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I have an idea fro a project which requires a few hundred ws2812 LEDs to be powered using relatively small battery which can be carried. I was wondering how you could power over 300 ws2812 LEDs similar the dress in this Creators Project Video on Youtube:

https://www.youtube.com/watch?v=oo_7s4TrL28

The dress looks like it has atleast over 250 LEDs (assumed to be ws2812s) , and they are all powered with a single rechargeable Li-Ion battery.

My calculations show that

300 LEDs × 60 mA ÷ 1,000 = 12 Amps minimum

How did she managed to power all those LEDs with a single battery one could carry?

Please forgive me for being a noob.

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    \$\begingroup\$ I didn't watch the whole video, but I assume she has a control circuit where she could also step down the voltage. Doing this you could use say, a 12V battery with 5V LEDs. 5V @ 20mA per LED is 6A and 30W. At 12V that is 30/12= 2.5A (probably more like 3A with losses). So assuming the battery must supply 12A is not true. By the same token if you aren't worried about the lifetime of the battery, you can pull lots of power out of it, just means lower run time \$\endgroup\$
    – I. Wolfe
    Commented Feb 5, 2016 at 21:52
  • \$\begingroup\$ Probably has a few li-ion cells stashed away somewhere. Its not too much of an ask ... \$\endgroup\$
    – brhans
    Commented Feb 5, 2016 at 22:06
  • \$\begingroup\$ That battery pack likely has 6 to 8 Li-Ion cells. Its about the size of a small laptop battery. That's plenty for an hour or two. \$\endgroup\$
    – Passerby
    Commented Feb 6, 2016 at 2:08
  • \$\begingroup\$ @I.Wolfe These are rgb leds with internal MCUs. Roughly 70 mA per led, for full white. 90+ Watts, not 30Watts. \$\endgroup\$
    – Passerby
    Commented Feb 6, 2016 at 2:09
  • \$\begingroup\$ @Passerby true, I was more pointing out one way his calculation could be wrong. Used 20mA by force of habit \$\endgroup\$
    – I. Wolfe
    Commented Feb 6, 2016 at 2:16

1 Answer 1

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Your calculations are reasonable for every single LED on at full brightness. However, there are a few reasons why the LEDs don't draw this maximum power. So, if you want this dress to work for an hour at max brightness, you need 12Amp hours of energy. That's on the order of magnitude of a small car battery (not as much, but it's a big battery). Also, the voltage plays an important role but let's assume for simplicity's sake that she has a battery that's just the right voltage for her application.... So, why does she only use a "small" battery (for what it's worth, that's a pretty large battery compared to something in your phone)? :

  1. Not every LED is on all the time, especially when she is doing blinking patterns. Let's assume that only 50% are on, on average. That brings you down to 6 amp hours. This drone battery gets you there. http://www.maxamps.com/proddetail.php?prod=Lipo-5450-111-Aton-Pack
  2. Not every LED is on at full color. That 60 mA number you gave is all 3 colors on at once. So, if a light is full red, green, or blue, you're only at 20 mA. So, let's assume that only 2/3 color is on at a time, on average. So, you're down to 4 amp hours.
  3. Not every LED is on at full brightness. The PWM signal that controls the LEDs allows them to only be on for a limited duty cycle to adjust brightness. I've used those WS2812s and they can get pretty darn bright. So, let's assume they have a max brightness of 75% current (especially in a dark room). That brings you down to 3 amp hours.

So, 3 amp hours is actually something that a normal spare phone battery can do, or many RC/drone batteries for higher voltage.

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  • \$\begingroup\$ How does 'Current Output of the battery affect the powering of the LEDs. Does this matter? Would the battery you've mentioned suffice to power that many LEDs at full brightness? (even for just 30mins).Sorry, I'm not to knowledgeable on batteries. \$\endgroup\$
    – Carlos Juan García Cortez
    Commented Feb 6, 2016 at 19:22
  • \$\begingroup\$ You'll need to do a bit more research or ask but there are plenty of answers on this site or google to help. The are dozens of configurations depending on battery voltage, LED arrangement, passive current limiting vs. PWM, etc. Basically, you need a minimum amount of voltage to turn on an LED and then a minimum amount of current provided by that voltage source to get to max brightness. We can help you out more if you ask a question and give specifics of LEDs you've researched and the specific application you want. \$\endgroup\$
    – scld
    Commented Feb 7, 2016 at 20:51

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