Smart water meter is commonly install lithium batteries inside to turn on and off the water valve.Lithium batteries are with light weight, high energy and low self discharge rate.However, the batteries have to be replaced when power run off after a certain period of time and can not provide energy for the control circuit,because there is no recharging circuit in the smart water meter.It is a tedious task for water meter manufacturers and water companies to replace batteries or water meters at home. What's more, the occurrence of battery power shortage is random. If the battery power is not accurately and timely monitored, it will not be able to reliably close the water valve, resulting in the phenomenon of unable to charge, water escape and so on. This is the fatal defect of smart water meter with lithium battery installed inside, which directly affects its promotion and use.

To solve this problem, the water meter manufacturer has designed many schemes, such as: reduce the power consumption as much as possible, control the leakage current within 10uA in static state, and ensure the battery can be used continuously for more than 5 years, which puts forward higher requirements for circuit design and component selection, increases the design difficulty and the process of finished product detection, also the cost of components will be higher.If we add a reliable battery power monitoring circuit, the cost will also increase.

Many manufactures have tried a new solution to break the development bottleneck of smart water meter, which is to use super capacitors instead of lithium batteries inside the meter.Super capacitors are a kind of passive device which has been produced in batch in recent years. They  are between batteries and common capacitors. They can be quickly charged and discharged in high current as common capacitors, and also can storage energy as batteries. And, they have a long repeated service life. When discharging, they uses electrons between moving conductors (rather than relying on chemical reaction) to release current, so as to provide power for equipment.

Compared with batteries, supercapacitors have the following advantages:

1. The ultra low ESR, big power density  which is more than ten times of lithium-ion battery, which is suitable for high current discharge (a 4.7f capacitor can release instantaneous current of more than 18a), providing guarantee for reliable opening of water meter control motor valve or solenoid valve.

2. Super long life, charge and discharge more than 500000 times, 500 times of Li-Ion battery, 1000 times of Ni-MH and Ni-Cd battery. If super capacitor is charged and discharged 20 times a day, it can be used for 68 years continuously.

3. It can be charging with high current, short charge discharge time, simple charging circuit and no memory effect.

4. Maintenance free and sealable.

5. The working temperature range is -40℃~+ 70℃, and the general battery is - 20 ℃ ~ 60 ℃. Green Tech can offer super capacitors for smart meters with operate temperature in -40℃~+70℃/85℃。

Compared with the smart water meter with built-in lithium battery, this scheme uses super capacitor to replace the lithium battery, which is encapsulated in the water meter and powered by external dry battery. At ordinary times, the dry battery provides the energy required by the water meter circuit and charges the super capacitor. When the water valve needs to be turned on, check whether the super capacitor stores enough energy first. The water valve will not be turned on if it does not have stored enough energy. When it detects that it stores enough energy, the external dry battery provides energy to turn on the water valve. When the water valve needs to be turned off, but the external battery cannot provide energy,the super capacitor will provide energy at this moment. Like a water storage tank, the water is usually stored and necessary water is provided when the water is stopped.

This scheme is obviously superior to the previous design, with the following advantages:

1.The battery is separated from the water meter, so that the influence of battery life on the water meter can be ignored and the service time of the water meter can be prolonged.

2. On the other hand, the high current discharge characteristics of the super capacitor ensure the reliability of the water valve shut-off. When the external dry battery is insufficient, the energy stored on the super capacitor can still be used to shut off the water valve.

3. In the past, the leakage current index was always pursued to ensure the service life of the battery. When the super capacitor was used, the leakage current index became unimportant. If the battery is low, the user can change it at any time. In this way, not only the circuit design is simplified, the factory inspection process of the product is reduced, but also reduced product cost.

This scheme overcomes the shortcomings of the smart water meter at present, and finds a new way for the development of the smart water meters.