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Please Help Me Out To Design A DC Fan Speed Controller Using SCR.

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Please Help Me Out To Design A DC Fan Speed Controller Using SCR.

I am designing a Fan Using Solar energy,So the voltage from solar panel is in DC,I want regulation i.e control for the speed of this Solar based fan using SCR.
asked Mar 4, 2016 by sanjaydgosavigmail-com (120 points)

While this is clearly feasible, it is not the method of choice.  Is this application of an SCR an engineering school project requirement?

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I have bad news; your idea will not work as stated.  When a SCR turns on, the current has to return to below the holding current so it can communicate off.  Since the only time this will happen you will have a two speed device, on 100% until the power is turned off, then when the power is on and the SCR is gated it will turn on.  If you must use an SCR you will have to force commentate it, this is on the difficult side.

 

My suggestion is to use a N FET and PWM it.  FET, heat sink sizing etc is load and voltage dependent.
answered Mar 11, 2016 by gilshultzhome-com (17,730 points)
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It is not going to work unless you get into some complicated circuits to force commutation.  This response is based on the DC characteristic of the SCR.  A SCR has a minimum holding current (relative low) which when exceeded will keep the SCR from turning off.  The proper way to turn the SCR off is to force it to commutate by reversing the voltage through it to reverse or bypass the SCR with a pulse that causes the current in the SCR to goto zero. A MOSFET would be one of the better solutions.
answered Sep 27 by gilshultzhome-com (17,730 points)

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