DIY LEDs - The write-up

[der_wille_zur_macht]

IMHO if you like it the way it is, keep it. Most of these "high power" LEDs are designed to operate at lower currents than many people run them at, and efficiency (lumens per watt) drops off above a certain point. For instance, the XR-E Q5 bin is rated at 107 lumens, at 350mA. Bump current up 100% (to 700mA) and you only get about 60% more light.

Now, maybe the extra two or three watts don't matter to you and you just want it brighter.

 

[OpCode1300]

Use an LM317T to regulate the current in LED lighting projects

the LM338 is good for 5-8 amps

the LM317T is good for 1.5amps

 

[der_wille_zur_macht]

<a href=showthread.php?s=&postid=15163896#post15163896 target=_blank>Originally posted</a> by OpCode1300
Use an LM317T to regulate the current in LED lighting projects

the LM338 is good for 5-8 amps

the LM317T is good for 1.5amps

Gasp, that ties in nicely with a thread I just posted, about using the LM317 to control fan speed:

http://reefcentral.com/forums/showthread.php?s=&threadid=1652008

How stable of a concept is this though? Their schematic is clearly way simpler than the guts of a buckpuck. I'd imagine you're placing a lot of trust on that one resistor. What happens when it heats up a bit and drifts a few percent?

 

[kcress]

qfrisco; Did you read above why running two strings with a current controller is a bad idea?

 

[der_wille_zur_macht]

kcress, correct me if I'm wrong (happens often), but his implementation is probably safer than others involving parallel strings, correct?

Since he's using a 700mA buckpuck to put 350mA through each string, and the strings are made from LEDs rated to handle the full 700mA, if one LED fails (open) then he'll just see that LED's entire string go dark, while the other string gets really bright - but doesn't actually go over capacity and pop.

As opposed to, say, using a 700mA buckpuck to drive two strings at 350mA where the LEDs used were rated for a max. of 350mA. If you were to do this and one LED failed open, you'd burn up the entire other string, correct?

In the end I suppose this doesn't make it "okay" or "ideal" but at least, safer than other potential implementations involving two strings, correct?

 

[luther1200]

<a href=showthread.php?s=&postid=15160464#post15160464 target=_blank>Originally posted</a> by Soundwave
Luther1200:

The first pic is April 15th 2009 - The day I glued this purple digi to a rock.

The second is today, June 8th 2009.

This is not in direct light from the LEDs but more centered in the tank. They seem to do just fine.

Looks pretty good. Thanks.

 

[kcress]

I shall NOT correct you as you are right!

I didn't notice the 700mA capable individual strings. That's a fine way to cover that with one current driver.

Nice catch.

<a href=showthread.php?s=&postid=15164298#post15164298 target=_blank>Originally posted</a> by der_wille_zur_macht
kcress, correct me if I'm wrong (happens often), but his implementation is probably safer than others involving parallel strings, correct?

Since he's using a 700mA buckpuck to put 350mA through each string, and the strings are made from LEDs rated to handle the full 700mA, if one LED fails (open) then he'll just see that LED's entire string go dark, while the other string gets really bright - but doesn't actually go over capacity and pop.

As opposed to, say, using a 700mA buckpuck to drive two strings at 350mA where the LEDs used were rated for a max. of 350mA. If you were to do this and one LED failed open, you'd burn up the entire other string, correct?

In the end I suppose this doesn't make it "okay" or "ideal" but at least, safer than other potential implementations involving two strings, correct?

 

[timmmysli]

Another option that was a bit over my skill level

current mirror

http://www.ledsmagazine.com/features/6/2/2/Recom_Fig4

From Wikipedia, the free encyclopedia

A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current being 'copied' can be, and sometimes is, a varying signal current. Conceptually, an ideal current mirror is simply an ideal current amplifier. The current mirror is used to provide bias currents and active loads to circuits.


Looking at the wiki entry just gave me a headache lol

Would this help if one string failed with der_wille_zur_macht's setup?

