Making a video light - 25.6V, 2.1A from batteries?

[Okin]

Hi everyone,

I've had an inclination for a while to try and design a high-powered, battery operated LED light for filmmaking uses. High lumen output is key, and after an initial plan of setting up 4 Cree MC-Es, I discovered this LED:

http://www.newark.com/bridgelux/bxra-n3500-00000/high-brightness-led-arrays/dp/74R9818

3400 lumen
25.6 Vf typical
28.3 Vf Max
2100mA

I'm trying to figure out how to power this thing off of batteries. I'm looking at getting 7 AW 18650s (http://www.lighthound.com/AW-18650-...able-Lithium-Battery--New-Version_p_3125.html), and running them in series. (4.2V*7 = 29.4V) Will this work?

There don't seem to be any drivers that could handle this, so I'm thinking of doing direct drive with a resistor. Do any of you have any thoughts on what resistor to use? It seems that when the batteries settle in to their regular output of 3.7V that I will be losing a lot of current. Is this going to be a poor way to power the LED?

Thanks for sharing your knowledge!

(Also, this is my first post here. )

 

[Okin]

Also, if anyone thinks I should return to the 4 Cree MCEs rather than pursue this LED, please let share your opinion!

 

[videoman]

Hi Okin and a warm welcome to our CPF forums.You have come to the right place. Is the light for a on-camera or off-camera placement ? Consider proper heat sinking on that 50 watt led. It tends to get mighty hot very soon if not properly cooled. If your design can call for multiple leds instead of one led, you can also consider using 18 CREE XP-G's driven at 600ma each for around 3600 lumens. They will deliver more light with less heat and less power drain from the battery.Check out Taskled drivers. Their new 6 amp units will do nicely to power them up, you can also add a dimmer to them. If it is a on-camera unit, remember that size has a direct influence on heat and you may be limited to under 2400 lumens with a properly designed enclosure. Heat is the enemy of leds.Also to consider is beam angle and optics as well as reflectors in case you wish to modify the beam spread.The narrower the spread, the brighter the light. Enclusure choice is critical, as a off-camera unit ,you may want to consider some active fan cooling also.Check the specs, take your time, you will make a nice light. Good Luck.

 

[Okin]

Hi Videoman! Thanks for the thoughts and tips.

I've definitely put some thought towards the heat sink, and have worked through the formulas for what I should grab. I'm also going to be running a fan off of a separate 9V battery to keep things extra cool.

The light will be an off-camera light, so I've got some room to play with. Right now it's mainly a prototype, so I'm not too worried about form at the moment.

The Taskled driver (The H6CC I think) would have been great, but its voltage does not go up high enough to match the forward voltage of the Bridgelux led. The LED requires 25.6, and the H6CC maxes out at 25. I'm assuming that would be an issue?

Once I get my electricity requirements balanced out, I'll definitely move on to lenses, but for now I'm fine with just getting a bright flood light.

 

[videoman]

You definitely would need a driver for that led, leds are very picky when it comes down to voltage and current requirements. A little volt or two over the led's limit will have it smokin' in no time.Under voltage isn't a problem, it's just that it won't be bright and will eventually dim out as the voltage drops.I also have checked many high voltage leds but I ran into the driver problem. I suggest you check out the sst50 or 90 leds that are discussed many times in these forums, they can be driven by available drivers that can be easily found. Another design is an array of XP-G's that are tightly grouped together to minimize multiple shadows and because of their high efficacy will produce less heat and more light. Having a single hi power led's big advantage is that it produces a hard single point light source without multiple shadows. You can achieve the single shadow effect on multiple leds by the use of a scrim or diffuser. For the price of that led, you d buy a dozen XP-G's that can easily be driven at 1 amp each with lots of headroom and deliver a whopping 4500+ lumens.Configuring them will be determined by the type and rating of the driver.If the enclosure is big enough, you may not need a fan after all as a finned heatsink in the size of 10 X 10 inch may do.

 

[blasterman]

IMHO, building a battery powered light off a Bridgelux N3500 has a lot of potential issues.

