Lithium Polymer (LiPo) battery is a type of rechargeable battery that provides high energy storage to weight ratios in an eternal variety of shapes and sizes. LiPo batteries has taken the electric RC gizmos world by storm,especially for Radio-Controlled (RC) toys like electric helicopters, airplanes and boats.
Unlike conventional NiCad (or NiMH) cells that have a voltage of 1.2 volts per cell, LiPo battery cells are rated at 3.7 volts per cell. The benefit here is fewer cells can be used to make up a rich battery bank. In practice, RC LiPo battery packs should have at least two or more LiPo cells hooked up in series to provide higher voltages. For larger RC models this number may be as high as 6 cells!
Charging LiPo cells/batteries is not an easy task. LiPo battery obviously have a very different characteristics from conventional rechargeable battery types. Therefore, charging them correctly with a charger specifically designed for lithium chemistry is critical to both the life span of the battery pack, and ofcourse your safety.
Note that a 3.7 Volt battery is 100% charged when its terminal voltage reaches 4.2 volts, and selecting the correct charge current is also very crucial when charging battery packs, because over charging will ruin the battery, possibly cause it to catch fire. As LiPo batteries require special charging algorithm, never attempt to charge these batteries with anything but a dedicated Lithium Polymer battery charger.
Fortunately, single-chip solutions are now widely available for Li-Po battery charging. The tiny chip TP4056/YP4056 is a good example. The TP4056 IC is a complete constant current/constant-voltage linear charger for single cell lithium-ion/Lithium Polymer (LiIon/LiPo) batteries. Its SOP-8 package and low external component count make the TP4056 ideally suited for portable applications.
Furthermore, the TP4056 can work within USB and wall adapter. Other features include current monitor,under voltage lockout, automatic recharge, and two status pin to indicate charge termination and the presence of an input voltage.
However, construction of the LiPo battery charger using this IC is a cumbersome task for an average hobbyist having zero skills in SMD prototyping. As an alternative (thanks eBay), just buy and ‘hack’ a ready-made module of TP4056 to complete the project without any difficulty.
First of all carefully observe the TP4056 module, and its circuit diagram.Thereafter, start the fabrication process as per the guidelines given here:
- Locate the position of the resistor R4 (1K2), and carefully remove it from the top of the PCB using a soldering pencil
- Extend short-length of two multi-stranded wires from the solder pads
- Attach the new resistor network (1K2 1’4 W resistor+10K LIN preset potentiometer) to the wire ends, ie in place of the original R4 smd resistor
- Feed USB power to the module input from any USB port, set the preset pot to zero Ohm (0R), connect a 3.7V LiPo battety at the module output, watch the onboard LEDs, and ascertain that everything is OK
Yes, your own portable LiPo charger, capable of charging any single-cell LiPo from USB power (5V), or from an external dc source (4 to 8V) is now ready for use. With the help of the 10K preset pot, it is possible to adjust the LiPo charging current from near 200mA to 1000mA. A current setting chart (obtained from the mfr.) is also included here for your quick reference.
Also refer the LED status chart for better system evaluation (remember, LED colors may vary from module to module).
Prototype tested with USB power input (5V) from a laptop, and external dc input (6V) from a lab power supply. Charging current for the battery (3.7V/1100mAh LiPo) is programmed to about 500mA using the 10K preset pot.
It’s Alive… and quite lovely as well!