DIY LEDs - The write-up

[Oblivionis]

Quick question: how many Cree XR-Es can be ran in series on one Meanwell ELN-60-48-D? I know 12 is usually the way to go but I think I've heard up to 15 can be done safely. True?

 

[Foxy Brown]

Foxy, not sure what you are geting at. But have you read the DIY driver thread? For About $1.50 you get the LM37 functionality and PWM that you described above. All you need is a sense resistor (ok the math is not as simple) and a couple capacitors. Still need the 24v supply.

Nope, I've not read that particular thread, though I would be interested if you can link it. The idea here was to provide a super simple (2 parts), cheap ($1), high current (1.5A), and current-CONTROLLED supply (ie. fail-safe and reliable). I also wanted to give a very simple and cheap way to generate the PWM signal for those less than comfortable with programming micro-controllers, and one which can control an almost unlimited number of lines, whereas a uC can at best do only a few.

 

[kcress]

Need some input on this little rig. Lets say I have Royal Blues and some True Violets on a meanwell ELN 60-48D driven at 1000mA. The True Violets has a max of 500mA. If I do this is ok? All LEDs in series but the true violets in parallel hoping to reduce mA down to 500

I like Fish's (3) idea. I'd also include (3) 0.1 ohm 1/2W resistors in series with each LED so you can make sure nobody's hogging the current. You should buy a few extras so you have some to swap in.

 

[TheFishMan65]

Foxy
Here is the link: DIY LED driver for reef lighting
It takes a few pages to get to the CAT4101.

 

[wld1783]

Quick question: how many Cree XR-Es can be ran in series on one Meanwell ELN-60-48-D? I know 12 is usually the way to go but I think I've heard up to 15 can be done safely. True?

The guys at Mean Well use an assumed 3.5 forward voltage for the Cree XR-E (yes it has been rated at 3.2 depending on how its driven).

The ELN 60-48D has a voltage range of 24-48 so 48/3.5= 13.71 LEDs.

I like 12 just because but theoretically no harm in adding a single red or green to the mix.

Bill

 

[Obi-dad]

edit

 

[Foxy Brown]

Foxy
Here is the link: DIY LED driver for reef lighting
It takes a few pages to get to the CAT4101.

There are a few problems with that chip, though it is a nice one.

The first one is that at 1A you are right at the rated capacity. In reality you shouldn't run such things beyond about 0.7x the rating, unless it has VERY good heatsinking.

This is exacerbated by the second problem. SMT only! While some folks don't mind hacking a toaster oven into a reflow station to work with SMT chips (I have one of these) most people don't want to cope with that. You COULD hand solder it down if you had the proper PCB made ($$$) but even then you wouldn't be able to get the back of the chip soldered to the ground plane for heatsinking unless you reflow.

Put together it means you wont be able to hit 1A true output for long unless you spend some serious money on equipment and custom PCBs. Using through hole components like the LM317, with much higher current ratings means no heroic measures to put the circuit together and get 100% output from the LEDs. Heck, you don't even NEED to solder, just wire wrap.

I'll stick with my drivers, thanks.

The second part is how you can get that PWM signal without a microcontroller, which I hope will be useful to those who don't want to spend $20-40 for an arduino with only a couple PWM outputs. This can do MANY output (dozens), and can even convert that 0-10V DC output from your current aquarium controller (profilux or whatever) to a PWM signal, by simply comparing that instead of the potentiometer voltage to the triangle wave. That way you can build you own drivers rather than buy the Meawells.

 

[TheFishMan65]

I will do a quick response, but if you would like to discuss it more lets go to the right thread to discuss the design.

1) These can be run in parallel so you could use 2 to reach your desired 1.5 amps. But since most are running below 1 amp it seems to be a good choice.

2) This a huge smt part and soldering the back plane is not a problem. Many have done it including me. My PCB is about $10 and wll hold 8 chips for 48 LEDs. Not sure what the three chip version is running.

3) It takes a 5 volt PWM signal so the same 555 circuit should work that you described above.

 

[Foxy Brown]

I will do a quick response, but if you would like to discuss it more lets go to the right thread to discuss the design.

1) These can be run in parallel so you could use 2 to reach your desired 1.5 amps. But since most are running below 1 amp it seems to be a good choice.

2) This a huge smt part and soldering the back plane is not a problem. Many have done it including me. My PCB is about $10 and wll hold 8 chips for 48 LEDs. Not sure what the three chip version is running.

3) It takes a 5 volt PWM signal so the same 555 circuit should work that you described above.

If I wanted to get one of your PCBs, where could I find one? 8 of those is about right for the tank I'm building.

 

[der_wille_zur_macht]

Foxy, the CAT4101 essentially fills the same purpose as you are proposing the LM317 for - they're both linear regs that can be run in constant current mode. The big differences are that the CAT4101 is made to accept a separate PWM control signal, so you don't have to PWM the power line yourself (which is probably not as simple as it looks if you want good control) and, even more importantly, the CAT4101 has a .5v minimum dropout, while the LM317 is something like 2.5v. This means it'll run more efficiently, and it'll be easier to run it "hard" (near it's current limit) without needing heatsinking. An LM317 run anywhere near it's 1.5A current limit needs a HUGE heatsink PLUS active cooling PLUS careful PCB design PLUS an ideal environment. A CAT4101 run at 1A only needs heatsinks or active cooling if your PCB sucks or you're running in a bad environment.

 

[koensayr]

small LED setup

small LED setup

Hi all. I've been lurking in the DIY section for a while and made a few posts with questions a while back. I thought since most I"m seeing are these very large builds, I thought I would just show my very ghetto small LED build for my 5 gal tank.

