How to Build a LiPo Battery Charger with the TP4056: Circuits, Safety, and BMS Integration

Introduction

LiPo (Lithium Polymer) and 18650 Li-ion cells power everything from RC drones to portable LED projects, but charging them incorrectly is dangerous — swollen packs, venting with flame, or outright explosions are real risks. The TP4056 is a tiny, cheap ($0.50) single-cell lithium charger IC that handles constant-current and constant-voltage charging safely with minimal external components. This guide walks through building a TP4056 charger from scratch, adding a protection circuit (DW01A + FS8205A), integrating a Battery Management System (BMS) for multi-cell packs, and understanding the critical safety rules every maker must follow when working with lithium batteries.

What You Need

TP4056 module or bare IC with supporting components
DW01A protection IC and FS8205A dual MOSFET (for protection board)
18650 cell holder or JST-PH 2.0 connector for LiPo packs
Micro-USB or USB-C connector for 5V input
10k NTC thermistor (optional, for temperature monitoring)
Multimeter and breadboard for testing

Understanding Lithium Battery Charging

Lithium cells charge in two phases:

Constant Current (CC): The charger supplies a steady current (typically 0.5C-1C) until the cell voltage reaches 4.2V. For a 2000mAh cell, 1C = 2A.
Constant Voltage (CV): Once the cell hits 4.2V, the charger holds that voltage while current naturally tapers down. When current drops below ~10% of the initial charge rate, charging terminates.

Never exceed 4.2V per cell. Never charge below 0°C or above 45°C. Never leave charging lithium unattended.

Step 1: Basic TP4056 Charger Circuit

The TP4056 needs only two external components to work:

PROG resistor (R3): Sets charge current. Formula: Icharge = 1200 / Rprog (kΩ). A 1.2kΩ resistor gives 1A. A 2.4kΩ resistor gives 500mA.
Battery connection: BAT+ and BAT- directly to the cell terminals

The TP4056 module (common on Amazon/AliExpress) includes both the IC and the programming resistor on a small PCB with USB input and battery output pads. These modules work out of the box but lack protection circuitry.

Step 2: Add Protection with DW01A + FS8205A

Standalone TP4056 modules do not protect against over-discharge, short circuits, or over-current. A proper protection circuit is mandatory.

DW01A Protection IC Functions

Over-charge protection: Disconnects load if cell exceeds 4.3V
Over-discharge protection: Disconnects load if cell drops below 2.4V
Over-current protection: Disconnects load if discharge current exceeds threshold (typically 3A)
Short-circuit protection: Instant shutdown on shorted output

FS8205A Dual MOSFET

The DW01A controls this dual N-channel MOSFET which acts as a switch between the battery and the output. The MOSFET turns on during normal operation and off when a fault is detected.

Protection Circuit Wiring

Connect DW01A VCC to BAT+, GND to BAT-
Connect DW01A OD and OC pins to FS8205A gate inputs
Connect FS8205A source to BAT-, drain to output negative
Output positive connects directly to BAT+
Add 100nF capacitor between VCC and GND near the DW01A

Most commercially available "TP4056 with protection" modules include both chips on one board.

Step 3: Multi-Cell BMS (2S, 3S, 4S)

For projects needing more than 3.7V, cells are connected in series. A BMS balances and protects the pack.

2S BMS (7.4V)

Two cells in series
BMS monitors each cell individually
Charge voltage: 8.4V (4.2V x 2)
HX-2S-JH20 or 2S 5A BMS boards are common

3S BMS (11.1V)

Three cells in series
Charge voltage: 12.6V
Standard for RC cars and portable power tools

4S BMS (14.8V)

Four cells in series
Charge voltage: 16.8V
Common for FPV drones and higher-power projects

BMS Wiring

Connect B- to battery negative (first cell)
Connect B1 to junction between cell 1 and cell 2
Connect B2 to junction between cell 2 and cell 3 (for 3S)
Connect B+ to battery positive (last cell)
Connect P- and P+ to your load
Connect C- and C+ to your charger

Always connect balance leads first, then main leads. Verify with a multimeter before powering anything.

Working out the right voltage, capacity, and expected runtime for a custom pack before you build it? The Battery Pack Designer tool handles the series/parallel math for you.

Step 4: Charge Current Selection

Cell Capacity0.5C Rate (Safe)1C Rate (Max)Rprog Value 1000mAh500mA1000mA2.4kΩ / 1.2kΩ 2000mAh1000mA2000mA1.2kΩ / 600Ω 3000mAh1500mA3000mA800Ω / 400Ω 5000mAh2500mA5000mA480Ω / 240Ω

For longevity, charge at 0.5C or less. USB power supplies typically provide 1-2A, which limits practical charge rates.

Step 5: Building a Complete Charger Module

Schematic

USB 5V ──┬── TP4056 VCC ├── USB+ input └── 10μF capacitor to GND TP4056 BAT+ ──┬── Cell positive └── DW01A VCC TP4056 BAT- ──┬── Cell negative ├── DW01A GND └── FS8205A source DW01A OD/OC ── FS8205A gates FS8205A drain ─ Output negative Cell positive ─ Output positive (fused)

PCB Layout Tips

Keep high-current traces short and wide (1oz copper minimum)
Place decoupling capacitors close to IC power pins
Include test points for voltage monitoring
Add a fuse between battery positive and output
LED indicators: RED = charging, GREEN = fully charged

Step 6: USB-C PD Charging (Advanced)

For faster charging, USB-C Power Delivery can provide 9V or 12V:

Use a PD trigger board (ZY12PDS or similar) to negotiate 9V from a USB-C PD supply
Feed 9V into a buck converter to step down to 5V for the TP4056
Or use a dedicated 1S/2S charging IC that accepts higher input voltages (IP2312, TP5100)

Safety Rules (Non-Negotiable)

Never charge unattended. LiPo fires happen during charging, not discharge.
Always use a protection circuit. Bare TP4056 modules are not safe for end-use.
Charge in a fireproof container. A LiPo safe bag or steel ammo can contains fires.
Never puncture or crush cells. Internal short = thermal runaway.
Inspect cells before charging. Puffy, dented, or damaged cells go in salt water, not the charger.
Use the correct charger voltage. A 4.2V charger on a 2S pack will not charge fully and is a fire risk.
Balance charge multi-cell packs. Unbalanced cells overcharge/overdischarge and fail catastrophically.
Store at 3.7-3.8V (50% charge). Never store fully charged or fully depleted.

Troubleshooting

LED not lighting: Check USB power, verify TP4056 is getting 5V
Not charging: Check PROG resistor, verify cell voltage is above 2.5V (deeply discharged cells must be trickle-charged)
Getting hot: Reduce charge current with larger Rprog, add heatsink to TP4056
BMS cutting out: Check for short circuit, verify cell voltages are balanced

Pro Tips

Buy name-brand cells (Samsung, LG, Panasonic) — cheap cells have inflated capacity ratings and poor safety
Add a voltage display module ($1) to monitor cell voltage in real-time
Use JST-PH 2.0 connectors for LiPo packs — the standard connector in RC and maker communities
For solar charging, add a 5V solar panel + TP4056 in parallel with a diode
Document your pack configuration on the enclosure: voltage, capacity, charge date

Conclusion

Building your own lithium battery charger is both empowering and dangerous — the TP4056 makes the circuit simple, but understanding protection, current limits, and safe handling is what separates a working project from a fire hazard. Always include a DW01A+FS8205A protection circuit, size your charge current appropriately, follow the safety rules religiously, and never cut corners on lithium battery projects. Done right, you will have a reliable, reusable power system for hundreds of projects.

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