On 2/3/2014 10:33 AM, Al Kozakiewicz wrote:
Yes, that is the defining characteristic of an induction motor!
The only way to vary the speed of such a motor is either by changing the
frequency of the power source or with a variable speed transmission.
How does Emtron do it? They use a sensor in the exhaust, just above the
tube and there is a substantial difference between high and low speed.
When that thing kicks into high it is not quiet.
73,
Roger (K8RI)
Al
AB2ZY
________________________________________
From: Amps [amps-bounces@contesting.com] On Behalf Of Jim Garland
[4cx250b@miamioh.edu]
Sent: Monday, February 03, 2014 10:24 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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