Hello there!

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

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 separately dimmable serial circuits of 6 super duper LEDs each. One for the white and another for the royal blue LEDs.

I originally designed a circuit with resistors but was advised that LED drivers are more fitting to this application and would serve me well – great, that saves me work.

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 drivers for each set 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.

175mm 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?

 

driver are qute large but - only 1mm high?
then you can stack them both into same enclosure along with knobs.
only external thing would be power supply.

and if you find someone with 3D printer, you can have custom made box just for you. that way you can have perfect fit into tank opening and smooth face.

 

driver are qute large but - only 1mm high?
then you can stack them both into same enclosure along with knobs.
only external thing would be power supply.

and if you find someone with 3D printer, you can have custom made box just for you. that way you can have perfect fit into tank opening and smooth face.

Sorry they are 19mm high not 1mm. Typo! I can't seem to edit the post at this point.

So back to what I originally said – I can fit them both in side by side but there will not be enough room for the LED's, Fan and Heatsinks etc.

 

...I would need two drivers for each set of LED's...

There is some opportunity here, I think, to find or build a single large driver able to drive all the LEDs. This is true whether the driver is remote or in the enclosure. Unfortunately that's as far as I've gone with the idea. You're not alone, though, there's another thread on this forum on a related topic.

 

There is some opportunity here, I think, to find or build a single large driver able to drive all the LEDs. This is true whether the driver is remote or in the enclosure. Unfortunately that's as far as I've gone with the idea. You're not alone, though, there's another thread on this forum on a related topic.

How do you think the linked eBay seller has done it then? A range of resistors? I think it all works off a 12v power supply.

 

A range of resistors?

Very unlikely, as any linear technique would be very inefficient and would generate a lot of heat. Dimming is likely accomplished by PWM, which uses a variable duty cycle square wave to efficiently vary the average current to the LED.

 

Very unlikely, as any linear technique would be very inefficient and would generate a lot of heat. Dimming is likely accomplished by PWM, which uses a variable duty cycle square wave to efficiently vary the average current to the LED.

I've briefly read though this subject before but it's a little out of my comfort zone.

If I refer you back to one of my previous queries..

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.

What I am thinking is having 240v mains coming directly into the light enclosure and immediately to a standard dimmer (I want the dimmer in an accessible place ideally). From there out of the light enclosure to both of the LED drivers and then back in to the device again to power the LED's.

Plausible or plain crazy? If not I will simply create two enclosures. One for the LEDs and the other for the drivers and dimmers.

 

... but it's a little out of my comfort zone.

You and me both. I don't feel comfortable giving design advice when I know so little about the details. There are safety issues here, and the power levels involved require careful planning.

Let me suggest a couple things. 1) Reverse engineer. If you can't find what you want commercially and need to build something, find the closest products you can find and study them. How do they accomplish the functions you need? How did those designers overcome some of the challenges? 2) Make a plan, and use the experts here to review your plans.

It's important to do your own homework and come here for critique. Asking for completed, complex design from the ground up is too big a hurdle and few folks will have the time and energy to do this for you. But if you have a schematic that's "close", you'll get lots of feedback. I'm not chastising you, I'm just saying...

 

You and me both. I don't feel comfortable giving design advice when I know so little about the details. There are safety issues here, and the power levels involved require careful planning.

Let me suggest a couple things. 1) Reverse engineer. If you can't find what you want commercially and need to build something, find the closest products you can find and study them. How do they accomplish the functions you need? How did those designers overcome some of the challenges? 2) Make a plan, and use the experts here to review your plans.

It's important to do your own homework and come here for critique. Asking for completed, complex design from the ground up is too big a hurdle and few folks will have the time and energy to do this for you. But if you have a schematic that's "close", you'll get lots of feedback. I'm not chastising you, I'm just saying...

I completely understand. It's just from a previous thread in another forum the questions have changed considerably.

To be fair I do know what I need to get the job done – but I will have to live with having the dimmer elsewhere which is okay really given I won't be adjusting it all the time. More just to find the perfect aesthetic balance and then it will be left alone to be honest.

Thanks for your time!

 

... I will have to live with having the dimmer elsewhere which is okay ...

To be honest, keeping everything farther away from the water sounds better to me anyway. Doo doo happens.

 

You don't dim the AC side. You send a 1-10V DC or 0-10V PWM signal to the drivers and they adjust the output current based on that input.

Constant current drivers of all sizes are readily available on ebay with dimming potentiometers,etc..

I know because I'm heavily involved in the DIY LED stuff for reef tanks and have built my own fixture and am about to start another very soon for my new tank. (4 x 100W multichip LED's)

We all basically started with 3W Cree xre/xpg LEDs (cool white and royal blue). I've had "decent growth with that but nothing comparable to MH or T5 bulb systems. The lack of a complete spectrum is the problem with only 2 colors of LED's. Most now are including a few warm white and even some red/violet and even UV LED's to try to get a more complete spectrum for coral growth.

