In this new entry I will present to you one of my last creations. It is a DIY load cycles tester for 18650 cells. And you’ll wonder, what’s that for?
Cell load cycles 18650
When carrying out a project where we make considerable use of cells 18650, it is important to know as best as possible the material that we are going to use. In my case, I have in mind to make a powerwall with 18650 cells. It will be approximately 10KW nominal and that means I will have to disburse a lot of money in cells (there are 840 cells). As you can imagine, the decision of which cell model 18650 to choose is very important.
Previously he had flirted with Liitokala’s NCR18650B cells for small projects: one battery for a drone, another for a drill, a small project of a photovoltaic solar system with surplus storage, etc. I have always considered that these cells meet very well and my idea is to make the powerwall with them.
The fact is that the powerwall has to last me for years, and that means many charge and discharge cycles. As you know, lithium cells are progressively losing capacity as they are used. As they are Chinese cells, there is always doubt as to how long they will last or how much degradation they will have. I haven’t found any information about it. We only have one data that the manufacturer gives us, but no real evidence (neither of Liitokala cells nor originals, of any).
Diy load cycle tester
All this is what encouraged me to make the diy load cyle tester. I leave you several photos of the device:
The following parts can be differentiated as a summary:
- A TP4056 charger with which we charge the cell up to 4.2V.
- A resistance I made screwing wire that we used to unload the cell up to 2.8V
- An arduino to control the cell voltage and go from charger to discharge and vice versa.
- I also added an LCD screen to display some parameters: cell voltage, whether it is loading/unloading, the full cycles it takes, and the time it takes in the current cycle.
- Finally, a couple of buttons to switch mode (load/unload) manually, and another button to reset the cycle counter.
I think to introduce you to the home tester of cycles is enough. In future entries we will go into more detail about how to manufacture, the code I have used, etc.
18650 cell load cycle testing
I leave you a table with the links to the different tests that I am doing:
I hope you find it interesting. Any questions, leave it in comments.
See you next time!!