Looking for advice on DIY LEDs - The Planted Tank Forum
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post #1 of 16 (permalink) Old 02-01-2015, 04:33 AM Thread Starter
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Looking for advice on DIY LEDs

I'm interested in taking on the DIY project of wiring up an LED setup for my very first planted tank. However, I have some concerns and questions with which I was hoping everyone could help me out. The tank size I'm working with is only 10 gallons, and I'm shooting for medium light. It's going to sit on our countertop and will have cabinets a foot or two above the tank.

I suppose the questions sort of all blend together, so here are my two concepts. Any advice on either direction would be super-appreciated. Both setups would be designed for use with dimming capability, probably an Arduino with PWM output to the driver.

First, I'm considering a semi-pendant setup. I could do two or three stronger LEDs (thinking Luxeon M 12W) a little higher above the tank. Since these LEDs run on 11V, I would utilize a heatsink/fan combo designed for 12V and typically seen on a computer CPU. Using narrower (40-degree) optics, it would keep the light focused into the tank, with a bit of a halo around the tank. I think this setup might look really cool, if done properly. But, concerns with this setup are: too much light for a smaller tank even when higher up, less flexibility on color, wiring may require a bit more knowledge, slightly higher cost.

And second, I'm thinking of an LED strip, composed of 8-10 LEDs in the 3W category (Luxeon ES LEDs) set up in two rows. Use of 60-degree optics and lower mounting would provide plenty of light for this tank. I like the additional flexibility of putting multiple LED colors on separate channels to control the color and provide individual dimming capability. This would make for nicer, more gradual sunrise/sunset stages. However, I'm not sure I'll like the look of a simple aluminum C-channel "heatsink" LED strip.

Lastly, what about hanging a single, high-powered (12W) LED with 60- or 90-degree optics over one side of the tank to cast shadows on the other side of the tank? Any examples of people trying this? Thoughts? Seems like it could be kinda cool.

In addition, I have some more DIY-oriented questions. I may be an engineer, but I'm no electrical whiz. So, I have a few probably-basic questions on the wiring side of things. Feel free to get a little technical, if you need to. But I definitely want to understand what's going on before I attempt anything. Components I'm looking at are found at Steve's LEDs. Drivers would be the digital drivers with dimming capability via PWM.

If a PSU is 25V, can you wire only one 12V LED into it? Will it simply let the rest of the voltage return to the PSU? Or do I need to connect a load that takes up the entire 24V provided? (resistor + LEDs?) The reason i ask is because if the PSU is 24-25V and two LED only equals 22V total, what happens with the rest of the voltage? Does it overdrive the LEDs if I don't dim them? Same question would apply to the 3W LEDs. If the PSU is adjustable, should I tweak it so that the voltage matches the requirements of the LEDs? (May not run at peak efficiency...) Either way, looking for direction on the proper method to wire the LEDs into the circuit. If anyone has a circuit diagram to describe this, I would love to take a look at it to help me better understand the concepts.

I figured this was more about DIY than lighting, which is why I posted here. If mods feel this should be in the lighting section, please feel free to move it there. And any help is greatly appreciated!
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post #2 of 16 (permalink) Old 02-01-2015, 06:30 AM
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Ok the first thing to understand is most current DIY designs use constant current circuits in the driver (unless using strips which are constant voltage).. Basically a Buck voltage regulator w/ feedback control of the amp output..
Put simply.. a power supply (constant voltage switching power supply) spec-d to the output needs of the LED string (more on this later) feeds a "driver" (buck voltage converter w/ feedback loop and reference) that lowers or raises the voltage to supply a set current.

If this is an all in one unit.. fine.. As separate parts you have to consider the design of the driver As an example a Meanwell LDD-H constant current driver ($7) will "lose" (don't ask me how) 3V from the orig power supply. So a 12V PS will only be able to output 9V ect.
LED's have a V(f) at which, at minimum they will light.. them Max before burn out..
Each one (types) are different (as ell as lot to lot variation) but using constant current in the string this becomes unimportant, as the driver will output a constant current, allowing each diode its V(f) at that current..
All that would be important is knowing the V(f)'s of the diode at that amperage , and adding the diodes V(f) together in series..

