Monday, February 22, 2010

Lithium Polymer (LiPo) Battery FAQ

Lithium Polymer Batteries is the favorite power source of electric radio-controlled models. They are relatively cheap, light, and hold lots of power. However, many new hobbyists may have some enquiries as to their operations.

Here are three frequently asked questions about them.

1. What is Cell Balancing?

Lithium Polymer batteries usually come packaged as a pack of more than two individual battery cells. For example, electric RC helicopters use 3-cell packs. Each of these battery cells has a nominal voltage of 3.7v; which means that each cell can operate when it maintains its charge between 3.0 to 4.2v. To go above or below or below this range can damage the cell and render it useless, or worse, become dangerously unstable and explode.

While the battery is in usage, the power drawn out of each cell is not equal. Therefore, at the end of each flight, the cells in the battery will be left out of balance. A non-balancing charger will stop charging the battery pack once the voltage of the overall pack is full without paying any attention to each cell. This causes the battery to be more and more unbalanced with each charge and would also result in a diminished performance of the battery pack.

A balance charger eliminates any unbalanced-cells symptoms of a battery pack by charging each cell individually; making sure that the cell's voltage remain balanced at the end of each charge. In essence, balance charger lengthen the life of the battery back and maximizes its performance as well as keep the pack stable and safe to operate.

2. What is C rating?

A lot of radio-control fliers quickly grasp the meaning of most of the battery-associated acronyms but one: the C rating. In fact, many experts have tripped over themselves trying to explain it. However, I've heard a graspable explanation of it from an old Chinese battery manufacturer/expert very recently. Which is: The "C Rating" is the number which you multiply to the capacity of the battery to get its discharge rate.

Still confused? Basically, a 1000 mAh battery rated at 1C will provide 1000 mA of power for 1 hour. On the other hand, if the same pack was rated at 2C, it would provide 2000 mA of power for 30 minutes.

3. How fast can I charge a pack?

Each Lithium Polymer battery pack has a different maximum charge rate. It is very important to never ever charge at a rating above the specified rate! Most batteries have a label that specifies this vital information. However, if the maximum charge rate is not specified, keep in mind that most Lipos are made to be charged at a rate of 1C. Which means a 1000 mAh pack can be charged at 1A and a 500mAh pack can be charged at 0.5A. Once again, never ever exceed the maximum charge rate lest the battery explodes!
(ArticlesBase SC #204098)

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