Handling circuits and batteries#

What you will need

  • Nothing

What you will get

  • Preliminary knowledge of circuits and power source properties useful in Duckietown

Duckiebots support several power bank models, although not all power sources will work. Here, we list the properties of the supported models.

The Duckiebattery (DB-C-DBatt)#

This battery has been the standard battery for the Duckiebots since 2021. For example, models DB21M, DB21J, and DBR4 use this battery.

The Duckiebattery is a special battery. It is special because it is programmable, smart, and designed specifically for Duckiebots.

Using this battery will allow your Duckiebot to monitor the state of charge and other diagnostics, and shutdown via software. Moreover, it enables advanced features such as auto-charging in Autolabs, because it will guarantee power to the onboard computer when being plugged in or out of charge.

../../_images/DB-C-DBatt_real2.jpg

Fig. 62 The Duckiebattery.#

Technical specification#

  • Capacity: 10Ah at 3.7V

  • Charging: Micro USB 5V at up to 2A

  • Output 2 x USB type A 5V at up to 4A (combined), max 2.5A on a single port

  • Charge time: 0-100% takes about 5h and 0-90% about 4h with a 2A power supply

  • Weight: 189g (fully charged)

Caution

Lithium-ion batteries like the Duckiebattery are potentially dangerous and must be handled with care.

Here are some things to do and not to do.

Warning

Keep reading the following safety precautions: do not skip this section.

Handling: things to do#

Things to do

  • Dispose of the battery pack immediately if it has been subject to moisture and/or the case is eminently damaged.

  • In case of fire use a CO2 extinguisher.

  • Store preferably in a cool, dry, and ventilated area subject to moderate temperature change.

  • Storage at high temperatures (>50 C) should be avoided.

Handling: things not to do#

Things not to do

  • Do not connect a charge voltage greater than 5V.

  • Do not connect an external voltage source to the USB output ports.

  • The battery must not be opened, destroyed, or incinerated, since it may leak or rupture, releasing in the environment its hermetically sealed chemicals.

  • Do not short circuit terminals.

  • Do not crush or puncture the battery, or immerse it in liquid.

  • Do not place the battery near heating equipment, nor expose it to direct sunlight for long periods.

LED description#

The battery has five LEDs on the top, used for indicating the state of charge.

../../_images/DB-C-DBatt_1.png

Fig. 63 LEDs indicate the state of charge of the Duckiebattery.#

Note

To see the battery state of charge, click once on the button. The state of charge LEDs will stay on for 10 seconds and the battery set in idle state, “waking up” the battery.

../../_images/DB-C-DBatt_2.png

Fig. 64 Wake up the battery by pressing the button once.#

Charge the battery#

After setting the battery in idle mode, charge it by connecting a 5V 2A power adapter. Note that using a higher amperage charger will not damage the unit. The LEDs will be flashing at 1 Hz, showing the battery is receiving charge.

../../_images/DB-C-DBatt_3.png

Fig. 65 Charging the Duckiebattery.#

When the battery’s state of charge is particularly depleted (e.g., as soon as you receive the battery), the LEDs might be unresponsive for up to 30 minutes while receiving charge.

Battery protection mode#

The battery is equipped with safety features to prevent damage to others and itself. In particular, it has dedicated hardware to protect its cells from low-voltage discharge.

When a certain low cell voltage level is detected, the battery microcontroller, together with all other active components will be turned off, except the charger. When a Duckiebattery enters protection mode, it will look unresponsive.

Nonetheless, the charger will “trickle” charge the battery cell until it has reached a safe voltage level, exiting the battery protection mode.

The battery protection mode can last up to 30 minutes, during which the battery might not indicate a state of charge nor that it is being charged. This does not mean the battery is dead, just “hibernating”.

USB outputs#

The battery has two separate 5V 2A USB type A outputs, namely USB OUT-1 (a.k.a. the muscles) and USB OUT-2 (a.k.a. the brains).

../../_images/duckiebattery-outputs.png

Fig. 66 Duckiebattery outputs behave differently.#

  • USB OUT-1: Connect this output to a non-sensitive power load, i.e., motor or LEDs. This output will experience short power drops when plugging and unplugging the charger cable.

