50W RGB LED Stage lighting

Easter2015_lights in use

Only 9 LED units

50W LED stage lighting Project. The photo above show some of the effect with only 9 LED units giving color to the stage and 18 LED light boxes give texture/effect to the background.  This artical will cover the process I went through creating the 50W LED units.

initial scaled drawing, to help layout placement. 50W LED final product

 

50W LED

50W LED

Lets start with the LED; I ordered mine from Ebay: LED-QUEEN. I’ve had good results from them. Now this is a 50W bulb or 16.6667W per color.

The data given on the bulb was 22-24V for RED @ 600mA and 32-34V on Blue and Green @ 600mA. So lets take a look at what this means. Volts*Amps = Watts RED: 24*0.6 = 14.4W GREEN: 34*0.6 = 20.4W BLUE: 34*0.6 = 20.4W

Total Watts = 55.2W

This may not seem like much but even just 5.2W over could damage the bulb. So how did this data apply to actual usage? It didn’t really. I found that the Red was well over 1amp trying to use the full 24 volts. With similar results on the green and blue at 34 volts. Pushing well over 70-80W through a 50W bulb lets the smoke out. Always measure when testing and to extended run tests. let the unit stay on for over an hour. Or  else you might think that it works. but it dies quickly and blame the product and never realized it was your fault, cause pushing anything 50% or more over its rating will burn it out fast.

The Real Data: In testing I found that running the Red at 18V I would get about 900mA of current; thats 16.1W. And at 26.5V on the green and blue i was getting 700mA or 15.9W. Also note that I’m using a current limiter(see Next Section), this is because when LEDs heat up they consume more power, so if you don’t limit the current you will ruin them or your power supply very fast. 

LED driver_1I’ve been using this simple constant current circuit for all my high power LED projects by Dan Goldwater. (I won’t be covering the process on how I etched my PCB as there are several tutorials and videos on the process, sorry. But I did include a link to the kit I used under the “Parts & Sources Section” )

Using the data from the LED seller as a starting point, I began testing the LED to see how it would perform. This new data helped me in fine tuning the circuit for a more  balanced operation.

First: RED, when using a 24 volts power source I would lose almost 6 watts in heat just from dropping down to 18 volts. I set R3 to 0.5 ohms for a 900mA limit and changed my input voltage to 20 volts. This lowered the heat lost and allowed me to continue using the smaller MOSFET I borrowed from the DMX-Decoders(A Cost Savings of $40+) MOSFETs are expensive.

Next: GREEN & BLUE, using a similar technique from RED; I lowered my input voltage to 27 volts and set R3 to 1 ohm for a 600mA current limit.

Now as you read  you will see that my current limits don’t really line up with what the original circuit calculated out.  This is because of the MOSFET I used; it has a very different internal resistance which changes the results in practice. So keep that in mind as you build your circuit. I will note that if you use the same MOSFET as in the original design; your measurements will be extremely close if not exact to what Dan Goldwater worked out.

LED Driver v1 – PCB layout Through Hole/SMD (TO-220 Mosfet)

LED Driver v2 – PCB layout SMD (TO-252 Mofet)

2015-03-24 23.01.15 2015-03-28 21.24.29 2015-03-28 21.23.39 2015-03-28 23.16.36 2015-03-28 23.20.39

— THE CURRENT LIMITER CIRCUIT–  LED Driver- Current Limiter :Download PDF

How does it work?

– Q2 (a power NFET) is used as a variable resistor. Q2 starts out turned on by R1.

– Q1 (a small NPN) is used as an over-current sensing switch, and R3 is the “sense resistor” or “set resistor” that triggers Q1 when too much current is flowing.

– The main current flow is through the LED’s, through Q2, and through R3. When too much current flows through R3, Q1 will start to turn on, which starts turning off Q2. Turning off Q2 reduces the current through the LED’s and R3. So we’ve created a “feedback loop”, which continuously monitors the LED current and keeps it exactly at the set point at all times. transistors are clever, huh!

– R1 has high resistance, so that when Q1 starts turning on, it easily overpowers R1.

– The result is that Q2 acts like a resistor, and its resistance is always perfectly set to keep the LED current correct. Any excess power is burned in Q2. Thus for maximum efficiency, we want to configure our LED string so that it is close to the power supply voltage. It will work fine if we don’t do this, we’ll just waste power. this is really the only downside of this circuit compared to a step-down switching regulator!

 

LED driver_2

schematic-2

Setting the current! The value of R3 determines the set current. Calculations: – LED current is approximately equal to: 0.5 / R3 – R3 power: the power dissipated by the resistor is approximately: 0.25 / R3.

 

Choose a resistor value with at least 2x the power(wattage) calculated so the resistor does not get burning hot.

 

For a 700mA LED current:

R3 = 0.5 / 0.7 = 0.71 ohms. Closest standard resistor is 0.75 ohms. R3 power = 0.25 / 0.71 = 0.35 watts. We’ll need at least a 1/2 watt rated resistor.