The most important thing with the drivers is making sure the total forward voltage of the series strings of LED's falls into the drivers capabilities. For example many have used Meanwell ELN-60-48D (or P) drivers with 9 to 13 x 3W leds in a series string. That is the perfect amount of LEDs for those drivers.
The drivers can really be mounted anywhere like under the stand,etc.. provided they get enough air flow to keep them cool.

Then comes heatsinking. Its VERY important. You must ensure the junction temps stay well below their maximums or you will just greatly shorten their lifespan/cause fires,etc..

IMO make an enclosure for above the tank with just the heatsinks/LEDs and mount the drivers remotely (under stand,etc..)

There are a few companies selling complete DIY LED kits specifically for reef tanks. I'd start there. Googling should get you there as I'm not sure about sharing links to those sites on this board. Some boards have goofy rules about that stuff.

How many gallons is your tank?
What types of corals do you intend to keep? (SPS will require stronger lights that just the shrooms you have in your tank now) LPS don't do as well as other corals with LED's but thats probably because of the poor spectrum that many users have with just the 2 colors (cool white/royal blue).

 

Here is an example of what we are doing now with the multichip LEDs'.
5 different types of chips that really gets "closer" to the MH/T5 spectrums.

This is a 5 channel 100 to 250W (if you can keep it cool) multichip LED
100 LED Chip includes:
1) 20 x 10000K
2) 20 x 455nm (blue, beneficial to chlorophyll C)
3) 10 x 420nm, 10 x 430nm (UV range)
4) 20 x 445nm (blue, beneficial to chlorophyll C)
5) 20 x 15000K

These are being mounted on large CPU heatsinks.

 

But its still new.. No one really knows how that multichip will perform "growth wise" yet.

If "growth" is your main goal. To date LED's are NOT the way to go "yet"

 

You don't dim the AC side. You send a 1-10V DC or 0-10V PWM signal to the drivers and they adjust the output current based on that input.

That was the idea.. I think. Let me attach my rudimentary diagram.

Constant current drivers of all sizes are readily available on ebay with dimming potentiometers,etc..

I could very well be looking for the wrong thing.

(3.7V * .75A) * 6 = ~17 Watt Load so I am looking for anything between 18 and 20watt. Ones with dimmers are a little rarer but I assumed that you would just stick a generic PWM Dimmer (even the light switch variety) before the driver?

IMO make an enclosure for above the tank with just the heatsinks/LEDs and mount the drivers remotely (under stand,etc..)

Yep, totally agree, that has been decided. I was just impressed with the compact design of this light. I suppose my issue is now if I can double back or not for the dimmer, wiring wise. Not a problem if not.

I will look into the DIY LED kits – I've not had much eBay luck in this respect so drop me a few hints if that's within forum guidelines lol.

My tank is an extremely modest 6 Gallon, Fluval Edge. Beautiful tank though. I wasn't planning on having any stony corals as of yet, just basic stuff like Mushroom, Brain, Star polyps etc. I'm not overly fussed on growth but the lights I currently have are not what we would class as suitable. The main reason for the light upgrade is aesthetics.

 

for now stay off ebay. It will just steer you in the wrong direction. Once you know what you need then go there to find it. Its mostly Chinese crap and their fixtures are garbage.
Reefcentral is an excellent site and has TONS of posts about DIY led setups.

You don't dim straight from the mains either. We always get a regulated 10VDC (or 9V) supply (wallwart that is fed from the mains) and use that 10V for the pot/dimming.


For driver size to make it simple.. Take the Vf of each LED (so 3.7V x 6 = 22V) and find a driver that does maybe 18-32V or something like that. Then find one with that voltage range and the desired amperage per string. So like a 18-32V driver @ 700mA (just a random example with numbers pulled outta my butt )

 

for now stay off ebay. It will just steer you in the wrong direction. Once you know what you need then go there to find it. Its mostly Chinese crap and their fixtures are garbage.
Reefcentral is an excellent site and has TONS of posts about DIY led setups.

You don't dim straight from the mains either. We always get a 10VDC supply (wallwart that is fed from the mains) and use that 10V for the pot/dimming.


For driver size to make it simple.. Take the Vf of each LED (so 3.7V x 6 = 22V) and find a driver that does maybe 18-32V or something like that. Then find one with that voltage range and the desired amperage per string. So like a 18-32V driver @ 700mA (just a random example with numbers pulled outta my butt )

I'm showing my lack of electronical knowledge here but I was under the impression that if the LED's needed a total of 22V for examples sake I assumed a 10VDC supply wouldn't cut it.. by far.

 

The 10V supply is ONLY for the dimming inputs.

 

i'd say make your own. PWM circuits are dead simple. I would make tiny PWM boards and fit them on the back side of the potentiometer. then you need very little room, you can fit them anywhere you like...

let's see, each PWM board built around some SOIC chip, few SMD resistors and capacitors, single DPACK hexfet and 4-pole PCB terminal for easy connection of power and LEDs.
should fit on something like 1.5"x1" or so.

one can use single 24V 30W PSU to power everything.