Summary:In electronics, a capacitor is a passive component that stores electrical charge...
In electronics, a capacitor is a passive component that stores electrical charge. A conventional capacitor consists of two metal plates (electrodes as anode and cathode) separated by an insulator known as the dielectric. The ability of a capacitor to store charge makes it an important part of many electronic devices, including computers and mobile phones. A supercapacitor is a special type of capacitor that exhibits unique characteristics and properties.
Ultracapacitors are a hybrid between batteries and capacitors. They provide a power source that is reliable enough to run a device in case of a primary power loss or fluctuations/interruptions. They can also recharge much more quickly than a battery and have higher energy density than a traditional capacitor.
A supercapacitor can store up to a coulomb of electricity. This is the same amount of electricity that goes through a circuit if it is drawn for one second at a current of one ampere. This ability to hold an extraordinary amount of electricity means that a supercapacitor can supply a lot of power in a very short time.
Ultracapacitor cells are submerged in an electrolyte consisting of positive and negative ions dissolved in a solvent. Unlike batteries, which are chemistry-based and have limited voltage limits due to their internal chemical reaction, ultracapacitors are non-chemical and can have their maximum allowable voltages boosted by the type of dielectric used as separator between the electrodes.
The low equivalent series resistance (ESR) of modern ultracapacitors is the result of extensive research and improvements in electrode material, manufacturing processes, electrolyte formulation, and more. However, even if an ultracapacitor cell is rated with low ESR out of the box, cycling and long-term time at temperature can cause this to increase significantly.
As a result, when using an ultracapacitor module or stack, it is important to use proper soldering and handling practices. This includes preheating the board from the bottom side only, and reducing conveyor speed to prevent overheating the ultracapacitor leads during soldering. Excessive heat exposure can cause the sleeves to shrink, crack or melt. The sleeves can also be weakened by repeated soldering, creating a weak point that may leak.
During the wave soldering process, it is also important to limit contact between the iron and the cell bodies as this will cause the insulator to degrade and reduce the cells’ capacitance. This is especially true when the soldering iron is in direct contact with the sleeve for extended periods of time. This will also lead to an increase in the ESR of the cell.
Another consideration when working with ultracapacitor modules is the use of a cell balancing scheme. Because the individual voltage of a single cell in a series-stacked ultracapacitor will vary with cycling and time spent at temperature, this can cause a voltage imbalance among the cells that will affect system performance. Various companies screw/bolt their ultracapacitor cells together or weld them end-to-end (better) to minimize this effect.