Current Limiter- Micro-controller interface

schematic-3

Parts used: R1: Approximately 100k-ohm resistor(1/4 watt)  Such as: Yageo CFR-25JB series R3: Current set resistor(1 watt+) A good 2-watt choice is: Panasonic ERX-2SJR series Q2: Fairchild FQP50N06L (N-channel logic-level FET) Q1: Fairchild 2N5088BU (NPN Transistor)

Maximum limits: The only real limit to the current source circuit is imposed by NFET Q2. Q2 limits the circuit in two ways:

1) Power dissipation. Q2 acts as a variable resistor, stepping down the voltage from the power supply to match the need of the LED’s. So Q2 will need a heatsink if there is a high LED current or if the power source voltage is a lot higher than the LED string voltage. (Q2 power = dropped volts * LED current). Q2 can only handle 2/3 watt before you need some kind of heatsink. with a large heatsink, this circuit can handle a LOT of power & current – probably 50 watts and 20 amps with this exact transistor, but you can just put multiple transistors in parallel for more power.

2) Voltage. the “G” pin on Q2 is only rated for 20V, and with this simplest circuit that will limit the input voltage to 20V ( Lets say 18V to be safe). If you use a different NFET, make sure to check the “Vgs” rating.

Thermal sensitivity: The current set-point is somewhat sensitive to temperature. This is because Q1 is the trigger, and Q1 is thermally sensitive. the part number I specified above is one of the least thermally sensitive NPN’s I could find. even so, expect perhaps a 30% reduction in current set point as you go from -20C to +100C. That may be a desired effect, it could save your Q2 or LED’s from overheating.

Source: http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/?ALLSTEPS

Coming Soon

DMX decoder DMX Encoder-Programmer XLR 3pin & 5pin dmx_connection

Coming Soon

Lens Heatsink-fan

Now comes the big question; “What power supply should I use?” Well there are a few questions I had to ask myself that helped me pick the right one. And also some info I found out by trial and error.

  • First off, I wanted to make the 50W LED units self-powered, have its own power supply in each unit. So that means a compact unit.
  • It needs to be fairly efficient, so it needs to be based on “switching” technology.
  • It will have to power everything, a 50W+ unit minimum.
  • Based on voltage requirements for the LED bulb (27 Volts for Blue/Green) I would need something over the normal 24 Volt PS units. Witch made it very hard to find.

Now in my searching I came across this 50W led driver/power supply and I thought sweet, it’s perfect and it’s made for LEDs, has the right wattage output and was a good price.50W PWR So I ordered a bunch for my project. Once I received them and began testing I found quick that it would not work at all for my design.

My failure to recognize that all the cool features built into the unit would make it inoperable in my application. It was listed as a Constant Current Power Supply with the features, Open circuit, Short circuit and Over loading. Now these are good features to have, but because this unit was expecting to have 50W pulled from it all the time, only using 10-15W for a single color would cause it’s safety features to kick in. This meant a pulsating voltage until I had dmx interface close to max on all three colors as the same time.

So basically the safety features of this type of Power Supply kept me from dimming the lights which totally defeated the purpose of this project. If I was trying to power a white 50w LED this unit might have worked.

Armed with this knowledge, I realized that I needed a simple voltage regulated power supply instead of a current regulated one. Which wouldn’t conflict with my custom current limiter and allow variable brightness via DMX. This led me to revisit one of my previous design of using a power supply that would be external and handle multiple units.Power Supply Enter the 350W unit I found on Ebay. Rated at 36 volts and 9.7 amps, it became the foundation of power that I needed. This unit has a small voltage adjustment for fine tuning. This unit will allow me to power up to 6 LED units (300W) and give room for spikes in power demand. Don’t want to max it out and burn it up.

 

So now the next step is to lower the voltage for each component. The LED needed 27V for blue/green and 19V for red; the cooling fan needs 12V and the DMX decoder uses 5V. To handle this I found a simple Switching Voltage Regulator. This little unit is adjustable from 1.3V-35V output and can handle up to 3 amps. Plus I found them super cheap ($0.7 per unit)

By using 3 of them I was able to give the appropriate voltage to each component. A forth wasn’t need cause the DMX has a built in voltage regulator.

VoltageREG

 

I used 4″ PVC pipe cut to 11.5″ long. You can make it any langth you want I just thought that this size looked good and gave plenty of room for the electronics. Drilling holes on one face for mounting heatsink/fan and  and then the opposite end for airflow; painted it black with Rust-Oleum High-Heat spray paint. Finished it off with a 4″ end cap and mounted XLR connectors. I used an aluminum bar for the mounting bracket; Cut to 12″ long and bent into a square “U” shape in 4″ sections.

2015-03-31 23.36.17 2015-03-31 23.36.02 2015-03-31 23.40.09 2015-03-31 18.14.33 2015-03-31 18.10.36 50W LED final product

Schematics Coming Soon
::Parts List::

Electronic Components:

Hardware:

  • PVC
    • 4″ PVC pipe Local Hardware Store: Lowes, Home Depot etc.
  • Aluminum
    • Local Hardware Store: Lowes, Home Depot etc.
  • End Cap
    • Local Hardware Store: Lowes, Home Depot etc.
  • Lens Kit
  • Heatsink & Fan
  • XLR Connectors
    • Ebay, Digikey, Mouser etc.
  • Screws/Bolts/Nuts/Washers Etc.
    • Local Hardware Store: Lowes, Home Depot etc.

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