Re: Electric motor & rheostat to vary blower speed?

darro@xxxxxxxxxxxx wrote:
The owners of a condominium apartment block in a temperate west coast
climate are looking for ways to adjust the incoming air volume of a
rooftop blower continuously supplying outdoor-temperature
pressurization air to the hallways (ie. low volume in winter, medium
volume in spring and fall, high volume in summer).

I'd appreciate your feedback on whether it will be practical and safe
to use a rheostat to vary the speed of the blower powered by an
electric motor, and whether there might be a better way to adjust the
volume of unheated/uncooled air which must be delivered non-stop.

1/4hp, 1725rpm, 6-pole 120vAC motor Belt-driven Delhi G9 standard squirrel cage air blower

Thanks in advance for your replies.
Darro


No, you can't use a rheostat in that application. The motor you describe is designed to run at its rated speed when operated on 60 Hz power.

Some of the things you could do would be:

1. Change the motor to a multispeed (most have just two speeds) type and install appropriate switching to change speeds when desired.

2. Get another slower speed motor and couple the two motors together mechanically, maybe through the belt drive, then install switches to run the proper motor for the speed you need.

3. Change the motor to a three phase type and buy a variable frequency drive controller to suit it, one which derives its operating power from the single phase power line. (Expensive, but speed is continuously adjustable.)

4. Change pully sizes seasonally (A big PIA.)

5. Have you considered just installing a damper system on the input side of the blower?

HYH,

Jeff



--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"What do you expect from a pig but a grunt?"
.

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