I'm bit stuck and at the end of my knowledge. I'm building a light stick that is controlled by a teensy micro controller and using programable rgb led's. (ws2812) the led's run at 5volt and need quite a few amps. I'm looking at approx 8 amps if all 288 are on at full brightness and white. testing g was done with it plugged into USB on laptop and a few led's selected and low brightness and all was good. I planned to use a ubec to convert 7.2 - 11.1 input from lipo's to 5v. Issue was the led's started acting odd. I moved the data cable away from the power to the leds and it was a lot better so there is some interference in the power upsetting the data signal but only when using the ubec. I tried a different one I had and same issue but different effects. Iknow the ubec is basically a switching psu but how do I clean it. I'm using the ubec as it's the only device I can find that can give high current output. Found loads of buck converters on eBay but 2-3 amp is the max. Im open to other ideas if anyone has them. Did think.of a linear psu but current was again the issue and now also heat. Thanks in advance Lee
Use shielded twisted pair wire for serial data.
5 volts is not enough.
The WS2812 VDD and VCC power requirements are 6V-7V.
All 3 LEDs drawing 20mA x 3 x 288 = 27.28 Amps.
That's the Amps. The minimum Voltage is 6V x 27.28 = 103.68 Watts.
The LEDs alone could dissipate up to 50 Watts, With an avaerage of 2.933 Vf (R=2.2v,G=3.2v,B=3.4v) x 3 x 288 = 50.688 Watts
But efficiency is less than 50%.
6v x 0.02A x 3 x 288 = 103.69 Watts @ 6V = 17.28A
Give your UBEC an 80% efficiency and we have 129.6 Watts
Add a 10% margin and the battery requirement is now 142.56 Watts
You could use a electric bicycle battery. You will need an NMC Li-ion (high capacity and high current). The LI-ion for my Segway is $1,400.
If you use the WS2812B with 5V VDD then you would need 86 Watts @ 14.4 Amp.
If you calculated the power requirements for the LEDs without taking efficiency into consideration the draw would be about 8 amp. 58% efficiency (not including UBEC).
You may want to consider using Cree RGB CLMVB-FKA controlled with a TI TLC5973 3-Channel, 12-Bit, PWM Constant-Current LED Driver with a single resistor to set the maximum current. Or a TLC59731 3-Channel, 8-Bit, PWM LED Driver which uses a resistor inline with each LED.
The Cree RGB have an average Vf of 3.6 vs 2.9 (less power) The Luminosity of the RG and B are better matched. The TLC5973 can be powered with 3v up to 6v so it could be powered by a single cell 3.6v Li-ion eliminating the UBEC, Over all the power requirements would be much less and reliability much higher.
Uses a single wire interface. The datasheet shows how to properly wire power and data signal.
There is an on-board shunt regulator that allows you to power multiple LEDs with one chip.
The TI parts are superior to the NeoPixel. And MUCH better documentation.
- Data Transfer Maximum Rate: 3 Mbps vs. 800Kbps
- Internal GS Clock Oscillator: 12 MHz
- Display Repeat Rate: 2,900 (typ) vs 30fps,
- 4096 steps grayscale control vs 256
- Output Delay Switching to Prevent Inrush Current