fan mail

[Howard E. Motteler]

In article <157 at bongo.UUCP> julian at bongo.UUCP (julian macassey) writes:
>
>		    This brings  me to a concern that  I have had 
>since  I  first  turned on  my  3b1.  I think it  runs  too warm. 

>I believe as far as electronic equipment is concerned, exhaust air
>should not be warmer to the touch than ambient and heatsinks 
>should never get uncomfortably warm.

Depends on the equipment: you could bake a potato (or a whole chicken)
on the exhaust heat from some of the radio or TV transmitting tubes I
used to work around.  Now, you're not pumping kilowatts thru this
little box, but you're consuming, say 150 to 200 watts, and *every
bit* (well, at least 99%) of this power ends up as heat, and gets
blown out the back.  (Not true, you say?  Where do you think that
energy goes!)  So "warm" is about right, for the exhaust air--the
waste heat has to go somewhere.  The other major energy consumer/heat
producer is the flyback transistor(s) in the monitor, which should
also feel warm.  About the same as a TV...

Heat sinks can run pretty hot--an old rule of thumb from my technician
days was to moisten a finger (the thumb was already burnt) and give
the sink a quick touch--if you get sizzle, things are too hot, but
fast evaporation is ok.  But beware of heatsinks in switcher supplies:
some of them may be "hot" in more ways than one!

> . . .  heat kills electronic  components - sooner  or later. So if 
>you hate fixing stuff, or just having it die, keep it cool.

Absolutely correct, but what's hot to you may be cool to an SCR that's
rated to dissipate heat most effectively while running at 70 C.

>If I can get an AC fan that really pushes wind, I will remove the DC 
>fan  and replace it with the super AC fan.  This will also remove 
>some  of the load from the  Power Supply which will  further help 
>with cooling - assuming the fan is powered by the Power Supply.

I think even the cheap R.S. AC fans are rated at more CFM than the
stock DC fans can give on "high"=12v.  On low the stock fan(s) are fed
about 9-10 V at 100 to 150 ma.  If you're really worried, you might
put a *pair* of AC fans in, acting as exhaust fans, in both fan slots.
(In "parallel"-- not in series!)

-- 
Howard E. Motteler       |  Dept. of Computer Science
motteler at umbc3.umbc.edu  |  UMBC, Catonsville, MD 21228