Supercapacitors complement batteries
The supercapacitor is an ideal power buffer, charged by the energy source at average load current and delivering periodic or sporadic bursts of peak current.
As an example, a tracking device in the shape of a pendant runs on a CR2032 Lithium battery with LoRa radio for data transmission. CAP-XX prismatic supercapacitors such as the DMF low ESR, high power, DMT long life high temperature, DMH ultra thin, or an HA series are small and thin allowing them to easily fit into the tiny tracker’s enclosure. Fig 2 is a 100mA, 0.5s pulse typical of a LoRa transmission drawn from a CR2032 battery alone, and a CR2032 battery paired with a HA202 supercapacitor, 120mF, 120mΩ. A typical CR2032 battery has an internal resistance, Rbatt = ~10Ω. During the 100mA pulse the battery voltage droop is around 1V dropping to 2.25V. This voltage level is approaching the minimum operating voltage for many circuits, and the battery is fully charged. This will likely cause data transmission to fail, especially when the battery is not new and fully charged.
However once paired with an HA202 the CR2032, the voltage droop is reduced to only 0.2V, keeping the supply voltage around 3V after one pulse. After the pulse the supercapacitor will be recharged to the battery’s open circuit voltage, according to the Rbatt-C time constant, so 95% charged after 3.6s.
Another key attribute of CAP-XX supercapacitors that make them ideal to place across a battery is low leakage current (IL), ~1μA/F. Therefore, the HA202 part across a CR2032 battery in Fig 2 has a typical IL of ~0.5μA. Leakage current is drawn from the battery continuously so it can be a significant drain on energy. With only 0.5μA IL, a HA202 only draws 4.4mAh/yr.
Sizing your supercapacitor
Supercapacitors, which can deliver high power due to their low ESR, have high C to supply sufficient energy to support the data capture and transmission for its duration, have “unlimited” cycle life, and can be charged at very low current are the perfect power buffer.
For more information please refer to Supercapacitor Inrush Current Limiting, Supercapacitor Cell Balancing, Coupling a Supercapacitor with a Battery, Powering Pulse Loads,
Charging a Supercapacitor from a Solar Cell, from a Vibration Transducer,
Powering LoRa and NBIoT.