I know that controlling the speed of an AC motor is "more challenging" than a DC motor, but is it really THAT tough?
The application I have in mind is for a variable speed pump on a saltwater fish tank. I'd like to be able to ramp a pump's speed up and down, but am having a lot of trouble finding a suitable DC pump, since everything in the aquarium hobby is designed to plug into a wall outlet and run at a constant speed. There are some "controllable" DC pumps for aquariums, but they are stupidly expensive.
So, how hard IS it to control a regular, AC motor in a pump? Or, should I continue searching for a DC pump that'll work?
Some examples. Here is a typical AC pump ("powerhead" in aquarium-hobby terms):
Here is a controllable, DC powerhead:
Rather than spend the extra $150 - $200 for a powerhead with a DC motor in it, I'd love to be able to control the speed of the AC-motor-equipped powerhead with an arduino.
I've read a bit about AC motor speed control, and it seems like unless you have a 3-phase motor and a VFD, you're out of luck. Is this true?