Say you have a 24V ps and a meanwell at 500mA you have 5 diodes that at 500mA have a voltage drop of 3V, 3.2V 2.1v 3.5v, 3.5v for a total of 15.3V.. Well within the ps -driver voltage (24-3= 19)
IF the diodes can take it and you want more output, changing the driver to say 1000mA will increase the V(f) of each diode, and you must recalculate.
But back to your orifg. question:
You could (if the PS allows it) trim the ps voltage down to more closely match the driver/led circuit to save the ps a bit of work.
The drivers themselves normally don't heat that much dissipating the excess voltage (part of the magic I don't understand but it has to do w/ the driver circuitry)
Of course the PS needs the amps (watts) but in larger ps this will usually exceed the simple setups..In the above example the ps needs to be capable of outputting 7.65W (15.3x.5) or to add a decent fudge factor 1A @ 24V (actually 1/2A)

It is simpler than I'm probably making it sound.;
steves drivers are a bit of an oddity since they are not true buck drivers.. you DO need to trim the ps to match the REAL V drop of any string.. and therefore "I" do not recommend them for a beginner.. It isn't hard, there data shhets have a good "setup" protcol but.. why??
Oh and instead of doing a full blown adruino Steves Typhon is a fair "clone" at a fair price.. Though simplistic.. BUT reprogrammable..
A recap:
Quote:
If a PSU is 25V, can you wire only one 12V LED into it?
Maybe but it depends on the actual v(f) at the current you want to drive it at and the type of driver (lossy or not).
Quote:
Will it simply let the rest of the voltage return to the PSU? Or do I need to connect a load that takes up the entire 24V provided?
no and no..
Quote:
Does it overdrive the LEDs if I don't dim them?
W/ constant current this is not possible.. You could decide to over drive them..Say max current is recommended at 700mA but you use a 1000mA driver..

As to optics.. Simple geometry..
Tan 45 degrees (1/2 of 90 degree optic) is 1 so 1" off the water and your cone is 2" in diameter..
So for full surface coverage of say 12" tank (front to back) each diode needs to be about 6" off the water surface.

I'm leaving strips out for now, but one obvious problem is at 120 degrees (native optics for most strip diodes) At 6" you have a 21" cone of light.. so light spill is a problem the higher the strip from the tank surface. W/out a good reflective shield they are fairly ineffective at distances of more than an inch or so..

Addendum:
re: 12V Luxeon-m's.. From the data sheet the V(f) at 700mA is
10.5 (min)
11.2 (ave)
11.7 (max)

Sooo running 2 in series w/ a 500mA driver (v(f) will be lower than 10.5-11.7) w/ a 24V PS "should" be possible IF you can tweak the ps a bit.. though it is close..
24(ps)-3(driver loss)=21V @ 500mA assuming a slight v drop you should be close to 21v... 2X11.05= 22.1)...PRETTY close..
A 350mA driver would be better ..or 2 @500 1 per LED.. You only need to double the ps output (2X.5) which would be easy enough to do (2A ps )


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Last edited by jeffkrol; 02-01-2015 at 06:57 AM. Reason: addendum
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post #3 of 16 (permalink) Old 02-01-2015, 03:46 PM Thread Starter
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Jeffkrol, thanks very much for putting all of that together for me. That's definitely helping me get a grasp on things.

From the looks of it, this basically summarizes what your telling me:

If a PSU is 25V and a single LED is only 11V and 1000mW, I'll need something in the circuit to dissipate the excess voltage properly. (Which would be very inefficient, dissipating 14W on that circuit...)

The driver specs do indicate the capability of power dissipation, to some degree. But the ones from Steve's LEDs only state they'll dissipate 3W per driver chip, with a good heatsink. Only going up a single 11V LED would be a poor choice. I'd need a large resistor, and waste a lot of power.

Does that cover things? I'm sure there's more to it, but basically I need to utilize the fill voltage of the line, minus what the driver will dissipate safely?

If that's true, I may do two 11V LEDs on a single driver to maximize efficiency of the circuit. (And adjust the PSU to lower voltage.) But I need to decide if I really want a pendant system, or would a linear array be the better option.

As for the Arduino, I know I could just pick up the Typhon. But tinkering is part of the project for me. It'll give me something to get into and play with.

EDIT: I noticed the specs on Steve's page display information for both 1000mA and 700mA. Is one preferred over the other? Will driving at 1000mA shorten the life of the LED, even though it's rated for it? (I saw that PWM doesn't actually change current levels, it just switches on and off at a certain frequency and duration to create the effect of dimming.)
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post #4 of 16 (permalink) Old 02-01-2015, 04:03 PM
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Quote:
Originally Posted by MrSpiffy View Post
From the looks of it, this basically summarizes what your telling me:

If a PSU is 25V and a single LED is only 11V and 1000mW, I'll need something in the circuit to dissipate the excess voltage properly. (Which would be very inefficient, dissipating 14W on that circuit...)

