6.5.6　Float Charge

For some applications when the charging process is complete and the battery is fully charged，the batteries should be maintained at 100% SOC for a long time to be ready for time of use.Uninterruptable Power Supplies（UPS）are one of such applications where the batteries should always remain fully charged.However，because of self-discharge of batteries，they get discharged over time；for example，they may lose 20% or 30% of their charge per month.To compensate for self-discharge，a constant voltage which is determined based on the battery chemistry and ambient temperature is applied permanently.This voltage is called“Float Voltage.”This technique is not recommended for Li-ion and Li-Po batteries and it is not necessary for EVs/PHEVs which are frequently used every day.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.In the split rate CC different rates of current are applied based on SOC，time of charge，voltage，or combination of them in different stages of charging.分割型比率电流是利用CC充电方式来实现不同比率的电流，这项技术在不同的充电状态下是SOC、充电时间、充电电压或三者综合一起考虑的。

★2.By changing the width of pulses the average of the current or voltage can be controlled.同时电流或电压的平均值可以通过改变脉冲宽度来进行控制。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）Charging in general is the action of putting energy back to the battery.

（2）This method can be used when the source is non-regulated.

（3）constant voltage

（4）constant current

◆2.Translate the following passages（expressions）into English（汉译英）

（1）浮压充电

（2）限流器

（3）此技术也被称为“打嗝充电”或“负脉冲充电”。

◆3.Directions:Answer the following questions briefly according to the text

How many are there charging methods？What are the charging methods？

Reading material（阅读材料）

1.Depending on the battery type to be charged，this preset voltage value is chosen.For example，for Li-ion cells the value of 4.200±50 mV is desirable，so the present value for the whole battery pack can be obtained by multiplying this value with number of cells in series.An accurate set point is necessary，since over-voltage can damage the cells and under-voltage causes partial charge which will reduce life cycle over time.Therefore，the circuit used for charging，which can be a simple buck，boost，or buck/boost topology depending on the voltage ratio of input and output，should be accompanied with a controller to compensate for source and load changes over time.When the cell reaches the preset voltage value，this causes the battery to be in a standby mode，ready for later use.The amount of this idle time should not be very long and should be limited based on the manufacturer recommendations.

2.In some cases，for prolonging dead batteries，CC method with high rates and low duration can be utilized to extend the lifetime of the battery.But，this is a very cautious procedure and must be done carefully.Ni-Cd and Ni-MH batteries are charged using CC.Ni-MH batteries can be easily damaged due to over-charging，so，they should be accurately monitored during charging.