DIY LEDs - The write-up

[der_wille_zur_macht]

I have a mean well eln 60-48P what do I need to dim my array? how do I wire it? I just to to be able to dim the brightness I will driving 12 LEDs 6 white and 6 blue.

The P models want a 10v PWM signal according to the datasheet. If you'll be using a controller (Arduino, PIC, something else) then this would be easy. If you aren't planning on something that complex, you can build a circuit based on a 555 timer to basically give you a pot that'll adjust the duty cycle of a PWM signal, then you'd use that PWM signal to dim the lights.

 

[Neogenocide]

The P models want a 10v PWM signal according to the datasheet. If you'll be using a controller (Arduino, PIC, something else) then this would be easy. If you aren't planning on something that complex, you can build a circuit based on a 555 timer to basically give you a pot that'll adjust the duty cycle of a PWM signal, then you'd use that PWM signal to dim the lights.

I can comment on this, I could not get the dimmable meanwell driver to operate unless applying some voltage to the dimmable circuit. I've got a 9 volt power supply on it now and I think it's functioning correctly.

Scott

 

[der_wille_zur_macht]

Right, that makes sense. No voltage is the same as a zero duty cycle from the PWM source so you'd expect it to turn the driver off.

 

[AFWX]

AFWX,

"If I bought a couple of Aluminum U channels mounted them parallel to each other and put fans on both ends would that be sufficient enough cooling for the LEDs?"

Yes that is exactly how I build mine.

However, I would not use the anodized aluminum, it will not transfer heat as well as bare Al.

Stu

Do you have a link or a picture where I can see how you set it up? Do you run your U channels across the length of the tank or the width?

I like the Idea of using the U channels because the lighting becomes easily customized. If I want I can add another row of LED lighting by just adding another U channel.

 

[AFWX]

My understanding was that anodization provides for better heat transfer than bare metal?

Did a quick search and you are correct.

"An anodized finish will add 4 -8% to the overall cooling effect in forced air."

http://www.aavidthermalloy.com/products/extrusion/anodize.shtml

 

[stugray]

Neogenocide,

"wouldn't corrosion of bare aluminum be of a concern?"

No - only submerged Al would be a concern.


g8gxp,

"My understanding was that anodization provides for better heat transfer than bare metal? "

Bare Al has a thermal conductivity ( W/mK ) of ~250, Anodized ( aluminum Oxide ) has a TC of less than 30.

So the junction between the LED & the Heatsink would be ~1/10 as efficient with anodized surfaces.

However, the Emissivity ( how well the Al radiates ) is Better for the anodized but only by a factor of ~2.
Using bare Al should be ~5X better than anodized, but the best would be anodized BUT grind off the surfaces where you put the Stars.

I mentioned before that sandblasted Al is very good at radiative cooling, but the tables I am looking at dont show the emissivity.

Stu

 

[MontyJack]

Best temperature?

Best temperature?

What is the best LED to heatsink junction temperature? I know, as low as possible! But I would like to keep my build as simple as possible (KIS). So I don't want fans at all. I found a heatsink which would fit my needs. By counting the heat, I got 78 °C (172 °F) for the LED to heatsink junction at 25 °C (77 °F) environmental temperature. Would that be fine? I think that the surface temperature of the heatsink will be also cooler than that, or not?
Thanks
Monty

 

[sammy113]

Will any of this work for a ELN60-48P?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190313319404&ssPageName=STRK:MEWAX:IT

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190331263241&ssPageName=STRK:MEWAX:IT

Also can you use just one 10V power supply and connect two PWM circuits in parallel?

 

[akindbro4u]

wow I have been loosely following this thread for a while now, and now am at the point of building an led rig for my self. The concept has evolved so much, I don't know where to start. My tank is 60"x24"x18. Any advice from the more knowledgeable on here?

 

[Canoe]

Will any of this work for a ELN60-48P?
...
Also can you use just one 10V power supply and connect two PWM circuits in parallel?

ah, no.

ELN60-48P is 48 volts
you still need a power supply
and a safe case to house everything in

you wouldn't be saving any money, while adding to the complexity of the build (more DIY failure points)

two PWM circuits on the same supply?
if both switch off and then on at the same time, how much instantaneous current do you think the power supply can provide
worse if you're in the 10V 5A range with parallel LED strings instead of a higher voltage (i.e. ~48) and a 750mA or 1000mA max drive current

Note that with a ELN60-48 you can drive 1.3A, so two parallel strings at 650mA.
I believe that many of the users here are driving their 750mA and 1000mA LEDs some or well below their max continuous current ratings.

