My project is to replace the high power (and expensive!) light in this stage light with a 100w LED light. I have the 100W led and associated transformer for it so no issues there. My goal is to remove the two large (and very heavy!!!) transformers at the bottom of the unit. The transformer on the bottom right is only involved in the light circuit itself so no issues to remove it. However, the transformer on the bottom left, while supplying power to the right transformer also (no concern to me) it has 3 wires (two red and one white) coming from the right side (right side of large capacitor in pic) which go back to the circuit board at the top (seen entering board on left) to run the light. I'd like to replace the huge transformer on the bottom left with something smaller that would run the power for these three wires. Voltage taken at the board where the two red and one white wire enter the circuit board are: white to red 10VAC (both) and red to red 20VAC. Supply voltage for light is 120VAC. Note: Voltage readings taken while loaded (running). Can I replace the large transformer with a simple 10-0-10 center tap transformer (small, maybe 1.2a or so) and attach reds to the outside and white to the center tap? The circuit board runs all the small stepper motors and the board but nothing else so I assume the power requirement is minimal.

 

That looks like a CDM-T metal halide lamp, either 70W or 150W. On a 230V supply it will be run from the mains via the ballast (lower right, underneath) and ignitor (above the ballast) without any other transformer in circuit.
On a 120V supply, it is usual to employ a different type of ballast incorporating an autotransformer, but it may possibly have been done with a step-up transformer and a 230V ballast. Check that first.
I can't see the rating on the left transformer, because it is obscured by the power factor capacitor, but it will need at least 50W to run five stepper motors.
When replacing the lamp with an LED light source, have you considered the etendue of the optical system? LEDs are only marginally more efficient than Metal halide lamps, and metal halides have a much better approximation to a point source.

 

It certainly appears that the unseen transformer is supplying quite a bit. Are you totally certain that it will be only powering the five steppers and all of their control systems? Are you certain that it provided a step up for the 230 volt light system?? And just what would be the benefit of removing that "big heavy transformer" that is providing power for all of those rather high performance stepper motors??? I seriously DO NOT recommend any change like that.

Consider that if the designers of that light system had been able to make it work with a smaller lighter and CHEAPER transformer, that would have been the one that they used.

 

Thanks for the comments! The reason I'm doing this is that this light weighs almost 40lbs. I have two of them and it take two people to get them up on a stand and mounted for use. They have to go up and come down every night I use them (I play in a cover band around town). I'm now 60+ years old and lifting these monsters is getting very old! All newer lights of this style are LED. I need to get rid of the transformers to lighten the load - significantly! Yes, the LED may degrade the light output some but not enough to make a significant difference - these are moving 'accent' lights and do not provide the primary stage light. Also, these things draw a boatload of power and I need a separate power source (circuit) from the band just to run them - that is not always feasible at many of our jobs. Dropping many pounds of weight and drawing far less power will make these lights much more usable for me.
Ian, your assessment of the light is pretty well on. Power (120VAC) enters the light at the top and after the capacitor (top left) comes directly to the transformer bottom left. That transformer I believe steps up the 120 to 230 and after going thru the cap goes over to the light transformer/ignitor on the right. However, the transformer on the left also has the three wires (red, white, red) coming off it and these are the power source for the circuit board (and the stepper motors). That is where I'm reading the 10VAC red to white and 20VAC red to red. That is the only power source for the circuit board and stepper motors (I am sure). As I said, if I can get a smaller transformer to supply this 10VAC/20VAC to the circuit card, this large transformer has no further use (I have a complete separate transformer, sink, fan, etc for the new LED light). I'll pull the capacitor from in front of the transformer on left and see if I can get a picture of the markings.
Again, I very much appreciate your comments and your assistance sizing up a transformer for the 10/20VAC supply.

 

What is the lamp power?
I assume that the luminaire is from a European manufacturer, as 120V ballasts for metal halide lamps are as rare as hens’ teeth this side of the Atlantic, so it would be easier for a European manufacturer to use the ballast he has in stock and have a transformer made with an auto transformer primary to supply the ballast.
If I am correct then the transformer will be supplying half the lamp power, and the rest of its VA rating will be for the motors.

 

Until you actually KNOW the required current for that PCB, it will be difficult to determine what the current requirements will be for any replacement.
How much weight will you save in just removing the light transformer??
Or are you telling us that aside from powering all the stepper electronics that the transformer ALSO steps up the mains voltage from 120 to 230 volts?? Have you examined that transformer to see what else it might be powering??

 

Finally got time to deconstruct a little. Took cap off from on top of transformer and learned a lot. Yes, that transformer does bump the 120V to 240V before it heads over to the lighting transformer on right (black and blue wires on left side of transformer). But is also peals off 9.5V at 5 amps (the two red and one white wire on right side of transformer). I know these pics don't show the transformer marking on the side but I could read it and it is clearly marked 2X9.5/5A (in addition to the 240 marking). I don't need the 240V when I upgrade to LED so I hope to find a smaller transformer that will give me the 2 legs at 9.5V/5A.

 

I suspect you’d be better off rigging a pair of small winches to do the lifting than trying to make this modification. I suspect the results with an LED will be disappointing at best.

