From: Gary Tait
Subject: Re: Help with motor speed control
X-Newsreader: Forte Free Agent 1.92/32.572
Date: Fri, 20 Dec 2002 11:09:36 -0500
NNTP-Posting-Date: Fri, 20 Dec 2002 11:10:57 EST
Organization: WorldCom Canada Ltd. News Reader Service
On Thu, 19 Dec 2002 18:37:42 GMT, "Dave White"
>We have a device in our lab which is used to rotate glassware in order to
>mix the contents. The shaft needs to rotate at approximately 30 RPM, with
>some control allowance (maybe 20-40 RPM). The company (actually a lone
>engineer) provided this custom made device with a 1/15 HP AC motor
>controlled by a rheostat. We have found that in operation, there isn't
>enough torque to get the glassware to rotate at much more than about 10 RPM.
>I have been asked to replace the motor and motor control circuit to give us
>more power. Looking at our local surplus store, there are a large number of
>AC and DC motors, ranging from 1/2 to 2 HP and priced between $20 - $40.
>I'd like to use one of these to control the system. The rheostat control
>seems very inefficient, and I expect I'd use some kind of PWM circuit.
>The DC motor is 120V, 2 HP 4800 RPM and 11.2A. If I were to use PWM, what's
>the slowest I could run this motor without it stalling?
>There are plenty of washing machine motors rated at 1/2 HP, 1725 RPM. Could
>this be slowed down easily, and how slow could I go?
>I will be able to include some gearing, probably in the form of a pulley
>system, so all of the slowdown wouldn't need to come from the control
>Any help/advice regarding design, best motor to use, gearing, etc. will be
>GREATLY appreciated - my expertise lies in digital and low power analog
>circuitry, not high power industrial electronics.
I'd gear it down a bit first.