Solar Battery Bank

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Those little solar garden lights have become pretty ubiquitous in the past few years. They don't last forever though because the rechargeable batteries in them eventually don't last through the night after a day's charging and they ultimately get tossed into the trash. This instructable will show you how to turn those old solar cells into a solar batter which can be used to energize any USB-powered device using some wire, some recycled batteries, some electrical tape, a case of some kind and a couple of chips which will cost you around a Dollar/Euro each.

Please Vote/Favorite/Share/Make this Instructable, see more of my projects at http://justintylertate.weebly.com/ and continue on to the next step...

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Step 1: TOOLS/MATERIALS

TOOLS:

• Soldering iron and solder
• Wire cutters
• Hot-glue gun and hot-glue sticks
• Scissors or knife

MATERIALS:

• Tape your batteries together in groups which will fit nicely into your project case. For example, my project case was quite long and narrow so I taped my batteries together in groups of two.
• Solder wires to connect the ends of your batteries. It is really important that all of your batteries are wired in parallel (meaning that all of the positive ends are touching connected to each other and all of the negative ends are connected to each other).
• Once they are all wired in parallel, tape your batteries together so that they are secured and the risk of shorting the circuit is severely diminished.
• Now you should have a battery bank that can be charged and discharged.

*It is really important that you don't accidentally wire your batteries in sequence or make a short circuit anywhere.

**Originally when I was making this instructable, I thought to use 6 Li-Ion batteries, wired in parallel, for storing power however 6 batteries would not fit in my project case so I removed 2 of them.

Step 3: SOLAR CELLS

• Solder wires to each of your solar cells, connecting them so that they are wired in-sequence.
• Now you have a solar cell which can produce 4.5v on a sunny day to charge your batteries.

*To attach my solar cells to my project case, I hot glued the seams and epoxied a piece of nylon strap to the back side of them after doing the wiring. This allowed me to sew the solar cells to my project case. Because most project cases will be different, I suggest that you attach your solar cells to the case in the way which provides them the most protection as well as giving them support and allowing for a good angle to catch the solar radiation.

Step 4: CIRCUIT

Now is the time to assemble all of your components; the battery bank, the two circuits and the solar cells.

Following the schematic, you will need to:

• Connect the wire coming from the positive end of the sequence of solar cells to the "In+" hole of the TP4056 5v charging circuit.
• Connect the wire coming from the negative end of the sequence of solar cells to the "In-" hole of the TP4056 5v charging circuit.
• Connect the wire coming from the positive end of the Li-Ion batteries to the "Bat+" hole of the TP4056 5v charging circuit.
• Connect the wire coming from the positive end of the Li-Ion batteries to the "In+" hole of the DC Boost Module step up Converter 3.7V to 5V circuit (the red circuit board with the USB port).

*The following are also detailed in the next step:

• Connect the center pin of the switch to the negative end of the batteries.
• Connect the right pin of the switch to the "-BAT" hole on the TP4056 5v Battery Charger Circuit Board.
• Connect the left pin of the switch to the "-IN" hole on the DC step up Converter 3V to 5V USB Charger.

For my project I was able to sew my solar cells to the project case because of the fabric I epoxied onto the back but Probably you will have a hard case so i suggest that you glue and mount all of your circuitry inside of your project case to the best of your abilities in a way that will keep everything safe. A step on installing the USB discharging circuit and the switch will follow in their own step.

Step 5: SWITCH

• Connect the center pin of the switch to the negative end of the batteries.
• Connect the right pin of the switch to the "-BAT" hole on the TP4056 5v Battery Charger Circuit Board.
• Connect the left pin of the switch to the "-IN" hole on the DC step up Converter 3V to 5V USB Charger.

Flipping the switch will change your charger's function between discharging and charging your batteries.

Step 6: INSTALLING USB AND SWITCH

• To finish your portable solar powered battery-bank, all you need to do is cut 2 small holes in your project box; one which will hold your switch and the other to hold the USB port.
• Insert the switch into the holes and (hot)glue it into place and then do the same with the USB port.

Step 7: FINISHED

Congratulations! Now you have a portable, solar-powered battery bank made our of mostly salvaged parts! You can use it to charge your phone, tablet, MP3 player, and anything else which runs off of USB power! Bring it out into the sun and keep your devices running.

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8 Discussions

re battery issue cont.
Note the battery neg are connected to the red lead which is the system positive. I believe that the batteries should show the pos end of the batteries not the ned end fastened to the red pos line.

Let me know if this is correct or not from my observation.

Not to be negative but, not having the time to do something like this and it is a little overwhelming, I have a mini timer that works just as well. Only about \$5.

5 replies

Your mini timer works just as well as what? I don't see the correlation between this project and a mini-timer.

Excuse me please. I thought I was commenting to the person who couldn't do anything until they had their coffee in the morning and made some elaborate gadget to start the coffee machine.

That's actually kind of funny. And if you read shapri278's comment in a sarcastic manner it sounds even more hilarious. But I'm sure we all know that this was just a misunderstanding. :)

P.S. emoticons would be useful here.

Hi,

nice idea, but a few things to mention from my side:

If you do connect batteries in parallel, it is VERY important so make sure,
that they are all loaded to the same voltage levels. Otherwise the whole
battery pack could light up in fire. The reason of that is that the batteries
will try to instantly "balance" the load on all cells, what
could lead to a rapid charging of a cell with lower voltage. Regarding the
datasheet of the batteries you have linked, the worst case is a max. discharge
of 105A(3x35000mA) from 3 cells to one cell which is supposed to be charged by
maximum 4A.

I would suggest cells with a protection circuit.

The other thing is the loading speed of the solar cells. If you combine 3
panels together, you would have about 4,5V and 50mA charging current. That
would take about 200 hours for the pack to get charged from zero to full.