Please excuse the very dirty tank

I have 6 CREE LEDs on there, it is driven by a 700mA buckpuck. The circuit is still on a breadboard because I am planning on eventually adding a PWM microcontroller (perhaps a PIC?) The heatsink is some old part salvaged off of an computer. The yellow box is a 24V 2.5A power supply. There is a pot on the breadboard currently for adjusting the light.

 

[kcress]

Awesome koensayr! A pico-projector.

 

[MaLi]

If I wanted to get one of your PCBs, where could I find one? 8 of those is about right for the tank I'm building.

Foxy,

I just ordered 10 PCBs for CAT 4101 and I need only 4. Stay tuned and PM your email address.

cheers,
MaLi

 

[widmer]

Koensayr- love how the picture looks like you're hanging an IV bag on the tank. Happy reefing.

 

[Foxy Brown]

Foxy, the CAT4101 essentially fills the same purpose as you are proposing the LM317 for - they're both linear regs that can be run in constant current mode. The big differences are that the CAT4101 is made to accept a separate PWM control signal, so you don't have to PWM the power line yourself (which is probably not as simple as it looks if you want good control) and, even more importantly, the CAT4101 has a .5v minimum dropout, while the LM317 is something like 2.5v. This means it'll run more efficiently, and it'll be easier to run it "hard" (near it's current limit) without needing heatsinking. An LM317 run anywhere near it's 1.5A current limit needs a HUGE heatsink PLUS active cooling PLUS careful PCB design PLUS an ideal environment. A CAT4101 run at 1A only needs heatsinks or active cooling if your PCB sucks or you're running in a bad environment.

I detect a little bit of an over simplification. First, I totally agree about having built-in pwm, which is why I'm interested in trying it. Second, you're better off putting that MOSFET in series between the resistor and the ADJ (and running the regulator on the low-side), for PWM on the LM317. rather than PWM-ing the power line. Third, at the same voltage both chips must dissipate the same number of watts. 24V x 1A = 24W. The LEDs drop ~3.5V so 6 dissipate ~21W leaving 3W. The resistor dissipates 1.25W, leaving 1.75W for the chip regardless of which one... conservation of energy. Now, because lower drop-out if you trim the output voltage of your supply lower, then you CAN decrease dissipation of the chip.... just to be clear to those trying this.

 

[coralfever]

Are there any drivers that can run a string of 25 or more leds at 750mah? I would rather not have 10-12 drivers if I don't have to. This is for a 72" 210gal build. TIA

 

[Foxy Brown]

25leds @ 3.5V gives a voltage of 87.5... there are some 90V MOSFETs out there, and it is possible to hack-up a very simple constant-current supply from such a MOSFET and potentiometer, so you could in theory do this... a pair of them would be more stable. I've not heard of commercial solution specifically for LEDs at this voltage, but maybe others have.

 

[SpacedCowboy]

Now, because lower drop-out if you trim the output voltage of your supply lower, then you CAN decrease dissipation of the chip.... just to be clear to those trying this.

IMHO you're nuts if you don't trim the voltage supply to match - we've found a *lot* of variation in individual LED voltage requirements, ranging (IIRC) from 3.2 to 3.8v per LED. Since you're going to trim anyway, (again IMHO) it makes sense to use the more-efficient driver, that wastes less energy heating up the surrounding air.

Another point: the CAT4101 is ridiculously simple to solder (even if it is technically SMT). If you go way back to post 292 you'll see where I made one using my isolation router and through-hole components. It's been running solidly ever since at ~700mA and only gets very slightly warm to the touch.

I only run mine at 700ma because I don't want to prematurely kill the LEDs, and looking at the efficiency/life expectancy/current curves, it seems like a good compromise current. It also fits in well with the 1A max of the CAT4101. If I really wanted to go higher, I'd simply parallel the drivers, but I don't

Simon

 

[Foxy Brown]

I totally agree about supply trimming, but with a couple of caveats. I wanted to be clear to those reading this, that you ONLY get that efficiency and power dissipation improvement if you trim. Second, that only works if all your strings run at the same forward voltage.

MY tank is using 5 colors of leds, and from different manufacturers though in multiples of 6 each. Many of them have different voltage requirements, and so it is not possible to trim for them all unless I buy several 24V supplies, at which point I should really buy Meanwells and be done with it (You can get 48V units for $22 US).

That's the great thing about current-control, those voltage differences don't matter any more. They just come out as slightly high or lower dissipation by the driver.

 

[rguyler]

New design - please give me your thoughts

New design - please give me your thoughts

I have designed the layout below (top diagram is a top view for LED placement and the second shows the light spread using 45-degree optics) for a typical 90G tank (48"x18" surface area) and would like to hear opinions on whether or not this is a good design. I am planning to use Cree XP-G whites and XP-E royal blues in a ratio of 24/32. The diagram below is the positioning I mapped out using 45-degree optics. I'm also planning to use the Meanwell constant current drivers (all from Rapid).

The questions I know I need to ask:

1) I'm thinking that I may not need them out quite so far to the edges. And if I don't need them out so far, should I still keep the same LED count and just move them closer together or just remove the outer rows/columns altogether?

2) Are 45-degree optics a good choice? Rapid also has a 65-degree option but I liked the idea of a tighter spread. But what do I know?

3) What other questions do I need to ask?

Any and all help would be appreciated!

<a href="http://s563.photobucket.com/albums/ss79/rguyler/?action=view&current=LEDFixtureInfo.jpg" target="_blank"><img src="http://i563.photobucket.com/albums/ss79/rguyler/LEDFixtureInfo.jpg" border="0" alt="Photobucket"></a>