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Fan induction motor ON/OFF modulation - is it OK or Harmfull for motor ?
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Miyuki:
Hi folks,
I have here air system fans and need to regulate them (simple induction motor with run capacitor)
Question is can I use slow speed ON/OFF modulation and what frequency is best. Control system can go up to 10Hz. But full phase control is not achievable, without external hardware, now they are connected with SSR controlled by logic signal.
At 5Hz fans run steady even at low 10% duty and make little audible switching noise but produce some shaking to mounts as they are relative strong 80W radial fans with big inertia
Noise is not a problem but I'm afraid of that vibrations can it damage motor and bearings ?
capt bullshot:
I've done this control scheme for water pumps in the central heating system - never noticed any issues. Afaik, for some time this was the "state of the art" method to control these pumps. They also were induction motors with capacitor. For the same concern as you have (movement and vibration), I had manually adapted the modulation scheme to avoid obvious mechanical resonant points.
james_s:
The only concern I'd have is if they're the type of induction motor that has a centrifugal starting switch, you don't want it slowing to the point that the starting switch is repeatedly cycling and activating the starting winding. You also might want to check the current draw, many types of motors draw considerably higher current while trying to accelerate up to speed than they do steady state. Otherwise it shouldn't be an issue.
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