Road to introduction of micro drone for beginners ~ 6th Basic knowledge of battery | VIDEO SALON

Sentence ● Yusuke Aoyama / Composition ● Editorial department

Lecturer ● Tetsuya Tagawa / A drone engineer whose main job is to design the IPEX connector, which is also used for drones. About six years ago, when he still called drones "multicopters," he started making aerial drones. He has also been involved in the production of racing drones since 2014. He is the founder and administrator of the Facebook group "U199 Drone Club". 2016 Dubai International Tournament Japan National Team He is an engineer. Currently the DMM RAIDEN RACING team he is an engineer.

One of the reasons for the practical application of drones is the appearance of "lipo battery". Currently, lipo batteries, which are widely used in drones, have a higher energy density than other rechargeable batteries and have the advantage of being able to be recharged because they do not have a memory effect *, and are used in many electronic devices such as smartphones and personal computers. I am.

In particular, the high energy density, that is, the characteristic that it can hold more energy than other types of batteries of the same volume and mass, makes it the best battery for drones as an aircraft that wants to reduce the weight of the battery as much as possible. increase.

Pay attention to the shape of the connector

The lipo battery used for micro drones is a very small one with a capacity of about 200 to 400mAh, which is 1 to 3S (cell). The connector on the battery is also very small, XT30 for 2S and above, and JST PH with 2.0mm pitch between pins and MOLEX Pico Blade with 1.25mm pitch for 1S. The small connectors on the 1S battery are similar in shape, so it's easy to inadvertently connect different connectors to each other, but be aware that if the shapes don't match, the pins and housing will be damaged.

Charging and discharging he is between 4.2V and 3.0V

Lipo batteries are currently the best batteries for drones. However, it has the disadvantage that it cannot be used as a battery unless it is used while properly managing the voltage. Furthermore, if the charging method is incorrect, it may generate heat, ignite, or burn, so care must be taken when handling it.

The nominal voltage of the lipo battery is 3.7V per 1S (equivalent to one dry battery), and 3.85V for the high voltage specification expressed as "HV" that has recently appeared. It is necessary to discharge and charge in the range of 3.0V for discharge voltage and 4.2V for charging voltage (HV is 4.35V) around this nominal voltage. If the battery is charged or discharged beyond this range of 4.2 to 3.0V, the performance of the battery will be significantly reduced and it will be virtually unusable.

When storing the lipo battery, it is better to store it at about 3.8V, which is about 50% used, not fully charged or used up. Also, batteries for micro drones can be very small and tend to be handled roughly like dry batteries. However, the lipo battery used in many micro drones is only packed with the aluminum pouch used in retort foods. Therefore, it is easily scratched, and there is a risk that the internal electrolyte will leak due to this scratch and lead to an ignition flame. Put the lipo battery in a special bag or case, avoid direct sunlight, and store it at room temperature.

Most likely to catch fire when charging

It is during charging that the lipo battery is prone to ignition and burning. In particular, the charging voltage should never exceed 4.2V. If you use a bad charger for the charger, it may exceed this voltage, so it is recommended to use a reliable one as much as possible.

In addition, do not place flammable materials around the battery while charging the lipo battery. And keep an eye on the battery as much as possible. If possible, place it in a metal or ceramic tray or container to charge it in case it catches fire. A battery that has been damaged by a drone crash may have a strange odor or sudden heat generation during charging. In such a case, stop charging immediately.

▲ Voltage is the force that pushes out water in terms of a water gun. The electric current is the amount of water produced by it. Resistance is the force that keeps water out, that is, the size of the water outlet in a water gun.

▲ If the force to push out water is strong, a lot of water will flow. The relationship between voltage and current is the same. The amount of current changes depending on the magnitude of the resistance.

mAh (Milli Amp-Hour) A unit that indicates how much current can be passed for one hour. As the value increases, the amount of electricity stored in the battery increases, and the amount that can be charged at one time increases.

V (volt) voltage. The power to push out electricity.