  • USB OUT-2: this is a 5V 2A USB output, uninterrupted by the charging process or the status of USB OUT-1. This port should be connected to the computing unit (i.e., NVIDIA Jetson Nano or Raspberry Pi) to allow the unit not to restart when plugging or unplugging the charger of the battery.

Troubleshooting#

The most common fault is not related to the battery pack itself but the connection between the pack and the charger and/or the load.

Note

Always make sure the USB cable is not damaged and is of good quality. Do not use a cable longer than 30cm. A faulty cable can cause excessive voltage drops between the battery pack and load, leading to low voltage issues.

Troubleshooting

SYMPTOM

My battery does not charge.

RESOLUTION

There can be several reasons why a charge is not being accepted. Below are the most common issues:

  • The input voltage is too low or too high. Make sure you apply 5V via the micro USB connector

  • The battery is in battery protection mode and does not look like it’s charging, but it is. Come back in >30 minutes and press the button once to enter idle mode.

  • The battery is in a fault state. This can be caused by over-temperature on the battery cell and/or its internal PCB. Leave the battery to cool down for 1h then attempt to charge it again.

Troubleshooting

SYMPTOM

One or both USB outputs are not working

RESOLUTION

There can be several reasons why the USB output is not working. Below are the most common issues:

  • The battery is not on idle mode. Press the battery button once.

  • The battery is in battery protection mode. Remove all loads, put in charge, and wait more than 30 minutes to have the battery exit protection mode. Then enter wake up the battery by pressing the button once.

  • The USB output is in over current/temperature mode. Disconnect all loads, enter idle mode, and let the battery rest for 30 minutes.

  • An external voltage was applied to the USB (output) port(s). This is a big no-no (refer to DO’s and DONT’s above). Disconnect all loads and enter idle mode.

The Duckie-power-bank#

The Duckie-power-bank (or Duckiebattery version 1) is the standard power source for Duckiebots in DB18 and DB19 configurations. Duckie-power-banks are easily recognizable:

../../_images/duckiebattery-front.png

Fig. 67 The Duckie Power Bank is the first version of the Duckiebattery, used in DB18 and DB19 Duckiebots.#

Overview#

The Duckiebattery is equipped with 2 USB type A outputs (ports A and B) and 1 Micro USB connector for charging.

../../_images/duckiebattery-ports.png

Fig. 68 The Duckie Power Bank ports.#

It also has 4 LEDs representing the state of charge. Push the button on the side of the battery pack to turn on the LEDs. The LEDs indicate the residual charge according to:

Table 4 Duckiebattery LED charge indicators#

LED

State of Charge

D1

3-25%

D2

25-50%

D3

50-75%

D4

75-100%

If D1 is flashing (0.5Hz) while not being charged, the battery pack is at a critical low charge (less than 3%).

Charging#

The battery pack is charged via the Micro USB port with a 5V supply. While charging, one of the LEDs will be flashing (0.5Hz) indicating where in the charge cycle it is.

Note

When the battery pack is connected to the charger, the output voltage of ports A and B will turn off for around 280ms:

../../_images/duckiebattery-voltage-profile.png

Fig. 69 The Duckie Power Bank output voltage drops when plugging in and removing the charger.#

This is an unwanted effect that will cause the Raspberry Pi, if on, to reboot.

Note

likewise, when disconnecting the charger, the outputs will turn OFF for 20ms causing the Raspberry Pi to reboot as well.

Furthermore, while the Duckiebattery supports pass-through (both outputs A and B will function while the Duckiebattery is being charged), during charge the output voltage of port A and B will drop around 300mV which might cause an under voltage warring of the Raspberry Pi. This will put the Raspberry Pi in a throttling mode limiting its performance.

Discharging#

The output ports A and B have an unloaded output voltage of around 5.1V. To turn the outputs on simply plug in a load on port A/B, for example, a Raspberry Pi and a Duckietown Hut, or push the button.

The output ports will automatically turn off if less than 100mA is being drawn.

To turn the outputs back on simply push the button or reconnect the USB connector.

The combined output current is limited to 2.8A.

The battery capacity is 7.4Ah at 5V with an efficiency as follows:

Table 5 Duckie Power Bank discharge statistics#

Load

Efficiency

Autonomy

1 A

91%

6h 44m

1.5 A

88%

4h 33m

2 A

85%

3h 09m

2.5 A

79%

2h 21m