Introduction: 2S LiPo/Lion Battery Charger Using Micro USB 5V/2A Power Supply

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About: https://www.iiests.ac.in/IIEST/Faculty/aero-joydeep

Introduction: This project will demonstrate an alternative process to charge 2 Lion cells simultaneously using two TP4056 1S battery charger while the output voltage (7.4 V) can be obtained as required. Usually, to charge Lion cells like the 18650 cells in series you either have use a 2S Lion charger which often requires a 12 V or a 9V dc power supply. However, I found it ridiculous to take out the cells and charge them and put it back in the project which in my case is an RC transmitter which I use it to fly planes, quad and more.

This project uses the TP4056, which is a low-cost single-cell Lion charger. It has built-in battery protection and is powered by 5V from a micro USB port. You might use 2 of these chargers to charge each cell separately from two different power sources but, you still have to take the cells out and charge them simultaneously which I still find annoying.

In this project, I will show you how you can charge the 2 cells (7.4V) using a mobile phone's 5V, 2A power supply without having to remove them every time for charging. Also there is no need to carry a separate dc power supply for charging the 2 cells. No boost converter or 2S Lithium charger is required. Simply plug in the USB cable and slide a switch when you want to charge. Remove the USB and slide back when you want to draw power (@ 7.4V).

Warning: As the 2 cells inside the transmitter are in series, connecting two Lion chargers directly will cause a SHORT CIRCUIT!.

Supplies

  • TP4056 charger (2 nos)
  • Sliding switch ( 2 poles, 3 connectors) (2 nos)
  • Connecting wires
  • Soldering iron, wire, flux
  • 18650 battery (2 nos)
  • Drill bit (1mm) and drill machine
  • 1.2 mm 20 mm self-tapping screw (1 nos.) You will find 4 such screws any micro servo
  • Micro/Mini USB/Type C etc breakoutboard (Buy anyone as you require)

Step 1: Making the Charge/load Toggle Switch

In order to understand how the switch works and why it needs a little modification, refer to the circuit diagram in the next step. Or if you are in a hurry just follow the instructions and understand later. This switch will toggle the charge mode when you want to charge while disconnecting the load simultaneously and vice versa when the battery is gets charged and you want to apply the load.

Important: Each sliding switch should have 2 rows with 3 pins on each side. there are many types of sliding switch. make sure the two rows of pins of the are not internally connected.

At first, align the two switches and apply some super glue. Be careful not to add too much glue or else it may get inside the switch and make it useless. Alternately you may clamp it in a vice while it is nicely aligned.

using the drill make a through-hole through both the switches. Use a small piece od wood between the space and secure with super glue

. Inset the screw through the hole and tighten it. Now both the switches should slide all together

Step 2: Circuit Diagram

You may solder the connections to the battery directly(Non-removable) or use a 4 pin male-female header to make the battery removable.

Depending on your type of application, keep the necessary wire length and solder all connections.

The circuit is a simple arrangement of 2 sliding-type switches which simultaneously switches OFF switch no. A,B and switches ON (C&D) for charging or loading as shown in in the figure.

The switches are shown separately in the figure and numbered 1-8. Just solder the respective pins according to the numbering.

Depending on your application choose appropriate lengths of the wire accordingly.

The power supply can directly be applied to either of the USB ports of the TP4056 or else use a micro USB breakout board(Optional) to mount the power inlet elsewhere

Step 3: Testing

Warning: Double-check all connections very carefully to avoid any risk of short circuits/damage.

Now connect the 5V from the supply and toggle the switch to charge mode. The red lights should indicate the charging in progress. When the batteries get charged, the light changes to blue.

Toggle the switch and check if the charging has stopped and the power is available at the output.