By Thomas Dittrich
Smart metering systems can reduce energy consumption by up to 15 percent, thus contributing to energy efficiency and climate protection. Batteries are used as the power source for gas, water and heat meters and must last between 10 and 20 years.
BATTERIES FOR METER FUNCTIONS
One typical application is an electronic gas meter using a lithium battery as the power source. The electronics require a mix of low and high currents to power microprocessors, sensors and flow measurement functions, and need a battery capacity of 16.2 Ah over 11.5 years without falling below 3.2 Volts when operating between -20OC and +60OC.
These requirements can only be met with a single cell by using the lithium thionyl chloride (LTC) system.
BATTERIES FOR PREPAYMENT METERS WITH AN RF MODULE
A common method of transmitting meter reading data is with low power radio (LPR). A prepayment gas meter with an LPR module and a shutoff valve could typically have an average current of 140 µA, valve current peaks up to 30 mA, and be required to work for 11.5 years with minimum temperatures down to –20OC.
Such a requirement can only be met in a single cell with an LTC system battery. Analysis shows that the battery voltage will fall below the minimum 3 Volts after about 10 years due to increases in internal resistance, even though there is still enough capacity to last much longer.
The addition of a capacitor of suitable size and low leakage current improves the expected service life to about 12 years.
BATTERIES FOR GSM RADIO MODULES
An attractive alternative to LPR would be the GSM network as used with mobile phones. This can transmit data over large distances. GSM operation requires very high peak currents up to 2 Amps every 4.6 ms for duration of 0.577 ms.
A typical meter-mounted GSM module would have no continuous current but needs to transmit for half a minute up to 80 times per year. This requires a battery capacity of 3.5 Ah over an 11.5 year life.
This combination of a very dynamic current profile (5 powers of 10), high minimum voltage and long lifetime requirement creates a difficult task for a battery. The solution would be a PulsesPlus™ battery, which combines a hybrid layer capacitor (HLC) with the LTC cells in a battery about the size of three AA cells. Such a battery can cover the entire power requirement of the GSM module during the Tx duration (30 seconds) and provides a small and very cost effective solution.