Projector cooling

[P3D Peter Penhallow <100767.21@xxxxxxxxxxxxxx>]

A submission from Colin Clay:

Following posting of my article on projector cooling, a number of
queries were raised and I reply as follows:

>From Dr George A Themelis on 2 Jan 1997
>In practical terms, does that mean that when we switch from the
>common tungsten to halogen bulbs we will need to change air
>circulation to reduce the cooling of the halogen bulbs?
>And doesn't that increase the potential of cracking the bulb
>holders, especially the bakelite ones in the TDC 116?

It is generally accepted that halogen bulbs should operate very
hot, but double stereo projectors (such as the Brackett and the
double Hawk) turn off one pair of lamps whilst the other pair are
operating, so that slides can be changed. This means that the
bulbs of the lamps are constantly being heated and cooled when
the projectors are operating normally, thus limiting the bulb
temperatures. The lamps seem to operate for about the normal
life, so it would appear that high bulb temperatures are not
essential, and I would not expect that special baffling to reduce
the air flow over the lamps would be necessary in modified
projectors of the TDC116 type.

Regarding the bakelite lamp holders, these will have to be
changed or adaptors made so that quartz-halogen lamps can be
fitted, and I would not anticipate any problems, particularly as
the lamp wattage is halved relative to 500 watt lamps.

>From Gabriel Jacob on 1 Jan 1997
>It would be interesting to know what type of lamps he was
>referring to in his original article.

In my article I was specifically referring to the very common 24
volt 150 watt or 250 watt Q/H lamps as used in most modern slide
projectors. The low wattage dichroic reflector lamps that Gabriel
intends to use should only subject the Viewmaster chips to a
low amount of heat if efficient heat filters are used, and I am
sure that convection cooling should be adequate. The early models
of the Hawk projector used 8 volt 50 watt integral mirror lamps
(designed for use in 8mm film projectors) and no fans were
fitted.

Colin Clay
as transcribed by his faithful scribe
Peter Penhallow (to whom any typos should be ascribed!)


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