Help/opinion needed for Luxeon III project...

[Apomike]

Hi everyone,
First, I'll admit, I am a NooB. I haven't really done anything electronic since physics II in university, and even that was limited to basic understanding. I hope some of you can bear with this post, and hopefully, thread.

I'm trying to build a bright display for my babies' room using Luxeon III's as illumination. It will be multicolored, don't know if it will be a rainbow, or a lightning bolt, but there will be a (white) illuminated cloud, too.
I'm using Luxeon III's, because they are basically free at work, as long as I can prove I used them, not sold them.

My problem, of course, is the driver. I saw the Xitaniums sold by futureelectronics, but I understand they can only handle 4 LEDs at a time, and would be expensive. The buck pucks seem the same. I really want to get this in under the wife's budget, and nose!

Here's the data for the LEDs, so you don't have to look at the info elsewhere:

At 700mA blues, greens have a forward voltage of 3.03 (min), 3.7 (avg), and 4.47(max)

At 1400mA, (I'll only run them at 1000) reds, oranges, amber have a forward voltage of 2.31 (min), 2.95 (avg), and 3.51(max)

I saw some drivers at www.hobbytron.de from **broken link removed**. They caught my interest because they cost only 16 euros each...

HKO700 constant current power source

startup ca. 5.8V (for one 3 Watts LED)
drop:ca. 2.5V
Max input voltage: 35 Volts
700mA constant output current
Input: reverse polarity protected
Tolerance <3%

Says it can drive with constant current up to 10 High-power LEDs in white, blue, or green, or up to 16 high-power LEDs in red, amber or orangs, depending on input voltage.


HKO1000 constant current power source

startup ca. 6.8V (for one 3 Watts LED)
drop:ca. 3.5V
Max input voltage: 35 Volts
1000mA constant output current
Input: protected against confusion of the poles
Tolerance <3%

Says it can drive with constant current up to 10 High-power LEDs in white, blue, or green, or up to 16 high-power LEDs in red, amber or oranges, depending on input voltage.

These say I can run 10 Luxeon IIIs off of each. I was planning to run 10 blues and greens off of a 700mA unit, and 10 red, orange, and amber one off of the 1000mA model. Do the numbers work out? Will they do the job? Could you recommend a better (lower cost) off-the-shelf solution?

What would it take to get these power supplies to work from a 220V standard european outlet?

I emailed the manufacturer, but never got a reply. Can anyone here help?

My only constraint is time. I have to get everything soldered (not running) by February 17th, before our next inventory.

I appreciate any help or assistance anyone could give.
Thanks.

 

[audioguru]

I hope your baby doesn't look directly at those extremely bright LEDs. Blindness might result. Use the LEDs for indirect lighting for safety.

Hiow are you going to cool the high-power LEDs?

 

[Hero999]

Have you considered using a simple series resistor?

The formula is:
[latex]R=\frac{V_{SUPPLY}-V_F}{I_F}[/latex]

Use a mains adaptor to safely power them off the mains.

 

[Apomike]

I was going to heat sink them onto some extruded aluminum rails, stuck on with either some Arctic silver or some kind of conductive epoxy.
I thought maybe some conductive tape, but after I read some here, I decided against it.

The LEDs would be placed behind opaque plexiglas or other plastic so the colors would seem to blend. I do want it to be somewhat bright, though. I checked out the blend effect with some of the same kinds, just individually mounted on little aluminum blocks behind some of the same plastic, so I already have an idea beyond "mental" visualization. I do appreciate the concern, though.

Do you mean a resistor between the mains adaptor and the LEDs?
I thought a constant-current power source would be best, from the literature, anyways.

I was planning to make three different arrays, in strings of ten, each having its own dedicated constant-current power supply. The ones I wrote about (the HK700 and HK1000) were the most economical -if they can really handle a 10-unit array- for the job, after considerable googling under "LED driver".

Thanks so far!

 

[Hero999]

Yes, I mean adding a resistor in series with the LED.

A constant current source is recommended but it isn't that improtant, especially if your suply voltage doesn't vary by much.

You can make a constant current from an LM317 regulator, the circuit is on the datasheet which can be found from Google.

 

[audioguru]

The forward voltage of the LEDs varies a lot. Maybe they are all from the same batch and are 3V or maybe they are all 4.5V. Testing the forward voltage with a resistor might blow them up.

Test with a regulated current source, record the forward voltages, connect a mixture of their voltages in series then caculate a current-limiting resistor for each series string.

 

[Apomike]

So it's not as easy as solder them all in series, and connect them to the power supply, no transistors because the current is constant?

I was under the impression that I could just add the voltages (the typical voltage) keep it a little under the what is supplied by the power supply's delivery, and that everything would be fine...as long as I used the 700mA ones and the 1000mA ones all on their own supply.

The drivers have a maximum output voltage, which I understand I can't exceed, and they keep the current constant, so I shouldn't have to worry about using resistors. I just figured these "plug and play" devices would do their thing for me.

 

[Hero999]

You do need current limiting, you can't connect a 3.3V LED to a 3.3V supply and expect it not to overheat. You could connect it to a 4.5V supply with an approprietly sized series resistor.

 

[audioguru]

Your constant current drivers might not be able to drive 10 LEDs in series if their forward voltage is high and adds to more than 31.5V and 32.5V. Maybe only 7 LEDs in series. you don't need resistors if they are used. You will need a power supply with no more than 35VDC output.

 

[flatfootskier]

Why do you need no resistors with a bunch of leds in series? Have a look as suggested at the LM317 as a constant current source & be sure about it. It's such a simple circuit you can implement it with chocolate block / terminal strip.
2 resistors, one chanky regulator.

Check if you need a heatsink with it though.

 

[audioguru]

A constant current source is an automatically adjusted series resistor.
It adjusts its resistance to keep the current constant.

A series voltage regulator IC is also an automatically adjusted series resistor.
It adjusts its resistance to keep the voltage constant.