[Amps] Air temps leaving the amp.

[Roger (K8RI)]

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 at contesting.com] On Behalf Of Jim Garland [4cx250b at miamioh.edu]
> Sent: Monday, February 03, 2014 10:24 AM
> To: 'Roger (K8RI)'; amps at 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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