Three key parameters of the shunt
The shunt used in the power battery PACK is essentially a resistor to detect the current value flowing. Since the current value is not easy to monitor, most of them are converted into voltage at present, that is, when the current passes, the resistor generates a voltage drop, and the voltage value is detected to calculate the passed current value, which is based on U=IR.
This method requires the shunt to have sufficient accuracy, and the resistance value should change as little as possible with temperature, and the temperature rise should not be too high, so the following three key parameters are derived:
1. Accuracy
As we all know, the resistance value will change with the use environment and temperature, but if the range of change can be well controlled, that is, the accuracy is high enough, the current monitoring requirements can be met. At present, the accuracy of the shunt (the deviation of the resistance value from the standard resistance value) includes ±0.1%, ±0.2%, ±0.5%, etc., which is related to the current detection application environment of the shunt.
2. Temperature rise
The temperature requirement in the application environment of the battery system is generally -40℃~+85℃. In order to ensure that the heat generated by the shunt does not affect the use of the surrounding components, the temperature rise control value, such as 100℃, should be guaranteed.
3. Temperature coefficient (temperature drift)
The temperature drift reflects the working stability of the shunt. The smaller the temperature drift, the better the stability. Characterize the performance of the shunt ratio [(R1-R0)/R0] changing with the temperature T, and its unit can be expressed as X%/℃. For example, if the shunt ratio is 0.2%/℃, it means that the temperature changes by 1℃. 0.2% of the nominal value.
The current method of testing the temperature coefficient is to use a high temperature (above 100°C) incubator for more than 30 minutes to measure the resistance value, according to the formula [(R1-R0)/R0]/(T1-T0), where R0 is the nominal resistance, T0 is room temperature.
