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Usually triac based speed control vary the phase angle of firing to reduce the amount of power goes in to motor, and hence control its speed. this is not very efficient method, also it may not be good for health of motor depending upon its built.

There are some suggestions that, if we can switch whole cycle on-and-off instead of part of cycle ( i.e. phase angle ), it may be more efficient and easy for motor. I would like to build and try that, and see if that the case. I am newbie in to power electronics, and did search on internet but not found any particular circuit for this.

Any suggestion on circuit of doing the same ? Due to cost and reliability, I would like to try it without micro controller.

EDIT: The common name for this method is , "integral cycle control". There are many circuit also available on net, but still, if micro controller less circuit is possible, that would be cool.

  • \$\begingroup\$ Phase angle is cool, find some old circuit like U2008B. You can even build your own interface with opto coupler to control the speed with MCU. \$\endgroup\$ Commented Feb 18, 2016 at 10:04

1 Answer 1


Motors are designed to cope with the torque variation from the mains frequency supply. A phase angle controller does not make this worse.

An integral cycle controller would lower the frequency of the torque variation. Say you fed your motor with 2 cycles on, one cycle off. It would judder at 40Hz. This lower frequency judder would be likely to cause damage.

Integral cycle control is just great for heaters, that take seconds to respond.

  • \$\begingroup\$ After bit of googling, I came to the same conclusion. Triac way is better for motor control. Thanks for the answer. \$\endgroup\$
    – iamgopal
    Commented Feb 18, 2016 at 9:33
  • \$\begingroup\$ Additionally, Single Phase AC motors are simply not good for variable speed applications. No matter what base motor design. For efficiency, use a multi-winding motor, or better a DC machine if you must stick to a single phase source. For larger (but still small) sizes, a three phase motor driven from a single phase input drive is the best bet, and maintains torque at all speeds. \$\endgroup\$
    – R Drast
    Commented Feb 18, 2016 at 12:08

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