 

[der_wille_zur_macht]

ah, no.

ELN60-48P is 48 volts
you still need a power supply
and a safe case to house everything in

Canoe, maybe you're misinterpreting his question. The ELN series drivers run off 120v AC, but they DO require an external DC power supply for the dimming circuit. The voltage required for this dimming circuit is 10v, regardless of the drive voltage or which model in the series you're working with. The ELN models do NOT need an external DC supply for driving the LEDs, ONLY for the dimming circuit, which is really low demand.

And, since each driver has it's own internal AC/DC power supply, there's no real worry about hammering an external supply by running multiple drives on it with the same PWM signal.

two PWM circuits on the same supply?
if both switch off and then on at the same time, how much instantaneous current do you think the power supply can provide

Again, since the external power supply is purely for the dimming control, it's totally fine to use one supply (one PWM source even) for many drivers.

Note that with a ELN60-48 you can drive 1.3A, so two parallel strings at 650mA.
I believe that many of the users here are driving their 750mA and 1000mA LEDs some or well below their max continuous current ratings.

Parallel strings are not ideal in these applications, for a few reasons. First of all, if there are any tiny differences in characteristics in your various LEDs, you'll have inconsistent performance. If you have one string that ends up requiring 10.3v to drive at 700mA, and another string that requires 10.5v to be driven to 700mA, then the driver will end up over driving one string and under driving the other. Since even a small variation in voltage can lead to huge variations in light ouput, this might mean poor performance from some LEDs. In practice, I've seen 3 - 4% variation in drive voltage to achieve a target drive current from LED to LED (even in the same bin) which is enough to make me worry about performance in parallel applications.

Secondly, running parallel strings is more dangerous. If you have one LED fail to short, the entire other string will get cooked. Or, if you soldered a short somewhere in one string, again - poof.

Hence even though the ELN60-48 CAN drive two strings at 650mA, IMHO you're better off just turning it down and running below capacity.

 

[der_wille_zur_macht]

Will any of this work for a ELN60-48P?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190313319404&ssPageName=STRK:MEWAX:IT

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190331263241&ssPageName=STRK:MEWAX:IT

Those are essentially meant to be drivers themselves, not to provide a PWM signal to a driver. If you want to make a PWM signal generator that lets you turn a knob to adjust the duty cycle, send me a PM and I'll forward you some links. It's a really easy DIY project with a 555 timer chip and about 4 or 5 external components. Same theory used in some fan speed controllers for PCs, or for the DIY Tunze wavebox controllers.

 

[sammy113]

You hit the nail der_wille

Thanks for the help again

 

[Joekneebone]

Hey,
I just wanted to know a few things before I started!
If I were to get these leds: http://ledsupply.com/creexre-rb.php and http://ledsupply.com/creexre-w107.php . And use the 1000 Ma drivers, does that mean I would have to have 6 drivers?
Thanks!

 

[sammy113]

Hey,
I just wanted to know a few things before I started!
If I were to get these leds: http://ledsupply.com/creexre-rb.php and http://ledsupply.com/creexre-w107.php . And use the 1000 Ma drivers, does that mean I would have to have 6 drivers?
Thanks!

probably not. First we need to know how many LEDs you will be using.Buckpucks can handle up to 6 LEDs per driver. Then do the math

 

[SpacedCowboy]

probably not. First we need to know how many LEDs you will be using.Buckpucks can handle up to 6 LEDs per driver. Then do the math

Well, that's assuming he has a 24V PSU that can crank out the necessary current.

The math is simple:

- Each LED takes 3.7 volts. Volts "add up" as you add LEDs to a chain, so
- A 24 volt power supply can supply (3.7 x 6 = 22.2) 6 LEDs
- A 12 volt power supply can supply (3.7 x 3 = 11.1) 3 LEDs

=> The higher the voltage, the more LEDs you can use per driver.

However, if you're using the buckpuck drivers, they have a limit of 32 volts input voltage, and 32v PSU's are harder to come by (and more expensive) than 24v ones. Theoretically you could put 8 LEDs on each string if you're using a 32v PSU, but almost everyone here seems to have settled on 24v PSUs. Unless you want to blaze a different trail, it might be safest to do the same.

