From: "Dave White"
Subject: Help with motor speed control
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
NNTP-Posting-Date: Thu, 19 Dec 2002 18:37:42 GMT
Organization: AT&T Broadband
Date: Thu, 19 Dec 2002 18:37:42 GMT
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.
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