Ultracapacitors have a maximum cell voltage of 2.7V, so they must be connected in series to reach the required working voltage. With any identical capacitors, the capacitance of a series array goes down as the capacitors are connected in series, but the working voltage increases by the rated voltage of each additional cell.
For a six-cell lead-acid battery, six ultracapacitors are required, because the maximum voltage a 12V battery is charged to is 14.4V. If five ultracapacitors were used, the maximum voltage across each cell would be 14.4V / 5 = 2.88V, which would cause premature failure of the cells.
At higher voltage battery configurations, it is possible to have slightly fewer ultracapacitor cells than lead-acid cells, but in general, the cells are equal to the number of lead-acid cells when directly connected in parallel with the battery. Since there is a minimum of six cells required and 250F was the minimum capacitance, the cell capacitance has to be at least 6F x 250F or about 1,500F.
There are several different sizes of ultracapacitors close to this capacitance that are offered by several manufacturers, including Ioxus
. For this example, a 2,000F prismatic cell manufactured by Ioxus will be used. The ESR (Equivalent Series Resistance) specified for these cells is 0.0006 Ω, resulting in a total ESR of 0.0036 Ω.
Clean energy production
Ultracapacitors offer better performance and longer life than batteries, leading to better operating conditions for environmental energy generation. Ultracapacitors are optimal between -40C and 65C, whereas batteries are best at -20C to 40C. Batteries require annual maintenance; ultracapacitors do not. The cycling capacity of a battery is only 10,000 to 50,000 in comparison to 1 million for an ultracap. Finally, the 10-year lifespan of the ultracapacitor dwarfs the two- to four-year expectation for batteries.
Brendan Andrews is the vice president of sales and marketing at Ioxus Inc.