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What Are Super Capacitors and What Might They Do?
September 3, 2007 |
A capacitor is simply a device that stores electricity, or more accurately electrons. The name comes from well, capacity. That ability is what makes them interesting as storage devices, which will become more important as our economy migrates to a more electrified state. You can be a capacitor when sliding your feet while walking across a carpet to increase your charge. Touch something with a lower static charge and you will discharge your electrons. A super capacitor is just more of the best characteristics. Capacitors offer a wide range of uses like filtering, signal processing, motor starting and motor running. It’s that motor starting and running that is most on point today.
Transport motors are going to need to start often and run at various speeds. A capacitor answers these conditions nicely. By offering a big dose of electrons instantly the capacitor fills the gap that comes when a battery needs to do its (relatively slow) chemical reaction to get electrons flowing. Positioned between a battery and a motor the startup can be full on from the capacitor as the battery reacts for running. The capacitor also can take a charge from regenerative braking and hold it for restarts. Capacitors offer a much better performance scale for all kinds of electric motor operations.
Super capacitors offer even more. They are designed with cycle lives measured in the millions. Very low impedance that optimizes the load handling ability when used with a battery. Quick charging that can take place in minutes or seconds with simple chargers as they charge to full and simply don’t take on more electrons.
Super capacitors have some remaining limitations. The discharge is linear, or power can come out to the level of voltage that is the load’s voltage leaving the charge below that voltage unavailable. The density of the energy contained is still very low, from about a fifth to a tenth of a battery by weight. By themselves they don’t operate at very high voltages, which requires a set wired in series to get a high voltage output. They self discharge pretty quickly compared to a battery, or the charge weeps away before it can be used.
What makes news is when one of these problems has a big improvement.
Will they replace the battery? When the problems are solved a super capacitor can sit for days or longer waiting to be used and not discharge away its energy, as it isn’t good to leak away the money represented by a full charge. They will come in packs or a design that provides the voltage with an installed set of management equipment in the pack at a low cost per unit so the designers and users can economically utilize the other attributes. The energy density needs to come way, way up, as the current super capacitors compared to a battery of the same watt-hour rating are much too heavy. The linear discharge issue will also benefit greatly when addressed so that more of the stored energy can be used.
It looks like there could be a much deeper integration of battery technology and super capacitors very soon. That would add a lot of benefits to both the “drivability” and the charge-discharge techniques. Over time its fair to anticipate that the integration will become more capacitor and less battery as the research and engineering improve the knowledge base for designs.
CAUTION
To wind up please note that capacitors are very fast (instantaneous) operating devices. The 1.5-volt battery that runs a disposable camera isn’t any threat. But connected to a capacitor that pushes the volts up to 300v or so and enough amps to fire the flash can deliver a nasty if not dangerous jolt. The capacitor in the back of a TV or monitor runs in the tens of thousands of volts and delivers lots more amps than a stun gun - so it can kill. If you don’t know how to discharge a capacitor don’t come into close proximity.
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