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Lithium polymer batteries have made R/C flying more fun. The performance they offer is revolutionary and remarkable. But, they are susceptible to damage and need to be treated carefully. One important device that protects and maintains your lithium polymer battery is the balancer. Let's examine how that is. Lithium polymer batteries are damaged by:
- Mechanical deformation
- High temperature (above 60degC / 140degF)
- High voltage (above 4.2V/cell)
- Deep discharge (below 3.0V/cell in use, 3.3V/cell recovered, or 3.7V/cell storage)
- Rapid discharge (shorting cells or using above recommend discharge rates)
Of these, high voltage is the most difficult to control. Batteries made of lithium polymer cells wired in series will naturally, with time and cycles, become imbalanced. That is, each cell will be at a slightly different voltage. This leads to high voltage while charging, as the charger can only read the average cell voltage. The charger will bring the pack to an average of 4.2V / cell, but one or more cells are above 4.2V / cell. Slight imbalance is always present -even in a battery that is new and balanced by the factory - and does no harm, but large imbalance does harm and is prevented by a balancer. A balancer connects to a battery via cell taps. Cell taps are small wires soldered onto each cell's tabs. The balancer thus has direct access to every cell, allowing it to adjust individual cell voltages by dissipating the energy as heat, or re-routing it to cells of lower voltage. The tangible benefits of this include:
- Stronger performance throughout the battery's life
- Longer battery life (more cycles)
- Ability to eliminate one cause of cell combustion, namely cell over voltage while charging due to imbalance
Though every brand and model of cell balancer works a little different, the general procedure for their use is: Connect the balancer to the battery before charging, charge, and remove balancer when charge is complete. Regarding frequency of use, a balancer can be used with every charge, though this isn't necessary if the battery is in good condition. Most users feel the extra effort of using a balancer with every charge is worth the added safety features. Examples of good commercially available balancers are the 205V and 210V from Thunder Power.
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