The Planted Tank Forum - View Single Post - DIY LED lighting for a 55gal long planted Tang tank
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10-01-2012, 06:20 PM   #4
RelatedToTheFish
Algae Grower

Join Date: Sep 2012
Location: Spring, Tx
Posts: 6

Quote:
 Originally Posted by iano7000 Well the arduino nano is a good starting point. It has 6 PWM outputs, so with a mosfet switch you could dim and individually control each set of LEDs. As for power supply, you would need two separate voltage levels. Then you could run three chains of spectrum filler LEDs off one voltage in parallel, and the other two chains of white LED mix off the other voltage in parallel. After you find out what voltage you need for the two chains, you can source a power supply of digikey or mouser. I think you have a good start. I completed my own DIY setup using an arduino Mega 2560.
Thank you. I'm going to try and work this out below. If I'm off base, let me know.

Quote:
 Originally Posted by magnum As for building your own driver, check out this link. http://www.reefcentral.com/forums/sh....php?t=1759758
Thank you, too. I've looked at that thread briefly before and got confused by the sheer amount of methods. CAT1401 seems to be the gold standard, but the STCS1 looks enticing given the example circuit is 500mA. Any circuit junkies out there have advice for me on what might work best?

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Alright. It's been a while so let's see if I can get this right. Additive for the forward voltages and dividing current for each parallel string?

Both the whites have a 3.2V to 3.6V forward voltage. That means if I use the STCS1 I have a range from 4.5 to 40V available. Let's say I go for a 24V at 1A power supply (or will the loss from the circuit take my parallel current below 500mA?)

24Vcc / 3.4Vf ~ 7 LEDs per string
1A / 2string = 500mA per string

So one power supply and 2 strings could get me one half my tank in whites? What happens with excess voltage would the 2 STCS1s need to be sunk somehow to dissipate that? Also I hear a lot of advice warning against parallel strings. That loss of one string or even one LED can blow the whole thing. Would that mean I would need some current-limiting fuses or could that be worked into resistors in the final circuit?

Now we move on to where things get odd for me. If we're working on one half at a time, I have one each of the the spectrum fillers.

Cyan 3.2 to 3.6 Vf
Violet 3.2 to 3.6 Vf
Red 1.9 to 2.3 Vf

All of those sit below 4V and can't be driven by an STCS1. So what do I do here? I've looked at using MOSFETs as a possibility and a really low voltage source. Is that the way to go? Or maybe a higher amperage power source, say 2.0A and a couple DC-DC converters to get 3.3 volts for the Cyan and Violet?
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Last edited by RelatedToTheFish; 10-01-2012 at 06:42 PM.. Reason: adding more details