Today I saved two older Thorn industrial high bay fixtures from being eventually thrown into the recycling bin. They are not complete sadly, but they are complete enough to the point where they are useable. They are missing their reflectors, however I think I know where I might be able to get my hands on a couple if I ask nicely!
I can also make custom fixtures with them, but I mostly wanted them because I have always been fascinated by high power discharge lamps. I do not have a actual use for ones this big, but they are cool to have and that is reason enough for me to grab them, especially when they were free and headed to the scrap!
But I have a few questions for those of you who have more experience with metal halide setups than I do. They are quite old, the fixtures have Thorn MBI ballast, 400W. They have ignitors with date code 1975 on them, so that puts a good age on the things. I am reasonably sure that the ignitors are dead, because I Cannot hear them make any sound when I plug the fixtures in. But I have not been able to confirm this sadly, since this brings me to my second problem. The fixtures came with two metal halide bulbs, Philips HPI 400W. Both bulbs appear completely dead. I even tested them on a known good HPS setup with a known good ignitor and ballast, nothing. They are dead. When I look into them, sure, the arc tubes have some hours on them, but not enough to where I would think they should be dead. I also think these high power bulbs have a thin metal wire going from the support structure and into the top of the arc tube, as a sort of fuse, if the outer bulb gets broken, the little nichrome wire will burn open to prevent the bulb from operating without a outer bulb for safety reasons. But I cannot see it, so I am suspicious of why... So I need to buy or ask around for some new bulbs for continuing the testing. But, this made me suspicious, why are they dead? super high hour? Wouldn't they power up and then cycle? So I measured the resistance through the ballast, from live in to the live pin in the lamp socket. 1.9 ohms. This seems rather low, doesn't it? Yes, this is high power stuff, but I would still expect there to be a little more DC resistance through the ballast, or is this fairly normal for a 230V 400W metal halide setup? Or are my ballasts shorted, and have blown up the bulbs? I don't really have any good way to test the ballasts to see if they actually limit current, these are so big that I can't just wire a normal high wattage light bulb in series to it and test to see if it limits current. I might be able to connect a heater or something to the output of the ballasts though, and measure what current goes into it to see if the ballasts still do their thing.
The third problem, is those old ignitors. I am sure they are dead by now, because even without a working bulb I Should still be able to hear them striking, right? Well, I cannot hear anything. the fixtures are silent when I plug them in, maybe a tiny buzz coming from the capacitor, but I am almost certain that the ignitors are dead. And they are some weird ignitor I have never seen before, I am used to the standard types that you simply connect in series with the ballast more or less, but this is entirely different, I am not even sure if modern replacements exist? Perhaps you guys who are more experienced within metal halide knows what kind I need. Or if I can retrofit them with the more standard type, since I do have a couple of those on hand
Thanks in advance, I hope I can find some bulbs
