The effect of temperature on the battery, and the significance of temperature compensation?

Effect of Temperature on Batteries

1. Temperature will affect battery capacity

At different temperatures, the viscosity of the sulfuric acid solution in the battery will be inconsistent. For example, when the battery is at a temperature below 0°C, as the temperature decreases, the resistance of the sulfuric acid solution will continue to increase, which will directly increase the weight of the electrode. The effect of polarization, thereby reducing the capacity of the battery;

2. Temperature will affect charging and discharging

In the initial stage, when the battery undergoes repeated discharge and low-voltage constant-voltage charge cycles, the battery temperature is not high because the battery has heat conduction, but if the charge-discharge cycle continues repeatedly, the temperature of the electrolyte will rise. When charging at a low temperature, the density of the diffusion current will decrease, while the exchange current density is in a state of little decrease, which will cause the concentration polarization to intensify, thereby making the charging efficiency of the battery lower.

3. Temperature will affect the available time of the battery

If the temperature is too high, it will directly affect the inside of the battery. When the ambient temperature exceeds 45°C, it will greatly destroy the chemical balance in the battery and cause side reactions. In addition, charging in a high temperature environment will lead to degradation of battery performance, thereby shortening the usable time of the battery. The ambient temperature not only affects the capacity of the battery, but also affects the life and storage life of the battery in the float state. The ambient temperature is particularly important in the floating charging state, and the floating charging current increases with the increase of the temperature. During the charging/discharging process of the battery, the chemical reaction is sometimes too strong/smooth, making the battery unable to work normally.

Response of battery at different temperatures

When the ambient temperature is high:

The high temperature environment of the battery is the main reason why the actual life of the battery cannot reach the design life. As the temperature of the battery rises, the acceptance of charging current under constant voltage will increase, and the life of the battery will be shortened due to the increase in the total accumulated power of overcharging.

At high temperature, the increase of float current accelerates the accumulation of overcharge, and also accelerates the corrosion rate of the grid and the generation and precipitation of gas, thus shortening the life of the battery. For every 10°C rise in battery temperature, the life of the battery will be shortened by 50% at a constant float charge voltage. High temperature will intensify internal chemical reactions, resulting in water loss and increased grid corrosion. When the ambient temperature of the battery is high, the discharge capacity of the battery will be higher than the actual capacity, and the depth of discharge will also increase. Under storage conditions, the temperature is high, the self-discharge is large, and the storage life is short.

When the ambient temperature is low:

The low temperature environment of the battery will reduce the capacity of the battery, the ability to charge and receive, and the cycle life of charge and discharge. The actual discharge capacity of the battery will become smaller. This is why all lead-acid batteries are less than ideal for winter use. In addition, over-discharge is not allowed when the temperature is low in winter, otherwise the battery will freeze as the density of the electrolyte decreases, resulting in irreparable damage such as bulging and crushing of the battery plate and bulging of the battery shell. When the ambient temperature of the battery is low, the discharge performance of the battery becomes weak and the capacity decreases. Under storage conditions, the temperature is low, the self-discharge is small, and the storage life is long.

By adjusting the "float charge voltage", the function of ensuring the normal energy conversion of the battery is "temperature compensation". Reasonable implementation of "temperature compensation" can effectively prolong the service life of the battery and improve the efficiency of the battery.

How to achieve temperature compensation

Taking the communication DC switching power supply as an example, in order to achieve temperature compensation, the communication DC switching power supply needs to be able to monitor the temperature of the battery in real time, and can timely adjust the floating charge voltage for charging the battery according to the measured temperature. The monitoring unit in the communication DC switching power supply has the ability to monitor the temperature and adjust the float voltage.

For a communication DC switching power supply using a 48 V battery pack, the temperature compensation is usually based on 25 ℃, the float voltage is based on 53.5 V, and adjusted at -3 mV/℃ per cell (2 V).

Example: For the communication power supply of the 48 V battery pack, if the detected battery temperature is 10 ℃, the floating charge voltage is calculated as follows:

V float charge=53.5 V+(10°C-25°C)×(-3 mV)×24=54.58 V

For the communication power supply, the floating charge voltage of the battery is higher than 53.5 V in winter and lower than 53.5 V in summer, which is the result of temperature compensation, which is conducive to better management and protection of the battery.

Range of influence of temperature compensation

The temperature compensation function is to minimize the impact of temperature on the battery, but it does not mean that the battery can be used at any ambient temperature with the adjustment coefficient of the charging voltage. Because the temperature compensation function is only to compensate the chemical reactivity of the battery under different temperature conditions.

When the ambient temperature is low, due to the increase of the float charge voltage, it will also cause a series of problems such as the increase of the float charge current and the accelerated corrosion of the grid; series of questions. Especially for sites with large changes in ambient temperature, this has a great impact on the chemical reaction speed inside the battery. Therefore, it is still necessary to use indoor air conditioners, fresh air systems and other equipment to try to keep the battery working at the optimal operating temperature of 20°C-25°C, so that the capacity of the battery can be used to the greatest extent without damaging the battery.

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