RGBW led lighting

[Sigmoid]

Hey,

I'm looking at cheap possibilities of getting a powerful and versatile lighting panel for my living room. I'm thinking some kind of RGBW led setup would be cool, as I'd like to be able to set up custom colors and/or temperatures of white. That color therapy relaxation thing that they do in infra saunas would also be a nice addition, with the slowly shifting colors.

I'm wondering, what would be the best choice for the controller? Should I get some WanHungLo "wifi" controller from Alibaba / Amazon market, or is it worth building something?

Also, how should LED devices be sized? I have no idea how much light a 12W string of 12V RGB or white LED modules would generate. I'd like the light to be at least equivalent to 3-4 100w incandescent bulbs.

[IanB]

Also, how should LED devices be sized? I have no idea how much light a 12W string of 12V RGB or white LED modules would generate. I'd like the light to be at least equivalent to 3-4 100w incandescent bulbs.

As a starting point, look at the lumens per watt figures. Similar lumens will give similar light output.

[Psi]

Yep, i've done this myself.  A normal 100W incandescent lamp is around 1500-1700 lumens which is good for a typical room.

When i did my LED setup LEDs weren't quite as efficient as they are now. I needed 30W of white LEDs to get that 1700 lumen output.
I think now you can do it with ~20W.

The cheapest controller is just a mcu/ardunio and 4 mosfets (for RGBW)
It's cheap to just use high wattage series resistors to limit the LED current, and you have a heatsink for the leds anyway so you can bolt/glue them to that.  I used thermal epoxy to glue typical 5W ceramic resistors to the side of the led heatsink.
Of course you can get a proper switchmode current limit LED controller if you want, it's more efficient.

Code the mcu to PWM the 4 mosfet color channels (above 200Hz) and your done.
I added extra code to provide IR lighting control, just because it was cool and why not

Obviously you want to put the LEDs into series strings and pick your power supply voltage carefully so it's only 1-2V above the total LED string voltage, that way you limit the wasted power in the resistors.
I had more red leds in each string than white due to their different forward voltage but the total LED voltage of each string was close to 13V for each color. (My psu was 13V)


As far as mixing goes, i have 30W of white and 10W each of RGB, which is great but probably a little excessive for the size of the room. It depends if you want to just "tint" the white or actually illuminate the room in a pure RGB color, which is always fun.

[Sigmoid]

I wonder what is the best "bang for buck" in terms of LED modules. Any good ones people have experience with?

[Psi]

DX has these 30W RGB emitters for $16 which seem good however i've not tested one.

http://dx.com/p/30w-1500-lumen-rgb-led-emitter-metal-plate-39960

[HackedFridgeMagnet]

I found if you are doing colour mixing, then you often get too much white. The result is a pastel effect for purple, yellow and orange. I think the way to fix this is to use filters over the RGB components. but I haven't tried.

[Towger]

The Chinese '100w' modules you can pick up on eBay, about $20 each. You will need a 36+v PSU, old CPU heat sink+fan, and led drivers. There is eBay seller also in China 'Sure Electronics' who sells 50w drivers which can handle up to 48v with an enable/PWM input. They are about $4 delivered, you could not build them yourself at that price, I'll post the chip they use later. I am replying via phone. You can set the current limit with jumpers. 900ma each is more than enough! Or 1050ma if you want to push... Remember these modules are really 90w.
If you want something with lower voltage the try RGBW Cree modules they are 10-12w each, but are about 13+ postage each.

[Psi]

$4 is damn good, don't bother with resistors if you can get a controller for that.

[Towger]

Re the Chinese LED module, I was thinking of this 100W (30Wx3) RGB type, but you can get them separate RGBW 10/20/30/50/100w modules: http://www.ebay.com/itm/RGB-Super-Bright-LED-Light-DIY-red-blue-green-Lamp-Light-10W-20W-30W-50W-100W-/161064759442

This is the driver, cheaper if you use best offer   http://www.ebay.com/itm/150-1500mA-Buck-Regulator-LED-Driver-for-1-50W-High-Power-LED-/161026417634


The driver board is based on an Allegro A6211, it appears (black PCB!) to use the reference design and adds extra protection by an additional diode and driving the enable through a signal diode and transistor: http://www.allegromicro.com/en/Products/Regulators-And-Lighting/LED-Drivers-For-Lighting/A6211.aspx


BTW these are bright, don't look directly at them...

