#501 Single-cell Lithium Charger
How to charge a single 18650 lithium-ion cell with a TP4056-based charging kit, with comparison to ETA9635/ETA9638-based modules.
Lithium Ion/Polymer batteries are all around us these days, but they are also have a deserved reputation for being a bit dangerous if not treated properly, in particular:
- over-current/short-circuit output (same situation can be created if the package is punctured)
- over-discharge - increases battery resistance and hence heat/fire risk during recharge
- over-charge - stresses the battery and compromises safety
Get anything wrong, and there’s heat & fire risk, maybe violent enough to be explosive. Great news for youtubers like Big Clive!
Charging is where things can most commonly go wrong. A little bit of knowledge can go a long way, especially if buying “cheap” chargers or going the DIY route.
There is an optimal charging profile for li-ion batteries:
- pre-qualification stage - a low constant-current charge to bring deeply-discharged cells back to a nominal voltage (usually 3V for 3.7V li-ion)
- constant-current fast chage - usually 0.5C until battery approaches fully charged voltage
- constant voltage saturation charge - until charge current falls below 3-5% percent of the rated current.
This sensitivity to charging conditions is why li-ion cells are ideally charged individually, or with a balanced charging circuit when multiple cells are in an array.
- Charging rates are specified in terms of
C, where 1 C equals the maximum current the battery can supply for one hour.
- li-ion with the traditional cathode materials of cobalt, nickel, manganese and aluminum typically charge to 4.20V/cell. The tolerance is +/–50mV/cell.
- some nickel-based varieties charge to 4.10V/cell;
- high capacity Li-ion may go to 4.30V/cell and higher.
Some guides to lithium battery charging:
- A Designer’s Guide to Lithium (Li-ion) Battery Charging
- BU-409: Charging Lithium-ion - Battery University
- EEVblog #176 Lithium Ion/Polymer Battery Charging Tutorial:
The TP4056 is made by NanJing Top Power ASIC Corp. It is a complete constant-current/constant-voltage linear charger for single cell lithium-ion batteries, described as: 1A Standalone Linear Li-lon Battery Charger with Thermal Regulation.
The charging charge profile is designed for 3.7V li-ion batteries, featuring:
- Preset 4.2V Charge Voltage with 1.5% Accuracy
- C/10 Charge Termination
- 2.9V Trickle Charge Threshold
- Thermal Regulation
Typicall application circuit:
Julian Ilett did a very good detailed review and test of the common TP4056 modules:
TP4056 Charger Kit
I picked up an 18650 charging & power pack kit from an aliexpress seller: DIY Kit Micro USB 5V 1A 18650 TP4056 Lithium Battery Charger Module +600MA SB Mobile Power Boost Board +18650 Battery Box Case. It basically includes a battery holder and two modules: a TP4056 charging module, and a boost converter for a 5V output.
The TP4056 charging module uses three main chips in addition to support passives and indicator LEDs:
- TP4056A for constant-Ccurrent/constant-voltage charge control
- DW01 battery protection IC
- 8205A Dual N-Channel MOSFET provides load switching - apparently from RZC Microelectronics but not listed on their current web site. OR it could be ML8205A by Mei Lai 美莱创新
The boost module is a standard switching circuit using a switching regulator marked E50D. Although some listings identify this as a CE8301 regulator, the package marking don’t seem quite correct (appears more like a SOT-89-3 CE8301A which I would expect to be marked “A50P”). Regardless, this is the simplest form of fixed output converter without frill like auto-shutdown.
Rprog/R3 is populated as 1.2kΩ, which correcponds to programs a charge current of 1000mA.
The recommended configuration matching the parts in the kit is a simple wiring together of the modules:
However, since neither the charge or boost module include any auto-shutdown capability, this means an “always on” configuration. I added a switch to the battery leads so that I can leave a battery in the holder without it being continually discharged.
TZT Single-cell Power Bank
As a comparison for the TP4056-based circuits, I opened up a TZT 18650 USB Power Bank I had kicking around.
This obviously allows for a much more compact product:
The ETA9635 features:
- 2 in 1: integrated synchronous boost plus charger without external load switching
- Short-circuit Protection
- Reverse current Protection
- Up to 1A Charging, 5W output
- 50µA of quiescent current during no load
Credits and References
- DIY Kit Micro USB 5V 1A 18650 TP4056 Lithium Battery Charger Module +600MA SB Mobile Power Boost Board +18650 Battery Box Case - example from an aliexpress seller
- TP4056 info and datasheet - original source NanJing Top Power ASIC Corp (chinese datasheet)
- TP4056 info and datasheet - English version from sunrom.com
- DW01 Plus battery protection IC
- LTC4056-4.2 - similar but not to be confused with the TP4056
- 8205A Dual N-Channel MOSFET
- ML8205A by Mei Lai 美莱创新
- Dual mosfet 8205A - lithium battery protection circuit - discussed on electronics.stackexchange
- CE8301 regulator
- Restoring/Recharging Over-discharged LiPo (Lithium Polymer) Batteries
- SS12D00G3 Toggle Switch 2 Position SPDT
- TZT USB Power Bank Case Kit 18650 Battery Charger DIY Box Shell Kit Black For Arduino - example from an aliexpress seller
- ETA9635 datasheet from ETA solutions, appears to have been superseded by the ETA9638