OP
OP
showjyr
Fishaholic
Woops I was still thinking about the DC pump I linked to. What I was thinking is that one of the voltage controllers would be plugged in to the night side and the other plugged in to the day side. Every 15 minutes the timer would switch over to either the day or night causing the pump to run at whatever the selected voltage on each controller is set at. It would be like a heavy flow then very light flow off and on. The pump would never shut off. Again, don't know how you would do this with an AC pump but I'm sure it's feasible.
. First, DC motor control. You can control DC motors in 2 ways. Most will tolerate voltage adjustment. So a 12VDC pump will operate slower at say 9VDC, draw less current, and turn slower. Usually there is a limit to how slow the motor will go before it stops turning. You could use 2 DC voltage sources and a timer to switch between the two to get some oscillation of flow. The other method of DC control is via pulse-width modulation. Esentially a controller turns current on and off thousands of times in one second. The number of times current is on versus the number of times it is off in that one second determins how fast the motor turns. For example, lets choose a 1000 time a second controller. If in one second the controller is set to be on 600 times and off 400 times alternatingly, it will turn the pump at 60% of its maximum speed. Anyways, you can buy these controllers, some designed for the aquarium trade, and others designed for industry. You can even buy kits to make them yourself if you like. They're common in industry and not very expensive.
