basic LED help

[salty joe]

I'm having a hard time trying to get some basic info on driving my LEDs. I'm hoping someone will be willing to share their knowledge.

I'm building an algae scrubber with 3W 660nm LEDs. I have 50 of them, but plan on using about 40. They have a forward current of 700mA and a forward voltage of 2.5-3V. I need to be able to dim them uniformly.

Would this driver do the trick?
http://www.ebay.com/itm/150W-Dimmabl...item3f29068c5f
This driver is adjustable from 0-4.5A. Is that current adjustable at the dimmer knob? If so, I could put a stop at 700mA.

This driver has 25-36V. So would 4 strings of 10 LEDs in series be the way to go?

I've been on YouTube and have been looking around and am having a heckuva time getting these basic answers. Any help would be greatly appreciated.

 

[perkint]

Driving LEDs in parallel is not ideal as they all tend to vary a bit in voltage, even at the same voltage, so your 4 strings of 10 could vary between (for example) 25 to 30V. The ones with a lower fV will pull much more current. Best case scenario, some strings are brighter than others. Worse case scenario is that the difference is so great the the lower voltage string simply blows immediately.

OK, so you spend the time measuring the voltage across each LED and build yourself matched strings of the same voltage. You dial your power supply to give 2.8A, so when the 4 strings (10 LEDs connected in series) to the PSU in parallel, each string gets 0.7A - bingo Until one LED fails, taking out a string (since the LEDs in the string are in series, like the old Christmas lights, one failing takes them all out). Now your three remaining strings are pulling over 0.9A each. When that causes another failure, the remaining two are on 1.4A. And the 2.8A thru one string...

Much better - get four meanwell LDD700s and use one for each string. And then you just need a power supply (constant voltage) that will give 36V and over about 110W. Connect all four LDDs in parallel to the PSU and the one string to each LDD. And then use an arduino nano to feed in a PWM signal (or any other 5V PWM signal).

Tim

 

[perkint]

Oh, and your eBay link is an invalid link

Tim

 

[mcgyvr]

That must be a MASSIVE scrubber..

LED driver specs are fairly easy to grasp..

-Determine Voltage rating-
For series strings the driver must be rated greater than the max Vf of the string (sum of all leds vf max) and less than the sum of the min.
So assuming 10 leds in series with a vf of 3-4v you need a driver with voltage output range of greater than (4 x 10=40VDC) and less than (3 x 10=30VDC) So a driver rated 28-42V (example) would be fine.

-Determine current rating-
If the LEDs are rated at 750mA then the driver must output 750mA (or less) Even if 10 in series or 2 in series the desired current rating is still 750mA as the current through the string is equal and you don't add up each LED like you do when determining the voltage rating.

Now I don't like telling newbies about parallel strings as some issues can arise and a single series string is just better. BUT
Now when you put 2 strings in parallel on a driver rated at 1000ma output each string "should" then get 500mA (1000/2).. or if 4 strings in parallel 250mA (1000/4)..
The current is divided equally (in a perfect world) by the number of strings in parallel.
If you wanted to drive 4 series strings at 1000mA each you need a driver with an output current rating of (4 x 1000=4000ma or 4 amps).

To help to safely parallel strings its HIGHLY recommended that you use a fast blow fuse in series with each string that is equal to the max current each string can safely carry..
If one string starts to "hog" more current for whatever reason the fuse will ensure each string never receives too much current and the cheap fuse will blow vs destroying the LEDs.

 

[zachts]

Many will caution you away from a parallel build but in this instance as long as you set it up correctly it will be just fine (there are several theads that discuss this in detail from a few years back) balancing strings is fairly straight forward and simple although time consuming.

A simple current mirror along with fuses (most will say this is a waste and too much work, but it really isn't) will eliminate the need to balance and regulate the voltage imbalance between strings and help to prevent a failed string, though it does use a little power and thus reduces efficiency (roughly like adding an extra led to each string that doesn't produce any light) it saves a ton of time on setup.

I HIGHLY caution you against buying any no name ebay drivers, some work fine but the majority are junk and can be unsafe in a DIY senario. Look to Meanwell or other name brand drivers. Powergate llc. is a great place to shop, or any of the DIY LED resellers though you'll pay a mark up from them.

Driver selection will in part depend on how you want to dim them. LDDs are great if you have pwm available and need to dim down to 0% however a simple driver like one of the meanwell HLG, or LPF allow simple knob dimming with only a potentiometer and are also apex compatable. LDD drivers require a controller or a pwm board for dimming which means more cost/or components.

 

[salty joe]

That must be a MASSIVE scrubber..

The plan is for it to be the primary filtration on my 600+ gallon tank that I've been working on forever. This is the last bit of hardware I need to build, getting so close.
I also have 50 3W 445nm LEDs on the way for the other half of the algae filter. I found a SPDT timer that I plan to use to alternate scrubbers. Nobody seems to use a lot of blue in algae scrubbers-I have a hard time believing blue won't grow algae well. I tried to research monochromatic algae growth, but kept running into a paywall. From the little blurb they show from the abstracts, some had the best growth from red, some from blue. IDK the exact wavelength they were using. If it works, I might get two distinct types of algae.