S (cell) A constituent unit of a battery (explained on the next page).

HV (High Voltage) A battery with a higher voltage than usual.

C C of Capacity. A number that represents the charge / discharge capacity of the battery. The description of "30C / 60C" is always 30C. It means the maximum instantaneous value of 60C. Generally, the higher the discharge capacity, the better the flight response. It is a unit that you should be aware of mainly when charging, but details will be explained in the next issue.

The battery used in DJI's aerial camera (lower left photo) is stored in a special case, but the lipo battery used in the micro drone has a bare cell. DJI's batteries have the ability to prevent overcharging and automatically balance the voltage between cells when charging, but Microdrone batteries don't.

A cell is a battery component (denoted as 1S, 2S). Up to 3 cells are the mainstream for micro drones, but some large drones use 6-cell or 12-cell batteries. The lipo battery realizes a large amount of power by combining multiple cells.

The voltage per cell is 3.7V (maximum 4.2V), and for 4 cells, 3.7V x 4 = 14.8V is the voltage of the entire battery. The HV specification is 3.85V (maximum 4.35V).

XT30 connector

● Mainly adopted drones: BETAFPV Brushless X Drones series, Vespa Nano Drone, etc.

A small version of the XT60, which is famous as a power connector for radio-controlled models. The allowable current value of the connector is 30 amperes in an instant. The allowable current values ​​for all of the connectors listed above are at a few amperes level. In micro drones, it is used for 2S specification high power drones equipped with brushless motors.

▲ Battery side (left), drone side (right)

JST PH connector (2.0 mm pitch)

● Mainly adopted drones: Blade Inductrix series and others

A connector that is currently the mainstream for TinyWhoop type high current (including HV specification) type 1-cell specification batteries.

▲ Battery side (left), drone side (right)

MOLEX PicoBlade connector (1.25mm pitch)

● Mainly adopted drones: BETAFPV Brushed Whoop Drones series

The connector used for the Blade Inductrix brush motor. Compared to PH connectors, the line on the drone side is thinner and no current flows, so with the evolution of motors, it has become less popular in recent micro drones that require more current.

▲ Battery side (left), drone side (right)

◉ Precautions If you forcibly insert it into the 1.5 mm pitch connector used in some chargers, it will be inserted, but be careful as the connector will be damaged and the battery will not be usable! The PicoBlade 1.25 mm connector has one lock hole in the center, and the 1.5 mm pitch connector has two lock holes. When charging, I want to look closely at the lock hole and use it.

The lipo battery is overcharged when charged to a voltage of 4.2V or higher. Do not fly until the voltage drops below 3.0V. The battery is damaged and swells. In the worst case, cell damage due to overcharging, cable disconnection, impact, etc. may cause ignition, so care must be taken when handling. Note that the battery may not be usable again if it is completely discharged.

On the left is a genuine BETAFPV 1-cell battery lipo checker ($ 8.99). On the right is G-Force's LiPo ANALYZER (2000 yen), which allows you to check the battery voltage of cells 1 to 6 released by G-Force. It is equipped with a balancer function that corrects the voltage difference between cells just by connecting the battery.

It is recommended to keep it in a safety bag for carrying and storage. It is made of heat-resistant material and is prepared in case of ignition. You can buy it at Amazon. The optimum storage temperature is 10 to 30 ° C. I want to avoid direct sunlight and keep it in a cool place indoors.

(1) For batteries that do not have a pain in appearance, protect the connector and check with the store to see if they can be collected in the lithium-ion battery collection box installed at the home electronics retail store.

(2) There are places where collection boxes are installed in drone practice areas. (1) Similarly, protect the connector part.

(3) If the battery cannot be recovered by the methods (1) and (2) due to scratches on the exterior, make a bucket of approximately 5% saline solution at home, soak it for about a week, and completely discharge it. After that, dispose of it as garbage according to the instructions of the local government.

● Reprinted from the July 2019 issue of Video SALON