Edit: Fixing links

[Kjelt]

If you want to build everything yourself including the controller go ahead.
If you like versatile and expandable lighting controllability make sure your led driver has an DMX(512) input.

[RobFromEarth]

I have one of the 50 watt rgb leds:

http://www.ebay.com/itm/50W-RGB-High-Power-LED-Panel-50-Watt-Lamp-Light-/161176213412?pt=LH_DefaultDomain_0&hash=item2586d9d7a4

I'm using a 24v power supply. Can someone help me with the resistors? I know how to do the calculations, but can't in this case- red is easy enough- the current is .5A for each channel,
and that gives me 14 ohms (at 17V forward V, 7v drop on the resistor).

But for the other two colors, i'm not dropping anything, the lowest voltage the specs list that will work is 24V, and that's what i'm using. a voltage drop of 0 volts means a division by zero, do i just not use a resistor here? I've never heard of not using a resistor on an led.

I think a simple way to bypass the problem, raise the voltage supply, but it's far easier to find 24v, and also, it would mean more voltage drop for red's resistor, which means a bigger resistor = less efficient, more heat etc..

Thanks

Rob

[mariush]

For such a power led, you really shouldn't use resistors... you'll dissipate a lot of power in the resistors, heatsing them up and so on.

It makes more sense to use a led driver for each of the colors. For efficiency reasons, you should get a higher voltage and the led driver will limit the current appropriately.

For example, get a transformer or power supply that outputs around 32-36v DC and then use such drivers to light up each color separately: http://uk.farnell.com/zmdi/zled7020-zi1r/led-driver-buck-1-2a-sot89-5/dp/1898428

You just set the Rs resistor to the value for how much current you want the IC to allow through led and choose the suitable inductor for the current you have. The datasheet explains what to look for.
The chip above will probably work with 24v as well, but you may not be able to set the current so high.

Those leds on the ebay link are 16w per color, so you need to limit current separately to about 1a for red ( 16w / 16-18v) , 600mA for blue and green  ( 16w / 24v)

[RobFromEarth]

This is the driver i'm using:

http://www.ebay.com/itm/DC12V-24V-Max-3A-CH-Output-High-Power-DMX-Decoder-LED-Lamp-Driver-Controller-/160818130517?pt=LH_DefaultDomain_0&hash=item257181ee55

From the specs, it will take 12 or 24V, but red on the led needs 16-18v and the other colors need 24-48v. This is how i did it with 10watt leds and a similar driver- the driver had power in and four outputs- one for common, one for each color. The common i hooked direct, and each color went to a resistor first that made the volts and current match what the led/color required.

I'm just not sure how i make the current and voltage match this 50w led's requirements without the resistor?

Thanks,

Rob T.

[mariush]

LEDs are current driven devices. The voltage specified is just the minimum voltage from which the leds are supposed to light up.

The driver does not output 24v, it will output UP TO 24v.  You configure the current through the DMX interface and then the driver takes the 12-24v input and gradually increases the voltage until the current going through the leds reaches what you set.
So for the RED leds, you know the voltage must be between 16 and 18v and they're supposed to use 16 watts maximum.  16 watts / 18 volts works out to about 888 mA.  Now you're supposed to connect to this driver box through the DMX interface, configure the RED channel to 888 mA and the box will then boost the 12v until there's around 888 mA going through the led, which will happen at around 18v.

Now, the DMX interface.. it's a standard for lightning. You need some software and a transmitter/controller the software can work with (you plug that in usb or a pci slot). You then connect that driver you bought to the transmitter with network cable or something similar. You then send commands to the driver through the software.

Or, you know... get a standalone led driver instead which would allow you to adjust current using a potentiometer or something like that, and forget about this led driver.

[RobFromEarth]

Yes, i have this working with 10watt leds on a different dmx driver:

http://www.holidaycoro.com/27-Channel-DMX-Controller-for-RGB-Lights-12v-DC-p/24.htm

It works great as i have it set up, i have each of the R G B and B going to a resistor that brings the current to where it needs to be, and the common hooked direct. It works fantastic.

