Re: 116 vs. 716 and more (part III - conclusions)

[P3D Steve Spicer <s.spicer@xxxxxxxxx>]

From: P3D P3D Patrick Boeckstijns  <pboeckst@xxxxxxxxxxxxxxx>
>
>Remaining question :
>How do you adapt a TDC to accept these hallogen lamps ? It sounds like your
>friend Max just plugged them right into the existing TDC sockett.:-) But I
>guess it's not that simple. :-(
>
>Can you please tell how to make the 250W hallogens fit the old TDC sockett's.
>I'm interested for three reasons: availability of the modern lamps, swiching
>from 110 V(USA) to 220 V(Europe) and of course the whiter light.
>Thanks.
>


Hello Patrick

It would be nice if it was as simple as just plugging them into the
sockets, but this cannot be done. To use these lamps in the TDC projectors,
the old lamp bases need to be removed, and new bi-pin bases that suit the
24V/250W or 36V/400W lamps need to be installed (I would imagine that some
special brackets may need to be made to mount the new bases to the
projector chassis). Of course the position of the lamps needs to be
adjusted accurately in relation to the existing condenser and mirror.

The most costly aspect of this conversion is providing the 24V or 36V
supply to the lamps (the lamps themsleves are cheap, only about US$8-10 for
the24V/250W units). Usually this is done with a transformer, although I
suppose a switch-mode power supply might be another possibility. In the
case of Max's TDC-716 projector, he was lucky enough to use spare parts
from a Rollei slide projector as the transformers. And indeed, he even
managed to fit the two transformers (one for each lamp) inside the base of
the TDC, so that the unit looks completely unmodified from the outside!
(The fan housing in the base is very big on the TDC's).

I think that he was lucky, and that it would be unlikely that any other
transformers would have fitted. I also suspect that transformers from
commercial projectors are designed to deliver the rated power with the air
from the fan cooling the transformer. Such transformers can be made smaller
and cheaper, but may not work for very long if a constant air current is
not provided. The Rollei 250Watt transformers were quite small.

Another option is to place the transformers outside the unit. For the USA,
it may be economic to use an auto-transformer, which is cheaper and
smaller. These  only work out well if the step-down ratio is between about
0.5 and 1. So with 110V line volatge, and with 2 lamps in series, 48Volts
would be required for the two lamps (or 72V for the 400W units).

John Bercovitz has has previously raised the issue of "filament notching"
when operating the two lamps in series. To circumvent that, I would put a
tap at 24Volts on the auto-transformer, and feed that to the junction point
of the two lamps in series. (Then the inputs are: 0 and 110 Volts. And the
outputs are: 0, 24V & 48V). The 24V tap carries zero current if the lamps
are matched, and very small correction current if the lamps become
un-matched, or full load current if one lamp fails.

If you need to operate from 220Volts in Europe (we have 240V in Australia),
but the original fan motor is 110V, then a 110V tap on the primary of the
lamp transformer could be arranged to feed the original fan without
modification.

Given the line-voltage drops noted in a post by DrT, it may be prudent to
provide some taps on the primary for various lines volts (like 105, 110,
115). These could double as a lamp-life/brightness control too. Although in
Europe this would less troublesome owing to the higher line-voltage.


Steve Spicer
Australia













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