Home Engineering Small Unmanned Fixed-Wing Aircraft Design. A Practical Approach
Airframe batteries will either be ground-charged on maintained by on-board generators. For batteries that are being ground-charged, good-quality charging systems should be used that monitor individual cell voltages during charge and control the overall current and voltage values. Charging should be carried out in appropriator locations and logs kept of the amount of charge added to a battery and the time taken to achieve this. Even the best quality LiFe, LiPo, and NiMHy batteries do not last for ever, and so after a given number of charges such items should be replaced. We would advise not recharging any airframe battery more than 50 times before it is recycled. It is also good practice to not allow airframe batteries to become too depleted unless safe recovery during a flight requires it. It is much wiser to stop a flight early or have sufficient excess capacity to ensure that batteries never go below 30% remaining charge.
When using batteries maintained by on-board charging circuits, it is tempting to almost “fit and forget” these items since the intention is that they are never heavily depleted and, moreover, have their status continually monitored by the charging circuits. However, on-board-charged batteries are typically much smaller than those that have to have sufficient capacity for the entire flight at the outset. Then, if there is any interruption to the charging circuit, they can very rapidly discharge. Thus such systems should be used only if ground-based monitoring of the battery charge is possible. Moreover, when not being flown, such batteries need just as careful maintenance as those that are routinely removed for ground-based charging.
All batteries should be periodically subjected to visual inspection to check that there is no damage or distortion to the external casing or connections. Slight bulging of the case is often the first sign of distress in a battery. Any battery with a less than perfect outer case should not be flown.
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