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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 RPROG (Rn-3), LED resistors (Rn-1 and Rn-2) and the VRCC (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
RPROG (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

RPROG resistors

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

VPROG = 1.1 V

                 VPROG
IBAT
  =  ________  x  1100

                 RPROG


                     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 (IBAT) current you want, you can calculate the RPROG like this:

                     1100
R
PROG  =  ______ (±10%)

                      IBAT


                     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

VRCC resistor

VRCC (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:

VBAT = 3.2V
V
CC = 4.6V
R
VCC = 0.3V
I
BAT = 0.6mA

PD  =  VCC - VBAT - RVCC * IBAT

PD  =  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

Links

EasyEDA Project Page:

https://easyeda.com/Ratti3/tp4056-18650-li-ion-battery-charger

YouTube Video:

https://youtu.be/Aoi0kJcRnSE

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