Every step of the way, I've tried to minimize energy demand. I want to see how few watts can be used to run a big system. Which I think leads me to using LDD700s and the arduino nano. Each piece is only about $5, so that fits the budget. Problem is, I don't have a clue what leg or pin from this component gets hooked to that component. Tim, thanks for that idea, is there any chance you could make a diagram of the hookup scheme?

zachts, Powergate is a great resource-thanks.

mcgyvr, thanks for the explanation-I would've thought the driver voltage output needed to fit in between the LEDs Vf numbers-that's interesting.

Thanks for chiming in you guys!
Joe

 

[mcgyvr]

mcgyvr, thanks for the explanation-I would've thought the driver voltage output needed to fit in between the LEDs Vf numbers-that's interesting.

yes if you have too few or too many LEDs then the drivers cannot regulate the output current properly.

as far as your "minimize energy" comment thats why you would want a dimmable driver so you can provide just enough light to get it to grow.

personally I think that 50 blue and 40 red is WAY..WAY..WAY overkill even for a 600G system. Heck I used 13W for a scrubber on a 150G system and had no problems growing thick mats of algae..
going off that then 52W total for a 600G should be plenty.

 

[salty joe]

I plan on using the same number of LEDs for both scrubbers-in the vicinity of 40. You are probably right about overkill, but I think I'll need the intensity of tropical high noon sun.

From what I've read, photosynthesis increases with intensity until a certain point, then photosynthesis starts to decrease with more intensity. I want enough light to find that point. Also, under intense illumination, photosynthesis goes like crazy for awhile then abruptly falls off a cliff. I believe that's called photo inhibition. Or maybe photo saturation, IDK. I hope to be able to find the photo inhibition point of both scrubbers then dim the intensity on the scrubber with a shorter time to bring the time it takes to reach photo inhibition the same on both scrubbers. That's the time the SPDT timer will be set to.

I will have access to a dissolved O2 meter to monitor photosynthesis.

 

[perkint]

Every step of the way, I've tried to minimize energy demand. I want to see how few watts can be used to run a big system. Which I think leads me to using LDD700s and the arduino nano. Each piece is only about $5, so that fits the budget. Problem is, I don't have a clue what leg or pin from this component gets hooked to that component. Tim, thanks for that idea, is there any chance you could make a diagram of the hookup scheme?

The arduino nano has 6 pins that can output PWM. You can simply connect all the LDD PWM inputs to whichever one of those is being used in the sketch (program) to output the PWM. Happy to help where i can there, but it's not just the wiring connection you need...

mcgyvr, thanks for the explanation-I would've thought the driver voltage output needed to fit in between the LEDs Vf numbers-that's interesting.

The quoted voltage for the LEDs is a typical voltage, not an actual voltage. So you tend to get a driver than can output a voltage that varies at least as far as the total of your LED fVs might vary, based on the available data - so if you are running say 10 LEDs that have fV from 3.2 to 3.5V, you get a driver that can output a range of at least 32V to 35V. A greater range is fine, a narrower range could leave you trying to run the driver out of spec, which may or may not work.

Tim

 

[salty joe]

The arduino nano has 6 pins that can output PWM. You can simply connect all the LDD PWM inputs to whichever one of those is being used in the sketch (program) to output the PWM. Happy to help where i can there, but it's not just the wiring connection you need...

Tim

I printed pin diagrams for the LDD700s and arduino nano.
What I think I understand so far is connect the power supply to all 4 LDD700s, in parallel, and connect each LDD700s to a string of LEDs in series.
LLD700s pin 14 is PWM DIM. So that would go to one the 6 arduino pins with a PWM label (leaving two of them disconnected)? Am I correct to assume a pot would need to be installed on this line for dimming?
Will I need a separate wall wart to supply power to the arduino?
The 6 PWM pins on the arduino were not labeled the same. Does that matter for this application?
Thanks, I hope I'm getting on the right track.

 

[perkint]

You lost me a bit there with that. Hopefully this will help.

The LDDs require +ve and -ve from the supply (two pins for each). They also have +ve and -ve for LED string (again two pins for each). Then they have one pin for PWM input. So, you connect your PSU in parallel to all the LDD input connections (one or both of the two pins, doesn't matter). You connect each LED string to the +ve and -ve of its LDD (again, one or both pins). Then, the PWM output pin used in your arduino sketch gets connected, in parallel, to every LDD PWM pin. They you have your sketch send the PWM setting to all the LDDs based on (I assume) the RTC (real time clock).

No pots needed. But yes, you probably will need a separate voltage supply for the arduino itself (there are other options, but cheapest is just give it its own supply).

Tim

 

[salty joe]

You lost me a bit there with that.

