Supercapacitors versus Battery Hybrid and EV powertrains

We recently saw the Lamborghini Sian, an 800 hp spaceship – the prequel to an upcoming Aventador. The distinguishing feature that has people talking is the use of supercapacitors instead of regular batteries. Lamborghini has emphasized that this change is because batteries charge and discharge too slowly for the Sian.

A capacitor is a device which stores electric charge. You can find these in pretty much any electrical or electronic device – a fluorescent lamp, or a ceiling fan, or phones and other devices. It is used in all cases where a large input charge may be necessary. A supercapacitor is a very large capacitor with a lot of energy storage capability.

A battery can hold a charge for a long time until it is connected to anything which draws the charge. On the other hand, a capacitor discharges by itself. Supercapacitors find a very specific application in the Sian – instantaneous velocity. The Sian has a mild-hybrid system which, on the track, will assist the car as much as it can. It’s got all the software and regenerative braking. All Lamborghinis have had a problem with low-speed driveability because naturally aspirated petrol engines only produce usable power in a fixed range of revolutions.

The electric motor fills in the gap in the low end. As soon as you press the pedal from a standstill, the Sian will use the electric motor to propel you until the engine’s power is significant. This car is built for going very fast, and the tiny electric motor can only do so much during hard acceleration. That’s why the supercapacitors. They will dump massive amounts of electricity the moment you press the pedal, eliminating wheelspin and getting the car moving until the engine takes over duties.

The Sian cannot drive around on battery-only mode, because the system tries to discharge itself quite quickly. But the car won’t fight you all the time when you’re driving around in the city.

Another benefit of the Sian’s unique hybrid system is that it can charge more effectively with brake regeneration. The supercapacitor will have lower transmission losses than a regular battery. Lithium-ion cells have variable charging capacities. So when you have an empty battery, it charges faster. A relatively fuller battery charges slower.

The plug-in supercapacitors mean that there is no limit to how fast you can charge them – the higher the input voltage, the faster the charge. Will even the most cutting-edge, high-voltage battery will take at least 20 minutes, the Sian will be good to go in just a few seconds. Sounds good, doesn’t it? There is a disadvantage. If you start your car after three or four days (it’s still decidedly a weekend toy), it’ll be back to the measly 770 hp SVJ spec. The capacitors would have discharged.

It is safe to assume that if Lamborghini wants to introduce an EV model, it will have a regular battery. The Sian’s capacitors will be there too. This technology is underutilized at the moment – the Sian’s effort will encourage more carmakers to incorporate it. On the street, there is little consequence of using these over batteries. But track days will be a lot more fun with supercapacitors.

 

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Nick Fox

Automotive Videographer, Photographer and general Car Enthusiast.