Views: 204 Author: Hedy Publish Time: 2023-07-17 Origin: Site
There are several elements to consider, including the need for rechargeability, projected battery longevity, required operating temperature span, size limits, pulse current capabilities, and so on.There are also rigorous requirements regarding the shipment of lithium-based batteries (the paper IATA Lithium Battery Guidance paper is a great place to start if you need to carry such batteries by air).You must determine how to deliver the chosen batteries to your customer. Will they, for example, come pre-installed in the devices, or must buyers input them?
Inaddition to answering all of these questions, you should know the expected power consumption of your upcoming product. As you would expect, this is a chicken-and-egg situation, and you'll need to revisit your decision later in the design process. Your estimate was not necessarily incorrect, but the application criteria have changed, and you must begin again.We've done a lot of low-power designs at HARDWARIO, and we knew there weren't a lot of possibilities for our customizable IoT gateway CHESTER. Because the device is frequently used outside, only a few chemical alternatives can meet the criterion for a wide working temperature range. Welcome to the primary lithium cell with a nominal voltage of 3.6 volts, lithium thionyl chloride (or LiSoCl2).
Apart from its working temperature range of -60 to +85 degrees Celsius, this LiSoCl2 chemistry delivers the best energy density of all lithium batteries. It is also well recognized for its extremely low self-discharge rate (how much capacity will it lose on a shelf over time).On the other hand, you must contend with several difficult elements of the LiSoCl2 batteries. One example is the comparatively high internal resistance. While multiple ohms may not be a concern for many devices, it will be for those with cellular IoT connection. In CHESTER, we employ Nordic Semiconductor's nRF9160 (which supports both NB-IoT and LTE-M). Despite its leading power consumption metrics, you must nevertheless supply at least 500 mA current capability.If you start draining any current, the battery voltage will decline in proportion to the current and its internal resistance. As a hardware designer, you must offer a minimum operating voltage to your circuits to ensure optimal device performance.
A voltage drop during NB-IoT or LTE-M transmission might cause a microcontroller to reset. Otherwise, your cellular connection module will be deregistered from the carrier's network.We cope with it in CHESTER by employing supercapacitors. While the primary cell battery offers bulk energy reserve, supercapacitors cover the requirement for high-current peaks that occur suddenly. Because their usual cell voltage cannot exceed 2.7 volts, you cannot simply link them in parallel, albeit you can utilize special supercapacitor chargers.The LTC4425 from Analog Devices was used. This chip can balance the voltage across the series-connected supercapacitors and restrict the current drawn from the battery.
We source supercapacitors with a capacity of 5 farads from AVX, part number SCCS20B505PRBLE.This part features a typical leakage current of 15 microamps - a critical parameter to consider when choosing supercapacitors for your design.Another issue with LiSoCl2 chemistry is its flat discharge curve. It will maintain its voltage at around the same level for approximately 90% of its lifespan (yes, it depends on how you discharge it, but we're talking about low-power devices). While this appears to be beneficial because it offers surface area (read energy) beneath the voltage/current curve, it is ultimately impossible to produce a fair estimate of the battery's remaining power. I've even seen a transient voltage boost before the abrupt voltage drop at the conclusion of its life cycle. Temperature has an effect on battery voltage as well. So measuring LiSoCl2 voltage alone to draw any conclusions is futile.
One way around this is to monitor its internal resistance. You may achieve so by measuring battery voltage "at rest" and "under load," and then applying a basic Ohm's law formula to a known load current:You may monitor resistance increase in your smartphone over time and notify users at least a few days before the battery expires if its internal resistance exceeds a specified threshold. Alternatively, you may improve your algorithm and observe the rate of resistance change over time. Finally, imagine you wish to be even more precise. In such situation, you may use advanced technical analysis / neural network models to estimate battery voltage, current, and temperature over time. I haven't used them, although certain firms, such as BatteryCheck, specialize in them.
The second way is to continually check the overall energy consumption by the gadget.This process is known as coulomb counting, and there are specialist integrated circuits (known as fuel gauge ICs) that may assist you with this tracking. To acquire any relevant data, you must configure them properly and supply a battery model (parameters).Finally, occasionally a single battery cell will not suffice, and you will need to employ many batteries in your project. Customers frequently want years of field operation from HARDWARIO, as well as assurances for the worst conceivable signal circumstances. As a result, deploying additional battery cells during deployments is typically more cost effective than dispatching specialists to replace them sooner rather than later.
It may be tempting to connect numerous lithium batteries in series to get a larger voltage and then utilize step-down converters to access all of the energy potential. But please, never, ever do that. You don't know the battery conditions before installation, and the cells are always somewhat unbalanced.Then, for safety reasons, one of the cells will begin to charge, and this is a prohibited zone for the LiSoCl2 chemistry!What is the answer? Connect them in parallel using a low-reverse-current Schottky diode. Manufacturers such as Saft will not allow more than a few microamps of reverse current to the battery, therefore diode selection is crucial. However, with this strategy, you don't have to be concerned about the health of the battery cells at the time of installation for safety reasons.
To make life simpler for our clients and partners, we invented the CHESTER-B1 carrier board, which can handle up to 6x D-cell or 8x C-cell battery holders. This battery holder array can take either Saft LS 33600 (total capacity of 102 Ah) or Saft LS 26500 (total capacity of 47 Ah). Furthermore, the carrier board is housed in a tough IP-67 waterproof casing and is ready to service IoT applications in the field in the next years.I hope this has provided you with some useful advice and insights into your battery-powered IoT project. I'd love to hear your ideas and experiences.