Powering 5v WS2811 LEDs from 4.2v 18650 lithium-ion batteries

Other Hardware LEDs and Multiplexing
1

I'd like to power a sizeable length (~10m) of this WS2811 ribbon (http://www.aliexpress.com/item/4m-WS2811-LED-digital-strip-60leds-m-with-60pcs-WS2811-built-in-tthe-5050-smd-rgb/633124138.html) from 18650 4.2v Lithium Ion batteries.

The strip needs 5v, and according to the specs, draws 14w/m. So 10m = 140watts! Now I don't have the strip yet, and don't know how accurate that figure is. I also won't be driving it at full brightness, so the power draw will probably be half this.

However, my question is does anyone know if this strip will run off the 3.7-4.2 range of a typical 18650 cell? Otherwise, if it needs bang on 5v, what it the most efficient way to drop the 8.4v from 2 cells to 5v? Putting that through a simple linear regulator like a LM317, would probably end in a rather bright flash and a lot of smoke.

I've looked at switching regulators, but i can't see any that come anywhere near this level of power draw. Is there something else that I can use?

2

Ok;

  1. In all that math, did you come up with a number for amps?
  2. I can only assume you will be using PWM to control the LEDs, Right?
  3. What amp hours is your battery rated at?
  4. So how long will the battery run the LEDs ?
3
  1. P = V * I, so I = 70/5 = 14A
  2. I assume that is how the WS2811 chip drives them, I don't know for sure.
  3. LiOn batteries are generally rated around 3000mAh @ ~4v
  4. 10 batteries would give me ~2hrs runtime: 10*(3aH * 4v) / 70w.

However...I've already built something using 12v RGB ribbon with a similar power draw spec (~14w/m) and 7m of that ran for 6hrs on 6 batteries, so I don't know how accurate the battery ratings, and ribbon spec is. Or my calculations might be wrong...

4

I looked at the specs from the URL, and it looks like they vary.

Model: 5050RGB WS2811
Input voltage: DC5V
Current: 11.5A
Led Qty: 60per SMD 5050 meter
Wave length(NM):R-650mcd, G-520mcd,B-460mcd
Power(W/M)::14.4W/M

current X voltage = watts, so looks like for one meter. 5v X 11.5A = 57.5 watts. Maybe I am not reading the specs. right.

But back to your first question, can it run on 4V, there is no way to know without trying it. Depends on how the leds are configured, with resistors.

But if the amps is actually 11.5/m, you may need a bigger power supply and regulator for 10 meters.

5

I've done this successfully. The WS2801 and WS2811 lights work down to about 3 volts. The controller will pause at about 3.2 volts which results in a frozen frame of lights.

I ran 75 lights on strandtest(20ma per pixel) for 3 hours off two 18650s in parallel.

Programming more conservative animations lasted for two nights at burning man.

BE WARNED: If you put one in the wrong way it will short circuit them together and can melt the wires in your hand.

6

FinBot:
Programming more conservative animations lasted for two nights at burning man.

I thought so...

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I'm using my strand in building an outrageous helmet for next year XD