Ultracapacitors are well suited to replace batteries in many applications. Voler Systems developed such a replacement for a company that makes RFID and wireless technology products.The battery replacement was cheaper with a longer life than a standard battery.
Ultracapacitors, also referred to as supercapacitors or double-layer capacitors, are electrochemical capacitors that have an unusually high energy density when compared to common capacitors. Conventional capacitors store only tiny amounts of energy. Ultracapacitors offer orders of magnitude higher energy storage. Larger ultracapacitors have capacities up to 5,000 Farads as of 2010, and 10 Farad capacitors cost only a few dollars.
Ultracapacitors offer some advantages:
- Longer lifetime than a battery (almost unlimited number of charging and discharging time)
- Fast discharge rates (hundreds of milliamps or Amps of current)
- Fast rates of charging compared to some types of batteries
- High energy density (but lower than batteries)
- Little thermal heat during discharge
- No danger of overcharging – simple charging circuit
- Not affected by deep discharges as are chemical batteries
- High charge/discharge efficiency (80%-95%)
- Large operating temperature range (-50C to 85C)
- Materials are not hazardous and may even be used for medical devices inside the body
The biggest advantage of the ultracapacitor over the battery is the simple charging circuit. A capacitor can be charged by just applying a voltage to it. A battery is easily damaged by overcharging, so it must be charged in stages, which is complex. The charging is usually controlled by a battery charging IC.
Ultracapacitors will not totally replace traditional batteries. When compared to traditional electrochemical battery, ultracapacitors shows these disadvantages:
- Low voltage ratings, usually less than 5 Volts
- Lower energy density
- Lower discharge rate than certain types of batteries
- Higher self discharge rate – the voltage leaks away in minutes to days
Ultracapacitors are well suited to replace batteries in some applications but tradeoffs must be evaluated. For our RFID and wireless design, the ultracapacitor was a good alternative to a battery. It cost less than a battery and had a higher temperature range than a battery.