Designing and making a 18650 lithium battery charger with the TP4056

Charging lithium batteries safely

Testing the module, 3 18650s charged to 4.18v

I needed a PCB module to charge four 18650 lithium batteries for my (battery powered) tube amplifier. I ended up making two different versions of the module, the first design was too compact and got a bit toasty. The second version has more heatsinks and is wider but still reaches 70°C, I could reduce the charge current but decided that if I reduce the supply voltage from 5v to 4.55v, this reduces the max power dissipation by about 0.25W.
The design of the module consists of four seperate TP4056X ICs that charge up to four lithium batteries individually, I've set the maximum charge current per battery to 600mA.

Before I made this module I considered the readily available TP4056 modules, but I could not find anything that could charge four batteries, had the correct cutoff voltage of 4.2 and used high quality components, it turns out nearly all the modules on Ebay are TC4056, this has a questionable cutoff and poor tolerances. I also did not need the additional protection ICs as I would make my own protection module which needed to be seperate.

The video below is of the first iteration of the module, the circuit and components are all the same.

The components

I opted for the TP4056 IC as this required the least amount of discrete components whilst offering safe charging. The version of the TP4056 I went for was TP4056X, its main difference is; better regulation, better accuracy and better thermal dissipation. The package is SOP8, so not too difficult to solder and there is a thermal pad on the bottom.

I used a 2W 0.5Ω resistor to drop between 0.25V and 0.3V volts, this helps reduce the amount of power needed to be dissipated by the TP4056X.

All other components are standard 1% metal films resistors with a temperature coefficient of 100ppm or better. Capacitors are X7R.

When I tested this, the cutoff was at about 4.18v, which is perfect.

The schematic

The scematic consists of four seperate chargers.

The circuit design is based on the manufacturers (TOPPOWER) standard design, the only changes made are the values for R_PROG (Rn-3), LED resistors (Rn-1 and Rn-2) and the V_RCC (Rn-4). The temperature sensor has been omitted, I do not plan on using this unattended or overnight (same as any charger boards that I would buy on Ebay).
There is not much to say as it is such a simple circuit. The resistors for the LEDs need to be selected for different types of LEDs and brightness.
The R_PROG (Rn-3) resistors were calculated to give about 580mA of charge current per battery. This helps keeps the power dissipation down of TP4056X.

The calculations

R_PROG resistors

R_PROG (Rn-3) resistor selection calculation, all results have a tolerance of ±10%:

V_PROG = 1.1 V

V_PROG
I_BAT = ________ x 1100

R_PROG

1.1
I_BAT = ________ x 1100 = 600 mA

2000

We can see that a resistor value of 2000Ω produces a charge current of about 600 mA.

If you know what charge (I_BAT) current you want, you can calculate the R_PROG like this:

1100
R_PROG = ______ (±10%)

I_BAT

1100
R_PROG = ______ = 1833 Ω

0.6

The table below shows some resistor values and the associated charge current, there is a tolerance of ±10%:

RPROG(K)	IBAT (mA)
30	50
20	70
10	130
5	250
4	300
3	400
2	580
1.6	690
1.4	780
1.2	900
1.1	1000

V_RCC resistor

V_RCC (Rn-4) selection

We calculate the voltage dropped by this resistor using ohms law, we know that 600mA or current will be flowing through the resistor:

V = I x R

V = 0.6 x 0.5 = 0.3 V

0.3V is dropped by this resistor, this mean the TP4056X has less power to dissipate.

Next we check to see how much power the resistor will dissipate:

P = I x V

P = 0.6 x 0.3 = 0.18 W

0.18W is dissipated by the resistor, I decided to use a 2W resistor as there was plenty of space on the rear of the PCB.

TP4056X dissipation

To work out the maximum power dissipated by the TP4056X, we can work it out by knowing the minimum battery voltage.

Lets assume the following values:

V_BAT = 3.2V
V_CC = 4.6V
R_VCC = 0.3V
I_BAT = 0.6mA

P_D = V_CC - V_BAT - R_VCC * I_BAT

P_D = 4.6 - 3.2 - 0.3 * 0.6 = 0.6 W

The maximum power dissipated by each TP4056X is about 0.6W, this power goes down as the battery voltage increases.

The PCB

Top side of the PCB.

The PCB is 70mm wide by 20mm high. There are lots of vias to transfer the heat to the other side and over to the heatsinks on the rear.
The rear of the PCB has space for six 11mm by 11mm heatsinks, there are no mounting holes so thermal glue has to be used.

Bottom side of the PCB.

A total of eights pins provide the charging interface and power input, the two ground pins are commonly connected, two sperarate 4.5v - 5v VCC pins provide power to two ICs each. The remaining four pins are the battery + connections.

Each IC has a charge and standby LED.

The reason why the silkscreen text appears upside down is the module is meant to be mounted upside down in my amplifier.

Bill of Materials

Name	Designator	Qty	Manufacturer Part	Manufacturer	Supplier	Supplier Part
KF301 5.0 6P	AMP/SPEAKER	1	PA001-6P	HIWA	LCSC	C173288
LED-0805_R	CHARGE3,CHARGE4 CHARGE1,CHARGE2	4	MHT170CRCT	MEIHUA	LCSC	C389523
10uF	C2-1,C4-2,C3-1,C3-2 C2-2,C1-2,C4-1,C1-1	8	CL21B106KOQNNNE	SAMSUNG	LCSC	C95841
0.5R	R2-4,R4-4,R3-4,R1-4	4	CSR2512FTR500	Stackpole Elec	LCSC	C346803
LED-0805_G	STDBY2,STDBY1 STDBY4,STDBY3	4	MHT170UGCT	MEIHUA	LCSC	C397047
2k	R2-3,R1-3,R4-3,R3-3	4	RC0805FR-072KL	YAGEO	LCSC	C114572
10k	R2-1,R3-1,R4-1,R1-1	4	RC0805FR-071KL	YAGEO	LCSC	C84376
4.7k	R3-2,R1-2,R4-2,R2-2	4	AC0805FR-074K7L	YAGEO	LCSC	C140869
HDR-M-2.54_1x4	J2,J1	2			LCSC	C124378
TP4056	U2-1,U4-1,U3-1,U1-1	4	TP4056	TOPPOWER	LCSC	C191323

Additional components not in BOM:

Aluminium heatsink

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