 1-59hz during their "off" state, slowing them to near their synchronous stall state (1-59hz, maybe 17hz??...). 60Hz is simple as I am doing that now.

How can I make a 120vac (+- 40v) 1-59Hz power supply? I have been scouring the internet for days and decided to just start posting were someone with the knowledge may see this and give me something I can plug into Electronics Workbenches MultiSim for trial and error.

For those of you who may care, a Hydor Koralia 4 (What I'm using) costs 30$. A Tunze Stream starts at 329$ plus the 12vdc controller. Both pump water, one just capitalizes on control via a large price hike.

Any input is greatly appreciated!
Gary

[Rigsby]

Hi gajopo,
The only way I know to control speed effectively on a synchronous ac motor is by frequency inverter. We usually buy these ready made so not sure how much is involved in building your own. Basically a frequency inverter converts the incoming supply (120v 60Hz in your case) and actually converts to dc first. Then a set of high power transistors re-create an ac waveform (sinusoidal) at any frequency you desire. I would say the control of the output transistors would be the most complex part of the circuit, most off the shelf units are microprocessor controlled. If you really want to simplify things then you might have to go back a step and purchase a dc pump, then you would only require a variable voltage dc supply - probably much easier to build or buy on a budget.