First, I think you're underestimating the heat-sink requirements. Bridgelux recommends a 12"x6" sink for this emitter, which will likely be bigger than your camera. The heat put out by a +50watt LED array is astronomical, even with active cooling.

Next, this is an old tech Array, and the LED's used on it are barely over 60 lumens_per_watt for neutral white. That's pretty darn lousy. Bridgelux has since bumped up the efficiency of their neutral white emitter arrays, but not with this one. Not sure if the efficiency specs for an SST-50 or 90 are that much better at 4100k, but they do require less voltage and might be easier to work with. Don't ask me where to find them though.

 

[videoman]

I would stick with Cree MC-E's or the much more efficient XP-G's. There is a wealth of drivers available for them. If you already have the 4 MC-E's. I would suggest adding 2 more, this way you would get approx. 3600 lumens out of them if you drive each die at 700ma. If they are parallel configured, you can run 2 strings of 3 (series) and driven by the H6CC buck driver. You have a handy trim pot on that driver so you can dial in 5.6A to the leds.Don't forget to add a pot to that.They will get hot, I mean very hot at max output.A fan in that case is a must unless the heat sink is big.Check out the Sunon fans (Available at DigiKey) they come in a huge variety of sizes.Also, if you properly space out the MCE's before cementing them (potting) , you can always add lenses or reflectors to them to further gain throw and lumens.

 

[HarryN]

I think it is worth considering whether by the time you are finished, if you can really match the efficiency and thermal path ( degrees C of rise at the junction per watt) using the various methods from a system perspective.

Consider the actual thermal path very carefully of the "pre-build arrays" from Bridgelux and LEDEngin vs individually mounting an array of single die packages from Cree or Lumileds. It is very difficult to match, much less beat, the thermal path of these pre-made arrays in the real world.

 

[qwertyydude]

This seems like a very difficult build with active cooling and customized electronics. The Bridgelux is only 63 lumens/watt and unknown cri. This is easily matched or exceeded by HID which usually hovers around 80ish lumens/watt and around 70 cri which is about what a good high power led can manage. A good 55w car kit can output around 4500 lumens, can be had in different color temps and best of all is cheap, about $45 for a two bulb and ballast kit. Then you won't need to worry about active heatsinks and can devote more time to light control out the front which should be easy as it's off camera.

I considered led video lights myself and came to that conclusion, also led video lights are only really feasible if you need it compact. My MC-E flashlight with a diffuser and screw mount for my camcorder worked excellent but just did not have the brightness of dedicated off camera lighting, even if that meant just a 45w cfl bulb in a standing lamp, which worked pretty good imo.

 

[videoman]

Looking at the 3400 lumen figure, that would roughly equate to a filament equivalent to around a 200 watt household frosted bulb in apparent brightness o a white wall. Now that may sound like a lot, but I am a video guy myself and I know what a production set may require as far as brightness levels. Distance is the key factor here and I am referring to light to subject.Light falls off drastically for every doubling of distance, so if your 3400 lumen requirement may be fine at 10 feet, you may need 4 times the lumen value at 20 ft and not twice.Or in camera terms " open up 2 stops on the aperture. It also greatly depends on the particular application for which the light is needed. Having more light than necessary is always a good thing.I have made my own not because of cost savings but that there wasn't a led tripod mounted unit that I liked. The main problems were that the units were too blue on the color cast and the beam angle was always way too narrow, and to correct that must involve a CC filter along with a diffuser which drastically lowered the output.By using for example, Cree Mc-E's , the beam angle is natively over 100 degrees (nice) and also has a neutral color cast. you just want to use your 4 MC-e's in a compact unit, my suggestion is to power the driver from a 12 to 18 DC power source with generous amp/hr reserve. I have powered mine with cheap 12v lead acid bricks (6A). You may also want to consider adding Carclo 70 degree reflectors to them, that would really make an improvement on throw and brightness by sacrificing a bit on spread angle. With that kind of set-up, you can easily illuminate somewhere in the vicinity of 30 ft. with little or no gain on the cam.You can also have a beautiful soft box effect at close range by shooting it on a white or silvered photo umbrella.

