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

Today, I found a reflector that I was allowed to take, so now I can make one of them a complete unit! I also was allowed to have one 400W HPL bulb, which means I have been able to test run one of the ficxtures today with great success. Since mercury bulbs do not need a ignitor, they fire right up despite broken ignitor The warmup time is so much faster on this high power stuff than on smaller mercury bulbs, too! The fixture draws a truly insane amount of apparent power on startup, causing my inverter to trip out unless I knock a few volts off the output. (I run all my lamp related experiments from my solar power system, for those curious why there is a inverter involved.) Adjusted to 220V instead of 240, it has no problems handling the high apparent power with a cold bulb. as the bulb warms up, the apparent power decreases dramatically, and eventually it settles at 490-500VA, with an Active Power of 420 watts including ballast losses. Not at all bad! (I also have some voltage drop in my cables, so the voltage at the lamp was 213 volts. so that is why the real power consumption is a little low. If I bump the voltage back up so I have 230V at the fixture after the VA has dropped, the power draw is closer to 460-470 watts, which seems about right. So I believe my ballasts are both perfect. The other fixture should also work fine with a mercury bulb, the ballast measures the same value on my ohmmeter. I havent tested it yet

The brightness is truly insane, and its important to keep in mind that a mercury bulb only produces half the light of what I would get with a actual Metal Halide bulb. So I am extremely excited to try metal halide bulbs one day in the future once I get this ignitor situation figured out...

Hmmm, you need a halide😀, I’d be VERY surprised if 1970s Thorn ignitors are dead, Thorn gear used to run literally forever 🤔
Do you have a SON you could test the ignitors on just for a second?
I’ve had Thorn gear that’s been underwater for years, (including ignitors), and it STILL works when thoroughly dried out 😎

The ignitors are indeed dead. No HV pulses at all. I've tested with a known good 400W HPS bulb too, nothing. I think the failed ignitors is the reason why these were once taken out of service.

HID ballasts are about 90% efficient. (Fluorescent magnetic ballasts about 80% old ones, 85% new ones). So 400W ballast have about 40W losses

In modern magnetic ballasts the winding resistance accounts for approx 80% of the ballast losses. In old ballasts it may be a little more towards the core but probably not by a lot

80% of 40W is 32W

32W = I^2 R. For 400W Halide on Mercury gear I=3.5A

R = 32/3.5^2 = 2.6 Ohms

Resistivity of Copper at ~100C (working temp of ballast) is about 1.3x higher than cold. 2.6/1.3 = 2 Ohms

So your 1.9 Ohms is about right

Since the ballasts are the typical 2 wire serial reactor ballasts, a standard superimposed ignitor should work fine with them if you really want to run pulse start metal halide lamps with them. Additionally, if you want to keep startup current down to a minimum, I recommend adding power factor correction capacitors to your fixtures as improving the power factor of your fixtures can help keep current draw and apparent power draw as low as possible. This can help minimize the possibility of your inverter tripping and can help you use one of a smaller size.

I bought some standard Philips 0.75kV two-wire ignitors, and ignored the 3rd wire in the fixtures which is just a neutral going to the terminal block. That works just fine, it seems. Flawless ignition of MH.

I'm not going to use these fixtures everyday, they're just really cool because of their sheer scale. They'll be more of a display piece that I'll power up on occasion. It's not realistic to run these as actual lights at home, while they do output incredible amounts of lumens, the power usage would just be too much. I can run one but definitely not more than that.

They do have working power factor correction capacitors, but the capacitive current at startup trips the inverter. They draw 10 amps or something capacitively before the lamps warm up, it'll never work to power these off of these small inverters. Because these fixtures won't be used regularly, it's easier just to run them from a old-school generator set

I don't understand how they manage to power entire industrial halls with these, they're fused with 16 amps per phase and that's like almost nothing, the fuses should theoretically blow from the apparent power on startup. It's absolutely ridiculous to have these installed in a small factory hall like the place I got these from, fluorescent lights would have been much more energy efficient and provided more than enough illumination, heh. There is 76 of these installed in that hall, so that's a insane power draw. They've all been retrofitted with LED bulbs now, but even those use 165 watts each. And their lumen output is lacking compared to the MH bulbs. It feels like the power usage just for lighting alone, the cost of that, far outweighs what they earn producing their item.........