# Power requirements on long strings of LEDs

Hi - I'm attempting to create a project similar to this:

I'm using a Teensy 3.1 w/ OctoWS2811 Adaptor board and 30/m neopixel strips. The battery I'm using is this:

http://www.amazon.com/gp/product/B00M30 ... ge_o08_s00

My question is: How do I calculate/determine where to place the 5v power leads from the battery along the strips running vertically on the vest(e.g. every 100LEDs or so)? I assume a single connection at one end of a 470LED strip will not be sufficient to power that entire strip?

Additionally, will I need to connect multiple grounds to the battery as well (unsure about this since it it may impact common ground?)

I assume a single connection at one end of a 470LED strip will not be sufficient to power that entire strip?

The length of the strip is irrelevant it is the number of LEDs. I have powered a 240 LED from one power supply. The problem is the voltage drop when they are all on full power. Your power supply has to be capable of supplying the current, which is 60mA per LED when it is on full white. Is that the way you will operate the strip?
A strip of 470 LEDs is a current of 28 Amps!. That is a lot of current. If you split that over a few power supplies it becomes so much easier. In that case the split is predetermined.

Additionally, will I need to connect multiple grounds to the battery as well

It is exactly the same as the positive lead.

since it it may impact common ground?

No it doesn't.

Thanks for the response. Yes, I should have said "many" instead of "long strings of" LEDs. My vest is going to be 310LEDs and I'm going to dial them back to about 33% brightness. In the essence of time, I'll probably just run strandtest, which should create a pretty cool effect(diffused through fur) with little coding overhead and also won't be at full white at any point throughout the loop.

I also just realized my link to the battery didn't paste in properly. This is it.

This battery is interesting in that it appears to be basically 3 batteries within a single chassis that is capable of supplying 3 or 4A per USB port depending on the configuration. Given that its only supplying 3A per port: 1. Will this battery be suitable for this application? 2. How do I calculate how many LEDs can be driven per port given 1/3 brightness and not full white?

Most of the larger batteries seem to be 6v, which introduces the need for a voltage regulator to be added to the circuit which means I'll need to breadboard. If I can avoid breadboarding this thing that would be great.

1. How do I calculate how many LEDs can be driven per port given 1/3 brightness and not full white?

Well assuming one third brightness then that is just 20mA ( I know brightness is not linear with current but for the sake of the calculation you can assume that it is being driven at 1/3 current not 1/3 brightness ) At 1/3 current it will actually be brighter than 1/3 brightness.

So at 3A driving 20mA you have 150 LEDs. -- (3/0.02) = 150

That battery looks mighty expensive, how about going for something from a "robot" or radio control model site.

Thank you for the sanity check! I'll plan on soldering power at LED numbers 0, 100, and 200. It's true it is expensive, however I already own it and serves multiple purposes. I guess the best approach as far as cabling goes will be to cut up a standard USB cable?

I guess the best approach as far as cabling goes will be to cut up a standard USB cable?

Well if it were me I would fit USB sockets on the project so I could connect to it with standard USB cables. I have done this in the past and it works very well.

Ah brilliant! So basically this should do the trick?

No wrong shape you need the type B the sort that is on the Arduino because normally there is an type A and B on each end of a standard cable. The type A is for the host and the device being powered has a type B.