Re: Fans on projectors

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Paul S. Boyer  writes:
>In his discussion of upgrading a stereo projector from 500 to
>750-watt bulbs, Dr. T. mentions a user-installed switch which enables
>the fan to run which the bulbs are off.  It is suggested that the fan
>can be run after projection to cool off the projector.
>
>This practice is no longer deemed advisable by no less an authority
>than the Great Yellow Father (Kodak).  When the projector is off, no
>further heat is being added, and there is little reason to run a fan.
> Running the fan simply cools the bulbs faster, adding to thermal
>stress on their filaments, and shortening bulb life.
>
>So, when you are finished, turn off bulbs and fan simultaneously, and
>patiently wait for the for the projector to cool.  It is best *not*
>to move the projector which the filaments are hot, as they are weaker
>in the warm condition, and are more easily damaged by jarring.


I've heard about the change in recommendation too and I don't completely
agree with it. One of the original reasons to keep the fan running is to
cool the glass envelope so it doesn't slump and deform (which will usually
happen after the lamp's been turned off, if it happens). It also helps cool
the other parts of the interior of the projector, which if the fan is off
will be absorbing the heat from the still hot bulb for a while longer. True
the filament isn't putting out new heat but the heat it has already
generated isn't finished dissipating. If the fan is shut off immediately,
there would be an increase of heat in the interior from heat that is no
longer being forced out with an air stream. This build up is what can be
damaging because it slows heat dissipation from the hot components. 

Perhaps it would be ideal to run the fan for one or two minutes only,
instead of leaving it on and forgetting about it for too long? I prefer
having the option to run the fan, so having an inexpensive switch installed
makes a lot of sense.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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