Charging and discharging characteristics of electric forklift battery
Take an electric forklift battery as an example. When stored at 30°C for 8 months, the remaining capacity of the battery is only half of that of the factory. Therefore, the newly purchased battery is matched with the UPS and generally takes a longer time to charge. This is called initial charging.
The initial charging current of the battery should be 0.1C before it can be charged, and the battery can be charged at the end of discharge, which is called normal charging. 'Currently, two charging methods are commonly used in UPS: floating charging and pulse charging and discharging. The so-called floating charging refers to the process in which the rectifier and the battery work in parallel while supplying power to the load. In fact, the current provided by the rectifier is divided into two channels, one is the load channel, and the other is the battery channel to supplement the internal loss of the battery itself. The floating charging method is simple, which helps to improve the transient response characteristics of the UPS output. The characteristic of pulse charging is that the charging current changes with the change of battery capacity. Charging in this way can shorten the charging time.
1. Charging voltage
Because the electric forklift battery belongs to standby work Therefore, under normal conditions, the battery of the electric forklift is in a charging state and will only discharge when the power supply is cut off. In order to prolong the service life of the battery, UPS chargers usually adopt constant voltage current limiting control, and change the electric forklift battery to a floating charging state when the battery is full.
For a battery with a terminal voltage of 12V, the normal floating charge voltage is 13.5 to 13.8V. If the floating charging voltage is too low, the battery is not fully charged, and the floating charging voltage is too high, which will cause over-voltage charging. When the floating charge voltage exceeds 14V, it is considered to be an over-voltage charge. It is strictly forbidden to over-voltage charging the battery pack of electric forklifts, because over-voltage charging will cause the water in the battery electrolyte to escape into the hydrogen and oxygen through electrolysis, thereby increasing the concentration of the electrolyte, shortening the service life of the battery, or even damaging the battery.
2. Charging current
The charging current of the battery is generally expressed by C, and the actual value of C is related to the capacity of the battery . For example, if it is a 100Ah battery: C is 100A. The best charging current for lead-free batteries is about 0.1C, and the charging current should not be greater than 0.3C.
Excessive or too small charging current will affect the service life of the battery.
The ideal charging current should be a staged fixed current charging, that is, charging with a larger current at the beginning of charging, and charging to a smaller current after a certain period of time. , To the end of charging, rather than a smaller current. 'The charging current design is generally 0.1C, when the charging current is greater than 0.3C, it can be regarded as overcurrent charging. Avoid using fast chargers to charge, otherwise the battery will be in the state of'instantaneous overcurrent charging' and'instantaneous overvoltage charging', resulting in the battery can be used to reduce or even damage the battery. Overcurrent charging will cause the battery board to bend and the active material to fall off, resulting in a decrease in battery power supply capacity and serious damage to the battery.
3. Charging method
The electric forklift battery discharge product is lead sulfate. If it is not converted in time, the battery will be charged Insufficient state, thereby reducing the discharge capacity of the battery and shortening the service life of the battery. Therefore, the battery pack must be kept in a fully charged state. For different situations, it can be divided into floating mortgage and unified mortgage.
(1) Floating mortgage. The online battery pack is a long-term parallel connection of the charger and the load line as a backup power source. Generally, floating charging is adopted, and the single cell voltage is controlled at 2.25V (relative to a 2V battery), and changes in floating charging voltage are regularly observed and recorded. If the voltage of the single battery is low, it means that the battery is insufficient and you should pay attention to tracking.
(2) Balanced charges. The so-called balanced charging means that each battery cell is connected in parallel and charged with a uniform charging voltage. If there is a reverse battery during floating charging (cell voltage is lower than 2.20V, relative to 2V battery), or after floating charging for three months, it should be evenly charged, and the single battery should be controlled at 2.35V for 6~8h (Note that the average charging time should not be too long). ), then adjust back to the floating charge voltage value, and then observe the change in the backward voltage of the battery, if the voltage is not in place, recharge after two weeks. Generally speaking, after six months of floating charge and uniform charge, the voltage of the new battery pack tends to be the same. The average charging current is usually 0.3C or slightly lower than 0.3C. The rated voltage is a 12V battery, and the balanced charging voltage is generally 14.5V. Contact: 18038382979
