Induction Motor Soft Start ?

[wp100]

Hi,

Have some small aquarium powerhead pumps using mains ac induction motors, typically just 5W.

They are often used in a 'wavemaking' mode switching on and off frequently.

There are commercial controllers that say they have Soft Start to help avoid the impellors being damaged.

While I have read about such soft start systems for large motors I do wonder if Soft start in this case actually exists ?

I know you can have a simple triac switch or the better way of zero crossing but is there another method I have not seen ?
Is it possible / practical to vary the cycles at start up with a micro ?

 

[chuckey]

Very small "AC" motors fall into two groups, shaded pole synchronous and DC brushed motors with an internal bridge rectifier and series capacitor. The shaded pole motor are bomb proof and will generate so little mechanical power that it is extremely unlikely that they could break a rotor. The DC type are more powerful, but again it is unlikely that their torque would be enough to break anything. So soft start would seem to be sales hype to me.
If soft start is required for some other reason, not to scare the fish?, then a series resistor to drop the mains to 70% or so for a couple of seconds at start up may help.
Frank