 

[blasterman]

The Bridgelux is only 63 lumens/watt and unknown cri.

It's around ~80 like almost any other neutral white LED. It's just not very efficient.

This is easily matched or exceeded by HID which usually hovers around 80ish lumens/watt and around 70 cri which is about what a good high power led can manage.

The higher the CRI the better, and other brands of LED can hit ~80 CRI at 4100k and 100 lumens per watt. I don't think HID is even close to that.

Autmotive HIDs don't exactly have high CRI.

 

[csshih]

I'm getting a video/photography light made from 3 sst50s and 2 red leds.. 1 warm sst50, 2 cool sst50s, and 2 osram red leds for CRI.

the most expensive component in my build was the 3 H6CC drivers.. at 32$ each. my build uses 3 of them.

1 for that warm sst, 1 for those 2 cw ssts, and 1 for the 2 reds.

potentiometer controls for each of those drivers for full adjustment

bad screenshot of the partial build:

 

[qwertyydude]

The Bridgelux as stated on it's site is 3400 lumens, if you divide that out by 25.6vx2.1amps it is only 63.24 lumens per watt. This is why everyone on the site is recommending using pretty much any other led but that Bridgelux. It's just about half that of high performance Crees.

HID lights are basically the same technology as professional "HMI" lights just without the exorbitant costs of being associated with film/tv making. So HID lights make perfect sense for cheap portable set lighting.

 

[Okin]

So it sounds like the consensus is to avoid the Bridgelux LEDs. I shall do that.

Does anyone recommend a site for looking at HID lights?

The goal here is something that can be battery powered, and ideally clocks in around $175 and puts out ~3,000 lumens.

 

[qwertyydude]

A $175 budget is on the extremely low side, which I figured you probably didn't have much budget to work with. Usually people trying to research DYI led set lighting are ones on a budget that can't afford $5000 for what amounts to a glorified light bulb stand. Take for example a 1000 watt halogen area work light, home depot sells for like $40 but once it's painted matte black and has some barn doors added, it all of a sudden costs $500.

There are lots of flashlights that cost more than $175 and even a good HID kit can cost more. Factoring in costs of led's, drivers, heatsinks, fans, lightboxes and power supplies you'd be hard pressed to make anything usable.

But if you had to put together a kit, best place to get budget HID is Ebay, about $45 buys you two 55w hid kits which includes bulbs and ballasts then just figure out the external accessories from there. I'd challenge anyone else if they can put together ~8000 lumens for $45 that wasn't incan and is also battery operated. The drivers for a massive led array alone can add up to more than $45.

 

[hannreuhieck]

hi qwertyydude
i'm newbie here, i did a couple test with 35 watts HID car bulb

here is the link :
http://cinema5d.com/viewtopic.php?f=57&t=33797

give comment please.....
thanks

 

[deadrx7conv]

Another option:
http://www.newark.com/bridgelux/bxra-n3500-00l00/high-brightness-led-neutral-white/dp/55T8714

Its your choice on whether you want to use it or not. It'll also take up to 3amps. And, with normal battery voltage drop, you could probably run it direct drive. It'll dim a little as battery voltage drops. Make sure your heat sink is large enough and has a fan.

Concerning the XPG, what is the cost of 18 80-CRI XPG's on mcpcb's, along with drivers, wiring?

Another option is to underdrive a larger LED:
http://www.newark.com/bridgelux/bxra-n6300-00l0e/high-brightness-led-neutral-white/dp/27T2286

You could use multiple MC-E, XML, P7, SST50, XPG, Rebel ES ...... But, good luck finding them at 80 CRI unless you go with 'warmer white'.

I'd give the Bridgelux a run!

 

[videoman]

How about using 4 XM-L's ( the 3200K variety for indoor video or 5500K for outdoor), 2S2P configuration driven off a H6CC Taskled 6700ma driver and 4 Ledil Boom reflectors ( the medium ones) ? you will surely get a lot more than 3400 lumens, or should I say Lux value at 3 ft. ? Solder a dimmer pot to that and choose your enclosure/heatsink wisely and you will not need a fan. That set-up will have a nice powerful beam up to 40 ft. away.