It is an honour and a privilege to be selected as one of the sponsored challengers for this “Experimenting with Supercapacitors” design challenge, thanks to element14 and Cornell Dubilier.
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About Me
My name is Dr. Gough Lui and I am an engineer and electronics hobbyist from Sydney, Australia. 
I currently work as a postdoctoral researcher in the Biomedical Engineering space with Western Sydney University and as a research assistant with Civil and Environmental Engineering in the University of New South Wales. I have an interdisciplinary background, which includes an undergraduate degree commencing in Electrical Engineering, finishing in Solar Photovoltaics Engineering with first-class honours and undertaking a Taste-of-Research in Spatial and Surveying Information Systems. I have a PhD in Civil and Environmental Engineering, specifically in Water Research. In my work, I support the design, assembly, testing and deployment of embedded electronics for applications in health, medicine and humanitarian fields.
Outside of work, I run my own personal blog site at https://goughlui.com where I blog about random things including product reviews, repair logs, computing, networking, retro-technology, radio, television, satellite, random observations and going on holidays. I am a licensed foundation-level radio amateur (VK2FGYL).
I have spent much time over the years at element14 as a Top Member, mostly lurking but occasionally responding to a comment here or there. I have benefited greatly from the RoadTest program which has yielded plenty of useful and interesting equipment for my bench. I have contributed a whopping 34 reviews as of this posting (with a 35th in the works in parallel with this Design Challenge) and have learned plenty from the experience. I have participated in a few Project 14 builds as well although not so much as of late. Previously, I entered three “experimenting with” style Design Challenges, and was awarded the Grand Prize for Experimenting with Thermal Switches and Experimenting with Thermistors; and Runner Up Prize for Experimenting with Current Sense Amplifiers. I’ve also completed one “normal” Design Challenge, achieving the Runner Up Prize for Save the Bees.
Why Supercapacitors?
I am interested in this challenge as supercapacitors have been a bit of an elusive class of components which I have been aware of, but never had the chance to use in part due to pricing and availability. Most people are aware of the humble resistor, capacitor and inductor as most circuits need some passive components to work. I think some people are already aware that supercapacitors are a bit of an in-between of the “slow” bulk-storage of batteries and burst-current capability of ordinary capacitors. But how often does one actually see a supercapacitor used in the wild? Rarer still, how often has one actually needed to use a supercapacitor in their designs? Perhaps, do they even know why they might want to have one in the first place and the benefits it might offer? Truthfully, at the moment, I can probably count the first on one hand, while having never used them myself and being somewhat uncertain about what sort of benefit they may offer – especially if I’ve gotten by without using them for so long.
That being said, curiosity is an important part of being a good engineer. Being willing to learn and experiment, I signed up for this challenge for the opportunity to find out for myself. Sure, I’ve seen them used in memory back-up applications (to avoid the use of primary lithium cells, for example) and being used in industrial contexts (for kinetic energy recovery systems, or in electric buses). But perhaps they have a lot to offer the embedded systems designer too – now that wireless connectivity is a big thing, those transmit current bursts need to come from somewhere! More than that, the need to be sustainable means energy harvesting and renewable sources are more important than ever – but they are intermittent. Perhaps supercapacitors can offer a good solution to tie-over short interruptions or provide those energy bursts on a highly repetitive cyclic basis in a way that a rechargeable battery just couldn’t.
Proposed Experiments and Learnings
As a result, I’ve decided to title my series of blogs “What’s Super about Supercapacitors?” as that’s exactly what my project seeks to learn. In some sense, this is both an exploration of how they can be used, how to treat them well, why they’re so special and how they differ from ordinary batteries and capacitors. This will be pursued through a mixture of understanding the theory via literature but will also involve some more torturous experiments where my test equipment and automation skills may come in handy. By the end, I hope to learn as much as I can from the following list of questions:
- Understand more about safely using and integrating supercapacitors into designs.
- Look into different supercapacitor options and position Cornell Dubilier’s products relative to them.
- Examine the differences visually and mechanically between supercapacitors and ordinary capacitors.
- Learn about the capacity/energy density of supercapacitors relative to batteries and ordinary capacitors.
- Measure the series resistance and frequency response of supercapacitors to determine self-resonance points and suitable applications.
- Understand the differences between conventional supercapacitors and lithium-ion supercapacitors.
- Examine the charging and discharging characteristics of supercapacitors – Are they linear with respect to voltage and what is the impact of the operating voltage window? Do they suffer from dielectric absorption? What is the cycle efficiency? How does this change with respect to discharge current?
- Examine the capacity and leakage current characteristics of the batch of provided supercapacitors.
- Determine the capabilities of various sizes of supercapacitors to power embedded systems platforms for intermittent load applications, and for memory back-up applications.
- Utilise supercapacitors into a simple battery-free design to demonstrate the ability of supercapacitors to harvest intermittent sources of energy to run devices which require bursts of energy.
