DIY LED driver for reef lighting

[der_wille_zur_macht]

84 LEDs on a 90g would be good at 680mA. For reference, SoundWave's original design was 48 on a 75, half at 700 and half at 1000.

Thanks for sharing the results. Interesting that you could "fit" 7 LEDs across a 24v supply - that knocks the price per LED down a fair amount.

FWIW the drops you're measuring are pretty consistent with what I've measured for Rebels in therms of variation, but your whites are indeed a hair lower than I've measured.

 

[kcress]

Just wanted to share my prototyping fun....

Steve

Thanks! Nice to see more numbers.

 

[der_wille_zur_macht]

FINALLY some PCBs!

ELN dimming shield on left, CAT4101 x 3 on the right.

 

[Skeptic_07]

oooooohhhh ahhhhhhh :lol:

 

[stephenrwright]

Nice! Do you have Eagle files for the dimming shield? I am trying to figure out what I want the arduino to do with the lights. One PWM for all? White and Blue? Or expand to 12 PWM and control each one string of LEDs?

Thanks
Steve

 

[stugray]

I am looking forward to seeing the results.

I would have gotten in immediately, but I am guessing there will be a Ver. 2.0 ;-)

Ohhh and corner holes so we can stack them.
Stu

 

[der_wille_zur_macht]

Ta daa!

Been running for ~15 minutes plus however long it takes me to type this.

6 cool white Luxeon Rebels on a pair of Endor stars on a PC heatsink under my hand. 3 x CAT4101 driver board in center (only one of the circuits is soldered up, I wanted to try it out before soldering the rest). 24v power supply on left, with RBBB Arduino stuck in the breadboard on top.

Here's the driver close up:

Seeedstudio shipped me 12 of the boards. I only ordered 5. Still, they're critically flawed - I forgot to ground the ground side of the output caps. It's an easy fix, since there's a ground plane on the top, so you can just scratch off the soldermask and bridge over to the ground plane.

Header on the left is GND, PWM, 24v, 5v inputs. Header on right is three sets of outputs.

Right now the 24v supply is trimmed all the way down (20.4v) and the LEDs are dropping 19.08v, so the chip is dropping ~1.3v. I'm willing to bet that if I could turn the PS farther down it would drop less. The IC is warm to the touch, and the PCB is a hair warm too, maybe body temperature. In hindsight, since these Rebels drop so little, I could probably run 7 on each IC as I commented above.

Right now the Arduino is just idling, I'm basically using it as a fancy 5v supply (to the 5v and PWM pins). As soon as I find my FTDI breakout board I'll put a program on it to fade the LEDs and see how it goes. But I want to do a full-power burn in for a few days, too.

 

[der_wille_zur_macht]

Oh and I know I probably don't have to say this to this crew, but eye protection is critical. This is my stylish eye protection for these experiments:

No current measurement yet but the voltage the LEDs are dropping is right in line with what it should be for the target current so I'm happy.

 

[der_wille_zur_macht]

And it dims beautifully on the Arduino.

Earlier we'd had a discussion about "cutoffs" and such. The Arduino has 8-bit PWM output (0-255). Set at 1, the device does indeed turn on, so the minimum signal required is below this threshold - we are able to get control over the whole range the Arduino can provide. It's quite dim at 1, but not SUPER dim. Hard to put into words.

And it does shut off 100% when the PWM signal is zero.

 

[der_wille_zur_macht]

Nice! Do you have Eagle files for the dimming shield? I am trying to figure out what I want the arduino to do with the lights. One PWM for all? White and Blue? Or expand to 12 PWM and control each one string of LEDs?

Thanks
Steve

I am going to assemble one of the dimming shields tomorrow. We've had discussion on them in a few other threads - they're specifically for the ELN P-type drivers from Meanwell - I just mentioned them here since I got the PCBs in the same shipment. Once it's assembled I'll test it with a multimeter but I won't be able to actually try it on an ELN driver, since I don't own any. I think I have a few people interested in "alpha" testing so I'll report back once we've determined if it works or not!

 

[shackscs]

FINALLY some PCBs!

Looks great.

What was the turn around time?

Just wondering when I should be posibly be getting mine from Seeedstudio. (Original design)

 

[Neogenocide]

If you need another tester, I've got a string of 12 whites on a 48-P. Been lurking here trying to learn a few things from you guys.


Scott

 

[Reefer08]

Any leds that are 420nm? Any ideas how many of the 3w cree's would be needed to match the par of a vho actinic? thanks

 

[shackscs]

This is thread for DIY LED drivers.You might want to swing this question over to one of the LED threads or even the main one:

http://www.reefcentral.com/forums/showthread.php?t=1678127&page=92

for an in depth response.

Here is the Cree data sheet:

http://www.cree.com/products/pdf/XLamp7090XR-E.pdf

Short version: Royal Blues 450nm and Blue 650nm.

It just keeps things on track if we stay on topic.

 

[der_wille_zur_macht]

Looks great.

What was the turn around time?

Just wondering when I should be posibly be getting mine from Seeedstudio. (Original design)

A long time! I ordered on 2/25 and they shipped on 3/4. Given the price though, it's hard to complain.

An update - last night I left it running on the "dim up and down every 10 seconds" cycle. Over breakfast I'm going to check the current at full blast and if it's in spec I'll let it run at full blast today. I'm half considering adding another LED just to see what happens.

 

[der_wille_zur_macht]

FYI: Getting ~685mA on full blast when cold - 768R sense resistor should be giving 700 according to the datasheet so we're within shooting distance. Time for a few days of full power burn in.

 

[SpacedCowboy]

Glad to see things are coming together - the 4101 really does seem to be the best chip so far

Not been paying so much attention recently since I've been busy printing up LED holders for the last few days. See my post in the other forum.

Simon

 

[der_wille_zur_macht]

With the voltage from the 24v DC PSU supplying the driver trimmed all the way down, the CAT4101 is cooler than the 7805 voltage regulator on the Arduino. :lol: I agree, the CAT4101 looks like the most promising chip at this point. Cheapest, dims well, reasonable efficiency, and it's bloody simple to put together (only 3 external components). The only catch I can see is that you MUST trim the power supply as close as possible to a particular LED string's Vf to get the most efficient performance. In that sense it's definitely not as forgiving as the NCP3066, which seemed more flexible (at one point I was running 6 LEDs from a 9v wall wart on it. )

I haven't tried it yet but I'm convinced you could run 7 LEDs on a 24v supply, as long as you used low-drop LEDs, i.e. Cree XP-G or Philips Rebels. XR-E would probably be pushing the 25v limit on the IC.

 

[shackscs]

Well, my boards showed up today. Yeah! Will post a picture when I get home. From work.

 

[biggs2003]

Have an order coming from Mouser with all my stuff for this LED project. $25 for the parts for five of them, $11.25 for a power supply, and $21 for 5 led's. Custom board I designed and will etch myself, a bit of Home Depot metal for heatsinks and I should have a working fixture.