# Aquarium LED Project

Discussion in 'The Projects Forum' started by Lee Chris, Oct 11, 2016.

1. ### Lee Chris Thread Starter New Member

Oct 12, 2015
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0
Hi I'm working on this project and the shop send me the wrong voltage LED driver that I've asked for, but I'm just wondering if it would in fact just work. Here are the details:

LED Driver Specs:
Output 30-36V 1200mA 40W

LED Specs (planned to put two in parallel):
20-25V 600mA 20W

The wattage and amps add up, only the voltage don't.

If this would burn my LEDs, I'm thinking of adding another two small loads in series to each of the two LEDs that takes up around 3-3.6V and 3W. This should sum up to 28.6v total which might be close enough to not to burn things out but eats up 3W from the LEDs which technically makes them not operate at maximum power.

What do you think?

Btw, does anyone have a way of how to calculate/estimate how big of a heat sink I need for these super bright LEDs? I have some small CPU fans that can also be used to cool down my LED shell which itself is designed to dissipate heat.

Thanks and appreciate for any help!

2. ### wayneh Expert

Sep 9, 2010
12,154
3,061
Is the driver a constant-current driver? If so, it might be fine. Do you have a link to the specs? The output voltage will settle where it needs to in order to hit the required current. The LED spec tells you that will be around 23V. The 30V lower limit on the driver spec might indicate a problem.

3. ### Lee Chris Thread Starter New Member

Oct 12, 2015
9
0
I don't have the detailed spec of the driver but yes it is a constant current driver.

I hooked it up with the extra load in each path of the LED and they work fine. I don't dare having them on for too long until I also have the heat sink ready. But I sure hope that the math checks out so they last.

Is there something that I should measure that guarantees things are working within limits? Like maybe the voltage between the LEDs are in fact within 20-25v?

4. ### wayneh Expert

Sep 9, 2010
12,154
3,061
The current through the LEDs is far more important. That's what dictates brightness, heat dissipation, and lifetime. It may be worth measuring the voltage for intellectual curiosity, but the value won't tell the critical story that current will.

5. ### Lee Chris Thread Starter New Member

Oct 12, 2015
9
0
Cool so sounds like we're set since it maxes out at 1200mA.

Having it work is good but I really want to understand this intellectually though.

Thanks Wayne!

6. ### wayneh Expert

Sep 9, 2010
12,154
3,061
One thing you should consider is the power being wasted by the voltage-dropping load in between the driver and the LEDs. It's an efficiency loss and will cause heat. If you don't care about those things, then you're good.

On the upside, the added loads may help the two parallel strings balance out better. In general you would prefer one controller on each string, because otherwise one can end up hogging more than its share of the load until it burns itself out, and then the other one takes the full current and pops like a fuse.

Lee Chris likes this.
7. ### Lee Chris Thread Starter New Member

Oct 12, 2015
9
0
Because it's an aquarium lamp, I didn't want to have too many LED drivers sitting around. Actually I also have a second set of lamps that uses pretty nice CREE LEDs. I have another question regarding that setup:

So I have 2 identical pieces of LEDs and one other that is different:

2 pieces: 10 XPG2 LEDs with specs: 30-36V 900mA-1200mA 30-40W
1 piece: mix of 12 white & 8 blue LEDs (made in Taiwan) with specs: 30-36V 900mA 30W
(attached the images)

So I attempted to put these in parallel under a 100W LED driver, they seem to operate fine for a day or so (on and off) with decent heat sink. Then out of no where the LED driver didn't work anymore. The driver was only merely warm.

Wondering if it in fact did what you said and pulled too much current and killed the driver?

Also, how (if it's possible) would you connect the 3 LED pieces together with only one higher power LED driver?
- perhaps using resistors to regulate current?

Thanks!

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8. ### hp1729 Well-Known Member

Nov 23, 2015
1,964
219
what type of fish yank do you have? Fresh water or salt water. If salt water do you have coral? What wavelength are the LEDs?

9. ### Lee Chris Thread Starter New Member

Oct 12, 2015
9
0
20W ones are basically grow lights at 660 & 450 red and blue.
White ones are 6500k white lights.

This is probably too much light, but I really want to try it out. Trying to grow HC and my current ones are likely not bright enough. I'm just using a few 5630 SMD strips with some SMD grow lights alongside. My HC had been surviving but not growing, so I'm taking a stab at it. At the same time I like playing around with DIY.