All other battery profiles exit because the OCV reaches a 0.6V cutoff voltage. One interesting observation is that the profiling of Murata CR2032R is the only battery that exits because the Open circuit voltage reaches 2.0V. The graphs below (Fig 3 & 4) show battery internal resistance when the battery is discharged, according to the LoRa profile. Our results show that coin cell performance differs a lot between the manufacturers, especially at higher currents. Results: Battery profiles for seven different coin cell brands By doing this, we got 10 battery profiles per month, which is pretty good when it comes to coin cells. To speed things up, we mounted ten Otii Arcs to the same computer and connected them to 2 virtual machines on this computer. Thus, if the voltage fell below 0.6V, the profiling stopped.Īs you might guess, it takes a very long time to profile coin cell batteries from seven manufacturers, each having two sizes. ![]() During the period when we had a high current consumption, we assumed that the voltage would be much lower due to the internal resistance. The profiling exit condition was when the battery had an Open Circuit Voltage (OCV) at 2V. We also considered the stated battery capacity from the datasheet. The low current consumption and timelow were adjusted to get a 30-day discharge time with a decent number of iterations. Settings for proiling CR2032 and CR2450 batteries in the Otii Battery Toolbox.Īs you can see, the high current consumption was set to 40mA for 1s, according to our generic LoRa profile (described above). We profiled all the batteries with Otii tool (using the settings shown in Fig 2. The batteries we tested, both CR2032 and CR2450, were: Murata batteries were not available in stores at the time for this test, so they were sent to us from Murata. We bought all the batteries from regular stores, with one exception. How to use Otii tool to measure batteriesįor this investigation, we bought random packages of batteries that we then profiled. The information above gives us the requirements that the battery must be able to handle. ln other words, the battery is considered dead. If the IoT device has a cutoff voltage of 1.8V, the battery voltage – most probably during a TX burst – will drop below the cutoff voltage, resulting in a brownout. Yes, this is a very simple power profile, but as a generic profile, it works. ![]() Let us assume that the IoT device has an TX/RX burst of 1s and that during this time the current consumption is roughly 40mA. Let us make the power profile of LoRaWAN devices more general. This peak sets the limit for the device’s battery lifetime. So the main question we wanted to answer was: Are there CR2032 and CR2450 coin cell batteries that can handle the power requirements of a LoRaWAN IoT device? Our problem, requirements and LoRaWAN profileĭuring a TX transmission, we get a current consumption peak that – considering the high internal resistance of the coin cell battery – will get a voltage drop below the IoT device cutoff voltage, thus creating a brownout. We also chose to test only CR2032 and CR2450 coin cell batteries. In this study, we focused on the battery, not the LoRa nor LoRaWAN parts. Our mission: To test the most common coin cell batteries with Otii But are coin cells really up for the task? We decided to find out by testing the most common coin cell batteries with Otii. Recent articles state that coin cell manufacturers have been able to lower the internal resistance and increase the capacity. A few years back, you could only use coin cells if you had a maximum of a few mA in peak current – otherwise, the battery would suffer damage, resulting in terrible capacity. ![]() For tiny and cheap sensors, coin cells are the obvious choice, considering that they allow for small form factor and are reasonably inexpensive.Īlthough coin cells are known for their small size, we also see that they have high internal resistance where tenths of ohms are common. With LoRaWAN being one of the most popular IoT connectivity standards, it is interesting to understand what kind of batteries work using this technology. TX/RX burst of 1s with a current consumption of roughly 40mA. Power profile assumption: We assume a simple, generic power profile for a LoRaWAN device. ![]() Our focus: The batteries, not the LoRa nor LoRaWANīatteries under test: CR2032 and CR2450 coin cells
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