The driver specs do indicate the capability of power dissipation, to some degree. But the ones from Steve's LEDs only state they'll dissipate 3W per driver chip, with a good heatsink. Only going up a single 11V LED would be a poor choice. I'd need a large resistor, and waste a lot of power.
No... only important w/ Steves drivers..which are NOT Buck topology..
Even w/ them the "heat" is being dissipated by the driver, which is why you need to tune the power supply down. Second problem is if you have multiple strings w/ different cumulative V(f). Which do you "tune" your PS to? At this point we are not talking LED dissipation yet.
And yes, you are running the PS at a less than optimal level BUT not really exactly as you are thinking about it..
http://en.wikipedia.org/wiki/Buck_converter
a more in depth explanation

BOTTOM line.. it changes the effective voltage via duty cycle (pulsed on/off) NOT as a heat generating resistance "sink".. so no (little in comparison to straight resistance loss)) heat is generated
Quote:
So, for example, stepping 12 V down to 3 V (output voltage equal to one quarter of the input voltage) would require a duty cycle of 25%, in our theoretically ideal circuit.
Quote:
Originally Posted by MrSpiffy View Post
Does that cover things? I'm sure there's more to it, but basically I need to utilize the fill voltage of the line, minus what the driver will dissipate safely?

If that's true, I may do two 11V LEDs on a single driver to maximize efficiency of the circuit. (And adjust the PSU to lower voltage.) But I need to decide if I really want a pendant system, or would a linear array be the better option.
Linear arrays are easier to tailor to the tank dimensions. at least in general.. Why deal w/ a circle or 2 circles when you don't have to..

Quote:
Originally Posted by MrSpiffy View Post
As for the Arduino, I know I could just pick up the Typhon. But tinkering is part of the project for me. It'll give me something to get into and play with.
All fine and good.. the "parts" are not the problem.. The coding is..

Trust me on this one.. the Meanwell constant current LDD's are efficient, simplistic, "cool running" w/ PWM dimming.. They can't make your life much easier..
Power supply voltage is relatively unimportant.. you could practically take a 48V ps one Meanwell at 500mA and run 6V of LEDs (2x3v(f) in series w/ no heat issues up to the LED itself .. A waste of a power supply though.

Except for the voltage drop ( aminor inconvience usually).. there is no concern about heat nor any need for resistors..up to the LED itself..

NOW getting to that point.. The LED will heat up more as you increase the current.. As my orig example your 12V chip run at 350mA only produces (10.9x.350) 3.8W

most modern LED drivers are basically switch mode buck voltage regulators w/ a fixed current output..
At least as I understand it.. (subject to any corrections)
Therefore your "heating" occurs here:
Quote:
Output is regulated using duty cycle control; the transistors are switched fully on or fully off, so very little resistive losses between input and the load. The only heat generated is in the non-ideal aspects of the components and quiescent current in the control circuitry.
http://en.wikipedia.org/wiki/Switched-mode_power_supply

A NORMAL linear power supply.. (Steves LED drivers are for all intents and purposes put here)

Quote:
IF regulated: efficiency largely depends on voltage difference between input and output; output voltage is regulated by dissipating excess power as heat resulting in a typical efficiency of 30–40%.[14] If unregulated, transformer iron and copper losses may be the only significant sources of inefficiency
.

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Last edited by jeffkrol; 02-01-2015 at 04:20 PM. Reason: add
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post #5 of 16 (permalink) Old 02-01-2015, 04:10 PM Thread Starter
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Interesting... So if the Meanwell driver doesn't cover the excess voltage with power dissipation, what happens to it?

I agree the array is more configurable. The pendant looks nice hanging there than some c-channel, though. And it provided an easier cooling package, using the CPU heatsink/fan combo.

Do you have a better source for components? Sounds like you've had a little experience.
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post #6 of 16 (permalink) Old 02-01-2015, 04:28 PM
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Quote:
Originally Posted by MrSpiffy View Post
Interesting... So if the Meanwell driver doesn't cover the excess voltage with power dissipation, what happens to it?
Magic.......................................


The esiest way to understand it is the driver gets full voltage.. and chops it (switching) so over time your voltage is less.. so no need to dissipate any "excess" since in reality there isn't any (besides resistence heating in the base components ie. inductor/transistor)

You "feed" the Meanwell 24V.. it turns on only 50% of the time.. AVERAGE voltage is 12V.. no losses..

BTW: same way PWM dimming (AT the output another long story) works ..
It doesn't change the output current.. only the on/off period.. AVERAGING a lower current..
1A of current pulsed at 50% of the on time is effectively .5A.. BUT not really .5A only 1A 1/2 the time.. see..

As to parts I shop everywhere my mouse takes me..

Last build most of the parts came from LED group buy.. Coralux LDD board and drivers. Some LEDs from Steves (cyan) some from flee bay., Typhon from Steves . Aluminum, wire from hardware store, Heatsink plaster flee bay..
PS from alleletronics corp.. list goes on..

