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Drones

Battery

LiPo?

• LiPo batteries are Lithium polymer batteries utilising a lithium-ion technology. They are commonly used for drones because they are commonly light weight, support large capacity and discharge rate.
• For long range, you can use Lithium-Ion (li-ion) batteries which support lower discharge voltages (down to 2.5V/cell)

Cells and voltage

The number of cells is indicated as number of "S". It refers to cells in Serial (S). Old LiPo batteries were found in Parallel (P).

# cells	Nominal voltage	Min voltage*	Max voltage
1S	3.7	3.3	4.2
2S	7.4	6.6	8.4
3S	11.1	9.9	12.6
4S	14.8	13.2	16.8
5S	18.5	16.5	21.0
6S	22.2	19.8	25.2

(*) the minimal voltage is 3.0V but I consider 3.3V since it is commonly accepted to never go below this value

Capacity, discharge rate and burst

Capacity (mAh)

The capacity of a LiPo is expressed in milliamps per hour (mAh). In racing/freestyle, 1300-1600mAh LiPo batteries are commonly used. Higher capacity LiPo batteries will increase the flight time but will also mean a bigger size and heavier batterie, what will affect the manoeuvrability. Higher capacity LiPo batteries are rather used for stable aerial photography drones.

Discharge rate (C)

The discharge rate of a LiPo (C rating) is the number of amps the LiPo can give instantaneously without damaging it. To calculate it, you have to multiply the capacity in amps by the C rating.

For a 1300mAh Lipo with a discharge rate of 45C, the current (Amps) that you can safely draw continuously is:

1.3A * 45C = 58.5A

Burst

The burst rating is the instantaneous current that you can get from the LiPo during a maximum of 10 seconds.

In our previous example (1300mAh 45C that delivers 58.5A), if the burst rating is 75C, you can get a maximum of:

1.3A * 75C = 97.5A (during 10 seconds)

Connectors and balance plug

Connector

Connector	Current Rating (A)	Burst Current (A)
EC2	20	30
EC3	60	70
EC5	120	170+
XT-60	60	70
XT-90	90	120
Mini-Deans	15	20
Deans	60	75
JST	5	8
Tamiya	15	25
Traxxas	70	100
4mm Bullet	75	100
6.5mm Bullet	200	250+
8mm Bullet	300	350+
MPX	35	?

(Source: http://www.insanitydrones.com/lipo-battery-guide/)

The most commonly used connectors in racing/freestyle drones is XT60. JST connectors are commonly used as 5V/12V connectors for various equipments (LED, camera, buzzer, ...).

Balance plug

LiPo with several cells have a balance plug that is used:

• during flight: to monitor the voltage of each cell and trigger an alarm when 1 cell reaches a given threshold
• during charge: to balance voltage between cells (it is critical that you don't have a too important difference of current between cells)

There are 3 different balancing connectors depending on battery brands:

• Thunder Power (TP)
• JST-XH
• Hyperion (Polyquest)

Control lipo voltage

You can use a lipo tester like this one:

This is very convenient because it will warn you once a cell reaches a given threshold (I set it to 3.60V), independantly from the total voltage of the LiPo.

How to choose your LiPo?

• Max supported voltage supported by your ESC
• Max supported voltage supported by your motors
• Flight style (racing, freestyle, photography)
• Capacity
• Number of C / burst

Charging

To charge LiPo batteries, you need a good charger. I use a Pro-Tronik AP681BLC.

I highly recommend that you charge your batteries using the BALANCE mode instead of the CHARGE mode. This mode will not only charge your batteries, it will also ensure that cells are balanced.

Here are the menus to select:

• Choose LiPo battery:

┌──────────────────┐
│ PROGRAM SELECT   │
│       Li-Po BATT │ 
└──────────────────┘

• Then select the BALANCE mode. Also choose the appropriate amps (e.g. 1.3A) and number of cells (e.g. 4S):

┌──────────────────┐
│ LiPo BALANCE     │
│ 1.3A   14.8V(4S) │
└──────────────────┘

• Long press ENTER:

┌──────────────────┐
│ BATTERY CHECK    │
│ WAIT....         │
└──────────────────┘

• It will check that the number of cells is correct. Press ENTER to confirm:

┌──────────────────┐
│ R: 4SER  S: 4SER │
│ CONFIRM (ENTER)  │
└──────────────────┘

• During the charge, it will display a similar screen:

┌──────────────────┐
│ Li4S 1.3A 16.42V │
│ BAL 025:03 00563 │
└──────────────────┘

where:

• Li4S: LiPo 4S battery
• 1.3A: current amps charged to battery (will decrease until it reaches 0)
• 16.42V: current voltage in battery (will increase until battery is fully charged)
• BAL: Balance mode
• 025:03: time since battry is charging
• 00563: number of cycles (increases until battery is fully charged)

First uses

For the 5 to 10 first uses, it is recommended to:

• 1st charge your battery (it comes only half charged)
• charge at 0.5C (e.g. charge at 650mAh for a 1300mAh LiPo) until it reaches 70% (16.2V for a 4S), then charge at 0.2C (e.g. 260mAh for a 1300mAh LiPo)
• Have easy flights and don't go below 50% of LiPo capacity (3.85V/cell)

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