Induction motor speed = 60 hz x 60 sec/min / number of poles on the motor.
If it is multi speed motor (multiple windings or taps) then one can select a
speed by rewiring.
If you need an airflow reduction on a single speed motor, then either change
the frequency of the power source (variable frequency drive) or just
throttle the inlet of the fan... i.e. partially restrict the fan's inlet.
Matt
KM5VI
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Garland
Sent: Monday, February 03, 2014 9:24 AM
To: 'Roger (K8RI)'; amps@contesting.com
Subject: Re: [Amps] Air temps leaving the amp.
This raises an interesting issue. How does one reduce the impeller speed on
a blower with a 120 VAC motor (capacitor start)? I've done some tests on
several blowers (3370 rpm) and find the rpm doesn't vary appreciably as the
voltage is varied over a significant range. Once the voltage gets low
enough, of course, the blower stalls, but the rpm doesn't vary with the
voltage. I suspect this is an inherent property of induction motors. I first
discovered this effect years ago when I tried to reduce the blower speed of
a Rotron blower in an 8877 amp. I switched in a 24V transformer to lower the
voltage from 120V to 96V, but discovered it didn't make much difference.
73,
Jim W8ZR
>Find what
> blower speed gives the required pressure. Then back off to where the
>noise is comfortable. Use a sensor in the output air so when the temp
>rises it can kick into high blower. Use a couple sensors to give more
>leeway. Normal, high, and afterburner. IOW. If a little more speed
>will keep the temp in range on SSB, there is little reason to run more
>pressure than required, but when heavy duty work like digital or slow
>scan heats things up, then go for max cooling,
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