So my DIY Powerwall (like the Tesla one) project is moving along quite nicely. I’ve just finished my mass charging station design and I’m quite happy with it. This design is a lot simpler/easier to make (for most people) than my normal designs. It doesn’t require any laser cutting because the laser cutter at HSBNE (brisbane hackerspace) was out of action briefly. It still requires 3D printed parts but a bit of extra work means you can use the normal 18650 holders.
1) Ply wood mounting plates.
I used two rectangular plywood plates that I cut out by hand. (yes, I didn’t use a laser cutter 😉 ) The top one is for mounting everything to, whilst the bottom one is to allow for a level bottom and to hide all the wiring. Cut out the two plates so you can fit everything on with some room around the edges for the wiring.
2) 18650 Chargers (TP4056)
These are one of, if not the cheapest Li-ion/LiPo battery chargers that exist. It’s an all in one board with through holes for 5v in and a battery output. They will charge any Li-ion or LiPo battery up to full from either a USB connection or 5v to the two pads either side of the USB plug. The cheapest place to get them I found was Aliexpress. (I got mine for 30c each on the 11/11 sale!)
3) Computer power supply
Any generic 5v power supply will work. However, you’ll need quite a lot of current to charge more than a couple of batteries at once. Old (or new) computer power supplies are perfect. Most can supply around 30 amps on the 5v rail. Each battery needs about 1 amp so this means it should be good for about 25-30 batteries at once.
Tech Tip: Some power supplies only watch the 12v line for voltage drop, so if there is no load the 5v rail could drop below 4v! The easiest way to fix this is to put a load on the 12v rail. I find putting a few 12 fans to cool the chargers down helps. See below for optional monitor.
4) Wiring, connectors and (optional) fan
You’ll need a bunch of wiring and a connector if you want to easily disconnect it from the power supply. I find old network cables are great for this job. A single 5m network cable has about 40m of wiring in it! The wires are tiny and can carry enough current for this job, making them the perfect fit. Solder one wire to each + and – near the USB connector, join them all up and use some thicker wire to join the bunch to a connector. Connect the fan to the 12v rail and glue it onto the side. If you get a small bit of cardboard/wood you can direct the flow a little better.
5) Voltage Monitor (optional)
I bought a few of these voltage monitors off eBay. They are super cheap and easy to wire, simply put the red wire on the positive side and black on the negative side of whatever you’re measuring. It even powers itself from the same source. This is great for watching the voltage of the power supply. I have mine on the 5v rail of the power supply so you can keep an eye on it. Cheap Voltage Monitor (eBay link)
Once it’s all put together this is what it looks like. Quite a good little package I think, and really cheap at about $1 per battery slot. (assuming you have access to a 3D printer, box of power supplies, network cables and connectors like me 😉 )