How to supply power to multiple 100 watt LEDs? - Page 1
Forum section: electronics / projects

author: MarkS
author_rank: Unknown
timestamp: May 22, 2015, 11:18:03 pm
content: I've been wanting to start up another marine reef aquarium after being out of that hobby for about a decade. One of the requirements is very high output lighting as most corals are photosynthetic. I've recently discovered high output 100 watt LEDs and have one to play around with, but for this application I'll need no less than six. Each LED has a forward voltage of 30 volts and requires 3 amps.I can only think of three ways to do this:1.) Use a 30 volt, 18 amp (!) supply and wire them in parallel.2.) Use a 180 volt (!), 3 amp supply and wire them in series3.) Use six 30 volt, 3 amp supplies. Or lower voltage supplies with boost converters. The issue is the quantity.None of those options seem rather optimal. Is there a better way to do this?

author: georges80
author_rank: Frequent Contributor
timestamp: May 22, 2015, 11:37:51 pm
content: You need current regulated drivers, whether one or many.cheers,george.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 22, 2015, 11:41:04 pm
content: How would six power supplies have problems with current distribution?There will be 18A in total but you would have 6 separate 3A circuits.A benefit of option 3 would be that if one goes down the others will still work.And keeping one spare 30V/3A PSU will be cheaper than a spare 180V/3A or 30V/18A PSU.You can also keep the low voltage/high current wires short by placing each PSU close to it's light and running mains wiring over the longer distances.(which would be the case for a mains powered LED lamp)And yes, LEDS are current driven.

author: grifftech
author_rank: Frequent Contributor
timestamp: May 22, 2015, 11:44:52 pm
content: get a 24 volt 20 Amp battery charger not perfect but safe

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 22, 2015, 11:51:19 pm
content: Quote from: blueskull on May 22, 2015, 11:42:43 pmOr a 180V CV PSU, although there you would need only one current limiter.Without knowing what kind of lamps the OP has it would be hard to say what kind of powersupplie(s) he needs.

author: rs20
author_rank: Super Contributor
timestamp: May 22, 2015, 11:55:06 pm
content: How did you calculate that you'd need 6? Did you take the specific spectral distribution of the LEDs, and the absorption range of plants into account? Or did you just assume that lumens are lumens (a measurement only relevant to the perception of the human eye)?On that theme, have you considered coloured LEDs? Plants appear green because theyreflectgreen light, they absorb red and blue. See this video for an experiment where they are using just red and blue light to grow plants, much more efficient. Now I have no idea how coral works/which specific wavelengths the photosynthesis in coral is happening on, but you could possibly optimize similarly.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 22, 2015, 11:57:21 pm
content: Unless your 100W LEDs have built-in power-supplies (constant-current regulators), you will blow them up if you attempt to connect them to an ordinary power supply.Get six individual power supply modules specifically made for 100W LED use. Any other scheme will be not only costly, but potentially dangerous as you blow up $$$ worth of LED modules.

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 12:04:49 am
content: Quote from: Richard Crowley on May 22, 2015, 11:57:21 pmWhy is that?

author: Rasz
author_rank: Super Contributor
timestamp: May 23, 2015, 12:11:39 am
content: Quote from: Richard Crowley on May 22, 2015, 11:57:21 pmits single $, those leds are $9 nowadays

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 23, 2015, 12:45:34 am
content: Quote from: MarkS on May 23, 2015, 12:04:49 amBecause, unless you limit the current to the design spec, they will burn themselves out in milliseconds.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 23, 2015, 12:47:25 am
content: Quote from: MarkS on May 23, 2015, 12:04:49 amLEDs are diodes and have a fixed forward voltage drop.If you apply more voltage than that the diode will conduct as if it was a short circuit and an enormous current will flow, burning out the LED.So you must limit the current, which can be done by a series resistor or by using a constant current PSU instead of a regular constant voltage PSU.

author: georges80
author_rank: Frequent Contributor
timestamp: May 23, 2015, 12:59:21 am
content: Quote from: jeroen79 on May 23, 2015, 12:47:25 amYes, as an approximation (fixed forward voltage), but in practice it is worse.The Vf lowers within increasing temperature, so as the LED heats up (especially a 100W device driven around 100W) its Vf will drop, so a CV supply is a really bad thing.Vf often drops with LED aging as well.Like I wrote at the top, you need a current regulated (CC) supply to drive LEDs and even more so for high power LEDs.Anyhow, the OP needs to verify his actual lighting requirements if he hasn't already and also the spectral composition.cheers,george.

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 03:47:07 am
content: This will be for a small tank, probably around 10 US gallons. I've used a 250 watt metal halide on one before, but don't want to go that route this time. The spectrum has to be simulated. At the depths that most corals live, seawater filters out nearly everything but blue and violet. It isn't possible to fully simulate the sun's intensity, even under meters of water, so people in the marine hobby use powerful low spectrum bulbs, typically around 6500K to 10,000K, and supplement them with lower intensity actinic bulbs in the 12,000K to 20,000K spectrum. My plan is to use these as the high intensity lighting and use CFL actinic bulbs to correct the spectrum. The result is remarkably close to the spectrum recorded at depth, just at a lower intensity.The LED I have is a single LED chip with no power supply circuitry added.Quote from: jeroen79 on May 23, 2015, 12:47:25 amI get that. It seemed like you were insinuating that this would operate differently than a "normal" LED. I don't expect to just pump current into it. Still, I need a way to power it.

author: djacobow
author_rank: Super Contributor
timestamp: May 23, 2015, 04:00:45 am
content: Quote from: MarkS on May 23, 2015, 03:47:07 amSeems like a lot of light. I guess you are trying to recreate sunlight levels?A standard 10 gallon tank is 11" x 20" or about 0.14 m^2. Let's assume an LED conversion efficiency of 15%. That would be a flux of 600*0.15/0.14 or ~630 W/m^2. Full sun at noon is on the order of 1kW/m^2, so this is on the same order.How will you cool this tank?

