5 months ago


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POWER PLAY Storing batteries Storing your LiPos when they will not be used for an extended period of time is best done when you employ a “storage charge.” I charge my packs to about 3.85 volts per cell; this storage charge keeps the batteries in the pack in balance for a longer time. Studies have shown that when battery packs are stored at full charge, the cells tend to drift out of balance more quickly than battery packs that are stored at a lower (storage) charge. Another cool tip: keep batteries stored in a cool area. An unused or extra bar refrigerator is ideal, and a new or used one can even be purchased fairly inexpensively. Just keep your packs and your snacks separate. Storing your packs in an ammo can is another great way to keep them safe and sound when they’re not in “rotation.” MORE EXPERT ADVICE NEXT-GENERATION STORAGE. Whenever possible, don’t store latest generation (circa 2009+) LiPo batteries fully charged for more than a few hours. Although some previous generation cells/ batteries could be stored at or near full charge with little to no discernible loss in power, or cycle-life delivery, the latest generation of cells/batteries can swell when stored at or near full charge (resulting in loss of performance and cycle life). But because these cells/batteries are typically capable of fast-charge rates, it takes less time to charge them when needed. It’s typically better to leave them discharged until the next flying session as it not only helps to prevent swelling and extend battery life but also ensures the battery has less potential energy stored for even safer storage. And if you’ll be storing them for more than a few weeks, be sure to charge them to 50-percent capacity (3.85V per cell). WATCH THE HEAT. For the longest possible battery life and to prevent swelling, don’t store LiPo batteries in areas where the temperatures exceed 77 degrees F. In fact, storing at temps as low as 40 degrees F, in addition to storing at 50-percent charged, can help to further extend battery life. Storing in temps above 77 degrees F can result in swelling and/or loss of performance, and while it’s often typical to leave batteries stored in a vehicle or when you’re flying, this is one of the most common ways batteries are damaged. When the sun is out, even on a relatively cool day, temps inside the vehicle/ trailer can exceed 90 to 100 degrees F, and even just an hour or two of sitting in these temperatures can result in permanent swelling and/ or damage. Handy little tools like this monitor your battery’s cell voltages keeping you informed of your packs performance. HANDLE WITH CARE. Protect and handle batteries with care during storage, transport and use. Even a small dent in the side of a LiPo cell, a slightly crushed corner, or other seemingly minor damage can cause micro shorts and/or plating within the cells that result in loss of power and cycle-life delivery. Even writing on a battery with a ballpoint pen can result in permanent damage if it makes an impression in the foil pouch of a cell (use a felt-tip marker and light pressure, or write on a section of tape separately and apply it to the battery after to prevent this issue). –Jason Merkle 46

Low-voltage cutoff and timers It is easy to tell when a flight is coming to an end without waiting for your speed control’s low-voltage cutoff setting to shut down the power system. If you fly a battery to the point at which your speed control shuts down, it’s more than likely you are using too much of its capacity. I try to leave 25 percent of a battery’s power in a pack after a flight. I know pilots who live by this, and they are the guys who have hundreds of flights on their packs. The signs of a battery pack losing its “oomph” are usually obvious: a drop-off in climb, or when a higher throttle setting is needed to keep your multirotor in the air. I advocate using a timer to monitor your flights and save battery life. Waiting until your speed control goes to its low-voltage cutoff is not the best way to keep your packs at their peak performance. Safety first — always charge and store your flight packs in a LiPo sack or similar; they are cheap insurance. Temperature Finally, keeping your battery supply cool will ultimately help them maintain a longer life, and LiPo packs will perform better at cooler temperatures. Of course, your flight will likely raise the battery’s temperature. The goal is to avoid overheating the pack, which can lead to swelling, a sign of chemical changes that inevitably will decrease the life of a LiPo. You know the feeling of a hot battery; guys are always asking you to feel their packs after flights as if to say, “Look! It runs so cool!” or “Holy cow! This thing is hot!” I know for me, I like to show off my “cool” packs. Airflow is imperative; there needs to be sufficient air moving over the battery pack to help cool it down in flight. Likewise, stressing a pack to its limits will heat it up quickly, so try to use a battery that has 25 percent more delivery capacity than your maximum power draw. If you use 50 amps at peak, have a battery that is rated at 70-80 amps discharge. This also will help to avoid unnecessary heat buildup. C ratings tell us how much power delivery a pack has available. The 65C Pro Power pack will put out more burst energy than the 45C battery and pilots will feel this difference in flight. So, there you have it. Follow these simple guidelines for charging, storage, balancing and temperature and your battery packs will last for literally hundreds of flights! K Gear & Gadgets 47

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June 2013
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July 2013
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