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New Power Supply

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  • New Power Supply

    Although I have been using a converted 16mm to run the GS1200 lamp for the last few years. I came across another slide projector Leitz Pradovit 253series that was being scrapped. The mechanics had given up working long ago, along with a burnt out lamp socket. I pulled it apart mainly for the transfomer. Its been a little project to make up another power supply just for the fun of it. The only thing I bought for it was a 15 amp illuminated rocker switch. Yesterday I finished it and compared the voltage output with the old B/H power supply.

    To my surprise with a 24volt 250watt lamp running the voltage drop was more than I thought it would be on low 20VAC on high 21.5VAC. Although the Leitz Pradovit slide projector never had a choice of low and high, only high. I did find a lower tapping. Checking the voltage again this time with the transformer from the Leitz and with the 250watt lamp running I got 22VAC on the low and a 23.5VAC on the high, ah! that's better.

    So now I have retired the old X B/H 16mm power supply with this one. I will run the Osram Xenophot ELC 24volt 250watt lamp at the 23.5VAC from now on and se how that works out.

    To be honest I had forgotten about the voltage drop when the lamp was on, although the old B/H did show 24 volts without the lamp running I did not think it would drop that much, adding another 2 volts bringing it up to a running voltage of 23.5VAC should be bit brighter. A good test would be some Scope films for home use this should be fine

    Glad to be at the end of projects both at the Historic Park and home, time to chill out
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    Last edited by Graham Ritchie; January 08, 2024, 10:17 PM.

  • #2
    Nice work Graham!


    • #3
      Thanks Janice


      • #4
        Graham, you should see a pretty significant increase in brightness going from 21.5v to 23.5v. My DIY power supply has some voltage adjustment capability and I slightly overrun my ELC lamps at 24.5v for a really bright picture. So far I am up to just over 30hrs on that lamp without failure.


        • #5
          Thanks Paul

          Its amazing how two extra volts makes. you have got me thinking that one higher tapping not being used on that transformer was I think I will have to check it again is 27.5 VAC, now allowing for a voltage drop with the lamp running that might bring it to around the 25VAC. I don't no at this stage but will remove the power supply into the garage and hook up a 24V 250Watt lamp and see what the voltage reading is.


          • #6
            Hi Paul

            Without trying that higher voltage as yet. I did run the projector with a 1200 foot of shorts running the lamp at 23.5 Volts. It looks nice and bright, so wont go any higher. What I did find that the power supply was getting a little bit warm, not to bad, but as its summer at the moment with the temp around 86F even inside when I ran the film, so will add a cooling fan to the box. That also had me thinking of what you did to improve the cooling of the GS1200 removing the speakers to improve air flow as well.


            • #7
              Graham. I have no measured data to quantify the effect of speaker removal on cooling air flow and temperature in the GS1200. It just seems to me that opening up those speaker grills has the potential to be quite beneficial. It certainly cant hurt, and it saves some significant projector weight ( always welcome!).
              In my DIY power supply I have an aluminum heat sink with forced air cooling from a 24vdc fan. Keeps everything nice and cool.


              • #8
                Hi Paul

                I bought a couple of 12 volt fans today, drilled a hole and fitted one also a grill on the top on the power supply. The other fan can go into the GS1200 in place of a speaker. I will get around to that very soon. My thinking is the same more ventilation the better
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                • #9
                  Finished with extra cooling yesterday removing the GS1200 speakers, that was simple enough and store them away to re-install at a later date. Fitted a cooling fan blowing inwards, using the same speaker lugs. Spent a lot of time cleaning the projector fan, those blades were pretty bad. I attacked them with cotton buds and a old tooth brush, finishing of with a light blast from my garage compressor. Refitted the lamp, gave the projector a final clean and lube, then refitted the back cover. The 12 volt power supply is wired to both 12 volt fans one being in the power supply the other in the GS1200 back cover. As soon as I switch on the power supply the fans will run automatically.

                  The end result seems good, I am all for keeping electrical things cool, one thing we should all remember that the actual projector cooling fan needs to be kept clean for it to work efficiently, even without doing any extra like I have done, keep an eye on those fan blades and make sure they are kept clean.

                  Anyway back to running films, oh! one thing I remember about moving the projector yesterday was how heavy the thing is, its really hernia material moving it around.
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                  Last edited by Graham Ritchie; January 14, 2024, 02:32 PM.


