# Marine Aquarium Light Circuit Design

Discussion in 'LEDs and Optoelectronics' started by fivezerothree, Nov 1, 2012.

1. ### fivezerothree

4
0
Nov 1, 2012
Hello there!

I have a basic understanding of electronic circuitry at best. I've spent around five hours reading up on LED / Light based circuits and have almost (hopefully) answered all of my own questions accurately.

I have a rather unique Marine fish tank which has been used for a 'Coral Reef' tank. I want to upgrade the lighting to improve coral growth and the aesthetics of the tank.

This is what I want to build.

So to cut to the chase there will be two separate serial circuits of 6 super duper LEDs each. One for the white and another for the blue LEDs.

Given I will be using a 12V/5A power supply that will be also powering one or two 12V fans (undecided at this point, there's plenty of Amps anyway) I obviously need a team of transistors to wind down the voltage as shown below. I have used that 'array wizard' so I do understand that I could have this all wrong at some point.

I could make it as it stands with a simple switch but I wan't the ability to chnage the intensity of the light in order to get the best balance for my tank. I've reached a point where I can no longer make any more progress without help given I want to be able to utilise the facilities of a dimmer. I'm totally confused as to what ohm the Potentiometer should be and whether the inline resistance would be enough to actually affect the brightness of the LED's combined with the two other resistors.

To all those who choose to glance over this post – thank you for your time and patience!

Leon.

2. ### CocaCola

3,635
5
Apr 7, 2012
The best way to go about this is to use a constant current LED driver... Resistors work well for low power LEDs not so good for the high power ones...

Your LEDs want 750mA so you balance to about that with the power supply...

You have 6 LEDs in your design, so we work some quick math to get the wattage of the driver you need...

(3.7 * .75) * 6 = ~17 Watt

So you need about a 17W @ 750mA driver...

Here is a 20W @ 680mA

http://www.ebay.com/itm/Waterproof-...527?pt=LH_DefaultDomain_0&hash=item3cc83713df

This will slightly under drive your LEDs but it's minimal so there will be no real perceived difference in 'brightness'... You can search around for a perfect 750mA match @ 20W but it's not real crucial...

The only potential issue is that they device want 20-36V to be stable, you have 6 LED @ 3.7 and that is is technically above 20 so it should work... But if it doesn't then you will want to add a 1N400x diode or two in series just to make sure you get above 20V of draw...

You would wire all the LEDs in series and simply hook them up to this device, and wire it to the mains...

If you want to 'dim' the LEDs you will need to find a driver with 'dimming' ability, they are out there...

File size:
9.2 KB
Views:
136
3. ### fivezerothree

4
0
Nov 1, 2012
Fantastic – thanks buddy. I looked at drivers and didn't quite understand whether they did a similar job to resistors or not.

In regards to Voltage and stability I'm sure my current power supply (12v / 5A) isn't adequate in this situation? I assume the device linked here acts as it's own transformer so I can literally wire a wall plug onto it?

I think this is adequate! http://www.ebay.co.uk/itm/18W-700mA...93567?pt=AU_Lighting_Fans&hash=item3a6becf15f

However, how/where do you add the (any type of dimmer!?) dimmers in relation to this device?

Thanks again for all of your help – much appreciated.

Last edited: Nov 1, 2012
4. ### CocaCola

3,635
5
Apr 7, 2012
They do in fact do a similar job as resistors just better

It is but you will have to waste a lot of power with big resistors... It's simply not the ideal solution here...

That would be correct, it's an all in one solution as long as the input side is rated for your mains voltage... If it has a DC input you would need another power adapter...

That has a 220 - 240 Volt input listed, if that is the mains voltage in your area it would be fine...

Generally you simply hook these up to a light dimmer, just like you would for any light in the house...

There are options like this...

http://www.ebay.com/itm/110V-220V-L...ing_Parts_and_Accessories&hash=item27cbaeef52

Or even in 'kit' form like this should work...

http://www.ebay.com/itm/AC-220V-200...859?pt=LH_DefaultDomain_0&hash=item4d04b86003

You hook this up on the mains (220 -240V) side of the driver not the LED side...

5. ### fivezerothree

4
0
Nov 1, 2012
This little project is a great deal simpler now thanks to yourself. If I manage to get it all sorted (there's a fair bit of modding and cutting required for the actual light box) I will make sure to show you the before and after shots.

Thanks again buddy, really appreciate it!!

6. ### fivezerothree

4
0
Nov 1, 2012
I've become aware of a rather large problem with the design – the drivers are too large for the enclosure in conjunction with the rest of the components required within the enclosure.

I am limited by the size of the aquarium opening. It's not a standard aquarium given it has a glass top and a smaller opening in the middle which the pump, heater and lighting unit all sit.
Given I would need two for both sets of LED's they essentially take up 2/3 of the enclosure and that's stacked shoulder to shoulder, they won't fit any other way.

Picture of the tank opening and current light unit.

177mm x 80mm x 55mm - Usable area within tank opening
120mm x 78mm x 43mm - Size of enclosure/instrument box
91mm x 41mm x 1mm - LED Driver

My only other alternative that I could think of is to house the drivers separately? However this would forfeit having the dimmers on the actual light unit (given they need to be before the drivers) unless I double back on cabling – I assume this isn't recommend, maybe even unsafe.

Any ideas anyone?