Benefits of Using VINATech Supercapacitors in IoT Applications

2022-12-16 [11:12]
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IoT Industry: Rapid Growth and Challenges

The Internet of Things (IoT) is a broad concept for connecting devices via the internet to simplify activities like stock reordering, predictive maintenance ,and remote control & monitoring. Data from remote devices is collected via an IoT hub or gateway where it is either sent to the cloud or analyzed locally. With the analysis leading to increased efficiency and productivity, reduced waste, improved service delivery, and optimization of resource usage. These benefits have resulted in IoT becoming a key technology in our homes, cities, and businesses across the globe. Although the rapid rise in IoT does present some challenges.

The explosion in the number of IoT devices rightly raises environmental concerns, with over 35 million devices already connect and a further 40 million projected to be added by 2025, about how we power these devices in a sustainable way. This is why new energy harvesting solutions are closely linked to IoT and also this explains the interest in supercapacitor solutions for energy storage.

IoT Communication Protocols
Communication protocols for IoT include LoRaWAN, NB-IoT, Sigfox, Bluetooth, Z-Wave, 6LowPAN, Zigbee, WiFi, and many others. Each of these protocols provides a trade-off between transmit range, data rate, and power consumption, details of which can be seen in Table 1 below:

Table 1 – IoT Communication Protocols
The use of supercapacitors in IoT is twofold; they can store energy from renewable sources (solar, wind, RF, vibration, etc.) that is then used to power the sensor and communications circuitry. Alternatively, where a relatively high transmit current is required, the capacitor can be combined in parallel with a battery. The battery provides the continuous current required by the circuit and the low-series resistance capacitor delivers most of the peak current required for data transmission. By doing this the peak current stress on the battery is reduced and its operating life can be extended by 2-3 times the expected duration using the battery alone, a benefit that is especially important in remote applications where battery replacement is time-consuming and expensive.     

IoT Application Examples
Asset Tracking:
There are several different types of asset tracking from tracking goods in transit by shipping container, truck, or train, tracking vehicles like taxis, company cars, delivery vans, agricultural or construction machinery, etc., and tracking individual assets like cattle. Each of these presents its own challenges and has different options for powering the electronics.

In vehicle tracking, the 12V lead acid battery is the main power source but when it’s disconnected, backup power is required to either: move data from volatile memory to flash, which is normally important when the system is monitoring driving style (speed, acceleration, breaking etc.) or support a last-time transmit, giving a leaving network signal and proving the last known location. For both of these, supercapacitors provide the ideal solution, with cells connected in series for 5V or 12V operation supercapacitors can be sized to support the required hold-up time even after 15-20 years of maintenance-free operation.

Remote Monitoring
Remote, battery-powered, applications include traffic, pollution, weather, river level, drain & manhole, commercial waste bin, and soil moisture monitoring. The batteries can be either primary lithium cells or rechargeable Li-Ion batteries utilizing solar PV cells for recharging, both of which present an opportunity to utilize supercapacitors.
The use of Li-Ion batteries presents some issues, including:
- Flammability concerns
- Poor low-temperature performance
- Relatively expensive
- Short service life (3-4 years)
These issues can be overcome by utilizing Electrochemical Double-Layer Capacitors (EDLC) or Hybrid Lithium Capacitors (LIC). For example, in a solar-powered sensor that might use Li-Ion batteries, the following alternatives are available:
1) VINATech Hybrid Capacitor VEL13353R8257G, 250F, 3.8V. It can be directly mounted on the PCB and provide reliable -25 - +70°C operation over 10–15 years of operating life.
2) VINATech WEC3R0107QD, 100F, 3V EDLCs (connected in series). This solution also has the benefit of -40 - +70°C operation and up to 20-year maintenance-free life.
Both solutions provide a very long cycle life, with none of the flammability or disposal issues associated with Li-Ion batteries. As such these options provide a much more reliable solution with a lower total cost of ownership than the main battery alternatives.

Smart Metering:
In gas and water meter applications the energy and power requirements depend on the communication protocol being used, with LoRa and GSM being commonly selected. The energy storage element in both cases is typically a Lithium Thionyl Chloride battery with a parallel connected EDLC or LIC where required. Using the following examples, we can look at the requirements for each protocol:

LoRa Water Meter
As can be seen from Table 1 above, current consumption for LoRa is ~50 micro-Amps continuous with a peak transmit current of 40mA for 5s. This level of consumption can be supported by 1 or 2 AA size Lithium Thionyl Chloride batteries with the pulse current accounting for 20% of the energy usage, assuming 1 transmit cycle per day.

The issue with this approach is that at sub-zero temperatures the battery impedance increases to a point where it can no longer deliver the required peak current. Also, repeated pulse currents stress the battery causing passivation and accelerated aging. So where sub-zero temperature operation or multiple daily transmit pulses are called for, the addition of a parallel connected EDLC is required to ensure reliable long-term operation. For example, the VINATech WEC6R0504QG, 0.5F 6V part with its low, 435mW, ESR and <1 micro-Amp leakage current would be a good choice. The additional load on the battery due to the leakage current would be less than 10% of the total battery capacity and the reduced peak current stress typically leads to a >2x increase in battery operating life.

GSM Gas Meter
Using GSM allows for a much longer transmission range but also requires much higher current pulses for longer durations, making the use of a stand-alone primary battery impractical. Where 1-2A pulse currents are required then either an EDLC or LIC solution can be used depending on the exact requirements, for example, a 1A peak current required during transmit period could be supported by:

1) 2 x VINATech WEC3R0356QG (35F, 3V) cells connected in series, the advantage of this solution is the excellent low-temperature performance down to -40°C and the ultra-low ESR (<50 mW). Also, the long cycle life, of over half a million cycles, makes this the preferred solution where transmission is required more than 7-10 times per day.
2) 1 x VINATech VEL10303R8107G (100F, 3.8V) cell, that provides an ATEX-approved, low leakage current (~2 micro-Amps), single-cell solution.
As with the water meter example above both these solutions significantly reduce the peak current stress on the primary battery, leading to double the increase in battery service life.

As IoT continues to expand, the challenge of powering each device in a sustainable, environmentally friendly way increases. For many home-based or mains-powered nodes there are no apparent cost benefits of using green energy storage technologies, so adoption is slow. In remote applications, however, there are clear advantages to using supercapacitors to either replace or support batteries, leading to solutions that have a long, maintenance-free, operating life resulting in a reduced total cost of ownership.
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