Constant current charging
Electric vehicle charger - constant current charging refers to the battery charging, using the method of segmented constant current charging, and the current is achieved by adjusting the charging device. The main feature of this charging method is that it has great adaptability, and the charging current can be arbitrarily selected and adjusted. Therefore, the battery can be charged in a variety of different situations and states (such as the initial charge of the new battery, the supplementary charge of the used battery and sulfur charging, etc.). It is especially suitable for charging with a low current for a long period of time, charging the battery pack with most batteries in series, and is beneficial for charging the battery whose capacity recovery is slow.
However, due to the charging current is too small at the beginning stage of the charging method, and the charging current is too large at the later stage of the charging method, the whole charging process takes a long time, precipitates more gas, has a large impact on the plate, has high energy consumption and low efficiency (no more than 65%), and the whole charging process must be attended by a special person. Therefore, only the initial charge of the battery and the need for a long time of small current desulfur charging to use.
The following points should be paid attention to when using constant current charging method:
(1) Because the variation of constant current charging is segmented constant current charging, the charging current should be adjusted in time to avoid excessive current in the late charging period. And the size of the charging current, the charging time, the timing of the conversion current and the selection of the charging termination voltage, etc., must strictly implement the charging specification;
(2) the remaining capacity of the charged battery should be close to each other, otherwise the charging current size must be selected according to the series battery remaining capacity is very small battery, and when the small capacity battery is sufficient, it should be removed, and then continue to charge the large capacity battery;
(3) In the charging process, test the single cell voltage of the battery every 2 ~ 3h, such as the voltage has reached 2.4V should be transferred to the second stage of charging in time;
(4) When the electrolyte temperature rises to 40℃ in the charging process, the charging current should be halved, if it continues to rise to 45℃ should stop, until the temperature drops below 40℃ to continue charging;
⑤ The density of the charged battery electrolyte should meet the specified requirements, and the difference of the density of the electrolyte between each cell cell should not exceed 0.01g/cm3;
⑥ Maintenance-free battery should not be charged in this way.
Constant voltage charging
Electric vehicle charger - constant voltage charging means that each single battery is charged at a certain constant voltage (generally take the number of single cell battery ×2.5V). Its main characteristics are: the initial charging current is quite large, the battery electromotive force and electrolytic liquid density rise quickly, with the continuation of the charging current gradually decreases, in the final charging period only a small current through; Short charging time, low energy consumption, general charging 4 ~ 5h battery can obtain its capacity of 90% ~ 95%; If the charging voltage is selected properly, 8h can complete the whole charging process, and the whole charging process does not need to be taken care of, so it is widely used in supplementary charging.
The shortcomings of constant voltage charging are:
Because the initial charging current is too large, when charging the battery with too large discharge depth, it will cause the initial charging current to rise sharply, easy to cause the overcurrent of the battery and charging equipment damage; During the charging process, because the charging current can not be adjusted, it is not suitable for the initial charging and desulfur charging of the battery; Because it is difficult to compensate for the voltage change of the battery during the charging process, it is difficult to complete the full charging of the battery whose capacity recovery is slow.
Note the following points when using constant voltage charging method:
① Choose the correct charging voltage. If the charging voltage is too high, it will cause excessive charging current at the initial stage of charging, which will cause plate bending, a large number of active substances falling off and high temperature rise of the battery. Too low will make the battery charging insufficient, resulting in reduced capacity, shortened life;
② The terminal voltage of the charged battery must be exactly the same.
For a battery pack consisting of many individual batteries, such as a fixed battery, balance charge should be carried out regularly after a certain running date. This is because when charging under the same conditions at ordinary times, the active substance of each part of the plate appears to have different degrees of charging, resulting in an unbalanced reaction of the active substance. In addition, considering the differences in some charging and discharging characteristics between individual batteries, some individual batteries will produce undercharging state. Therefore, after the end of normal charging, continue to use about 20h rate of current to charge for 1 ~ 3h. This charge is also called overcharge. Where the battery is normally used under the same conditions, it is good to carry out balanced charging regularly on battery maintenance.
Users have different regulations on the length of time between balanced charging, some of which stipulate that it should be carried out once every three months or half a year. According to the progress of battery design and manufacturing technology, the characteristics of the battery is not different, so there is a trend to extend the interval time of balanced charging.
Batteries that are used intermittently or only when the AC power is off are charged in floating charge mode. For example, for the fixed battery, add 2.15 ~ 2.2V voltage to each individual battery, and charge with a continuous small current. The charger is in parallel with the battery, and the charging current can mainly supplement the loss of self-discharge, that is, the range of 0.3% ~ 1.0% of the rate of 10h, and the usual load is borne by the charger, and the large load for a short time is also powered by the battery. At this time, the terminal voltage of the battery drops and charges automatically.
Constant voltage current limiting charge
Constant voltage current limiting charging is mainly used to remedy the shortcomings of constant voltage charging when charging current is too large (the method is the same as constant voltage charging), through a series of resistance between the charging power supply and the charged battery (current limiting resistance) to automatically adjust the charging current.
When the charging current is too large, the voltage drop on the current limiting resistance is also large, thus reducing the charging voltage. When the charging current is small, the voltage drop on the current limiting resistance is small, and the voltage loss of the charging device output is small. In this way, the charging current is automatically adjusted so that it does not exceed a certain limit. This method is widely used in maintenance-free battery initial charging and ordinary battery supplementary charging.