- Learn more about how best to place supercapacitors in series for higher voltage applications.
- Perform some initial cycle-life testing, potentially at different temperatures using a modified car fridge.
In order to find out, I will most likely need the help of my Keithley 2450 SourceMeter SMU, Keysight U1733C LCR Meter (or B&K Precision BA6010 Battery Analyser) and Rohde & Schwarz MXO4 Oscilloscope as test and measurement equipment for on-the-bench testing. I will combine this with some practical embedded systems platforms (e.g. ESP32 Bluetooth/Wi-Fi, Arduino MKR WAN 1310 LoRaWAN, or Raspberry Pi Pico) to be able to implement practical systems that can benefit and demonstrate the capabilities of the components in an actual systems application combined with the kit’s solar panel as a power source. In the process, I may inadvertently end up overstressing or damaging some of them (hopefully not), but that is all part of the fun (as long as nobody gets hurt). Perhaps this may even lead into a teardown and examination of the construction of such a device. In the end, I’m happy to explore wherever the road takes me …
The Kit
As it turns out, a shipment arrived on my doorstep today.
The box was slightly crumpled and the whole package was taller than I expected.
Inside, paper and bubble-wrap kept the component sorter box in-place for its long journey down to Australia.
The kit, as promised, contains two of each type of supercapacitor, of which there are 13 types in total.
Bubble-wrap was used to ensure the capacitors remained in their compartment and it certainly did the job. Good work element14!
There were a mixture of radial supercapacitors of different sizes – some conventional and some lithium-ion. From just looking at the packages, it’s virtually impossible to know these are supercapacitors without looking at their rating! They’re in aluminium cans with vent scores just like ordinary wet aluminium electrolytic capacitors. The printing is a rather “bland” grey-white on black as is traditional with most capacitors – not the exciting bright yellow you might have seen on the datasheets … not that this affects its performance in any way!
The PCB-mount ones look a lot more like batteries and are definitely something that I’ve seen around for memory and RTC timekeeping. I saw a very similar one from a different vendor back in the Maxim (now Analog Devices Inc.) MAX31343SHLD# MEMS RTC RoadTest that I did back in 2021.
The promised PV solar panel isn't included here, but I was notified this morning that I have a second shipment on-the-way for me, which I presume may contain the solar panel. If not, I've got a few I could probably repurpose in some way ... but I'd have to step-down their voltages first!
Experiment #0: What’s the Charge?
Time for the first experiment. Traditionally, when you are shipped a batch of capacitors, you expect there to be zero charge – the terminals will be at zero volts.
Indeed, for one that I did pick out, it was exactly zero according to my Fluke 279 FC.
But this was not always the case – some other traditional supercapacitors in the bundle measured non-zero voltages, although less than a volt. I wonder if this is a result of dielectric absorption.
Fascinatingly, the lithium-ion based supercapacitors all measured much higher voltages – more than one volt! Given that the datasheet seems to claim that the minimum voltage is 2.5V and working voltage is 3.8V, I’m not entirely sure of its significance at this time not having read deeply about this. Lithium-ion batteries are considered over-discharged, can suffer reduced capacity and increased leakage even if revived and are considered unsafe for use due to the possibility of developing copper dendrites when they stay below about 2.5V for a period – does this mean that these lithium-ion supercapacitors are not safe for use? Or is the minimum voltage the minimum needed to obtain the rated capacitance? I guess I’ll need to find out.
Measuring all of the capacitors, the record-holder had 3.328V on it which means quite a bit of charge. Shipping charged capacitors with their legs not restrained somehow doesn’t sound like the wisest move … I wonder if there is a risk of a spark if they touched or whether the charge is so low that this is not a problem (because of non-linearity)? Lots to learn!
Conclusion
I hope you all enjoyed this introductory blog where I admit just how little I know about supercapacitors. However, I am determined to learn more and hopefully through the experience of having some on my desk, I’ll be able to answer these curiosities through practical experiments. Please join me in my future blogs as I explore what’s super about supercapacitors.
[[What’s Super about Supercapacitors: Blog Index]]
- What’s Super about Supercapacitors? – Part 1: Me and the Kit
- What’s Super about Supercapacitors? – Part 2: Types, Vendors, Safety & Specifications
- What’s Super about Supercapacitors? – Part 3: Measuring Capacitance & ESR
- What’s Super about Supercapacitors? – Part 4: Measuring Leakage, Sizing a Solution & Lifetime
- What’s Super about Supercapacitors? – Part 5: Safety Under Abuse & Power Back-Up Application
- What’s Super about Supercapacitors? – Part 6: Solar LoRaWAN PM Sensor, Low-Temps, Imbalance, Cyclic & Short Circuit Life, LED Blinker
- What’s Super about Supercapacitors? – Part 7: Quite a lot, actually! (Final)