                  • #10
                    I work on computers frequently and the subject of ventilation can be controversial. I remember being told that when working on a machine, do not leave the side panel of the case off for long periods of time. It disrupts the intended air flow and can result in over heating.

                    It's a "do as we say, not as we do" sort of situation... In practice, you probably aren't going to solve your cooling issues by removing the side panel of your PC.
                    The principle of air cooling, as described well in this ExtremeTech guide, is to create either positive or negative air pressure within the case. Both have pros and cons, and there's tons of disagreement over optimal fan placement, but the point is: bring cool air in, heat it up, and get it out. When you remove the side panel, you disrupt the intended airflow of the case—whatever it may be—and also invite more dust to settle on your components. So it's not recommended.
                    Just google, "is it ok to leave computer case side panel off?" for more discussion of optimal ventilation.

                    When modifying ventilation, a thermometer at the end of a wire running to a readout panel can be helpful. You can place the thermometer in different locations to find hot spots within the interior when the machine is running.


                    • #11

                      The problem can sometimes be getting the cool air in to begin with, some of those projectors draw the air in from a vent down near the transformer. As the projector is running the transformer will get a bit warm. The problem with that is the air is no longer cool before it gets blown towards the lamp. Drawing the air direct from the outside is the best bet as you mention Ed above "bring cool air in, heat it up, and get it out" When you look at some of the projectors that cool air flow can be a bit restrictive.

                      Its certainly an interesting subject, an eg the 36volt 400watt lamp I use on the 35mm is designed to run hot, blowing cold air onto the hot glass will cause the lamp glass to go black at that point of cold air contact, however drawing air away from the lamp rather than blowing towards it, in this case seems to work the best


                      • #12
                        Well done Graham! Looking again at your pics though , I think you should remove the mesh cloth screen in front of the fan as it will greatly reduce air flow from the fan.

                        ​I think I will do the same thing to my GS1200's. I love these DIY improvements which are totally reversible, if required at a later date to sell the projector in its original condition.
                        Ed is right of course about the potential dangers of disrupting the original air flow dynamics, and I can appreciate that leaving off a computer cover could reduce air flow velocity and heat transfer coefficients on critical components. In this case, the addition of a cooling fan to the GS1200, I feel that it can only be beneficial. The addition of even low velocities of cool air into the interior electronics will greatly lower component temperatures and, as Graham has pointed out, the projectors own internal fan will now be getting cooler air, thereby lowering lamp house temperature. The benefits will not be seen in projector performance but in long term reliability

                        Last edited by Paul Adsett; January 15, 2024, 09:31 AM.


                        • #13
                          This looks very good Graham. Many Years I did it like you with the 250W ELC Lamp from Osram.
                          But since 2018 I found a much brighter Light Way. I use the Two Pin Base Lamp 250W EHJ from Osram in a cut of Mirror of the ELC Type.
                          It gives a much brighter Light than with te ELC Type. I can give 25,2V on this Lamp and the Life is 45 to 47 Hours. It is very bright on my 9 foot Scope Screen.
                          Attached Files


                          • #14
                            Graham, I have done some quick testing with a 3 ins square vanaxial fan bolted up to the speaker grill on the GS back cover, similar to what you have done. I found that when the fan is mounted on the inside of the grill, that is the air is being sucked through the grill, that the fan is actually running in a stall condition with minimal air flow coming through, and it is also noisy under this condition. If you attach the fan on the outside of the back cover , so that the air is pushing through the grill, you will get far better air flow, and the fan will be quieter. And the mesh cloth should be removed as it will severely reduce air flow.


                            • #15
                              Thanks Paul

                              I will do as you suggested.


                              I did try cutting a hole in a mirror and having a 250 watt lamp sliding back and forth through it. It did work but not enough. I think I used the wrong mirror that was my mistake. I never did get back to that project, but still have the complete assembly sitting on the shelf. The hardest part without damaging the mirror that I remember was cutting the hole. Also now I remember the lamp filament on the 250 lamp I used was horizontal and not vertical. I am pretty sure had I used a lamp with a vertical filament the light reflecting of the mirror would have been a lot better. I did try it at the time on the GS1200 even moving the lamp back and forth inside the mirror with the projector running still did not work out.

                              I might return to it one day Thomas, I must say thanks for the idea of moving the present lamp back that extra 10mm from the gate, it really did make a difference when using those 250watt lamps.

                              I will get back to removing the speaker grill later today Paul, thanks for the advice.