Australia’s CAP-XX Ltd is developing supercapacitors to provide high power support to automotive stop-start systems, protecting and extending the operating life of the car’s battery in the process. Supercapacitors are lighter than a battery, can operate at low temperatures and be charged and discharged almost without limit. To find out more, Matthew Beecham talked with CAP-XX’s CEO Anthony Kongats and Pierre Mars, Vice President Applications Engineering & Quality.
Could we start by asking if you could explain what your stop-start supercapacitor module is and how it works?
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In a stop-start system the engine is turned off by the engine management system every time the car stops in traffic. When the driver goes to move off – for example, by depressing the clutch in a manual, or releasing the brake and depressing the accelerator in an automatic – then the engine management system starts the engine. This means the car never idles, saving fuel and reducing pollution. Depending on the traffic conditions, this could save anywhere from 2% – 10% in fuel and emissions reduction.
The downside is that instead of having to start a car 3 or 4 times/day, the battery now needs to start the car 30 or 40 times/day, or more. Typical peak starting currents are in the range of 500A – 1000A. This is a severe strain on the battery and shortens battery life. Batteries store and deliver energy by chemical reactions. This process degrades the battery over time.
Ordinary capacitors, on the other hand store and deliver energy electrostatically, not chemically, so they do not suffer the degradation than batteries do, but they cannot store anywhere near as much energy as batteries.
Supercapacitors, however, can store orders of magnitude more energy than ordinary capacitors, though still not as much as batteries. The CAP-XX supercapacitor module is a bank of very high power supercapacitors that are charged by the alternator to approximately 14V while the car is running. When the car is stopped for a stop-start cycle, the supercapacitor module retains its charge, and when the car is started again, the supercapacitor provides all the starting current, with the battery providing none. The CAP-XX module stores sufficient energy to easily start the car. The cells within the module should be kept at the same voltage. Also, since the module has such low internal resistance, it’s charge current must be limited so as not to overload the alternator. The CAP-XX module includes the electronics, developed by CAP-XX, to manage these tasks. Tests have shown the CAP-XX supercapacitor, when charged to 14V, stores enough energy to start a Subaru outback 7 times. It delivers sufficient power to even start the Subaru when only charged to 7V.
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By GlobalDataHow does the performance of a supercapacitor module compare with an existing battery used for stop-start applications?
We simulated the stop-start load on a car using the New European Drive Cycle. We had a 255A load with one second duration to represent the starter motor, a 45A load that was always on which represented hotel loads such as lights, radio, power assist, etc., and a 100A 14V power supply which substituted for the alternator. These current levels came from a Japanese car company and used for battery testing.
In our test, the battery alone lasted 44,000 starts before collapsing. The battery supported by the supercapacitor lasted 119,000 starts. Even then, the supercapacitor still started the car successfully, only discharging from 14V to 10.73V while supplying 255A for one second. The battery collapsed while supplying the 45A hotel load during the stop period. This is because the battery could no longer accept charge. This phenomenon is known as Dynamic Charge Acceptance and is a major problem for lead acid batteries in stop-start systems. Supercapacitors have no such problems.
To date your main focus has been on supercapacitors used in hand held devices, phones and cameras. In what ways has this experience and know-how advanced your application for use in cars?
The materials and construction method we use for our small prismatic supercapacitors result in a part with the best power density in the world at 90.9KW/L for the GS211. We have scaled up this technology to produce large prismatic supercapacitor cells with an Equivalent Series Resistance of only 0.26mOhms and 1400F capacitance in a package that is 195mm x 110mm x 9.5mm and weighs 230gm, giving a power density of 22.4KW/L and energy density of 5.6Wh/L.
From what we have heard, your trial with Club Assist has gone well. Who is Club Assist?
Club Assist are the people whose van turns up when you ring your local motorist organisation/ road side assistance firm with a flat battery. They provide assistance to drivers with flat batteries around the world, badged as the various car clubs. They are the world’s largest sellers of aftermarket batteries.
What’s the next stage for your supercapacitor module?
We have just established a low volume production line to provide samples for evaluation to potential manufacturing partners and customers. In the short term, there will be incremental improvements in the process to improve power, energy and the form factor. We also have hybrid supercapacitors under development which have some characteristics of batteries and some of supercapacitors. Made well, they have the long life and high power of supercapacitors but with double the energy. We expect the first samples of these to be available this year.
By when do you expect your technology to feature on a mass-produced vehicle?
2015 at the earliest.
The automotive market opportunity is clearly huge. If demand takes off, how will you manage the process?
We are already in discussions with possible partners who have the experience, skills and reputation in the automotive arena to successfully scale production and supply the automotive markets. This might be done by way of either a licence agreement or joint venture arrangement. CAP-XX does not intend to supply the automotive markets directly.
Over the years, we’ve seen the application of certain auto technology designed to last the lifetime of the vehicle. LEDs in front and rear car lights is one example. Presumably, your module will last the lifetime of the vehicle, too?
The supercapacitor module is certainly capable of lasting the lifetime of the vehicle. But in practise the life of the module will be very heavily dependent on engineering approach taken by the automotive manufacturer; how they integrate the module into their platform; and how hard they push the module. The module will certainly out live any comparable battery module whether lithium ion battery or lead acid battery.
Stop-start systems have been on the road for the past six or seven years. Why do you think the automotive industry has not already made the switch to supercapacitors?
Good question. The automotive industry is already in the process of switching to supercapacitors – look at PSA Peugeot-Citroen, Lamborghini and Mazda. Despite CAP-XX being a relative new comer to this market and this application we are already generating a lot of interest.
Any thoughts of the comparative cost to an OEM using adopting your system over conventional rechargeable batteries for stop-start systems?
The remainder of this interview is available on just-auto’s QUBE research service