The following assumes you're using a 24 volt PSU.

Now you probably require more than 6 LEDs, so you need multiple buckpucks, and each buckpuck will require 1000mA (or, 1 amp) of current to drive its own string of 6 LEDs.

So, to use my own 90 LED design as an example (with 15 strings of 6 LEDs), I'll need a total of 15 amps of power at 24 volts if they're all running at 1 amp (in my case they're not, but let's keep it simple for now).

One PSU to handle 15A is an expensive option, so split it into 2, and get 2 of the 8.3A PSUs at mpja.com ( http://www.mpja.com/prodinfo.asp?number=16855+PS ) for $20 each. I intend to drive 7 of the strings (the blue LEDs) from one PSU (which would use 7A of the 8.3A available) and 8 of the strings (the white LEDs) from the other PSU.

It's generally a good idea to give the PSU's some "headroom" as well, not to run them at their peak output constantly. In my case, to add slightly more margin to the PSUs, I'll be running the white-led drivers at 0.9 amps, not 1 amp, so the {white,blue} LED PSUs will have to supply (8x0.9)= 7.2 amps and (7x0.7)=4.9 amps respectively. I'm not using buckpucks though, I have a circuit with 8 drivers on it that costs a total of $30 (not $130!) in parts - just waiting on Digikey to deliver

So, to summarise:

- The voltage of the power supply determines how many LEDs each buckpuck can support. Divide by 4 to get number of LEDs.
- The current of the power supply determines how many buckpucks the PSU can support. Each amp of PSU can support one buckpuck.
- You can use the maths above to determine how many PSUs you need.

HTH,
Simon.

 

[Joekneebone]

I forgot to mention how many leds I would be using!
I would be using 12, six blue and six white
Thanks!

 

[Joekneebone]

Thank you very much for both your replies! They were very helpful!
And SpacedCowboy, what exactly were circuits with drivers on them?

 

[der_wille_zur_macht]

However, if you're using the buckpuck drivers, they have a limit of 32 volts input voltage, and 32v PSU's are harder to come by (and more expensive) than 24v ones. Theoretically you could put 8 LEDs on each string if you're using a 32v PSU, but almost everyone here seems to have settled on 24v PSUs. Unless you want to blaze a different trail, it might be safest to do the same.

FWIW, the buckpuck drivers become fairly unreliable above 6 LEDs per driver, despite their 32V max input rating. The datasheet backs this up:

For example, a 350mA rated unit will drive up to 6 Luxeon I LEDs connected in series

So maybe it would have been fair of them to spec a maximum output voltage, too. Or put that "max 6 LEDs" up in the summary chart instead of burying it in a paragraph on the second page.

The datasheet also specifies a 2.0V head between output voltage and input voltage, but clearly you can fudge this a bit (as you pointed out many people are running 6 LEDs on a 24v supply, which technically should need 24.2V input assuming 3.7v forward drop).

 

[SpacedCowboy]

Thank you very much for both your replies! They were very helpful!
And SpacedCowboy, what exactly were circuits with drivers on them?

It's a circuit (http://www.0x0000ff.com/imgs/drivers.gif) that puts 8 of the STCS1 LED-driver chips on a single board, and which ought to drive 48 LEDs when coupled with an 8A, 24volt PSU. Costs around $30 to make. It hasn't actually been tested yet though... Digikey *still* hasn't delivered my SMT resistors, and I'm waiting on LEDs from dealXtreme (I only ordered them a week or so ago, and they've already been shipped, so it won't be too much longer). My plan is to put the thing together over the Xmas period - I have a couple of weeks off then.

For only 2 strings of 6 LED's each, you're probably better off going with the commercial buckpuck or meanwell drivers. It's a lot less hassle, and the net savings aren't really worth it IMHO.

Oh, and one thing: if you're tempted to order the 10" heatsinks from heatsinkusa to get more width for the LEDs, just don't. I got 3 of the 16"x10" ones and they weigh 17 lbs each! Each of them is about the weight of 3 of the 16"x8" ones because idiot over here didn't realise the fin heights were so different... Now I have to figure out if I want to lift ~60 lbs (rather than ~25 lbs) every time I move the lighting rack...

Simon