Energy / Final – Day 1

Design

The battery and Solar Li-Po Charger

With three days to the Energy final my project has hit a major snag: the Li-Po is not supplying power to the arduino. The assumption was that when not recieving solar, the load would be powered by battery… assumption wrong.

After thinking that the Adafruit Solar Li-Po charger was not meant to be used from battery to load without the presence of solar, Roland helped me out by showing me that when connected to this massive 6000 mAh battery, current does indeed flow into the load even when a solar input is not included. He offered to let me use his battery for the final, but I declined since it was too big for my purposes. I would continue the original plan and go small. However, I did learn that a 1200 mAh Li-Po was too small to be used with the Adafruit charging board.

I went to Tinkersphere to buy a new 2400 mAh Li-Po, hoping that doubling the capacity would allow the charger to be used properly. This was a hypothesis that I hope would work. The 2400 mAh Li-Po was also too big for my design (it was very thin but too large in terms of surface area) so I had the idea of buying another 1200 mAh Li-Po and wiring it in parallel with my current Li-Po. I had no idea if it would work but it did… thank God!

Reducing the current draw to a bare minimum

Because I am designing this thing with the purpose of lasting forever, and because the board needed to be ON forever, I wanted the board and LED to draw the bare minimum amount of current.

The batteries (now 2400 mAh, instead of 1200 mAh) would start fully charged and be drained most at night and hopefully be recharged during the day.

Evolving Concept & Structure

My design was heavily influenced by Amitabh’s workshop on concrete, in which he showed how to encase acrylic and LEDs in a small concrete object. The combination of light and concrete: the juxtaposition of something soft and ephemeral with something very gritty and hard was a very esthetically pleasing mix.

My design originally was for a buddha, type statue, but I designed to scale down my ambition given the complexity of the project and time constrains. The complexity of the project is from the need to encase all those electronics: a solar panel, a Li-Po charging board, 2 Li-Po batteries, a Arduino Pro Mini, a Neopixel LED and a piece of acrylic for light form — that’s a lot of stuff.

I decided upon a simple concrete cube that collect solar during the day on one end and emits light at night on the other. The cube size would only be slightly bigger than the small Adafruit solar panel, which is just over 2 inches in length. The cube would then be 3″x3″x3″.

Safety of Encasing Batteries in Concrete

I was warned by Amitahb that it was potentially dangerous to enclose batteries in concrete, since the heating of the concrete while it was hardening could cause the batteries to explode. He also warned me there is also danger that the microscopic crystal needles poking out of concrete could puncture the battery itself and cause an explosion.

Further, I am told concrete expands

I no nothing of these matters so decided to take precautions by ensuring the concrete itself does not come into contact

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