Phil Rhodes
Well-known member
A few times over the last few months I've mentioned a little side project I had going on to build a 575W HMI. That project is now largely complete and I thought it'd be worth reporting my experiences.
This comes with two caveats. First, I'm describing doing things involving both mains electricity and considerably higher voltages than that, going through connections I made, and you do this at your own risk. Also, I must make it clear that I am an enthusiastic tinkerer, and this was largely a for-fun project, if a rather expensive one. This is not a cheap way to HMI - it's only a little cheaper than the cheapest Chinese stuff, which I suspect will have many of the benefits and caveats of what I describe here.
I retrofitted a Source Four PAR housing with an Osram 575W HMI in an appropriate G22 base. This necessitated making an entirely new back cap assembly for the PAR housing, because the G22 base will not fit in the existing back cap, even the larger ones intended for 575W MSR. This does mean this can be done to any Source Four PAR, not just the MSR ones, although the halogen ones, or the 150W metal halide type, may need the hole in the middle of the reflector enlarged slightly.
The new back cap is made of two lengths of extruded aluminium, one mounted on the back of the reflector and one bolted to the side of the first, to house the ignitor. The ignitor I used comes potted in silicone with the high-voltage output leads already attached, and they're short, so there was no option to mount it on the yoke. This may be a necessary side-effect of the high voltages required of a hot-restrike ignitor. Some fiddling was required to properly centre the arc in the reflector. Quite a few bits of metal and nuts and bolts are required to achieve the final arrangement as there isn't really anything flat or true on the back of the reflector to hold things in place - eventually we mounted it on four of what look like the runoff pillars used to vent the mould during the casting process.
The ballast and ignitor came as a pair from these people, although appears to have been made by these people. Before anyone starts crowing about how terrible Chinese parts are, they are exactly the same unit as supplied by GAM for their theatrical lighting devices (you can see a picture of one at that link). It has DMX control, which I really don't need. I built the lamp head and cable with appropriate 7-pin Amphenol Ecomate connectors.
The results? Well, it works. It strikes and it hot-restrikes. The ballast fan is relatively easy to replace with a much quieter one, which is probably in an acceptable zone of quietness. It is a 575W HMI PAR.
If there's a problem it's that the lamp head makes a certain amount of noise, the sort of noise you'd get from an Arri HMI with the ballast switched to "flicker free". This is understandable given that these ballasts often operate at around 150Hz (unlike more conventional metal halide ballasts which frequently run at many thousands, or tens of thousands, of cycles per second). GAM advertise the associated light as "flicker free" and this is the sort of design behaviour that's typical of HMI ballasts designed for film and TV work. Better ballasts provide lower-noise options. Working on this assumption it probably isn't possible to entirely shut it up, but I'd like to try it on a better ballast to isolate the problem to the electronics.
I strikes (ha!) me that it may be possible to come up with an HMI ballast based around a stepper motor driver. They're generally very programmable to provide the sort of flexibility we need, handle these sorts of power levels without fan cooling, and are a hell of a lot cheaper. You'd still need the ignitor. Better tech, I think, but that's a project for another day.
P
This comes with two caveats. First, I'm describing doing things involving both mains electricity and considerably higher voltages than that, going through connections I made, and you do this at your own risk. Also, I must make it clear that I am an enthusiastic tinkerer, and this was largely a for-fun project, if a rather expensive one. This is not a cheap way to HMI - it's only a little cheaper than the cheapest Chinese stuff, which I suspect will have many of the benefits and caveats of what I describe here.
I retrofitted a Source Four PAR housing with an Osram 575W HMI in an appropriate G22 base. This necessitated making an entirely new back cap assembly for the PAR housing, because the G22 base will not fit in the existing back cap, even the larger ones intended for 575W MSR. This does mean this can be done to any Source Four PAR, not just the MSR ones, although the halogen ones, or the 150W metal halide type, may need the hole in the middle of the reflector enlarged slightly.
The new back cap is made of two lengths of extruded aluminium, one mounted on the back of the reflector and one bolted to the side of the first, to house the ignitor. The ignitor I used comes potted in silicone with the high-voltage output leads already attached, and they're short, so there was no option to mount it on the yoke. This may be a necessary side-effect of the high voltages required of a hot-restrike ignitor. Some fiddling was required to properly centre the arc in the reflector. Quite a few bits of metal and nuts and bolts are required to achieve the final arrangement as there isn't really anything flat or true on the back of the reflector to hold things in place - eventually we mounted it on four of what look like the runoff pillars used to vent the mould during the casting process.
The ballast and ignitor came as a pair from these people, although appears to have been made by these people. Before anyone starts crowing about how terrible Chinese parts are, they are exactly the same unit as supplied by GAM for their theatrical lighting devices (you can see a picture of one at that link). It has DMX control, which I really don't need. I built the lamp head and cable with appropriate 7-pin Amphenol Ecomate connectors.
The results? Well, it works. It strikes and it hot-restrikes. The ballast fan is relatively easy to replace with a much quieter one, which is probably in an acceptable zone of quietness. It is a 575W HMI PAR.
If there's a problem it's that the lamp head makes a certain amount of noise, the sort of noise you'd get from an Arri HMI with the ballast switched to "flicker free". This is understandable given that these ballasts often operate at around 150Hz (unlike more conventional metal halide ballasts which frequently run at many thousands, or tens of thousands, of cycles per second). GAM advertise the associated light as "flicker free" and this is the sort of design behaviour that's typical of HMI ballasts designed for film and TV work. Better ballasts provide lower-noise options. Working on this assumption it probably isn't possible to entirely shut it up, but I'd like to try it on a better ballast to isolate the problem to the electronics.
I strikes (ha!) me that it may be possible to come up with an HMI ballast based around a stepper motor driver. They're generally very programmable to provide the sort of flexibility we need, handle these sorts of power levels without fan cooling, and are a hell of a lot cheaper. You'd still need the ignitor. Better tech, I think, but that's a project for another day.
P
