How should I run an 82V projector lamp on 120V without a transformer? « on: October 05, 2023, 08:31:50 AM » Author: HIDLad001
Should I use another incandescent lamp in series to limit the current? If so, what wattage? The lamp I want to run is 360w.
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #2 on: October 05, 2023, 11:47:31 AM » Author: HIDLad001
I have a fan from an old microwave oven that I could use, and yes these (even with the fan) do get very hot. But this overdriving also makes them incredibly efficient, because as you increase the voltage to an incandescent lamp, it gets more efficient (but at the cost of service life). But somebody also told me that they had an overhead projector that ran the 82V lamp off of a tap on the fan motor winding, and I have seen overhead projectors with 82V transformers, so maybe they are sometimes ran on 82V to increase the service life.
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #3 on: October 05, 2023, 02:14:41 PM » Author: Robotjulep
Don't run 82v halogen lamp on 120v. It will burn out in seconds within testing. I had ruined my MR-16 Osram 360w 82v lamp doing that. If you took apart an old overhead projector, they contain a fan and a diode. The diode is wired in series with the lamp and steps down the voltage to 82v. They can also be used to run incandescent lamps at 82v. I have 1 Apollo 410w 82v lamp and a Sylvania 250w 82v lamp though. I don't think I have a use for them as I don't have a proper enclosure to operate them safely. Now that you brought up halogen projector lamps, I have quite a few in my collection and will get to posting them!
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #4 on: October 05, 2023, 02:33:45 PM » Author: HIDLad001
I understand that the diode would reduce the voltage because it is only rectifying half of the side wave while the other half is not present, therefore reducing the RMS voltage. I do probably have some suitably rated high-power diodes, so I will try that with a normal incandescent lamp when I get the chance.
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #7 on: October 05, 2023, 09:19:02 PM » Author: HIDLad001
Yep ENX spec sounds right for 360w. The lamp would be running off of the fan motor much like how you can get different voltages off of the taps of an autotransformer HID ballast. I also wonder how much these lamps flicker when run half-wave off of a diode, although since it is a filament lamp being run on 60Hz, probably not a lot.
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #9 on: October 08, 2023, 11:49:22 PM » Author: Robotjulep
Quote from: HIDLad001 on October 05, 2023, 09:19:02 PM Yep ENX spec sounds right for 360w. The lamp would be running off of the fan motor much like how you can get different voltages off of the taps of an autotransformer HID ballast. I also wonder how much these lamps flicker when run half-wave off of a diode, although since it is a filament lamp being run on 60Hz, probably not a lot. I haven't seen my incandescent or halogen lamps flicker when using the diode. But why are some overhead projector bulbs 360w 82v and others 600w 120v? Is it so the halogen capsule is so small that it can fit in an mr-16 reflector when a 120v lamp will be too big?
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #10 on: October 09, 2023, 10:48:29 AM » Author: AngryHorse
Tungsten lamps were quite hardy things, I remember running a bank of 24 x 25 watt common candle GLS on my Petter AVA back in my rally days, sometimes the generator would sneak up to 300 volts during the day, for hours on end, and not one of the little candle lamps burned out!  Although I did fry Jo’s phone charger on it once at Llandudno Transport Festival at 300 volts!  , she wasn’t suitably impressed!
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #11 on: October 09, 2023, 11:50:22 AM » Author: HIDLad001
Quote from: Rommie on October 06, 2023, 07:33:03 PM Try to get a Variac, they are invaluable for things like this. Here in 240V land, I can run a lamp at any voltage from 3V or so up to 280V. I would love a variac but I can't find a good one that's UL listed, and it would be kind of impractical for a semi-permanent installation.
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	Re: How should I run an 82V projector lamp on 120V without a transformer? « Reply #13 on: October 09, 2023, 03:06:56 PM » Author: HIDLad001
Thanks for the idea! Do you know where I can get the 85V buck transformers as well?
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