A few months ago, I asked about whether it's possible to ballast a 125W HPMV lamp using a resistor (incandescent/halogen) in series.
I completely forgot about ti and finally got around to trying it out and photographing it.

As per suggestions from quite a few people, I wanted to use a 500W/240V halogen but I had none at the time. Instead I got myself some used 36W fluorescent chokes, and as suggested by @RRK, added three in parallel to use as a ballast for the lamp. This worked just fine  ...until I put my hand to them and noticed them getting extremely hot within the first minute, so I decided to kill power to it. At least I saw the lamps lit for the first time.
In hindsight I can say this is due to the arc voltage difference—the MV lamp requires nearly 20V more than the ballast is designed for (100V vs 125V). However this allowed me to take a look at the lamp in operation and this satisfied me for a while.

A few days ago I got around to doing it the right way and used a 500W halogen lamp instead. And, well, it's a decent solution. Here is the warmup of a 125W HPL-N running with a 500W/240V halogen in series. It kept cycling horizontally so I moved it to V-BD, where it stays lit for longer (around 3 minutes) but still cycles.  Anyone know why this happened?



It was rather difficult to get the color of the lamp right on camera but it is a 4500K-5000K cool white color with decent CRI, definitely not 4200K though and a 942 CDM-T is worlds apart. The camera over-exaggerates the colors, it looks like a cyan-pink during warmup and there's almost no visible yellow that the camera has captured at full brightness (don't mind the three chokes, that's to get the holder to stay upright).

I have tried this with a Crompton 125W HPMV too and it works perfectly in any position, which is a bit surprising since I'd expect the Crompton lamp to be of lower quality. I didn't take pictures of it though, it's quite time-taking. This is done though .
It was a pretty interesting experiment, just wish I could've gotten the philips lamp to work as well.

A few months ago, I asked about whether it's possible to ballast a 125W HPMV lamp using a resistor (incandescent/halogen) in series.
I completely forgot about ti and finally got around to trying it out and photographing it.

As per suggestions from quite a few people, I wanted to use a 500W/240V halogen but I had none at the time. Instead I got myself some used 36W fluorescent chokes, and as suggested by @RRK, added three in parallel to use as a ballast for the lamp. This worked just fine  ...until I put my hand to them and noticed them getting extremely hot within the first minute, so I decided to kill power to it. At least I saw the lamps lit for the first time.
In hindsight I can say this is due to the arc voltage difference—the MV lamp requires nearly 20V more than the ballast is designed for (100V vs 125V). However this allowed me to take a look at the lamp in operation and this satisfied me for a while.

A few days ago I got around to doing it the right way and used a 500W halogen lamp instead. And, well, it's a decent solution. Here is the warmup of a 125W HPL-N running with a 500W/240V halogen in series. It kept cycling horizontally so I moved it to V-BD, where it stays lit for longer (around 3 minutes) but still cycles.  Anyone know why this happened?



It was rather difficult to get the color of the lamp right on camera but it is a 4500K-5000K cool white color with decent CRI, definitely not 4200K though and a 942 CDM-T is worlds apart. The camera over-exaggerates the colors, it looks like a cyan-pink during warmup and there's almost no visible yellow that the camera has captured at full brightness (don't mind the three chokes, that's to get the holder to stay upright).

I have tried this with a Crompton 125W HPMV too and it works perfectly in any position, which is a bit surprising since I'd expect the Crompton lamp to be of lower quality. I didn't take pictures of it though, it's quite time-taking. This is done though .
It was a pretty interesting experiment, just wish I could've gotten the philips lamp to work as well.

if the ballasts where getting overly hot, that will be for other reasons, a higher arc voltage will actually cause a choke to run cooler, not hotter as less voltage is dropped across the choke so less current flows through it, you can see this in visual form with the 500W Halogen setup how the halogen dims down as the lamp warms up as the lamp voltage goes up and less voltage is dropped across the halogen lamp, the only reason I can think why your chokes got hot is when a HID lamp is cold its arc voltage is low and so an increased current flows, normally a magnetic ballast has enough thermal mass and is well designed that this is not a problem, but I suppose if your using perticularly low cost/small ballasts already close to saturation in normal operation, then they might get unhappy with the low starting voltage of a HID lamp, but really i would just let it run and see how it behaves


as for the cycling how well used is the lamp? if its a well used lamp that might be why it cycles on the resistive ballast

I'm guessing the ballasts are aluminum-wound but they became insanely hot, much more than in regular operation. Another thing is that even though they were all from different brands, they got pretty equally hot without significant difference between any two ballasts. They were below the deltaT=70C/Tw=135C but it was hot enough that it could have burned me if I touched it for >5s, and these ballasts can do just fine in parallel configs for example two in parallel for a 70W lamp.
I don't know why the ballasts got that hot since, as you say, they'd have to drop less voltage. I've done two in parallel for a 70W CDM-T, which worked just fine and barely got warm. Even with a 36W PL-L, the ballasts remain quite cool to the touch. One of the ballasts is by philips too...

The lamp is brand new, made in 2021 and as per the arc tube has almost zero use (ends are clear), and the crompton lamp is unused as well. Quite a mystery.