Battery Monday channel update! Today we will share with you the voltage difference between the cells of a battery pack.
Actually, the difference within a certain range is acceptable, usually within 0.05V for static voltage and within 0.1V for dynamic voltage. Static voltage is when a battery is resting, and dynamic is when a battery is in use.
For battery packs, the voltage difference between individual cells is one of the main indicators of consistency. The smaller the voltage difference, the better the consistency of the cells and the better the discharge performance of the battery pack. Conversely, the larger the voltage difference, the less consistent the battery pack–and as a result, the discharge performance will be adversely affected. The discharge energy of the battery pack becomes insufficient, and it gradually deteriorates as the number of cycles increases.
Causes of the voltage difference
Individual cells do not have voltage differences, but in order to obtain higher discharge rates, capacities, etc., we use multiple cells in parallel and series to form battery packs, where voltage differences may occur. In fact, no two cells are exactly the same and the capacity, impedance and temperature characteristics of the cells are always slightly different.
This is true even if the batteries have the same model number, manufacturer and production batch. In addition, the battery pack is affected by factors such as charging conditions and temperatures, which can cause voltage differences to appear and gradually increase.
If we compare a battery pack to a reservoir made up of individual tanks connected together with the water pressure in each tank being the same, their output will also be the same. If they are not equal, this will result in the water inside one tank being nearly dry while the other tank is still full.
Without protective measures, the battery pack will pull the voltage of the weaker one lower or even over-discharge when powering.
If there is a BMS or other protection circuit measures, any cell voltage will reach the limit of undervoltage protection, and the protection circuit will stop the discharge of the entire battery pack to prevent over discharge–in other words, the discharge time will be shortened.
The main factors affecting the voltage difference are the materials and manufacturing processes used by the battery. Therefore, you should pay attention to the brand from which you are purchasing your batteries. If there is a gap in the voltage of the battery pack, you can correct it with additional equipment, such as with a BMS, balance charging, etc.
Stay tuned for Part 2 of voltage difference: How to prevent voltage difference.
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