OK so a variac or resistor or other voltage-based control doesn't tend
to behave very well on a simple AC mains motor, a pump will probably be
an induction/shaded pole motor with either a good shaft seal or a
membrane between the stator and rotor. If it's a very small pump it
might be a simple DC/universal motor in which case voltage regulation or
high-speed PWM will work.
Simplest would be just an on/off timer if you only care about the total
average flow rate. If you need to actually modulate the instantaneous
flow rate downwards then a VFD is the most elegant solution. A PWM
system where the frequency is low (circa 10Hz) can operate but it's
noisy (electrically and audibly) and is very rough on bearings.
Things to watch out for, you may need to start the pump and full power
and then back down to overcome starting torque issues, and many water
pumps are arranged so that they're cooled by the fluid they're pumping
so there's a potential for overheating as the flow rate drops
Non-electronic options, so long as the pump isn't a positive
displacement type you may be able to use a simple valve to either
restrict the flow or to provide a bypass path around the pump. Either
will make the pump dramatically less efficient but don't know if that
> You received this message because you are subscribed to the Google
> Groups "rLab / Reading's Hackspace" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to reading-hacksp...@googlegroups.com
> To view this discussion on the web, visit