Power Considerations

A project log for LED Cubular - LED Desktop Cube

Arduino based; 6 PCBs all with 64 LEDs on the outer face to form a li-po powered cube of 384 LED coolness!

Jack FlynnJack Flynn 03/29/2019 at 16:250 Comments

Power Requirements and Battery Selection

In order to select a suitable battery, I needed to first estimate the overall power consumption of the LED Cubular. I started by going over the datasheet for the main active components and the Max7219 had a great section about estimating the current draw based on number of LEDs active and other factors. I combined this with my other estimations to give a rough total current draw and added an additional 10% for possible other loses; such as regulator efficiency. You can check out the results here;

As you can see the tested values are for Brightness; Low, Medium, High and then ALL LEDs on and Half LEDs on. This gives us a peak value of ~750mA max draw when all of the LEDS are on (unlikely in normal usage) and at full brightness which I would expect to be rather blinding. I can prevent this situation in code by either maintaining a much lower max brightness or only allowing a max number of LEDs turned on at one time. Either way it gives us a rough estimate of what load a battery might be under. 

I found 2 possible battery choices at 400mAH and 300mAH that would physically fit inside the cube. I estimated the liftime of the cube based on the capacity and draw for each battery which shows we should get at least half an hour with all of the LEDs on at a medium-high brightness. Which is well within my hopes and should give far more time under more animated lighting patterns.

Battery Selection

As mentioned, I found a 300mAH battery and there are a tonne of 400mAH drone batteries available but all of questionable specifications due to buying from ebay/amazon. The drone batteries would also require changing out the connector on either the board or the battery due to not using a standard JST connector. For now I'm considering this 400mAH Battery with dimensions of 26.5mm x 36.9mm x 5mm. Which you can see below will fit into the cube with a tight squeeze of space;

The major problem I haven't solved is how do I secure the battery down? I was hoping there might be some kind of "cable tie smd mount" that would allow me to cable tie the battery in place. I found these SMT cable clips which can be used to hold down wiring so I thought I could maybe do something like this;

Which would allow me to get 2 cable ties looped around the battery. Does anyone have a better idea?