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 04:08:27 am
content: Quote from: djacobow on May 23, 2015, 04:00:45 amExternal chiller. This was a hobby that I was deeply involved in for well over a decade. I've had multiple tanks of various sizes using many different types of lighting and filters and designed and built my own tanks and filters. I was heavily involved in the DIY scene at the time. If you guys want information on it, I will be happy to provide links to a plethora of sites where you can learn all you want, but I'd like this discussion to stick to the LED. If this LED idea isn't possible, I'll accept that and go with a metal halide set up, but this is also a hobby of mine, so I might as well use it.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 23, 2015, 04:30:44 am
content: You have a "single LED chip" that is 100W? That is quite remarkable. Please cite the specifications.

author: georges80
author_rank: Frequent Contributor
timestamp: May 23, 2015, 04:35:49 am
content: Quote from: Richard Crowley on May 23, 2015, 04:30:44 amI know you are 'fishing'but obviously the OP has one of the 100W LED arrays, either a bridgelux or one of the cheapo ebay/china clones... After all, he's already stated nominal 30V Vf so it can't be a single LED device...cheers,george.

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 04:45:14 am
content: Quote from: georges80 on May 23, 2015, 04:35:49 amYes, thank you. It's an array...Unfortunately it does appear to be one of the China clones. I cannot find a manufacturer, part number or data sheet. All I have to work with is the limited data found on the order page.I bought it because it seemed like a fun thing to play around with, but I was hoping to find a use for it. This may be a no go...

author: SeanB
author_rank: Super Contributor
timestamp: May 23, 2015, 05:25:27 am
content: Just buy the matching ready made driver, and place in a diecast box near the LED chip, and connect the two with some 1.5mm wire. You will need a very big heatsink, probably with fan cooling, for the chip, it does have to keep it at under 40C with 100W of heat coming out of the die.

author: Corporate666
author_rank: Unknown
timestamp: May 23, 2015, 06:42:24 am
content: Quote from: MarkS on May 23, 2015, 04:45:14 amI've done some fish tank lighting. Using 100W LED's is a bad idea. Especially with the 100W Chinese shit sold on eBay and the likes. Who knows what the spectrum of that LED is, but being a Chinese POS, it won't be controlled and as long as it produces "something like white", it will be sold.Successful fish tank LED setups use white lights for general illumination mixed with blues for depth penetration. I forget the exact wavelength you want for tanks but it may be the "royal blue" instead of the standard blue. Anyway, you want a mix or cool white + blue... and you want *efficiency*, which you won't get with a POS Chinese LED or with a 100W multi-die LED. You want efficiency because whatever energy doesn't turn into light will turn into heat, and in a tank setup you are removing that excess heat. It is a false economy to buy cheap/shitty LED's that heat the water up, then spend more chilling the water back down.It is a common misconception that you can save a lot of $$ rolling your own fishtank LED's. IMO, you can't save money. A large tank lighting manufacturer will get such a huge economy of scale on LED pricing (not to mention aluminum extrusions and such) that you will probably pay more for similar quality by doing it yourself.

author: sleemanj
author_rank: Super Contributor
timestamp: May 23, 2015, 08:03:03 am
content: Quote from: MarkS on May 23, 2015, 04:08:27 amHow will you cool these LEDs.LEDs are more efficient at converting power to light than other lighting, but they are still NOT very efficient at all in practice, a large proportion of that 100W is just waste heat that you MUST get away from the LED, it takes a big active (fan cooled) or ridiculously big passive heatsink to get rid of 100W and keep that LED cool enough to touch....Anyway, I would just get six "100W" drivers, mains powered. If it's 100W chinese watts then the 100W drivers will be more like 50 to 60W which is what you want to run those 100W leds at anyway, for better longevity and lower cooling issues.Bigclivedotcom has looked at lots of these array LEDs and their drivers...https://www.youtube.com/channel/UCtM5z2gkrGRuWd0JQMx76qA

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 08:44:21 am
content: Thanks all. This just isn't a good idea. I'm really concerned by the lack of a data sheet. All I have is a little blurb on the product page and not much else. I'm guessing it is 30 volts and 3 amps, but I've seen similar LEDs on other sites with higher voltages and the spectrums run from 3000K to 6700K. I was hoping to find a use for it, but I don't think this is it.

author: Zero999
author_rank: Super Contributor
timestamp: May 23, 2015, 01:40:22 pm
content: White LEDs are fine for general illumination but not much good for photosynthesis.You want 420nm violet LEDs.

author: MarkS
author_rank: Unknown
timestamp: May 23, 2015, 03:49:05 pm
content: Quote from: Hero999 on May 23, 2015, 01:40:22 pmI understand. That is why I am going to supplement with actinic CFL bulbs. This is normal in the marine aquarium hobby, as I've previously stated. Regardless, this isn't going to work. I cannot find enough hard data on this LED to use it properly or safely.