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There are several common questions that are regularly asked regarding the operation and maintenance of electric RC systems. Which Lithium Polymer Batteries Should Be Balanced? Any Lithium Polymer (LiPo) battery with more than two cells should be balanced. A LiPo battery is composed of individual cells, and each cell can charge and discharge at different rates. Eventually, the difference will increase between the cells until it could harm the entire pack. When charging the pack, a balancer will set all the cells to the same voltage. By not having certain cells charged and discharged beyond their limits, the life of your entire LiPo pack is increased. What Does the KV Number Mean? The KV number on a brushless electric motor shows what speed it will rotate at per volt of input. This will allow you to determine the unloaded speed you can expect from the motor at different battery levels. This number is measured under the assumption that there is no resistance keeping the motor from turning. In reality, when using a motor you would have a load attached (for example, a propeller). This load will cause the motor to slow down. The KV rating will not show exactly what the performance of a motor is with a propeller attached, but it will give you an approximation. Faster motors have higher KV numbers, and slower motors have lower ones. What’s a BEC? A BEC is a battery eliminator circuit. It eliminates the need for a separate battery to power the radio system. It does this by drawing power directly from the flight battery and using it to power the radio. A BEC can also act as a backup system, continuing to draw the last bit of power from the flight battery for the receiver and servos to use even after there is not enough to power the main motor. This will enable the pilot to maintain control of the aircraft even after the engine stops. Most of the time these devices are part of the electronic speed controller; but they are also available as a separate unit. What Size ESC Do I need? There are two factors to consider when choosing an ESC: the voltage, and the amperage. The rated voltage and amperage should always be above the maximums that will be used in the aircraft. Select an ESC that is rated for the same or more cells than you plan to use, and with a current rating at least as high as what your motor is rated for. What’s the C Rating On a battery? The C rating on a battery relates to the maximum current that can be drawn from that battery. A 15C battery can have current drawn from it at up to 15 times the rate that would discharge it in one hour. A 1320mAh (milliamp hour) battery would be discharged in one hour if you were to draw 1320mA from it for one hour), and would be discharged in 1/15th of an hour if you were to draw 15 x 1320mA (19800mA or 19.8 Amps) from it. There are three types of C ratings: the continuous C rating shows the amount of current that can be drawn constantly until the battery is depleted; the sustained C rating shows the amount of current that can be drawn for a short period of time; and the burst C rating shows the amount of current that can be drawn only for an instant. Most lithium batteries will have all three of these ratings printed on them. Should I use a Watt Meter? Yes. The watt meter will show how much electricity your plane is using. You will need a watt meter to determine if your aircraft is exceeding its rated limits. What Size Prop Should I Use? The best size of propeller to use is the one recommended by the airplane's manufacturer. You can experiment with different propeller sizes; but use a watt meter to determine if your aircraft is exceeding the limits of its electric system. The motor specification sheet will show the voltage, amperage, and RPM of your motor with different propellers.
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