We couldn’t carry on our series of articles « How to create a successful ecosystem for your IoT project? » without addressing the question of choosing the right source of energy.

Billions of sensors and IoT devices are being deployed, some of them in very remote areas, buried undersea, or embedded into concrete infrastructures, where providing power becomes a challenge. Choosing the right source of energy is paramount to the correct functioning of the device and its sensors and hence, the success of the project.

So we’ve asked Brian CONLEE Applications Engineer at Saft America, to share his experience on the matter. Under his guidance, we will explore what is at stake, the various power options available to an IoT designer and what processes to apply when selecting a source of energy for an IoT project.  
 

Hello Brian, can you tell us about your role at Saft?

I’m an application engineer at Saft America and also the product manager of lithium-sulfur dioxide (Li-SO2) and lithium-manganese dioxide (Li-MnO2) chemistries. My main role is to be the first technical voice to the customer and to provide technical support to the sales team. In short I’m the go-to person for any technical question. I also take the customer information and develop the conceptual solution: chemistry, technology, the number of cells to be used, how to assemble them, how to protect them, at which cost, and so on.
 

What is at stake when choosing your source of energy and what processes should you apply?

Managing power is a transversal topic to any IoT project, and touches on both software and hardware. A successful power management strategy can make or break an IoT deployment, and managing power efficiently is particularly important for remote devices and long-life devices.

To start off, the architect must build a power budget for the device, reflecting the sum of all the energy-consuming components (sensors, microprocessors, microcontrollers, passive components, actuators and motors…), the frequency of data collection and communication, the wireless radio communication strength and power, without forgetting the energy loss from leakage or power supply inefficiency.

We have just launched a tool that helps developers do just that: Wisebatt for Saft. It’s a virtual prototyping platform that helps you estimate your device’s power consumption and battery life, and its potential components price and availability. Once you’ve built your prototype, you can try out different hardware and software options to optimize your power consumption. You’ll need to ask yourself questions such as: How often you are using your device? Does it need to take 15 measurements a day? Or less? Does it need to do calculations? or to send the data to do the calculations in the cloud? It all depends!

Voltage is also an important factor to understand. Batteries are not constant voltage generators. As the temperature/rate changes or (in some cases) the battery loses energy capacity while discharging, the voltage will drop, as shown in the batteries’ datasheets. If the battery drops below the device’s minimum cut-off voltage, it won’t be able to activate it. So what is your minimum voltage? And can you go lower, as it might offer new possibilities? 

The temperature and deployment conditions in the field will influence greatly the choice of source of energy. If your device is deployed in the middle of nowhere, in the Russian tundra for example, there’s little chance that you’ll be able to harness solar energy to power it. In such conditions, batteries are the singular most reliable source of energy you can find. But beware that temperature equally affects batteries – at low temperature, the electrolyte viscosity is higher which slows electrochemical and diffusion reactions; at high temperature, the self-discharge is more important and Lithium batteries with liquid cathode material can be prone to another phenomenon: passivation.

The size can also be a sticking point. Some designers have their design all set up by the time they start looking into the source of energy and tend to underestimate the needed space for the power source. We often have to challenge the size or the type of cell they think they need. At the end of the day, finding the right source of energy for your device and optimizing your power consumption is all about finding the right balance between the energy needed—how far and how long your device can last— vs. the power needed, ie, how fast do you need the energy to be delivered. Just think of the mileage of a car. In general, the slower you drive, the further you can go. I can drive 90 miles an hour but my gas mileage is going to be terrible. Or I can roll along at a leisurely pace and go as far as 400 miles. That’s the trade-off you have to find with your device.

Make sure you keep in mind the initial needs covered by the device to make sure it will live and be powered long enough and sufficiently to perform its duty and be profitable.

You might want to read our article: “How can primary batteries achieve their expected lifetime?”

From there, we can go deeper into the choice of the most efficient technology and chemistry for your project.

• Li-SOCl₂ for example, exhibits the highest nominal voltage among primary battery chemistries (3.6 V) and the highest energy density, even at low temperatures.
• MnO₂ exhibit a lower nominal voltage of 3.0 V for applications with a cut off voltage below 2.4 V. It is one of the most economic options with a good trade-off between energy and power and will be suited for applications that require a good current pulse capability over a long period of time.
• Our LSP range combines a low self-discharge Li-SOCl₂ cell technology with a Lithium-ion Capacitor to augment the pulse capability and performance stability over its lifetime at a range of high operating temperatures.
• Our medium prismatic MP and cylindrical small VL rechargeable cells will be recommended for devices that are frequently used and need to be recharged and used again and again but they take more space….

Each one of these solutions can be adapted to the device and to the needs it serves. A lot of misconceptions come from lack of knowledge so the earlier customers come back to us, all the more knowledgeable.

You might want to read our article: “Which types of batteries for your IoT devices?”

We’ll take them through our product study request, we plug the data into our calculation models, we do background research and discuss with the client the options, and we determine the best solution and its cost. The customer performs tests with the sample batteries we provide. Most of the time, once the customer has tried one of our solutions, they become regular customers.
 

If you had to give 3 pieces of advice to someone looking at choosing the best source of energy for their project, what would they be?

1. Get us involved as early as possible, even if you don’t know what you are going to build. The sooner the better. Let the plumber do the plumbing!
2. Think about the total cost of ownership (TCO) from the device’s cradle to grave. When you choose your source of energy and buy power, look at the quality! A cheap battery could go to sleep and never wake up and the failure of batteries coupled with the cost of replacement can become expensive. Quality, service and the manufacturers’ know-how should play a big part in your choice. For example, some manufacturers don’t manage passivation effectively. And that’s information that isn’t in the battery’s datasheet so the service is worth its weight in gold.
3. Test, test, test! Compare the various power supply options, test the various cells price ranges, test to make sure it works, but also compare the options and their impact on the TCO.
    

Do you see any trends in your market that you’d like to tell us about?

There are a lot of trends in the IoT world!

Each person is carrying 5 to 6 IoT devices now. The amount of data to be sent and/or stored is growing, applications necessitate higher pulse but in the meantime, they need to last longer. Long life, high power, cost… the requirements and physical challenges are becoming extreme, which drives us to work on new battery technologies. I’m very excited about solid-state technologies and the possibilities they will offer.

As a product manager for our LM and M ranges, I lately have seen a lot of ATEX applications coming my way —devices that are deployed in potentially explosive atmospheres. Batteries that are compliant with these kinds of projects are hard to find, and the tests are particularly difficult to pass. Not many battery manufacturers are selling ATEX compliant lithium-manganese dioxide (Li-MnO₂) chemistries but the demand is growing.  

Thank you Brian!