[Amps] Air temps leaving the amp.

[Al Kozakiewicz]

The EBM/Pabst blowers are specifically designed to vary speed via voltage control.  They are a bit unusual in that what one would consider to be the field winding is what turns, while the center is stationary.  Under the covers they may be brushless DC motors for all I know.

Al
AB2ZY

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Roger (K8RI)
Sent: Monday, February 03, 2014 6:53 PM
To: amps at contesting.com
Subject: Re: [Amps] Air temps leaving the amp.

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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> Amps at contesting.com
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