 

There are some good LED stage lights these days and they are quite cheap, so it may just be easier to replace than to try and modify. The optics required to collect and focus light from LEDs are not the same as those for metal halide lamps, which are almost equivalent to a point source

 

Very interesting indeed. But removing just one transformer will provide a good weight reduction. Unfortunately the 9.5 volt times two secondary at 5 amps is not a very standard voltage, BUT if the only application is a rectifier power 12 volt supply for the steppers and logic, probably a ten amp switcher will be an even lighter replacement.
So my best advice would be to go with a switcher with a lot more capability, and hang on to the transformers in case of some unintended consequences. (That is, "CYA" just in case we all missed something.

 

Those are all good points. I already have the 100W LED (with sink and fan) from another experiment. Maybe I'll pull the MH light (without destroying mounts, connections, etc) and place the LED in using temporary mounts (and electrical supply) to see what optics I get out of it. If it works - not expecting or needing it to be as bright as it currently is - I was thinking of using a Hammond 187F20 transformer to give me two 10vac legs to power the board/steppers. I'm measuring 10vac each leg at the board from that existing transformer and the board uses that power to run itself and the steppers. I'll post pics of the light's performance with the MH bulb and then with the LED temporarily installed. I'm curious what the difference will be. No worries either way. I've got nothing invested (but my time!) so far and the lights are nearly useless to me at their current weight - the other band members are older than me and won't touch them!! BTW the light is a 20 year old American DJ Ultrascan 250 and I have two of them. Long ago discontinued by ADJ but I've certainly gotten my money's worth out of them. And the bulb alone costs more than what the light goes for on the used market.

 

As a side: researching an LED replacement for a MH light has been ... illuminating!! . First, the Ultra Scan 250 uses a 250W MSD250/2 bulb. For standard lights (warehouses, etc) it is recommended that a 250W MH bulb be replaced with a 100W LED bulb. However, all 'conversion' charts point out that light fixture efficacy can significantly influence the conversion. Obviously, as Ian points out, this particular MH bulb is a rather focused point source while the LED I have is small (~1 inch x 1 inch) 'panel'. Even though I have a reflector for it and a focusing lens, I will lose significant lumens/watt - especially if I must use the focusing lens. I am truly curious what the real world test will show! I also note that MH bulb's brightness and color degrade over time and I have never changed the existing 20+ year old MH bulbs in these lights.

 

For the low voltage transformer, the CURRENT RATING is the important one. And if a source is not forthcoming on supplying that data then it is clear that they have something to hide. And at least one very big on-line supplier is notorious for refusing to supply adequate product descriptions.

 

The 187F20 has a 100VA rating. Should easily supply the board and steppers .... if I get that far!

 

OK, probably. If 100VA can equal 100 watts, that is about 8 amps at unity PF. That should be a reasonable margin if the other transformer is rated five amps. So now the voltage problem appears to be solved by finding another transformer with a similar voltage. I am quite impressed with that.

 

Here's the test optics. Used both lights, one configured with the LED and one 'stock' with the MH light. There certainly is a lower light output from the LED (left light in pic) but not that much! Actually, the pics show less of a difference than 'real life' as the right side (the MH light) is definitely brighter. I'm willing to give that up for a more usable light for sure. Also, the LED seems to be a bit more 'true color' and even than the MH. I might even look into a 150w LED to up the game a bit but we'll see. Pics show the difference in light output. Also last pic shows the two different stage light configurations - jammed that LED in with a little block of wood! Note that the transformers came out as a unit and are on the side of the LED equipped light.

 

Here's the marking plate for the transformer that I need to replace. I don't need the step up section of the transformer, just the SEC1: 2x9.5V / 5A. Hoping that Hammond 187F20 will do the trick. I'm not savvy on reading transformer specs so if I'm off here please chime in. Guess my question is, does that marking mean I need 5A total from those legs or does it mean I need 10A total (2 legs at 5A each)? The 187F20 gives the full 10A but if I can do with just 5A total I can move to a smaller transformer. Any help appreciated!!

 

One thing just popped into my head here at 3:52 AM, is that the weight distribution will be very different without the transformers in place. That might lead to a stability issue with the center of mass suddenly much higher. But if these lights are used when secured, and not just sitting, that may not be an issue at all.
BUT moving the C.G. is a secondary effect of removing all of that weight, and that needs to be considered. Secondary effects do need to be understood, at least.

 

Good Point. I noticed that CG effect as I moved the light last night. Current suspension points are in the middle of both sides. I suspend the light using cables looped around the light bar. One thought is to just suspend it upside down now (the light won't care!). Another thought is to put new suspension bolts further up towards the top of the light. An added benefit of the lower weight is that I should be able to use my light weight aluminum light stands rather than my weighty monster steel winch stands! I'll weigh both light configurations once I get the new transformer but it will be significant! Also significantly less heat produced from the light.

 

Interesting side note as I wait for my transformer to arrive. Today I measured the amps drawn for each light configuration. First was the light with the MH bulb removed and the LED light running. It drew a surprising approximate 5.5A. The other light is the stock light with MH bulb running. It drew about 2.8A. Interesting! So disconnected just the MH bulb from the stock light and measured about 5.6A. Yep, the light draws more amps with the bulb disconnected than it does with the bulb running. BTW, I measured just the LED light itself (as currently it is configured with a separate plug for testing) and measured about .8A.