Sunrise and sunset for an Aquarium lit by LED strips

[sa]

I need to light a 3 meters long aquarium and I bought 30 meters of LED strips.

Here's a picture of the water tank I saved from a demolition site:




I have two 12V constant drive power supplies that can draw up to 20A.



I've been looking for a fade in/out solution on the net and didn't find much.
Then I stumbled upon Giorgos's examples and video.

They are so great that I wanted to settle on this forum and share my journey.

One very important thing for keeping healthy fish is to keep them away from stress.
Turning on and off lights is an uncomfortable situation and that is why fading light is very important for them.


I have similar needs as D-the-geek but wanted to start another thread.
http://www.pcbheaven.com/forum/index.php/topic,1463.msg5524.html


The LED_Fade_In_Fade_Out_Dimmer project may be a starting point because I plan to use a programmable switch to light up the LED strips.
But I don't know if I can scale it up for such a high current.
I understand I will have a hard time setting up a long fade time but I'm OK if it's achieved in minutes.
http://pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

The other solution, as I understand it, is using PWM.
I have to dig deeper and it looks more difficult to implement:
- giving the start/stop signal to the PWM controller and the fade in or out instruction
- the AC/DC is not marked as "dimmable" but I guess I could open it up and try to understand how it works

Is it possible to branch a PWM controller between the power supply and the strips?

The last solution could be to use a microcontroller (because I'm a software guy) but it seems overwhelming.


I will start withe the LED_Fade_In_Fade_Out_Dimmer and see if I can scale it up to very high current.
Will you please point me at components and especially transistors I could use with 15 to 20 amperes currents?

[sa]

Some links.

PWM intro:
http://blog.makezine.com/2011/06/01/circuit-skills-pwm-pulse-width-modulation-sponsored-by-jameco-electronics/

How to Control LED Brightness with a PWM Circuit:
http://www.robotroom.com/PWM4.html

Arduino PWM controlled RGB LED Strips:
http://www.ladyada.net/products/rgbledstrip/

Interesting LED lighting project (in french):
http://www.rudyv.be/Aquarium/Bricolages/Eclairage%20LED/Eclairage%20LED.htm

[sa]

I think I will use the first fade in/out circuit because I don't care about the delay.
I will add a power transistor for the LED strips.

The 12V transformer will be powered by a programmable timer but that will be a problem for the fade out.
I want to keep the transformer off because it consummes 5W power.
Maybe I'll use two programmable timers: one on the 220V and the other on the 12V.

Could I handle it another way?

[kam]

Hello sa, nice post, with lots of details. ! 

So, first let me give you some criteria which you can use to select between PWM or linear pulser. Or better, let me tell you in which situations you cannot use a linear pulser. All my fader circuits are linear, so they are simple t make, but they carry a huge disadvantage (like all linear circuits): They dissipate the excess of power on the power transistor in order to reduce the power delivered to the load (LEDs). What this means is this (with an example):

Suppose that you want to fade out completely a set of LEDs which need 12 volts to operate and they draw 1 ampere. Also lets assume that the LEDs will be completely off when the voltage goes under 4 volts, but a few volts before this point, the strip will still draw a lot of current since the voltage to current characteristic is not linear. Maybe the strip still draws 700mA at 6 volts (this is something that you need to measure and confirm for your strip).
Taken the above assumptions as correct, this is what happens. The output transistor will be called to "hold" 6 volts (12-6) while 700mA are still flowing within the load (and the transistor itself). Putting these numbers into the power formula we get:

Pt = Vce x Ic = 6 x 0.7 = 4.2 Watts

The number may sound small, but believe me, 4 watts is a big number for dissipation and will need a serious heatsink. Additionally this number is fr only 1 amp of strip. I suppose your strip draws a lot more. If this is true, just forget the linear fader.

Now for the PWM method. I happened to test one chip (A6210) some time ago. Check this out:

High Efficiency High Current LED Buck Driver using the A6210

This chip has a great advantage that it is actually a constant current buck regulator, which means that the excess of power is not dissipated on any component, instead it is not delivered. It can get a PWM input from a microcontroller or other sort of PWM circuit, and dim the output LEDs according to the duty cycle. I think that this is an one-way solution for you.

[cheerio]

Alway put NPN transistors AFTER the LED. Or use PNP. Never let the base current go through the leds

[kam]

Alway put NPN transistors AFTER the LED. Or use PNP. Never let the base current go through the leds

NPN after the LEDs will be common emitter, but the connection must be emitter follower

[sa]

but the connection must be emitter follower

That's what I understood.

Now for the PWM method. I happened to test one chip (A6210) some time ago.

I had checked this video but you said the chip could drive up to 3 amperes current.

I have separated the lights in two circuits to avoid a full blackout.
Each circuit will have 12 to 15 amperes current.

Would the solution be possible with A6210 in parallel or do they have chips that can deal with more current?

Tell me if I'm mistaken, but as I understand it, the A6210 is used to receive the PWM signal and control the current.
I will also need a microcontroller like an arduino to control the A6210.


Any chance a PWM mechanism might be hiding inside the transformer?




Someone with some electronics skills is going to help me with this project but in anything I achieve I like to have a good understanding of what is going on.
The more heads , the better!

Thank you for your help Kam and Cheerio!

[kam]

Each circuit will have 12 to 15 amperes current.

WOW! 15 amperes is too much for linear circuit. Forget it. Can;t you just break these 2 lines of 15 A each into more, like 20 lines of 1.5A each? Or power them in series with more voltage, lke for example instead of one line 12V 15A (12*15=180W) make it 120V 1.5A (again 180W) How is that?

