# Curtis whine



## EVfun (Mar 14, 2010)

It's a whiner. All 1221C and 1231C controllers rated for a maximum voltage of 120 volts or greater switch at 1.5kHz below 15% duty cycle and silently at 15 kHz above that. They have smooth low end response, but cause motor noise at low speeds.

The older Curtis 1221B-7401 switches at 15 kHz at all duty cycles. These are a little jumpy at low speeds and shouldn't be used with a low impedance motor like the ADC 9 inch FB-1 motor. 10% of pack voltage is about the minimum the 1221B can apply to the motor. They are nice and quiet, I used one in my Buggy until last year.


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## djbills (Apr 7, 2010)

thanks - very helpful


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