AC fans do help in the UNIX pc (was Re: fan mail)

[Lenny Tropiano]

In article <157 at bongo.UUCP> julian at bongo.UUCP (julian macassey) writes:
|>
... [ finding out about the two-speed fan feature (or mis-feature) ] ...
|>
|>    This  was  a revelation.  I  mailed Jim Gottlieb  (jim at denwa) 
|>about this and he told me that yes  indeed, there was a two speed 
|>fan and it was controlled by a thermistor, possibly on the  Power 
|>Supply board.
|>
Yes, this is quite true.  I had an up-close-and-personal experience
with the fan problems.  As many of us UNIX pc veterans know, the fan
is probably the weakest link in the entire computer.  I've discussed
this on occasion here, but since it was brought up again, I'll be
glad to reiterate.  The two-speed fan "feature" does have one advantage,
and that is to only reduce the noise the machine makes.  The major
disadvantage is that it seems to cycle on and off in semi-warm 
environments, therefore not doing much for noise output.  The cycling
of the fan from low to high speed seems to add the extra wear on the fan.
I'm not sure the fans actually just burn out, but instead they
will stop running (or don't start up when initially turned on) because of
extra dirt around the casing of the fan.  When the fans switch to low
speed, and there is a lot of dirt on it, it will sometimes just halt.  This
is what causes the "melt-down" ... trust me this is very unpleasant,
the dimple in my case proves that.  Luckily I was there to power it down
when it was going on and off!!

|>    Recently  on  this  group there  has  been  discussion  about 
|>ripping out the installed DC fan and inserting an AC fan from Rat 
|>Shack. Obviously unless modifications were made, any change to an 
|>AC fan would loose the 2 speed feature. It could be done, I could 
|>do  it  with a bit of fiddling  -  schematics would help  though. 
|>Obviously  for a margin of safety, as a single speed fan,  the AC 
|>fan at single speed would have to shift as much air as the DC fan 
|>at   high  speed.  [...]

Yes, the Radio Shack 120VAC 35 CFM fan does work better (much better)
than the unstable DC fan.  Now I'm sure there will be people out there
who have had UNIX pc's for X amount of years and haven't changed
their fan, and never had a day's worth of trouble.  I'd rather not
take that chance ... My machine runs much cooler now, even with 3.5MB of
RAM, a VOICE POWER board, and a DOS-73 co-processor.  My room temperature
has gotten up to (and over) 80 degrees... it's lasted through that. 
I do have air conditioning now for this hot summer days ... I'd rather
not push my luck that much ;-)

Putting the AC fan in place of the DC fan won't really be a bad move,
since having it will have only one speed (but a faster speed than the DC fan, 
even at the highest speed).  You really don't need schematics for this,
since I just tied the two leads of the AC fan to the back of the UNIX PC
where the AC comes from the power switch.  Disconnect the DC fan from the
power supply, tape up the old connector, and that's it.  Just make sure
that you place the new fan such that the air is blown OUT the back, and
NOT into the machine...

-Lenny
-- 
Lenny Tropiano             ICUS Software Systems         [w] +1 (516) 582-5525
lenny at icus.islp.ny.us      Telex; 154232428 ICUS         [h] +1 (516) 968-8576
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