The 50W led needs different power supply and resistors. Red isn't a problem, though according to the specs, red needs 500mA max not 888 (or is the spec wrong? I've seen that on some of these generic leds), and with 24 volts going to the controller, it means (1) 14ohm resistor at 3.5watt (call it 5)

But my question is for the other two colors. They call for 24 volts minimum, and the controller calls for 24 volts max. If i feed 24 volts into the controller, here is how i calculate what resistor i need:

Vfwd = 24v
I=.5 (500mA)
I calculate the amount of voltage drop (Vd) on the resistor by subtracting the supply voltage from the required voltage for green or blue which are both 24v, so for example, blue:
Vd= 24V supply voltage - 24V required for blue = 0v
to calculate resistance it's:
R=Vd/I
which is:
R=0v/500Ma
which isn't possible.

I hope that was clear, i used to work with ohms law a lot but it's been awhile.. So i was hoping to find out what should i do to make it work? I can't increase the supply voltage since it's the maximum the driver will allow. I can't lower it since it's the minimum the LED needs to operate. Leaving it as is gives me a mathematical problem of trying to divide 0 by 500mA.

Thanks again

[Psi]

But my question is for the other two colors. They call for 24 volts minimum, and the controller calls for 24 volts max. If i feed 24 volts into the controller, here is how i calculate what resistor i need:

If the LEDs forward voltage min is 24V and your controller max output is 24V then unfortunately you cant use that controller.
The max controller output voltage isn't enough to run the led, as evident by the calculation giving a 0 volt difference.

[mariush]

The 50W led needs different power supply and resistors. Red isn't a problem, though according to the specs, red needs 500mA max not 888 (or is the spec wrong? I've seen that on some of these generic leds), and with 24 volts going to the controller, it means (1) 14ohm resistor at 3.5watt (call it 5)

From the ebay page:

This is a high power RGB LED capable of outputting 16W per channel, total 48W. High power RGB LEDs are in one aluminum backed package. The product is packed in sealed anti-static bag. Do not look into the light.     


DC Forward Voltage (VF):Red 16-18V;Green 24-28V; Blue 24-28V.     

DC Forward Current (IF):1500mA     

16 watts @ 16v = 1A .. .16 watts @ 18v = ~ 888 mA

16 watts @ 28v = ~ 570mA

[RobFromEarth]

It indicates 1500mA, which would be 500mA for each. I didn't see where it said 16W.

I guess i still don't understand, if the minimum operating voltage for blue and green is 24v, and the input voltage is 24v, how is that not enough to work? I'm sure there will be a certain mA lost as heat in the controller, but the volts will still be the same (i think?).

Thanks

[Psi]

Sorry, i deleted my post before.
I wasn't really sure and didn't want him to blow up his leds with 1.5A if that wasn't correct.

The voltage ranges are because the led forward voltage at spec'ed current changes with temp.

[RobFromEarth]

I saw it, but thanks. I did think it was 1.5 per channel when i got it, because it shows as just 1500mA without specifying per channel or overall.

[Psi]

1.5A is not crazy high, some high wattage LED arrays take 3.5A per channel.

You could connect up a powersupply in current limit mode and check what sort of current the leds draw inside their spec'ed voltage range.

[RobFromEarth]

Yeah, i've seen that, would be fun to have one of those working, but i figure i best stick to lower power devices until i can make it work. I'm surprised that 50w is a problem, it seems to be all the same as 10w LEDs mathwise, if i can just figure out how to make it work. Each of the two channels G and B require 24volts min, controller will take 24v maximum input, how to calculate the resistors when it results in dividing 0? The voltage drop across a resistor would be 24-24=0v, so to find the value of the resistor, it's r = Vdrop/amps, so r = 0/.5 (500mA), which can't be done.

[Kjelt]

The voltage ranges are because the led forward voltage at spec'ed current changes with temp.

Correct but I thought also with age ?

[Kjelt]

The forward voltage of a led increases by: Current and I thought also Age.
The forward voltage of a led decreases by: Temperature.

[peter.mitchell]

Yeah, i've seen that, would be fun to have one of those working, but i figure i best stick to lower power devices until i can make it work. I'm surprised that 50w is a problem, it seems to be all the same as 10w LEDs mathwise, if i can just figure out how to make it work. Each of the two channels G and B require 24volts min, controller will take 24v maximum input, how to calculate the resistors when it results in dividing 0? The voltage drop across a resistor would be 24-24=0v, so to find the value of the resistor, it's r = Vdrop/amps, so r = 0/.5 (500mA), which can't be done.

Hey rob, I'm not sure how much money you have, or want to spend, but for me personally, $20 for a dmx controller is dirt cheap, i'd try feed the controller like 26v see if it does anything.