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General Category => Your projects => Topic started by: sa on April 27, 2012, 11:03:45 AM

Title: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on April 27, 2012, 11:03:45 AM
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:

(http://i.imgur.com/MO2JZ.jpg)


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

(http://i.imgur.com/jhmZk.jpg)

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?
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on April 27, 2012, 12:32:48 PM
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
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on April 27, 2012, 22:03:31 PM
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?

(http://i.imgur.com/ssvBG.png)

(http://i.imgur.com/2twuE.png)
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on April 28, 2012, 20:35:57 PM
Hello sa, nice post, with lots of details. !  8)

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 (http://www.pcbheaven.com/userpages/high_efficiency_high_current_led_buck_driver)

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.
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: cheerio on April 30, 2012, 14:55:15 PM
Alway put NPN transistors AFTER the LED. Or use PNP. Never let the base current go through the leds
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 01, 2012, 11:05:29 AM
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
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 01, 2012, 11:45:55 AM
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?

(http://i.imgur.com/WZyy9.jpg)


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!
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 01, 2012, 13:30:11 PM
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.
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 01, 2012, 14:24:09 PM
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).

Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 01, 2012, 16:27:05 PM
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









Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 01, 2012, 17:17:52 PM

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!


Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 01, 2012, 22:10:50 PM
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.
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 11, 2012, 18:06:48 PM
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)?
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 11, 2012, 19:03:13 PM
i suppose that you can indeed. get one from ebay, or futurlec.com
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 13, 2012, 20:14:01 PM
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
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 14, 2012, 20:50:45 PM
I believe this can be related to my project for the high voltage supply.

Xantrex 300V 4A Power Supply Teardown
http://www.youtube.com/watch?feature=player_embedded&v=27c4RTntAPw#t=466s
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 14, 2012, 22:33:09 PM
basically, the theory behind this filtering-rectify-smoothing unit is awesome!!!
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 14, 2012, 22:45:05 PM
Do you have some links about how to make simple high voltage power supplies with circuits (and theory)?

I'm still asking myself what is the least dangerous, high voltage or high current?
I could also stay at 12V and split in more PWM controllable circuits but that might be a hasle.

Can't wait to play with the MSP430 microcontroller!
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 15, 2012, 08:10:15 AM
As a beginner, i suggest you stick to transformer with linear regulator, a set of capacitors and bridge rectifier. That will be enough. Safe voltage is generally considered anything below 50 VDC.

Here is a page how to make a linear regulator.
http://www.satcure-focus.com/tutor/page5.htm
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 17, 2012, 09:57:57 AM
Thanks, I've been looking at a lot of designs and I begin to have a better understanding of the process!

There is an IC inside the 12V power supply named SDC7500.
I could only find the datasheet in chinese but it may be interesting.

It is a DC/DC converter and in the title of the document, there is PWM written.
Is the chip using PWN to achieve its duty or can it be controlled by PWM?
I need a little help on this one, thanks! :)

Chinese datasheet for SDC7500 DC/DC:
http://www.sdc-semi.com/UploadFile/SDC7500_CN.pdf
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 17, 2012, 10:11:11 AM
SMPS converters use PWM pulses to achieve the desired output, by altering the duty cycle of the pulses. Usually there is some sort of feedback from the output back to the chip, and according to this feedback it increases or decreases the duty cycle. I suppose that this feedback is the pin 1 (page 5 of the datasheet) which gets the output voltage. The PWM pulses are then applied to the switching transistor (top-right), so they musty come from pins 8 and 11 (C1-C2). Why are 2 pins? Not a clue!  :-\

Anyway, the point is that the chip probably generates the PWM pulses to maintain stable output.
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 17, 2012, 10:32:22 AM
You're quick! :)

So there might be a possibility to hijack the feedback from the output and to control it from there.
Whether I can do it is another  big question. :)

I think I will try to spy the signals with the voltmeter in the first time.

--

You suggested to go with a linear regulator.
From what I read, those circuits are efficient if the input and output voltage don't differ much.