Would the solution be possible with A6210 in parallel or do they have chips that can deal with more current?

There are no other chips with internal mosfets like the a6210 to control 15A load, or at least i do not know of any. What you can do though is make your own smps with a big mosfet, that won't be easy though unless you know how to design an SMPS

Tell me if I'm mistaken, but as I understand it, the A6210 is used to receive the PWM signal and control the current.
I will also need a microcontroller like an arduino to control the A6210.

Correct

Any chance a PWM mechanism might be hiding inside the transformer?

This looks like smps flyback topology. The left side pcb from the transformer might be the pwm circuit, the right side might be the filtering.


In any case, best solution is to increase the voltage so to decrease the amperes, or to break the circuit into more divisions with less current each. If i were you, i would power the LEDs with 220 V and i would use a triac to control the power delivered, something like a dimmer. this will have excellent operating characteristics. What you are trying to do with the 15amps is kinda brutal. You will need thick wires, thick PCBs and a LOT of heat to dissipate.

[sa]

My only constraint is the led strip.

Each 5 meters led strip consists of 300 SMD 5050 leds.

The leds inside the strip are put in 100 parallel circuits of 3 leds with two rectangular black resistors with 101 written on them.

I can cut the strips every 3 leds and plan to cut 1.4 meters strips to make two different light fixtures for the 3 meters long aquarium.

The indications were 12V, 72W per led strip (though the real consumption is 48W) and that's why I bought those 12V 20A transformers.

Now, if you tell me I could power them up with 220V, that is interesting, I didn't know I could as this is my first dive into the electronics world.

No problem with the difference in voltage? I believe there is some tweaking to be made there and maybe put the leds in series (though that will be difficult because the strips).

[kam]

Please be careful with the 220V, will you? 

Some math:
Each led strip needs 12V an consumes 72 watts of power. That is:
P = V x I => I = P / V = 72 / 12 => I=6 Amperes each

101 means 100 Ohms, 200 for 2 resistors in series, so each led row can draw max I = V/R = 12/200 = 0.06 Amperes. So there are indeed 6/0.06 = 100 rows of 3 LEDs each, a total of 300 LEDs.

Now that we have the volumes, we can do some more calculations. By adding circuits in parallel, you maintain the supply stable but the total current is the sum of each circuit's current. So, if you add 2 of these strips in series, you will need 12 volts to power them, but 2 x 6 = 12 amperes.

Connecting circuits in series, you maintain the current stable but the total voltage is the sum of the 2 circuits. If you connect for example 2 of these in series, the total current will maintain 6 amperes, but you will need to provide 24 volts instead

(for the previous cases, the connected circuits must have the same voltage and ampere characteristics).

So, if you connect 20 circuits in series, you will need 6 amperes and 240 volts.

Here is a case: You have 2 strips of 5 meters that you can cut at any length (almost). At 5 meters they draw 6 amperes, so it is normal that each 0.5 meters they dray 1/10 of the current, that is 0.6 amperes. So you could cut them every 0.5 meters and then connect them in series. You will have 20 strips connected in series to have 5 meters of strip. So if you rectify the 220 volts with a proper bridge rectifier and some high voltage electrolytic capacitors, you will only need one limiting resistor to control them.

Now, regarding the dimming. LEDs have the advantage that they can be dimmed directly by injecting PWM pulses. Therefore, a high voltage power mosfet such as the IXFH12N50F can be used to directly control the LEDs in series. An optocoupler can be used to couple the gate of the fet with the microcontroller. The power dissipation from this huge 140 Watts circuit will be as less as the I2R losses on the mosfet, that is
P = I x I x Rmosfet = 0.6 x 0.6 x 0.4 = 0.14 Watts. You won't even need a heatsink for this.

Again, please be careful with the 240V

[sa]

Add to the fact that we have the circuit above water, I am aware that this is very dangerous.

The led strips are covered with an epoxy film, rendering them waterproof.
When the strips are connected, I will seal the welding and cables with epoxy glue.

--

Your post is very enlightening and the beginning of the solution, thank you!

Let the 0.5m strip (0.6A) be the building block.

With 30m of strips, I will need to build 3 led circuits with 20 blocks in series each.

I will need 3 power sources, 3 IXFH12N50F, 3 optocouplers and a microcontroller, am I right?

Where do I buy such power sources? (I can't find some online, is it do it yourself?)


I'll do my homework now and learn about mosfet and optocouplers.

Thank you for so much help Kam!

[kam]

basically, you will need to make the switching circuit yourself. It is not as easy as 3 mosfets 3 micros and 3 optos, but it is simple enough for beginner. But please be careful with high voltage. Ar you going to have the LEDs directly above water? I thought they are on the outside. That migt be a problem with vapors and staff. Take that also into account. Also, a 1:1 transformer will be a very good idea for protection.

[sa]

I've just ordered an inexpensive microcontroller from TI and will start playing with it.
http://processors.wiki.ti.com/index.php/MSP430_LaunchPad_(MSP-EXP430G2)

Still have to think about the circuits.
Can I use a breadboard for this, any advices on which one to order and where (in europe)?

[kam]

i suppose that you can indeed. get one from ebay, or futurlec.com

[sa]

I've been investigating for a better multimeter than then entry level meters.

Which one of those two would you go for and why?

Extech EX430:
http://www.extech.com/instruments/product.asp?catid=48&prodid=272

B&K Precision 2709B:
http://www.bkprecision.com/products/multimeters/2709B-auto-ranging-true-rms-tool-kit-digital-multimeter.html