DIY LED for small tank problem.

1806 Views 7 Replies 5 Participants Last post by Baadboy11, Nov 8, 2010

Hey Z

Discussion Starter · Oct 23, 2010

I need a little help from some electrical engineering-minded folk. A little back story: I was given a 20 gallon tank last year, only recently changed it over to a planted tank, and the lighting unit was falling apart. It worked, but all the interior plastic was brittle and literally crumbling and it didn't have a plant bulb. I've been looking all over on this site and was really intrigued about LED lighting, and since I'm planning on getting a much bigger tank in the future, I thought I'd try to light my little tank with LEDs just to play with it. I've barely gone over the cost of a new hood so far, so I'm not really out anything. I was thinking just a 4 led setup using the existing hood.

Anyway, I ordered a few things from Deal Extreme, and I'm not sure if I got it right. I got this driver and 5 Cree Q5's (one extra) and some thermal plaster.

I hooked it all up quite easily, but it was blinking. So ok, back to square one, and I start quadruple checking everything. I think I got the wrong driver, as it's output voltage (18-43v) is way too high for 4 leds. I guess I was thinking 3w leds x4 in series needs a 12w driver. I'm not much of an electrical genius, that much I've come to figure out. So, basically is there any way to throw a resistor or regulator, possibly even a dimmer into the system with what I have so it works, or do I need to get a whole new driver and which one should I get?

Thanks.

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Shawnts106

· #2 · Oct 25, 2010

I believe you need a meanwell or buckpuck driver.. Look at Rapidled.com.. that should help

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Baadboy11

· #3 · Oct 25, 2010

How did you wire your leds? In series or parallel? I would look at that first...I believe you want series. If thats the case then I would say the driver isn't putting out enough mA...its rated for 320mA but the leds like to be driven at 350mA - 1000mA. Don't order anything till hoppy chimes in, he's the resident expert.

If you do get a new driver check out these

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Hoppy

· #4 · Oct 25, 2010

You can drive the XR-E LEDs as low as 175 mA with no problems - my light fixture is set up to do that for "low" light. I suspect the problem is related to the driver producing more voltage than the drop across the 4 LEDs in series, which is about 12-14 volts. If you try a 2 watt, 20 ohm (or 22 ohm) resister in series with the LEDs, that should use up the surplus voltage. I can't say this will work, but it would be a cheap thing to try, and it won't damage the LEDs or driver.

A bigger question is whether 4 LEDs will give you enough light for a 20 gallon tank. I doubt that they will, and I suspect that you will have extreme "spotlighting" - 4 brightly lit spots on the substrate. You can look at this and see if it helps: http://www.plantedtank.net/forums/diy/84212-designing-building-led-fixture-22.html#post1102937

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Hey Z

Discussion Starter · #5 · Oct 26, 2010

Hoppy said:
You can drive the XR-E LEDs as low as 175 mA with no problems - my light fixture is set up to do that for "low" light. I suspect the problem is related to the driver producing more voltage than the drop across the 4 LEDs in series, which is about 12-14 volts. If you try a 2 watt, 20 ohm (or 22 ohm) resister in series with the LEDs, that should use up the surplus voltage. I can't say this will work, but it would be a cheap thing to try, and it won't damage the LEDs or driver.

Ok thanks, that's what I was thinking would work. Now to track down resistors...

A bigger question is whether 4 LEDs will give you enough light for a 20 gallon tank. I doubt that they will, and I suspect that you will have extreme "spotlighting" - 4 brightly lit spots on the substrate. You can look at this and see if it helps: http://www.plantedtank.net/forums/diy/84212-designing-building-led-fixture-22.html#post1102937

I thought about that too, but considering how bad my current lighting unit is, anything's an upgrade. This is more of an exercise in just putting an LED system together in an existing strip light hood. It's $45 for a new hood/bulb, and so far, I've spent about $35 and I'm learnin stuff. As far as diffusion and spotlighting goes, you're probably right, but I'll see how bad it is before I get all worked up about it, gotta make the damn thing go first.

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redfishsc

· #6 · Oct 31, 2010

Hey Z said:
I think I got the wrong driver, as it's output voltage (18-43v) is way too high for 4 leds. I guess I was thinking 3w leds x4 in series needs a 12w driver. I'm not much of an electrical genius, that much I've come to figure out. So, basically is there any way to throw a resistor or regulator, possibly even a dimmer into the system with what I have so it works, or do I need to get a whole new driver and which one should I get?

Thanks.

That would be your problem, as Hoppy referred to.

Thsi driver has a minimum voltage output of 18v, which would be 5 of your Cree's, although I personally would max it out at 10 or 11 LEDs.

Reason--- if you only use 5 LEDs and something pops one of them, the other 4 get over-voltage and you risk a cascade.... blown LEDs can happen, even Cree isn't immune to making a bad LED once in a while. I blew an XPG the other day.

I'd also have to suspect you'll want more than 320mA for lighting this tank for plants, even with 10 LEDs. You might want to consider this driver:

http://www.dealextreme.com/details.dx/sku.42906

9-12 LED at 670mA. Would be a good driver for your XRE's.

May I suggest you throw in at least a few royal blue LEDs? I run a 50/50 mix and it looks wonderful (around a 10K look). Most folks will prefer a 2:1 mix though, white to blue. The royal blues put out blue in a peak that is very photosynthetically active.

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Hey Z

Discussion Starter · #7 · Nov 8, 2010

'lil update: I did a little tinkering with resistors, but I got it up and going without them and wired up all 5 LEDs I had, since I had ordered a spare. It's not blinding bright, but it's a ton brighter than the old florescent bulb. I don't have a meter to tell you how much brighter, but after almost 2 weeks now, my plants are a lot happier and growing faster. Here's what it kinda looks like:

This was before wiring and while I still had 4 on the bar, but you get the idea. Drill 2 holes in the top of the hood, carriage bolts through the top, suspend an 1/8th inch thick aluminum bar with nuts on each side of the bar, thermal plaster on the LED's, wire it up and tuck the driver in back.

A blown LED was essentially what I was simulating when I had 4 wired, so if one blows, it'll just go back to blinking, possibly damage the remaining ones if I don't catch it soon enough, and it'll give my epileptic fish seizures.

More LED's would mean a custom hood, or suspended hood to spread them out more, and more money. This is at best a year long setup and trial run, but I see everyone's point. More LED's and a few blue ones would look better, but if I had more money to spare atm, I'd be building this thing into a sump for a bigger tank instead of trying to light it optimally. $40 total spent, still under the cost of a new hood and plant tube.

Thanks for all the advice though, I really do appreciate it and will use some of it when I start my big build.

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Baadboy11

· #8 · Nov 8, 2010

Just fyi, the leds at least on my setup look dull, but I'd still say i'm in the mediumish range...they put out more light then they look like is what i'm really trying to say. :confused1:

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