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How to Charge Multi String LifePo4 Battery

Author: Source: Datetime: 2016-10-18 17:38:20
Lifepo4 batteries with high energy density, small size, light weight, and other advantages in the mobile phone, notebook computer market has been completely replaced by other cells share reached almost 100%. Currently, lifePo4 battery is quickly extended to power tools and other applications, its broad market prospects are increasingly recognized by the industry. However, compared with the nickel-metal hydride, nickel cadmium, lead-acid batteries, to promote faster lifePo4 battery applications and development, but also must continue to improve its safety and service life. This article from the perspective of the charger to discuss a new charging solutions to improve the safety of lithium-ion batteries to extend battery life, while reducing the cost of the charger.
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Using the battery in the process, we often hear the battery industry this sentence: "less bad battery in use, more is a bad charge." This sentence could be interpreted as, incorrect charging conditions or methods will be easier to damage the battery and reduce battery life. To 18650 cobalt lithium-ion battery, for example, when charging over-temperature at about 70 ℃: electrolyte interface (SEI) mode begins to decompose and fever; around 120 ℃: electrolyte, the positive terminal of the thermal decomposition, resulting in a rapid increase in temperature and gassing ; in to about 260 ℃: battery to explode. solar powered portable generator Charging or over-voltage, over-voltage to 5.5V, the lithium metal tends to precipitate, the solvent is oxidized, the temperature rises, creating a vicious cycle, and even the battery fire and explosion. Therefore, how to charge for, we work together to explore the following several important issues.

Why pre-charge function?

Battery voltage from 2.5Vto 4.2V . When the voltage is less than 2.5V, the battery discharge termination. At the same time because the discharge circuit to close the internal protection circuit current consumption is also reduced to a minimum. Of course, the practical application due to the different internal materials, discharge termination voltage can range from 2.5V-3.0V. When the voltage exceeds 4.2V, the charging circuit is terminated to protect the battery safety; and when the single battery voltage down to 3.0V or less, we can state that the over-discharge, discharge circuit termination to protect the safety of the battery. So without the battery, the battery should be charged 20% of the electricity, and then save moisture.

Since the lifePo4 battery has a higher energy than that, so the battery should strictly avoid overcharge, over discharge phenomenon. Over-discharge will lead to the restoration of the active substance difficult, if at this time directly into the fast punching power mode (high current), the battery will produce damage, affecting life and may therefore pose a security risk. First a small current (C/10) charge to 2.5V to 3.0V, converted to fast charge is necessary.

Although lifePo4 batteries in the application comes with protective plate, in the usual case, the occurrence of discharge will be very small chance, but without pre-charge function, in both cases the situation is still possible to bring over discharge risks. First, the failure of the protective plate, and second place for a long time (5% -10% / month) self-discharge rate. Therefore a small current pre-charge can effectively solve the over-discharge of the battery charging problem.

However, the charging current is not always better used for portable solar power generator. In single lithium-ion battery, for example, it includes a charging constant current, constant voltage charging, constant voltage is typically 4.2V (with LiCoO2 battery, for example), set the value of the constant current 0.1C ~ 1C. Although large current charging will shorten the charging time, but it can also result in shorter battery life cycle and reduce capacity, so we need to choose the appropriate charging current value.

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