DIY Powerwall 1 – Charging Cells

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DIY Powerwall 1 – Charging Cells

Difficulty level: IntroEasy – Intermediate – Expert

Dear fellow battery enthusiasts,

This is a first article of a number of write ups about upcycling batteries, powerpacks, and powerwalls. The fine folks at Battery Market have asked me to make some content to spark your interest in green energy. Let me introduce myself, I’m Franky Beuselinck, and work as a microwave engineer for the national phone company. The body is 48yrs old, but I remain 18 till I die. Facebook reminded me a few weeks ago that I have been building powerwalls for 4 years now. Today I have a 15kwh powerwall with over 2000 18650 batteries.

Next month I’ll extend the powerwall with another 9 kwh. My goal is to share my tips, tricks, findings and my fails. Don’t let the size of my powerwall scare you off. We start with basics and all info can be applied to a small powerpack too. Hence, I recommend starting with a smaller powerpack to learn the basics and acquire the skills. My powerwall concept is built with basic hardware. I specifically choose not to work with the most expensive hardware, so that it’s usable in developing countries too. Important notice, I never cut down on safety. My main powerwall has been running fine for 2 yrs now. I recently had to change my charger, but never had a fault in my upcycled batteries. So, that was the intro. Let’s dive into the world of batteries.

Building a powerwall is a process that can be split up in smaller tasks. Charging batteries, testing capacity, sorting batteries into packs, building, ….Today and next episode is about charging 18650 batteries.

Some take this step lightly. They buy a few commercial chargers that charge the batteries and even display the capacity. Later they’re surprised to find heaters. Heaters are cells that getting hot while charging and losing capacity over time. Due to these heaters, your system can get out of balance and cause serious problems. Today the number of solutions is limited. Let’s focus on a DIY solution. It’s easy and rewarding to build something yourself. The main component is a small circuit you can buy off the shelf, the TP4056.

This little nifty board takes care of charging the battery at the right current. The price for the module is around 0.25$, a real bargain. When the battery voltage is low, it will start charging with a very low current, once it exceeds 3V it will ramp up to 1A. Many builders have asked me if they could use their low voltage cells (cells ranging from 0 to 2,5V). My answer is YES. I have successfully revived cells with 0V, cells that were sitting idle on a shelf for years. Back to our charging module, the TP4056. The module will stop charging when charging current drops below 20ma. The end voltage of the cell may vary between 4.1V and 4.2V. Through experience, I have learned that if cells are closer to 4.1V, they will have a lower capacity, probably due to higher internal resistance.

If you have a faulty battery, the TP4056 will keep charging…as a result the battery will become very hot. Remove these hot batteries, discharge them and put them in the appropriate recycling bin according to your local regulation.

In the next article I show you how to built your own charging station, with many tips & pictures.

Franky goes green –

Franky goes green –

Note: Franky is a valued contributor, however, his advice and opinions are his own.