Multiple power sources/batteries?

Hi everyone,

for a fun project I am building a device with 108 WS2812b LEDs. A measurement of 36 LEDs showing bright white yielded 1.9 amps, which is in line with my previous calculations.

As I need the device to be portable, I obviously need some kind of battery. I have looked into LiPo batteries, but besides being pretty expensive, I do not like to carry around such dangerous stuff. Since there are USB power banks that supply 5V, I would like to use them. Many of them have 2 or 3 output ports. Can I just combine them by supplying 1/3 of my LEDs to one port and providing a common ground? Or do I need to add some other electronics? Besides, do you know of any USB-Powerbanks (or similar) that can supply 6A from a single port?

Thanks in advance Velines

I don't know of any USB power sources that supply that much current from a single port. That is well above the USB spec.

Get a different battery then http://www.mpja.com/6V4AH-Rechargable-Gel-Cell-Battery/productinfo/17280%20BT Will last a couple of hours at 1.9A draw. Add a switching regulator from pololu.com or similar to efficiently bring the voltage down to 5V.

Yeah, that's what I thought.

I do not need all the 6 amps, as I do not need to have all LEDs showing white at the same time. Lots of power banks have two or three ports, allowing 2 amps per port. So my idea was to combine them. Another plus of power banks is that they come in a stable case, which I can just put into a bag or something else to carry around. Any suggestion if that combination can be done easily?

Your idea to use multiple and connect all grounds together will work. Power various sections/groups of WS2812s individually so you don't have two or more battery pack outputs connected together.

Great to hear, thank you very much :)

Sorry to dig this up, but I have another small question: Why can't I directly connect both parts of an USB power bank using cables like this? Or, to ask the same question another way round: Why do such cable exist and work without frying your computer or external hdd?

your external stuff probably doesnt pull more current than the USB hub in your computer can supply.

power/connect multiple -small- current devices

are you using the USB port(s) in your computer? or to a 'power bank' (which to me is usually some sort of battery pack/case that has USB connection instead of just a straight +/- connections.)

I believe USB is standard +5v.. and if USB 2.0 can (roughly) supply 500mA only.. (some hubs only supply around 200ma or so)..

I read USB 3.0 can give roughly 900mA? (not sure myself though)

Velines: Sorry to dig this up, but I have another small question: Why can't I directly connect both parts of an USB power bank using cables like this? Or, to ask the same question another way round: Why do such cable exist and work without frying your computer or external hdd?

You CAN use these, but just understand that power sharing isn't necessarily going to be 50% for each USB port. In general, the port with the higher output voltage will supply a higher fraction of the total current (and power). So it's best not to connect the cable to two different devices, but using two USB ports on the same device is usually just fine.