 

[timmmysli]

My three spot led system is running 20x xr-e WC's and 6 RB'S all @ 1amp 95W?

What I'm wondering is with the 20 deg optics on the whites will the system be equal to a 150w MH or 250W MH in terms of photosynthetically usable radiation? I have the led's in three groups and in each group the leds are positioned roughly 1.5 inches apart.

My tanks 700mm cube x 380mm high so its a shallow and small tank.

Any ideas what my light system will be capable of. (I will be keeping my water quality as near perfect as possible)

 

[der_wille_zur_macht]

<a href=showthread.php?s=&postid=15164993#post15164993 target=_blank>Originally posted</a> by timmmysli
Another option that was a bit over my skill level

current mirror

...

Would this help if one string failed with der_wille_zur_macht's setup?

IMHO the best approach is to just not design LED systems with parallel strings, at least not with LEDs that aren't capable of taking the full blast of the driver. There are enough drivers out there that you should be able to mix and match to design a system without having to go to the extent of balancing current on the output side of a single driver.

Looking at the article referenced in the link you provided, it seems like our systems can avoid some of the problems they are trying to address. In their example, they want to drive 10 LEDs but want to do it from a low-voltage power source. Hence, running two parallel strings off a single driver makes sense. If you're designing a system from scratch for a reef tank, that probably won't be a restriction you'll face, as you can just buy a higher-voltage power supply to begin with. (Using the classic example of MPJA, you can spend about $15 and get a suitable power supply in just about any voltage imaginable.)

 

[Soundwave]

As promised, here are the pics of the Bonsai Acro.

For those of you that think Acros can't grow under LEDs, check it out.

 

[NanoReefWanabe]

awesome write up...i am glad to have found this...

i will be doing an LED system for my new pico i am building...just wanted to make sure you guys could tell me if i am on the right track here...

i plan on using 5 white and 5 blue 3 w LEDs...from what i have read i add the forward voltages to find out the size of power source i need...the blues i found are 3.2-3.5V....so five of these would be 17.5 volts...if this is the case would one of these wall warts work to power the 700mA buckpuck?
wall wart

furthermore: if that would work then i could get one in 24V to power the whites...

if those wall warts wont work can i use a single 24V power supply that has a 2A output, and run two buckpucks off it in parallel i assume, for each set of lights...i am not worried about the blues and white coming on at the same time...although i would prefer it...i dont want to have to go through the trouble of trying to figure out the relays etc...

 

[lilmonster]

<a href=showthread.php?s=&postid=15166566#post15166566 target=_blank>Originally posted</a> by Soundwave
As promised, here are the pics of the Bonsai Acro.

For those of you that think Acros can't grow under LEDs, check it out.

WOW!!! that's Great Growth!

 

[james3370]

<a href=showthread.php?s=&postid=15166674#post15166674 target=_blank>Originally posted</a> by NanoReefWanabe
awesome write up...i am glad to have found this...

i will be doing an LED system for my new pico i am building...just wanted to make sure you guys could tell me if i am on the right track here...

i plan on using 5 white and 5 blue 3 w LEDs...from what i have read i add the forward voltages to find out the size of power source i need...the blues i found are 3.2-3.5V....so five of these would be 17.5 volts...if this is the case would one of these wall warts work to power the 700mA buckpuck?
wall wart

furthermore: if that would work then i could get one in 24V to power the whites...

if those wall warts wont work can i use a single 24V power supply that has a 2A output, and run two buckpucks off it in parallel i assume, for each set of lights...i am not worried about the blues and white coming on at the same time...although i would prefer it...i dont want to have to go through the trouble of trying to figure out the relays etc...

i bought the wall warts from the same seller for LED moonlights....he also has a 20v/1a (what i got) that you should look at getting instead of the 18v since your LEDs will require 17.5, you need a bit of "headroom"

for what it's worth, i did mine w/ (5) 3watt white for t5 "shimmer" & (5) 1watt blues for moonlights each w/ it's own 20v/1a wall wart & seperate buckpuck....the blues i used a dimmable to turn the moonlights down to the level i wanted

here is my post w/ materials used list & some pics:
http://reefcentral.com/forums/showthread.php?s=&postid=14835287#post14835287

here is my post later w/ a short vid & explanation:
http://reefcentral.com/forums/showthread.php?s=&postid=14883697#post14883697

