soft start for powerhead
Hi,
I am being a bit picky, but isn't it V(t) = sqrt(2) * 120 * sin(2 * pi * 60 * t) ?
As for soft starting, motors look like inductors and during the initial power up...it looks like a dead short. So, it needs to time energize and create a back emf. Usually, the electromagnetic strength is proportional to the AC current. So, during the inital power surge, the electromagnets are pulling and pushing the stator very hard -- hence the rough start. Once the back emf kicks in, less current flows through the electromagnets and the motor returns to its normal operating point.
So, if you can control the current (i.e. slow down the in rush current), then the motor will start up with less stress. You can use voltage to control the in rush, but the circuit is even more complex. The voltage envelope needs a x^2 like shape to work...rather than x like shape for current control. Another voltage method is by varying the frequency of the AC power supply (VFD), but that's even more complex.
Hope that helps.
- Victor.
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