Hello everyone.

I welcome you to my series about Cornell Dubilier supercapacitors as part of Experimenting with Supercapacitors design challenge. In my first introductory blog I want to describe experiments which I want to do as part of this design challenge. My supercapacitors are on the way. I have not seen them yet. According to tracking the package today travelled from the USA to Europe and now is on the way over Europe to my home.

Before I start, I would like to thank Cornell Dubilier company for sponsoring this Design Challenge.

Application

I based my application mainly around solar powered sensor nodes. One of them I recently did and posted to the Project14 competition (blog is here: Mini Solar Powered Wireless Temperature Sensor). This project used no battery and instead it is built with very small solar panel and supercapacitor which is used for storing energy when energy from solar panel is insufficient. This happens, for example, at night and supercapacitor backup storage allows my sensor node to work 24 hours every day.

Readers of my article about sensor node may notice that I spend very few efforts with selecting supercap and I did not do any comparison or proper evaluation of supercap used. In my original project I just selected intuitively large supercapacitor and hope that it will be sufficient. It was sufficient. As part of Experimenting with Supercapacitors, I want to compensate my ignorance in my original project and properly evaluate supercapacitors from the kit which I should receive soon.

One of my goals as part of this competition is to provide guide for selecting capacitors. At the first look it looks that idea “higher capacitance is better” is sufficient but practical working with supercapacitor shown me that opposite is true. Supercapacitors with higher capacitance have several drawbacks and generally idea on selecting supercapacitor for such project is to select supercapacitor with as low capacity as possible with limitation that it must work for all the night. Low-capacity supercapacitors (or even standard capacitor) are cheaper and are smaller. I learnt that physical dimensions of supercapacitors are important because I had hard time when designing PCB and placing capacitor with pitch over 1cm to the board while keeping in mind that capacitor must fit the box with bend wires and must not collide with other large parts like terminal blocks.

As part of the design challenge, I will do several experiments which will help me to achieve my main goal.

Experiment #1: Capacity Measurement

At beginning I want to measure capacitance of provided supercapacitors. While it looks like simple task, with so high capacitance it is not. I have multimeter which can measure capacitance, but it is limited to 0.1F which means, that I will be able to measure only one capacitor from the kit. For measuring other I will have to deploy other manual measurement procedure which I studied in last days. For me it will be more complicated because I do not have all test equipment needed for such analysis, so I will have to do it in DIY way, which hopefully at the end will be at least funny, or maybe interesting solution.

Experiment #2: Effective Energy Capacity Evaluation

The second experiment will be about evaluation of effective supercap provided in the kit. In the kit we have capacitors DGH105Q2R7 and EDC105Z5R5H. Both mentioned capacitors have capacity of 1F, but they differ in another parameter – rated voltage. One of them is rated for 2.7V and the other is rated for 5.5V. 5.5V unit is about 4× more expensive. Is it 4× better? Can it store 4× more energy while it has “the same” capacity? Are there use cases where one of them have benefit and are there different use cases when the other capacitor has advantages? In my second experiment I want to answer questions like these.

Experiment #3: Leakage Evaluation

As part of third experiment, I want to evaluate and characterize leakage of supercapacitors. They are frequently used for long term energy storage, so leakage (self-discharge in other words) can significantly influence their performance.  For example, in my project, they store energy for whole night but there are use cases when supercapacitors power circuit for much longer. For example, two years ago I RoadTested MAX31343 RTC. On this board supercap was able to power RTC chip for several weeks. RTC chip have extremely small power consumption, but in case when supercap have high leakage, then it will discharge faster just because of it’s own self power consumption. In this experiment I will play with caps to measure their leakage in several conditions and how it changes when supercapacitor is exposed to different conditions. This experiment will consume lot of time, because leakage can be very small in general, and it may take several days until capacitor self-discharge to measurable level. For this reason, I will start it as soon as possible. It should also differ per capacitor type, so I will look at this also.

Experiment #4: Evaluation Supercapacitor on Solar Sensor Node

This is in fact goal of my experimenting. I will desolder supercap which I used on my solar node as part of my original project, and I will try different supercapacitors form the kit instead. This kind of evaluation will include all properties mentioned above and allow me to investigate their impact in overall. I will need to resolder some parts on board. For example, for limiting voltage applied to capacitor because each supercapacitor has different rated voltage. But otherwise I will use almost unmodified boards. I will monitor behaviour of my sensor nodes with different capacitors. For example, I will monitor how long will it take to start-up (charge to level suitable for running), how long will they work when no light is provided, psychical dimension evaluation, and so on. Outcome from this experiment will be recommendation on supercap selection for this kind of circuits and guide for selecting supercapacitor including listing of parameters which influence such selection.

Conclusion

This is all from my first blog as part of Experimenting with Supercapacitors. I will write some intermediate blogs describing details about my experiments results, notices and opinions about Cornell Dubilier supercacitors after I gain some experiences with them. While I have prepared plan as described in this blog, I do not consider it final. Maybe after practical experience with supercars I find some other interesting topic and will write (and will experiment) about it.

I hope you enjoyed reading this blog. I would welcome any feedback in the comments bellow, and I am looing forward for experimenting with supercapacitors which should arrive soon. Thank you for reading this blog and have a nice day.

Next Blog:  Supercapacitors Overview and Comparison