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post #7 of 16 (permalink) Old 02-01-2015, 06:15 PM Thread Starter
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That actually makes sense. Again, thanks for explaining it, even in layman's term. It makes planning this whole thing out a lot simpler. I'll definitely look into all of the items you've mentioned, and the drivers in particular. Sounds like they really make things easier.
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post #8 of 16 (permalink) Old 02-01-2015, 07:45 PM
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Wish I could build my own but since I have no money no materials and no tools, the 60$ lights on Amazon are looking good for when taxes come back http://www.amazon.com/gp/product/B00KJB1BD0/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A2RP4VCLOBWX64 idk if will even work for a 20 long so I'm going to wing it


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post #9 of 16 (permalink) Old 02-01-2015, 08:27 PM
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Wish I could build my own but since I have no money no materials and no tools, the 60$ lights on Amazon are looking good for when taxes come back Amazon.com : Lifegard Aquatics 18" Ultra Slim Plant Led Aquarium Light : Pet Supplies idk if will even work for a 20 long so I'm going to wing it
that has very low output..
20L is 30 inches long..
http://www.aquatraders.com/LED-Aquar...f-p/56545p.htm
$70.. 3400 lumens.. and the correct fit..
yours.. $67.90 374 lumens.. ONE tenth the lumen output.. wrong size..same price..

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post #10 of 16 (permalink) Old 02-01-2015, 08:34 PM
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Awesome �� thanks I'll post pics when I get it ��


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post #11 of 16 (permalink) Old 02-02-2015, 09:21 PM Thread Starter
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Looked into those LDD drivers, and I'm sold. They really sound great. I think sticking with the 700mA driver will be best in this case. Looks like the data sheet was out together using test data from that current level.

Now, the challenge is finding the PSU that fits my setup. If I want 2 strings of 5 LEDs (3W, 3V each) plus the driver (3V), that's about 18V required for each string and a total of around 36W.

EDIT: Any recommendations on where to get PSU? How many fans should I run on an array like this on aluminum channel?

(edited for my poor math skills... twice)

Last edited by MrSpiffy; 02-03-2015 at 02:58 AM.
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post #12 of 16 (permalink) Old 02-03-2015, 04:49 AM Thread Starter
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Having some difficulty finding an adequate 18V power supply. I'm seeing some simple power bricks for things like laptops, but not really any switching power supplies that I was expecting to see for an LED setup. I found a couple PSUs from Cosel (LDA and LEA series) in 18V, but they're quite expensive. Seems like it's an odd voltage. Anyone have suggestions on either where to find one that will work, or what to do to make this easier?

I suppose I could wire everything on one driver. Then I'd need a 36V power supply. But, I'd prefer the independent controls, if possible.

Looks like some of the Mean Well drivers take AC input directly. Would it be better to go with one of those that has dimming capability, rather than the LDD drivers and a separate PSU?
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post #13 of 16 (permalink) Old 02-03-2015, 05:10 AM Thread Starter
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*sigh*....

Guess I'm answering some of my own questions just with some additional research. Hate to keep pestering when I can find answers with a little Google searching.


Looks like some of the Mean Well ELN drivers will work. I'm thinking it may be better to go with one of those to avoid the extra wiring and chances for error. I'm also reading about how I'd need to set the current on them to the specified amount needed for my LEDs. Seems simple enough, if I can borrow a multimeter. If I end up getting one, would I set the current with enough juice to power both strings combined? (So, 1,400mA, since both strings require 700mA?)

From what I can tell, I'll need to stick to the Mean Well ELN-60-24 or ELN-60-27 drivers to stay within my voltage range. Will probably go with the "P" type drivers for the PWM input.

Last edited by MrSpiffy; 02-03-2015 at 05:28 AM. Reason: added driver models
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post #14 of 16 (permalink) Old 02-03-2015, 05:24 AM
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Quote:
Originally Posted by MrSpiffy View Post
*sigh*....

Guess I'm answering some of my own questions just with some additional research. Hate to keep pestering when I can find answers with a little Google searching.


Looks like some of the Mean Well ELN drivers will work. I'm thinking it may be better to go with one of those to avoid the extra wiring and chances for error. I'm also reading about how I'd need to set the current on them to the specified amount needed for my LEDs. Seems simple enough, if I can borrow a multimeter. If I end up getting one, would I set the current with enough juice to power both strings combined? (So, 1,400mA, since both strings require 700mA?)
Meanwell ELN drivers are "old school" at this point in time, and offer poor dimming performance . Use a 24V supply and the LDD's. They're quite common on Flea bay and can be purchased cheap. You don't need to be concerned with matching the Vf of your led strings to the actual power supply. The Meanwell LDD's will handle that for you. Your only concern is buy a power supply with a current/wattage rating that exceeds your lighting systems needs. Chances are, a good meanwell 24V/6.7amp supply would fill your needs nicely.


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post #15 of 16 (permalink) Old 02-03-2015, 05:29 AM Thread Starter
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Thanks! That actually simplifies things quite a bit.
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