How Does a Capacitor Work
Capacitor Charge-discharge Cycle
How does a capacitor work? The capacitor works by discharging excess electrons out one side in response to an electric field impressed from the current on the other side of it.
As the very simplified animation to the right shows, an excess of negative charge builds up on the incoming plate in response to the current in. When the capacitor will accept no more current, it is "full". Then, when the power supply is shut off, and leads from the capacitor to the load or device are connected, or switched, the excess electrons flow out the other side of the capacitor.
The flowing electrons produce the current out. The capacitor is discharged, and the
cycle can start over accepting more charge.
As shown on the previous page, the capacitor is very good at accepting and releasing charges quickly. However, It is not so good at holding energy a very long time: at least not yet. At present, a capacitor holds just five percent as much energy as a Li-Ion battery.Research to extend storage time is underway.
How does a capacitor work for the EV? Regenerative braking for one thing. Capturing the energy normally lost to heat slowing down the car can be used to quickly charge a bank of ultracapacitors. This is great for situations where you need to fill up the tank fast and then use it for an extra boost during acceleration.
While the stored energy may not be enough to power the car very far just yet, ultracapacitors can provide plenty of accessory power. This can be a significant amount of power in the case of an EV. Although electric cars are not yet powered by ultracapacitors, some city buses are.
Capacitors are now being used in the electric bus for short hops between charges. This works out well as the buses can recharge from overhead wires. Since the capacitors do hold some charge for a few miles or so, this means you only need the wires at the bus stops rather than all along the route.
However, there is not as yet a bank of capacitors developed that can hold the same amount of charge for the same length of time as a set of lithium batteries. When and if this happens, look out internal combustion engines everywhere!
You can watch a very good 6 minute YouTube capacitor explanation video.
The Maxwell Company (NASDAQ: MXWL) mentions healthy sales of their Boostcap line. They have made over 1,000 installations of their ultracapacitors and ultracap banks in transit buses in the first 9 months of 2010. Maxwell sees strong growth going forward.
Worldwide, there are some 2,400 Boostcap-equipped hybrid transit buses now in service. The projected growth is 3,000 by 2011.
In terms of market value, Maxwell has already processed $13.5 million of purchase orders for some 850 hybrid busses for 3 Chinese bus manufacturers.
Maxwell will soon manufacture a boostcap for Peugeot that is to be installed in some 1 million diesel vehicles. The boostcaps will enable the vehicles to shut down and restart rapidly in traffic with resultant big fuel savings and cleaner air.
The Loxus Company has a prototype Li-Ion/ultracapacitor unit now in the testing. The first generation of hybrid capacitor is about the size of a "C" cell battery, holds twice the energy of a regular ultracap, and can be charged up in seconds. The new devices will first be used to run electronics like power door switches and be scaled up over time.
Ultracaps are seen as the future of the EV by at least one important EV pioneer: Tesla Motors. The CEO of Tesla has been reported saying that "a coming revolution in electric transportation would not be based on batteries but on ultracapacitors." Mazda Motors apparently agrees.
Mazda has produced a capacitor braking recharge system called the iLoop. Upon braking, the Mazada unit charges at 25 volts, running through a DC-DC converter to recharge the onboard 12 volt battery. The power can be used to power auto accessories, and is estimated to improve fuel economy by around 10% in stop and go driving.
The market for ultracapacitors is projected to grom 30 percent in the next 10 years or so. Maxwell is ramping up production 30 percent and the manufacturer Nesscap is aiming to triple output. Large transit and EV projects are expected to be the market for the super capacitors.
Cable Car Caps
Cable cars in London, UK are employing ultracaps to power accessories on cable cars crossing over the River Thames. The
Emirates line is made up of 34 - 10 passenger cabins and transports up to some 20,000 passengers per day. The banks of ultracaps get recharged at each end of the line and provide power to lighting and air ventilation systems, and multimedia entertainment units. The weight savings of ultracaps over batteries is significant states the operator.
Lamborghini Aventador to use Ultracaps
Lambroghini will be installing ultracap packs in its 2015 model 700 hp Adventor car. The ultra caps will help kick the
12 cylinder engine after slowing and idle shutdown. Less fuel use will contribute to less CO2 output, a company goal.
Ultracap Packs: power for
cable cars and other EVs.
Ultracap Packs to be installed in
the 2015 Lamborghini Aventador