This Data-Logging Battery Tester Recycles Its Power

The only way to truly test a battery’s functionality is to run it through charge and discharge cycles. You want to look at the voltage at full charge, that the voltage during charging and discharging looks as expected for the supplied current, and more. But that testing process isn’t exactly simple for big battery packs that store a lot of power — that power has to go somewhere, after all. Eric Tischer’s data-logging battery tester has an interesting solution: it recycles power.

You’ve probably heard that “energy can neither be created nor destroyed,” which is one way to describe the law of conservation of energy. Knowing that, how do you get the energy “out” of a battery? You can’t just destroy it and instead you have to put it somewhere. For a large battery, like what you might use for an electric bicycle or a solar-powered backup system, that ends up being a lot of energy. If you want to perform a discharge/charge cycle, you need some way to get that energy out and somewhere for it to go.

Most battery testers simply turn that energy into waste heat, as a resistor acting as a heater is incredibly cheap. That waste is acceptable when you’re talking about a 5V 2000mAh lithium battery for a phone, but what about something like a 48V 10Ah battery for an e-bike? We’re talking about roughly 500Wh, which would be enough to run an electric space heater for 20 minutes or so. That’s a lot of heat and a lot of wasted energy! Tischer’s tester recycles all of that power instead.

The primary component of this tester is a SparkFun Thing Plus ESP32 development board. Its job is to measure voltage and current, while logging those values over time for later review. It takes measurements through an Adafruit INA3221 power monitor board, which can handle up to 26V and 3.2A. Tischer wanted to measure more current than that and added a shunt to bump it up to 100A. A real-time clock module provides accurate time stamps and there is an SD card module for data logging. Adafruit rotary encoders let the user adjust settings, like data recording intervals.

To “recycle” the power, Tischer uses an EcoFlow power station — the kind of large battery backup device that is often marketed as a “solar generator.” During the charge cycle, the battery tester pulls power from that. Then, during the discharge cycle, the battery tester uses the energy coming from the tested battery to recharge the EcoFlow. Then, rinse and repeat!

There is, of course, always a loss each way due to imperfect efficiency. But that’s certainly better than wasting all of the energy and Tischer doesn’t have to deal with the sweltering heat from a battery tester that has become a space heater.