[ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity

[Paul Christensen]

> Re 12V DC fans, I recommend using a zener diode instead of a resistor to
> slow them down.

Jim,

Yes, I had a problem with initial start torque and noted that the initial 
in-rush of current is quite high at start-up.  I had to choose an R value a 
bit lower than I would have liked just because of that reason.

Re: using a zener on DC fans -- Is that connected in traditional fashion? 
IOW, a series R from the power source, followed by the reverse-biased zener 
diode in parallel?

Paul, W9AC

----- Original Message ----- 
From: "Jim Garland" <4cx250b at muohio.edu>
To: <eto_alpha at mailman.qth.net>
Sent: Thursday, March 26, 2009 8:23 AM
Subject: Re: [ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity


>I too have been looking for a low volume very quiet muffin fan for
> exhausting air from a desk compartment that houses a computer. I recall a
> number of years ago that there was a muffin-type fan called a "whisper" 
> fan
> that was extremely quiet and ran on 120VAC. However, I've not been able to
> find it. I ended up just choosing the quietest fan in my junk box and
> slowing it down with a light dimmer, but it's still too noisy.
>
> Re 12V DC fans, I recommend using a zener diode instead of a resistor to
> slow them down. One doesn't lose starting torque that way, which aids
> startup at reduced voltages.  120VAC fans can be slowed with series
> capacitors, though I've normally used filament transformers to buck 
> 120VAC.
> Again, this preserves starting torque.
>
> 73,
>
> Jim W8ZR
>
>> -----Original Message-----
>> From: eto_alpha-bounces at mailman.qth.net [mailto:eto_alpha-
>> bounces at mailman.qth.net] On Behalf Of Paul Christensen
>> Sent: Thursday, March 26, 2009 4:45 AM
>> To: ETO_Alpha at mailman.qth.net
>> Subject: Re: [ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity
>>
>> About two years ago, I rebuilt my Alpha 86.  (BTW, Glenn and Molly were
>> very
>> helpful during this time.)  Part of the re-build consisted of finding a
>> fan
>> that was reasonably silent, but produced adequate air flow.  I must have
>> experimented with nearly a dozen fans.
>>
>> All ball-bearing fans were too loud.  I ended up with a sleeve bearing
>> type
>> at about 50 CFM.  Even then, the noise could be heard over the blower.  I
>> ended up slowing the rotation by placing a 10W chassis-mounted power
>> resistor (Dale/Vishay), in series with the positive fan lead.
>>
>> My next attempt will be inclusion of a temperature-sensing switch.  I had
>> a
>> similar issue in cooling an HP 6652A linear station power supply.   I
>> decided to try the circuit that appeared in the June, 1994 issue of QST.
>> This circuit works very well and uses MOSFET switching of the fan.  A
>> 10K-ohm NTC thermistor is used to bias the junction of a generic NPN
>> switching transistor that activates the MOSFET.  Settings are repeatable
>> and
>> the circuit is very stable in an RF environment.
>>
>> Paul, W9AC
>>
>> ----- Original Message -----
>> From: "Glenn AE0Q" <gm5bkc at gmail.com>
>> To: <ETO_Alpha at mailman.qth.net>
>> Sent: Wednesday, March 25, 2009 10:32 PM
>> Subject: Re: [ETO_Alpha] Alpha 87A/89 Muffin Fan Capacity
>>
>>
>> Hello Bob,
>>
>>  When we (Alpha) recently posted a fan kit on eBay I got the specs
>> for the fans that we currently have, here is it all:
>>
>> "External Muffin Fan Kit, 230V 50/60Hz, 82 CFM;
>>  for mounting on the rear opening of the Alpha 87A and 89 Amateur
>> Radio amplifiers, pre-wired with lug connectors and includes mounting
>> hardware.  This fan pushes cooling air into the amplifier, aiding air
>> flow through the internal tubedeck blower and reducing the exhaust air
>> temperature of the tubes."
>>
>>  The CFM rating might be slightly different from the Etri 5-blade
>> fans that we used until last year.
>>
>> 73 - Glenn AE0Q
>>
>> On Wed, Mar 25, 2009 at 8:02 PM, Robert Dorchuck W6VY <w6vy at yahoo.com>
>> wrote:
>> > Anyone know the specs for the optional muffin fan for the Alpha 87A or
>> 89?
>> > In particular the CFM rating.
>> >
>> > Thanks,
>> > Bob W6VY
>> > ______________________________________________________________
>> > ETO_Alpha mailing list
>>
>> --
>> "Remember, any tool can be the right tool!"   Red Green
>>
>>  AE0Q / V31RY              ex: GM5BKC, ZB2WZ, SV0WY, WA0VPK
>>  ae0q at arrl.net      --SOWP 5558-M, ARRL LM, QCWA LM, OOTC, NCVA--
>> http://www.radiotipsandtales.com
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