Hi I’d like to build a monster sky search light - I’m thinking 5 gallon metal pail using 15 - 20 Cree XHP70.2 leds. I’ve learned (reading here at blf) that they each need a driver limiting their individual currents to about 4.8 volts. I would use our 12 volt truck battery to power it and I’ve learned (reading here at blf) that the voltage forward actually requires more than the rated voltage, so I would use 6 volt leds to give them some voltage head room. I’ve also learned here at blf that this will generate a lot of heat that I will need to dissipate to protect the leds and the drivers from running wild and destroying themselves. I can fabricate a heat sink to handle this load. I was thinking of using one driver for each led - such as these China ebay drivers XHP70.2 Led Driver 26mm 1 Mode 5 Modes For XHP70 6V LED Chip Emitter Bulb | eBay I have heard however that they are remarkedly unreliable at keeping the current at 4.8 amps - often far less or dangerously higher. My question is this: Is there a better way of driving these emitters? Perhaps a large shared driver which might be of better quality? Perhaps several large drivers powering gangs of 5 or 6 emitters? But still be budget friendly. Or is there a manufacturer that makes better quality budget friendly individual drivers other than these Chinese units? I would really appreciate some part numbers or links or diagrams to keep me going. Thank you Lake Carlson
I’ve worked with these emitters a lot. If you try to drive a 6v emitter at 12 volts it will die quickly (pop). they need a buck driver to run off a 12v source. Those Chinese buck drivers aren’t the mot reliable, but they work fine if you don’t run them.l near their operating limit and keep them cool. You need a very efficient thermal path as well (and a lot of thermal mass-a hige aluminum heatsink). You also need a focusing solution, like a big aspheric or fresnel lens. You could go with I individual reflectors for each LED, but focusing them would be very tricky. There really isn’t a viable way to drive these since they need a constant current output. You could look into using a single driver for each LED. There were some youtubers who did a project like you are thinking of.
you will also need some way to focus the light, or it will just spread out everywhere
having a 2 square foot light source, makes this kind of hard
Realistically you need a separate reflector for each LED. Putting them in a cluster in the middle won’t get you a well focused beam.
Xhp70.2 is not the best led as the dome makes the surface intensity lower. You want domeless LEDs for a thrower ideally. You may be able to get 70.3 hi LEDs but I don’t know what’s available yet. They’re a recent development.
You may be better off using SFT40 LEDs. They have a high surface intensity with a middle size die.
If I were to try to make something like that I would probably try to buy multiple reflectors from convoy and line them up with a sheet of aluminum in the back to cool the LEDs and a sheet of glass in front to align the reflectors. That might get your aiming pretty good.
He could do 70.3. They’re available as a bare emitter from Comvoy, but $15 each.
Yes those ebay drivers would be fine but it would be better paired with smaller 6V XHP50.2/3 LEDs at 4A current. Or Osram WF1 LEDs wired in series, two per driver.
Putting a bunch of emitters behind single large lens is not a good optics solution. Each LED should have its own optic.
That thing didn’t produce a beam to speak of. It was basically a giant mule because each LED did not have its own optic.
It is not very tricky to focus an LED in a reflector, depending on the LED and reflector. For centering you can often just eyeball the LED on center and that’s good enough. For focusing, adjust the height of optic/reflector until the beam looks good or your lux meter shows the highest readings. Shim the reflector to this level. If the array consists of identical reflector / LED combinations they can all be shimmed the same. There are also centering gaskets available for some LED/reflector combinations. For example this + this from the Convoy store.
Is the battery going to be in a running vehicle or is it removed from a vehicle? A large subwoofer / car audio system capacitor may be advisable to smooth the voltage spikes than come from vehicle electrical systems.
If you switch multiple drivers at the same time from a single switch they can get out of sync if they are multi-mode drivers. A single-mode driver will not have this problem. There are some applicable drivers on KaiDomain. This one or this one can provide 2500mA, which is not a lot of current and is best paired with three Osram WF1 LEDs in series per driver. Small LEDs like this work good with small optics.
C8 reflectors are cheap and there are centering gaskets for this combination at the Convoy store. Or an L21A reflector with 9mm hole and matching gasket. Convoy offers some glass windows too and an aspheric lens offering.
Taskled Ultraboost is another driver option, but again XHP70.2/3 isn’t the best choice for this driver, and it will only be good for ~120W of LEDs at ~12v input. Taskled also has some buck drivers such as H6CC.
You can get an idea of the voltage and output characteristics of the XHP70.2 in this thread and this thread.
XHP50.2 test threads here and here.
Osram LEDs tested here.
If you’ve got a lathe you can make your own centering gaskets. They aren’t entirely necessary but they do make things easier. Adjusting the overall height of the entire reflector array by moving the frame / bezel is another way to achieve focus.
There are a lot of combinations of LEDs, Optics, drivers, etc. that you could use to make a monster sky beam. Kaidomain has a lot of reflectors and optics and stuff. Glass windows too. Many people use plastic for these larger projects for the front window since they can cut it to size. flashlightlens.com can cut large custom plastic windows from optical grade plastic.
200W HID will eat them for a breakfast. And will be cheaper.
Mike
It occurs to me that for larger LED projects, using an RD Tech power supply as a driver would work quite well. That one is 20A out max, 60V IN max but there are cheaper ones that put out less current. You’d need to be a little careful not to kill your LEDs, you know, have the voltage / amperage setting properly adjusted but besides that, you get a fancy display and a whole lot of power for $47.
Great suggestions. The truck be be off, I know that when it’s running the voltage can vary from 12 to 15 which I thnk might create more problems. Here’s a link to the video testing these Chinese drivers Cree XHP70 LED driver - YouTube I think if the amperage is low, the lm output is greatly diminished. Thanks
Are you going to have it project the Batman symbol?
Sounds like an awesome project!
OPTICS, I see he OP never even gave it a thought, without it it will be a bunch of leds in a bucket, pointless waste of time. been there done that. you want throw, forget about xhp70, you need xhp35s and very tight optics, 70 has too big of a die to focus it tight. 35s HI are what you want, with no dome, as for optics, ledil iris with thin tunnel comes to mind, tightest lenses i've seen for the size. i mean actual beam in real world not a number on paper.