What is 'balanced' in the lithium battery protection board?

by:CTECHi     2021-08-10

When I first stepped into the industry of lithium battery protection boards, I was also faced with a lot of problems. As a lithium battery protection board, as the name suggests, it can protect lithium batteries and specifically has overcharge protection. Main functions such as over-discharge protection, over-current protection, short-circuit protection, and equalization. Today, I will take a look with everyone. What is 'balanced' in the lithium battery protection board?

What is equilibrium? Balance, all enthusiasts who do lithium batteries or use lithium batteries or lithium battery DIY can not do without the word balance, but some people have not yet deeply understood the word balance. In fact, the purpose of balance is to make every string of batteries fully charged. What causes lithium batteries to be balanced is the consistency problem, such as different internal resistance and different self-discharge, rather than being able to make up for the difference in capacity caused by the backward battery cell! There is a mouse feces in a pot of porridge, and the whole pot of porridge is discarded. So the same is true for lithium batteries, and the entire battery pack is basically scrapped. In terms of balance, there are two ways: active and passive.

Passive balance: By discharging the number of strings with high voltage and recharging repeatedly, the voltage of each string of the battery can reach the expected voltage (that is, basically fully charged) over time. Passive balance is a dissipative type Equalization is to dissipate electricity through heat. Therefore, there will be a problem of heat generation of the protection board during equilibrium. This problem also leads to the fundamental reason why the equalization current of the protection board is not large.

Active balance: Use the peripheral circuit to transfer the power of the high voltage string to the low voltage. Over time, everyone's voltage is the same. Active balance is also called lossless balance, because the power is between internal Transfer and heat generation are only the problem of conversion efficiency. At present, most electric vehicles are used in passive equilibrium. Why? Because of low cost and high reliability.

Many people like to use a protection board with a relatively large equalization current. In fact, in terms of protection board design, the passive balance scheme is nothing more than a choice of resistance. Most of the protective plate is wrapped in the battery pack. How can the heat be dissipated? For example, a 100ma balanced current protection board, according to Ohm's theorem, the heat of each balanced resistor is I*I*Ru003d0.1*0.1*35u003d0.35W, and the worst case of 24 series protection boards is 24 balanced lights ( Or 23) at the same time, the total power is 8W, you first try to put an 8W bulb in your battery to see the situation. Therefore, the Chinese Genesis will remind you at the end that it is best to have a certain gap between the protective plate and the battery to prevent the direct transfer of heat to the battery and cause various problems.

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