Sorry about that. Thanks Tim, I think I've got what you are saying about the hookup except for the arduino PWM pin. There are six PWM pins on the arduino and none are labeled as output. I have PWM interrupt digital, PWM 12C:SCL, PWM digital, another PWM digital, PWM SPI:SS digital and PWM SPI:mosi digital. Which one should be connected to the LDDs?

They you have your sketch send the PWM setting to all the LDDs based on (I assume) the RTC (real time clock).


Tim

I feel like I'm missing something. Do I need another piece of hardware to make this happen? BTW, I have never touched an arduino.

 

[perkint]

The arduino pins can often be used as input, output, communication, interupts, etc, depending on which pin and how you code it. If using it for PWM it's output only tho - I'd use one which is not also used for anything else:

So looking at that I'd use D5, D6 or D9.

You need a laptop to load the sketch to the arduino, but nowt else

Do you want to write the code for the arduino yourself, or use one of the many (many, many!) free ones out there?

Tim

 

[salty joe]

I'd definitely need to download something. I googled arduiono led dim and got hits-when I get a chance to look them over and think I might have found one that would do the trick, would you be kind enough to take a look at it before I download?

Once this is up and running, how is the dimming achieved? Would there be a knob to turn?

 

[salty joe]

Here’s a link to a thread about dimming a PWM input with a pot.
http://www.electro-tech-online.com/threads/how-do-i-dim-a-pwm-input-with-a-pot.101739/

Here’s a schematic to make it happen. I honestly don’t understand how or why most of the parts work, but I have taught myself to build from a schematic.
http://www.dprg.org/tutorials/2005-11a/index.html
I anticipate making a lot of changes to the intensity with this scrubber. I’m not sure how the dimming is actuated with an arduino, but if it means hooking it up to computer every time, this circuit or something like it would be well worth it to me.
Thanks!

 

[perkint]

You can connect a pot' to your arduino, and an RTC. Then you can code the arduino to read the voltage from the pot and set the PWM based on turning the pot' - and of course, set the lights to come on and off based on the time from the RTC. And once you've put something together using an arduino, you'll then be on to the next project

You would only need to hook up the computer to alter the time schedule.

The only good reason for using an arduino and pot is to have a play. A standalone PWM source and time switch would be easier. But not as much fun

And yes, I'll quite happily help reviewing sketches or help coding where i can

Tim

 

[zachts]

Here's a link to a thread about dimming a PWM input with a pot.
http://www.electro-tech-online.com/threads/how-do-i-dim-a-pwm-input-with-a-pot.101739/

Here's a schematic to make it happen. I honestly don't understand how or why most of the parts work, but I have taught myself to build from a schematic.
http://www.dprg.org/tutorials/2005-11a/index.html
I anticipate making a lot of changes to the intensity with this scrubber. I'm not sure how the dimming is actuated with an arduino, but if it means hooking it up to computer every time, this circuit or something like it would be well worth it to me.
Thanks!

The arduino does the same function as the 555 chip, just the arduino allows you to do a whole lot more as well if you want.

All you need with the arduino for dimming manually is a potentiometer 10kohm works well to be used as an input to tell it how much to dim the pwm output signal.

There is some very basic code for dimming with the arduino via a Knob for manual control posted around here somewhere by asid61 if i recall, but I have a copy somewhere I could send you if you want, sort of defeats the purpose of the arduino, but for a scrubber I guess you really don't need sunrise/set, etc just intensity control.

 

[salty joe]

8 LDD700s and 3 arduinos are on the way. Since the 445nm LEDs also have a forward current of 700mA, 4 of the LDDs are for the blue scrubber.

Will I need a SPDT timer to switch back and forth between scrubbers, or can the arduino do that? Will I need two 36V constant current power supplies to run both scrubbers? Only one scrubber will be on at a time.

Can a single arduino dim both scrubbers at different intensities, or should each scrubber have its own arduino?

I'm about to drill and tap the heat sinks. Am I good to go for 4 strings of ten LEDs on each scrubber? (445nm)Fc 700mA, Fv 3.4-4 (660nm)Fc700mA, Fv 2.5-3.

Thanks a ton you guys! I really appreciate the help.

The only good reason for using an arduino and pot is to have a play. A standalone PWM source and time switch would be easier. But not as much fun

And yes, I'll quite happily help reviewing sketches or help coding where i can

Tim

I am all for the easy way. The only reason I mentioned a pot is that's all I've known.

There is some very basic code for dimming with the arduino via a Knob for manual control posted around here somewhere by asid61 if i recall, but I have a copy somewhere I could send you if you want, sort of defeats the purpose of the arduino, but for a scrubber I guess you really don't need sunrise/set, etc just intensity control.

If that code for dimming shows up, I'd very much appreciate a copy.

 

[zachts]

Found it

 

[perkint]

One arduino nano can output 6 independent PWM signals. Each signal can be used to control multiple LDDs. So one nano can set 6 different light levels which can be different colour channels within one light or completely different lights. And the LDDs will dim down until completely off!

If a power supply has a high enough voltage for the highest string of LEDs and enough wattage for all the strings, you only need one supply

Tim