 

[apt220]

<a href=showthread.php?s=&postid=15161818#post15161818 target=_blank>Originally posted</a> by fernandokng
My only issue is that with the 44" optics and 48 leds, and about 12 inches off the water, the overall coverage is not that great for a 36"L and 18"W 58 Gallon. The sides of the tank does not have that much light, so I can't put corals there, which bumbs me out.

Fernandokng, so just to clarify, you don't put corals here?

Have you tried and the corals didn't do well? What corals did you try?

FWIW, There are some 60degree and 80degree optics out there for the Crees, but I'm not sure where to find them.

 

[der_wille_zur_macht]

<a href=showthread.php?s=&postid=15166674#post15166674 target=_blank>Originally posted</a> by NanoReefWanabe
awesome write up...i am glad to have found this...

i will be doing an LED system for my new pico i am building...just wanted to make sure you guys could tell me if i am on the right track here...

i plan on using 5 white and 5 blue 3 w LEDs...from what i have read i add the forward voltages to find out the size of power source i need...the blues i found are 3.2-3.5V....so five of these would be 17.5 volts...if this is the case would one of these wall warts work to power the 700mA buckpuck?
wall wart

furthermore: if that would work then i could get one in 24V to power the whites...

if those wall warts wont work can i use a single 24V power supply that has a 2A output, and run two buckpucks off it in parallel i assume, for each set of lights...i am not worried about the blues and white coming on at the same time...although i would prefer it...i dont want to have to go through the trouble of trying to figure out the relays etc...

As James said, that 18v supply will NOT work. You need 2v of head room for the buckpuck. So if your LEDs are spec'd at 3.5v and you want five of them, you need 3.5 * 5 + 2 = 19.5v. From what I've read lately, LEDs can vary significantly (like 10% or more) from the spec'd voltage drop, so you'd probably want one or two more v than this equation calls for.

 

[fernandokng]

I'll try to get pics up this weekend of the current set up, and I'll point out what I'm referring to.

<a href=showthread.php?s=&postid=15167538#post15167538 target=_blank>Originally posted</a> by apt220
Fernandokng, so just to clarify, you don't put corals here?

Have you tried and the corals didn't do well? What corals did you try?

FWIW, There are some 60degree and 80degree optics out there for the Crees, but I'm not sure where to find them.

 

[der_wille_zur_macht]

I know there have been one or two posts in here about DIY drivers (instead of buyung buckpucks or all-in-one drivers), has anyone else had thoughts or experience in this direction?

Alternately, does anyone have technical information (besides what is available on the web) about buckpucks or any of the other common drivers? I'm guessing it would be either difficult or not cost effective to try to exactly duplicate a commercial design, but it would be helpful for reference purposes. I'm seeing lots of designs on the web for DIY LED drivers, but having a hard time evaluating them compared to commercial units. Clearly, some of them are inferior, but some of them look promising. For instance, here is a schematic for using an NCP3063 from On Semi, in a constant current mode:

Looking at the datasheet for the NCP3063, it'll be around 75 - 80% efficient run like this. I know people have talked about buckpucks being in the 80 - 90% range, is that something that is verifiable?

I'd love it if lynxvs or someone else who has DIY'd a driver could provide some more detail.

 

[spjames]

A great resource is National Semi's 'webench' online application...

You enter your led requirements and it will design the circuit, provide a bill of materials, allow you to decrease footprint/ increase efficiency, run sims etc, etc...

http://www.national.com/analog/led

 

[der_wille_zur_macht]

Thanks for the link. I found that a few minutes ago and am already playing with it. Unfortunately many of their monolithic LED driver ICs are in really tiny surface mount packages, which I would be nervous about soldering by hand.