I know there are lots Q&As about LEDs and in fact this one in particular sounds very close to my situation but, maybe I'm missing it, none of them seemed to match my experience below.

Ultimately I want to run 15 5meter 300 LED strips or 4500 LEDs, if possible controlled by one Teensy 4.0

I bought 2 strips to start. The specs

  • Model: WS2812B 5050RGB 300 LED Tape
  • IC Type: WS2812B IC
  • Power: DC 5V
  • Power: 6~18W/m 0.1~0.3W/LED Total 30~90W
  • Recommended Power Supply: DC5V20A (100W/M)
  • LEDSMD Count:60LEDs/m 300LEDs/5m

90 watts at 5v is 18 amps

Not knowing what I'm doing I originally I hoped to power a single strip 2-4hrs, using a 20000mAh Anker Powercore USB recharger. It's specs are

  • 20,000 mAh / 72 Wh
  • Output: 5V 3A

That's all that's listed in the manual

That didn't seem like enough. For one the 3A on the power supply is much less than 18 amps needed by the LED strip. My second option was to use 4 D-Cell batteries at 6V with something to take them down to 5V but even that seemed to be less energy though maybe I could pull out more at once to get closer to the 18 amps needed?

Ultimately though I just plugged in the Powercore to the Teensy 4.0 just to see what would happen. I figured at best it would run 1hr because they LEDs require 18amps and I guess there are 20amps available in the USB battery. I thought maybe it might go 3 hours because this adafruit article said they usually calculate they only use a 1/3rd of the power (not all lights are always on). I didn't understand how if the strip requires 18 amps or 6 amps if only 1/3rd of the lights are on how it would work with a power supply that only supplies 3 amps. But, I saw one article powering a 60 LED strip on 4 AA batteries so I thought I'd try it.

It ran for over 15 hours!

enter image description here

Is that expected? I was using the adafruit strandtest program that comes by default with the arduino IDE to test. It makes all 300 lights red full brightness, then green full brightness, then blue full brightness, then it does a theater marquee in white 1/2 brightness, followed by all a rainbow of all lights, followed by a theater marquee rainbow. There are never less than 1/3rd of the lights on at full brightness. Most of the time all of them are on but they aren't white.

Why were they able to run for over 15 hours? Would someone who understands electrical engineering look at the specs above and expect them to run in the ballpark of 15 hours with that battery?

> 1/3 of the lights on = min 5v @ 6a = 30w.
power supply has only 72wh so it should run for max 2 hours 20 minutes?

I'm not getting something fundamental I think. I've probably read 15 articles on powering LEDs by now and all of them seemed to suggest this wouldn't work. In fact the same adafruit article shows an example in the middle of the article, 60 LEDs = 1.2 amps minimum. This strand is 300 leds so 5x which is 6amps. They mention above that a 2 amp wall transformer being underpowered for more than a meter strip. This battery claims to only deliver 3 amps and I was testing on 5 meters.

The battery never got remotely even warm to the touch. The teensy chip got warm but not to the point that felt too hot.

First I thought these batteries would not work. Sorry there are so many questions but

  1. Why did this work?

  2. Would 4 D-cell batteries at 6v with something to convert to 5v be expected to have a similar performance? Wikipedia says a alkaline D battery has 12000mAh at 1.5v so 4 would have 12000mAh at 6v converted to 5v would be ~14400 mAh? so if I got 15 hours from 20000 mAh 5v above I should get ~10.8hrs of usage?

  3. Are there any pros and cons of the USB battery vs D cells? I prefer the USB because it's easy to recharge and has plugs but like I said I thought it wasn't going to work at all.

  4. Can I use the same USB battery for 2 or 3 strips (15 hours / 3 = 5 hours) or will that try to pull too much energy too fast?

  5. Is it safe to wire 5 to 15 of these usb-c batteries (1 per strip or 1 every 2 strips or 1 every 3 three strips) in parallel (Between strips) of either type? I've heard about lithium batteries exploding. What do I need to do to be safe? Obviously the fewer batteries the better.

  • \$\begingroup\$ You are most likely not supplying the max current to the LEDs. They will still light up even at 1/100th of their max rated current (albeit pretty dim). What hardware are you using to drive them? \$\endgroup\$
    – Daniel V
    Commented Jun 14, 2020 at 0:29
  • \$\begingroup\$ Everything I used is listed in the question above. There is one 5V 300 LED strip (specs above), one Teensy 4.0, one Anker Powercore 20000 (specs above). That's it. Nothing else. The LEDs seemed bright to me. \$\endgroup\$
    – gman
    Commented Jun 14, 2020 at 1:45
  • \$\begingroup\$ What pin on the Teensy are you using? \$\endgroup\$
    – Daniel V
    Commented Jun 15, 2020 at 3:50
  • \$\begingroup\$ There's only 3 wires. G on Teensy to GND on the LED strip. 5V on Teensy to +5V on LED strip. Pin 1 on Teensy to Din on LED strip. \$\endgroup\$
    – gman
    Commented Jun 15, 2020 at 8:19

2 Answers 2


(I am not an expert , i am just a student. So my answer might not be accurate and please correct me if i am wrong.)
your power bank of 20,000mAh at 5v gives 100Wh.The output of power bank is limited to 5v 3A so it can output 15w.So at rate of 15watts per hour your power bank should be drained in 100Wh / 15w = 6.67 hrs. But i think your strip is consuming less power than that. So first measure the power consumption of led strip in watts and then divide battery capacity (in wh) with the power consumption of your led strip (in watts).That will give you the amount of time for which the strip will be on. In your example the 100wh battery was able to light the strip for 15hrs. so i think the strip consumed about 6.67w .
BTW tell me how it works out.
Thank you.


OK. So I assume you are connecting the strip to the 5V (as in the Vin) pin on the Teensy. If so, that is the same as just connecting the battery directly to the strip. Assuming the Anker really had 72 Wh capacity and you were outputting 5V the whole time (for simplicity of the math), then you would have had 4.8 hrs of life. This also means that the LEDs are only running at 3A which is anywhere from 1/6 to 3/5 of their max brightness. This is usually hard to tell unless you had a way to fully drive them at max current (e.g. 18 A @ 5V).

So why did it last for 15 hrs?

My guess is that these particular LEDs only draw 1/3 of their rated current at 5V so instead of getting the 4.8 hrs you got three times that much. This kind of variation in LED current is not uncommon but seems a bit on the high side to me.


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