Category:Drones/Battery

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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.

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)

Drones-lipo-balance-plug.jpg

There are 3 different balancing connectors depending on battery brands:

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

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) │
└──────────────────┘
  • 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)

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