GS1200 External Power Supply

[Paul Adsett]

Been doing some more work on my 24v 250w dc power supply for the use of the ELC lamp in the GS1200. It's still basically the same design which has been working extremely well for over a year now, but I have improved some of the ergonomics. The main change has been the relocation of the control switches to the front panel of the box, which really makes things easier, and also the addition of an LED illuminated power switch. I have also vibration isolated the cooling fan for quieter operation, even though it only powers up in pre-heat mode.
All in all I am very happy with this design and I love the so much brighter pictures it produces in the GS1200, and the use of dirt cheap ELC lamps.

[Graham Ritchie]

Look great Paul I like the idea of a volt meter as well, that power supply will last forever

[Paul Adsett]

Thanks Graham. Incidentally, the displayed voltage of 25.1 does not mean that I am overdriving the 24v lamp. I adjusted the output until I got exactly 24v measured at the lamp socket, so there is about a 1 volt drop in the 4ft connecting cable from the PS to the projector. I am getting very long lamp life with this power supply, maybe due to the very gentle warm up and the DC voltage.
I think this is the best single thing I have done to really step up the visual impact of my screenings. With a 2 bladed shutter and f1.0 lens the GS projector is a real screen scorcher! No going back to the dim EJL lamps, or even the ESC.
Thanks to you and Thomas for leading the way!

[Alan Gouger]

Very nice, Paul. It is said and do you find running the lamp on DC extends the life of the lamp? Also nice to see you are achieving a brighter image, good work. This will give the HID conversion guys some competition.

[Arnau Pell]

very nice conversion!

[Paul Adsett]

Alan, I definitely feel that I am getting much longer lamp life with this set up. I don't keep track of lamp hours so I have no hard data to present, only to say that I was replacing the 200w ESC lamp 2 or 3 times a year, whereas I have just replaced the 250 w ELC lamp after over a year. There could be several explanations for this, one being that DC power eliminates vibration of an AC powered lamp filament in the presence of a magnetic field. I have seen this happen with magnetron cathode heater coils, but in that situation you have a very high axial magnetic field from the magnetron magnets. So almost zero possibility of that being an issue in a film projector. One thing that a DC power to the lamp does do for sure is the elimination of audio hum associated with high current AC power.
The second possibility is the very gentle lamp warm up of the external power supply design in conjunction with an appropriate resistive load. In my power supply the lamp filament takes several seconds to attain a nice warm glow.
The third possibility is that the 250w ELC lamp is, for some reason, inherently more robust than the existing 200W ELC lamp.
Whatever the reason, the longer lamp life I am experiencing with this particular ELC conversion is welcome icing on the cake!😊

[Paul Adsett]

Further improvements have now been carried out. A digital hours meter has been added to monitor lamp run hours and total equipment run time. The lamp life can be reset to zero hours when replacing the lamp, by means of the little push button. Lamp hours are only measured at full on voltage, pre heat hours are ignored as the life at 2 volts preheat would be huge. Total equipment run time is not resettable.
Also the addition of a blue pilot lamp which lights up when the unit is in lamp preheat, and also two handles to facilitate lifting of the unit ( its not heavy at all, but the handles make grasping the unit a lot easier).

[Shane C. Collins]

That external power supply is a thing of beauty Paul! These sorts of custom units are interesting to me. The Elmo GS-1200 sticker is also a nice little touch! How long did it take you to build this unit, and have it 100% functional?

[Paul Adsett]

Shane, I had the breadboard circuit up and running in about a week. I soon realized that I had to incorporate a pre-heat circuit for the lamp, not only to extend lamp life but also to enable the DC switching power supply to even start up at all. So the full up power supply and control circuit took about a month to get assembled into its box. Then I decided to provide forced air cooling to the finned heat sink so that there was no limitation to how long the unit could be run in the pre-heat mode. And I also added an over-temp thermostat that would shut everything down if the fan failed. So at that point I was about 6 weeks into the project. Since then it has been operating flawlessly for over a year and its just in the past couple of months or so that I have re-configured the front panel to include the digital voltmeter and digital lamp hours meter and pre-heat pilot light , and finally the handles. I think the design is now complete (famous last words) !😃

[Alan Gouger]

Hi Paul, thanks for the additional information. To add to Shanes's comments, can you go into more detail about the pre-heat circuit? Are you feeding the lamp with limited voltage? How did you come up with this? I think you are on to something here. You have me doing some experimenting and the gain in extra light output is enough to forgo considering a Zenpow conversion plus the ELC lamp delivers better color rendition versus the Zenpow. I like what I am seeing so far. Of course, my setup is not anywhere as elaborate as yours. You have a polished-looking product ready for resale. Good work.