Internet PLC Forum
General => Technical support => Topic started by: Andy on December 18, 2003, 12:23:43 PM
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We need the PWM functionality @ 250V/16A. Can we directly drive a solid state Relay from the PWM outputs? Any Suggestions? Thanks in advance
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As long as your PWM frequency is set to within the response speed of your solid state relay that should be possible way of driving your high voltage, high current PWM circuit.
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Thanks for the feedback.
That leads to some other Questions:
1 ) Should we use Zero Switching or Instant on (we asume Instant on)
2) The Response time you mentioned: There are several informations : operational frequency rate 45-65Hz, Response time pick-up <= 1 ms, control pulse width >= 0.5ms, Response time dropout <=1/2 cycle.
Is this O.K? at which frequency can we drive this relay?
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Your are controlling AC load using your SSR? Then PWM may not be the suitable choice since PWM is used to chop up DC voltage into deterministic duty cycle and typically operates at several thousand Hz. In your case you probably have to turn ON and OFF at much slower speed. It may be still possible if you use the lowest frequency (16Hz) PWM but do check with your SSR supplier to find out if a zero crossing or instant on type is more suitable to be driven by the PWM.
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yes, we need to regulate AC load with the PWM.
Do you have some other ideas? Basically we have to drive two AC Fans with variable loads from 30%-100%.
Thanks in advance
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I had thought that you wanted to control something like power applied to heating element, then by controlling the duty cycle of turning ON/OFF the power to the load you can change the applied power.
However, AC fan speed cannot be controlled by PLC's PWM output! It just won't work that way. The only way to control the speed of AC fan is to use VFD (variable frequency driver) which will vary both the frequency and amplitude of the applied AC power to the motor in order to control its speed.