Powering led strip directly from Arduino Pro Micro powered directly from powerbank

Other Hardware General Electronics
1

Hi, I have a portable project on my hands and I plan to use a 5v 3amps power bank to power it, a sparkfun Arduino Pro Micro - 5V/16MHz to control it (or a clone board with 5v and micro-usb), and a ws2812b led strip.

I'm not a 100% i will be able to have 3amps available so let's say its 2.4amps. What I plan to power are some LED strips containing 45 LEDs in total with max 40 mA per led, so 1.8amps consumption from the LED strips, the 2.4 (or even 3) amps are enough.

In every other LED strip project, I have made I always powered the strip and the Arduino board from the same source, a power supply, so I have no experience powering portable projects. However, for this one I wonder if I can power just the Arduino from the power bank via the micro usb cable, and then the led strips from the Arduino board directly, without going into the hassle of cutting a usb micro cable and finding which wires I need to use for power and separate those.

So, my question is, why all the suggestions always point to separate the power from the board after a certain number of LEDs on the strip? Can I power it from the micro usb directly without running into problems?

Or, are there are important reasons not to do this? such as: I will damage the board, I won’t be able to get 2.4 amps if I power the board via usb micro, etc... so, Is the only solution to cut the usb cable and power the board and the LED strips separately?

Thanks for any info you can give, it wasn’t easy to find an answer for this specific issue.

2

Micro usb is pretty darn small & fragile for currents over 1A. It'll probably hold, but it wouldn't be my preferred solution.

3

I see... so the issue with this solution is that the micro usb itself has problems handeling such current, i guess it is matter of testing how much current i get from the 5v pin then?

5

This is sounding somewhat confused.

If you are not connecting it to a PC, you connect the 5 V power to the "5V" ("Vcc") pin and ground as well as the addressable LED strips (55 mA per LED).

If you are connecting it to a PC, you do not connect the 5 V power to the "5V" ("Vcc") pin (but of course connect the ground).

You do not use a micro USB cable, but a standard USB cable with a standard "type A" plug and the other end cut off for the bare wires. Red is 5 V and black is ground - the data wires are green and white. You connect that to your LED strip and the Arduino when it is not connected to USB.

There is generally no difficulty finding an old USB cable to cut up - but it needs to be of sufficient calibre.

6

First of all thanks for your reply,

I get the confussing part, i meant usb, not micro (so "type A" indeed)

I usually do connect Vcc directly, however this time my question was if I could do it instead from the usb micro (With a type A to usb micro cable from a power bank external battery). Btw 55-60mA is at full bright white, its not gonna use more than green+blue at full bright so i estimated 40mA.

I knew this was "the propper way" I just dont know why (since plugging a micro usb directly to the board is easier than cutting off a "type A" cable) did not know it was colored and so easy, so probably i'll end up doing it this way.

Thanks a lot for your answer, I'll do it this way probably, I was just wondering why not the other way...

7

One/ the reason is pretty much as koraks explained in #2. The Micro USB connector is pretty small for any substantial current - and USB cables with such a connector are often rather lightweight, so the voltage the Arduino and LED strip sees may not be quite the same as the power pack is supplying!

Soldered connections with a cable no longer than absolutely necessary are likely to be much more reliable - less likely to be dislodged.

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