G+_Kyle Boyington Posted October 21, 2015 Share Posted October 21, 2015 OK, where are the electronic gurus? I am hoping to find a way to control a high power LED with my Raspberry Pi. I have successfully controlled a RGB light strip with pi-blaster, but not sure how different an LED like this would be. Anyone have any experience with this? Can I use it just like a LED strip? Link to comment Share on other sites More sharing options...
G+_Arcturus Lancaster Posted October 21, 2015 Share Posted October 21, 2015 Something like that will need a power switching sub system. These days a mossfet will do it. Just make sure it can handle the current and voltage of said led. You setup the pi to control the fet. Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 21, 2015 Author Share Posted October 21, 2015 Thanks for the reply Arcturus Lancaster. I currently use a mossfet on the led strips I run. Do you think I can just replace the strip with this LED? Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 21, 2015 Author Share Posted October 21, 2015 Fr. Robert Ballecer, SJ answered me on Twitter: If you want to fade it, use a Tip31C transistor on a 3.3v digital output on the Pi. If not, use a 3V relay on the same pin. Link to comment Share on other sites More sharing options...
G+_Arcturus Lancaster Posted October 21, 2015 Share Posted October 21, 2015 Not tip.. Those are so wasteful. They dump so much power into heat. Mossfet and pwm will be way more efficient. You can still dim. If that is a 100w led I think they run at 32v area. Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 21, 2015 Author Share Posted October 21, 2015 OK I think I am using the monsters now. I'm a total noob. Lol. Thanks for the input. I'm going to start with a 10w led and see how that works. Link to comment Share on other sites More sharing options...
G+_Fr. Robert Ballecer, SJ Posted October 22, 2015 Share Posted October 22, 2015 Are you making a LED floodlight? -- Don't forget that you need to mount the LED on some kind of heatsink. At those power levels, they WILL get hot enough to eat themselves. :) Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 22, 2015 Author Share Posted October 22, 2015 Fr. Robert Ballecer, SJ I'm making a lamp...lol. Maybe it's a bit overkill, but I'm just not sure how bright a 10w LED is. The other thing is the lamp sides are going to be acrylic, so I need enough light to diffuse through the translucent plastic. I'll try to show a picture at some point. Link to comment Share on other sites More sharing options...
G+_Stephen Vincent Posted October 22, 2015 Share Posted October 22, 2015 you'll need an LED Driver capable of powering that LED. More or less it'll be a constant current driver that uses a separate power source to power the LED but is controlled via the GPIO pins on the raspberry pi. http://www.parts-express.com/sure-electronics-high-power-led-driver-10-20w--073-054 I've used the smaller version of those before and they use a PWM signal to enable the led. Basically if you have a GPIO pin connected to it and pulled high, its on, pulled low its off, and if you PWM depending on the duty cycle it can dim the light. Link to comment Share on other sites More sharing options...
G+_Stephen Vincent Posted October 22, 2015 Share Posted October 22, 2015 also, don't forget a heat sink... I think parts express even has a kit that has a controller, 20watt LED and heat sink for around $20. I've used the sure electronics stuff in the past and it always worked well. Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 22, 2015 Author Share Posted October 22, 2015 Stephen Vincent This sounds more complicated than I hoped....thanks for the info. I am getting the LED tomorrow, hopefully Ill get a chance to look at it! Link to comment Share on other sites More sharing options...
G+_David Dennis Posted October 22, 2015 Share Posted October 22, 2015 There are PWM drivers which are controllable via I2C. I'll try to find a part number for you later today. That would be even easier than writing code for the Pi to module the gate of a FET. Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 22, 2015 Author Share Posted October 22, 2015 Does anyone know what happens if you try to power a 10w LED with 12v? David Dennis Link to comment Share on other sites More sharing options...
G+_Fr. Robert Ballecer, SJ Posted October 22, 2015 Share Posted October 22, 2015 Kyle Boyington Watts and Volts are not the same, so we can't really tell you. Watts = Volts * Amps There should be a voltage range for the device. For example, if it's a 3-12 volt/10 watt part, then at 3 volts it will pull 3.3 amps to make 10 watts. At 10 volts it will pull 1 amp to make 10 watts. At 12 volts it will pull .83 amps to make 10 watts. Peace, Padre Link to comment Share on other sites More sharing options...
G+_David Dennis Posted October 22, 2015 Share Posted October 22, 2015 Kyle, it's really not a question of voltage but a question of current. You will find in the datasheet for that LED a specification for Forward Voltage drop. Once you exceed that voltage the LED will turn on. How bright depends upon how much current you allow to flow through it. Let's say the Vf for that LED is 2 volts. And you put a 2 ohm current limiting resistor in series with it. You will drop 2 of the 12 volts across the LED and the other 10 volts will be dropped across the resistor. 10v /2 Ohms = 5 amps of current. So at that point the LED will be dissipating 2V * 5A = 10watts. And you are meeting your 10watt spec. But be careful. That resistor is now needing to dissipate 10 watts. 2 ohms * 5 amps = 10w That is a whopping big resistor. So you see how steady state this gets ugly in a hurry. That is what makes PWM so attractive. With PWM you are switching the current on and off and not needing to dissipate a lot of energy in the form of heat. By the way, that 2 ohms mentioned above will be just about the on resistance of the FET you might be using to switch the current on and off. So you may not even need this resistor in series. The FET will be your power dissipation point. Link to comment Share on other sites More sharing options...
G+_David Dennis Posted October 22, 2015 Share Posted October 22, 2015 As promised, check out this device. AS3693B It is an I2C controllable PWM modulator for LEDs. With it you can drive a huge LED. In fact you can drive 16 of them at different levels of brightness. As others have suggested you use a FET to turn the LED on and off and this will control the pulsing of the gate of the FET. I2C makes this very easy to code in Python. And it offloads the heavy lifting from the PI and leaves the PI twiddling it's thumbs doing nothing until you tell it to change brightness of the LED. Link to comment Share on other sites More sharing options...
G+_David Dennis Posted October 22, 2015 Share Posted October 22, 2015 If you're not familiar with I2C here's a primer written for Arduino. It's gives you a few of the basics of the protocol. If you haven't explored I2C I'd highly recommend it. It opens up the door and allows you to do much more complex things quite easily. Have FUN! Link to comment Share on other sites More sharing options...
G+_Ben Reese Posted October 23, 2015 Share Posted October 23, 2015 David Dennis? - do you have a link for that primer? Link to comment Share on other sites More sharing options...
G+_Kyle Boyington Posted October 23, 2015 Author Share Posted October 23, 2015 Fr. Robert Ballecer, SJ thanks for the lesson! David Dennis Thats a lot of information! I think I followed....maybe. I am no electronic engineer, but I can code the Pi to output PWM fine. Im hoping that combined with the FET will do it? Or it will be a learning experience at least! Link to comment Share on other sites More sharing options...
G+_David Dennis Posted October 23, 2015 Share Posted October 23, 2015 Sorry Ben Reese I left out the link. Here it is buddy. http://howtomechatronics.com/tutorials/arduino/how-i2c-communication-works-and-how-to-use-it-with-arduino Link to comment Share on other sites More sharing options...
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