Now, I'm also questioning myself if I really want high voltage in the tank, I'm not current Mohan.

I have found this chip, it looks interresting, it can drive up to 20A current:
http://www.linear.com/product/lt3743
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: kam on May 17, 2012, 10:59:46 AM
Have you decide how you will connect your LEDs? If they are close to water, i strongly suggest that you use transformers (220 to 48V for example), for 2 reasons: first to have lower voltage to play safe, and second (and most important) to isolate between earth and your circuit.

Now, regarding the linear supplies, you are right. in mathematical words, you need to dissipate the amount of power you don't want to be delivered. It goes something like this:
If you have 48 volts supply but you want to regulate it to 40 volts, and your circuit draws 1 ampere, no matter what sort of linear supply you will use, there will be 8 watts of power that must be dissipated as heat. That is because your power transistor must "hold" 8 volts (48-40=8) at 1 ampere. Generally, anything above 1 watt will need a TO220 transistor with heatsink. Above 4 watts you may consider using a small fan or a large heatsink, otherwise the transistor will fry in seconds.

On the other hand, SMPS deliver only as much power needed, and that is why they achieve that high efficiencies. I've just made an SMPS LED driver with the A6210 and a PIC. The controller gets 2x18 volts AC and drives up to 8 3W LEDs in series, a total of 24 Watts at 700 mA. The chip can drive up to 3 amperes (!!!) so i can scale it up (almost easily) to about 65 Watts, but i certainly need to change the linear supply with something else (not sure what). The AC power comes from a transformer (for isolation) which is driven to a linear regulator (only to sink the over-voltage from the transformer). I can fully dim the LEDs with PWM pulses with 1024 duty-cycle steps. That is only possible with SMPS, otherwise, i would need to sink 24 watts (3watts x 8 leds) to maximum dim the LEDs

Now, why i wrote all these????  ::) ::) ::) ::) ::) ::)
Oh yeah, to point out that you may consider using both linear and SMPS
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 17, 2012, 11:16:35 AM
Lights will be close to the water, it is very important for plant growth.
I will go with 48V, I don't want the fishes or their owner to die.


I enjoy reading you, it's enlightening!
And now i don't know if I want to do this project for the result or the fun of it! :)

I'm considering ordering samples of a chip, but there are two references:
LT3743EFE#PBF
LT3743IFE#PBF

I don't know what EFE and IFE mean.
From the specs, FE is for TSSOP 28 design (there is also QFN but i believe TSSOP will be easier to solder).

Does the "E" and "I" mean something special?
Which one should I chose?
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: George on May 17, 2012, 12:53:23 PM
Refer to Note 2 on page 3 of the datasheet E is spec'd 0C -125C junction temp, I is spec'd -40C - 125C junction temp
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 17, 2012, 22:45:45 PM
Thank you George!
Title: Re: Sunrise and sunset for an Aquarium lit by LED strips
Post by: sa on May 24, 2012, 16:01:38 PM
From http://www.edaboard.com/thread221063.html

Quote
Re: Control 20A- 12V DC motor
Yes, you can use PWM to control this motor. To control the speed only, you can use one MOSFET/BJT to control the motor. To control the direction as well, you need to implement a full-bridge circuit.

At this power level, I'd recommend that you use a MOSFET. What is the frequency of PWM that you are going to use?

You can use a POWER MOSFET, which has a low Rds(on). So, you minimize power loss and increase efficiency. However, this will require a driver circuit that will provide the MOSFET with around 10v from the logic level of the microcontroller and also supply more current.

Alternately, you can use a logic level MOSFET. However, they tend to have higher Rds(on). By using a logic level MOSFET, you can drive the MOSFET directly from the microcontroller. STP55NF06L is among the better logic level MOSFETs I've come across. It has an Rds(on) of about 18mohm. This is quite low for a logic level MOSFET and even comparable to POWER MOSFETs. The IRFZ44N has a higher Rds(on) than STP55NF06L. Using a logic level MOSFET simplifies the drive circuit.

Hope this helps.
Tahmid.