Motorcontrol

May 09, 2006 4 Replies
H

Hello group,



I am trying to build a motorcontroller for a 24V 50W DC motor. Maximum operating current is 8 amps, when the motor is loaded. My plan is to rectify a 24VAC and feed it to the motor directly and then control its speed by PWM'ing a mosfet. The manufacturer says it is OK to use the higher voltage on the motor. I continously monitor the motor and adjust the speed to my desired value, regardless of the load.



But I am wondering: What amount of capacity do I need on this rectified voltage? Is ripple a problem for my motor, with 8 amps there is quite alot.



Thanking you in advance.



Henrik


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J

Zero.

No. It will average the voltage quite nicely.

By the way, a 28 volt motor that draws 8 amps is using 224 watts, not 50.

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T

With straight rectification of the AC PWM'd into the motor there will be significant ripple current. Your motor will dissipate more heat for the average torque available -- but unless you're pushing it really hard it should be OK.

If you need information on control related stuff see my website.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
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J

I have successfully used a series inductor to smooth the current in rectified phase controlled DC motor applications.

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H

Oh yes, The 24V 50W is nominal, the 8 amps is maximum according to the motors torgue table for maintaining the desired torgue at a given load.

Thank you both for your answers.

Henrik

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