This is an analysis/reverse engineering review of the Zanflare C4 4-slot Li/Ni battery charger/tester.
List of Features
- Voltage Range (Charge): 0-4.2V
- Max Current (Charge): 1A (charge mode only, 0.5A max in charge test mode)
- Max Current (Discharge): 0.5A
- Efficiency: xx% (charging, single slot at 1A, 3.8V)
- Modes: Charge, Nor Test (C/D/C), Fast Test (D/C)
- 10mV voltage resolution (3 digits), xHz update rate
Buck Converter (Charger)
Reverse polarity protection is achieved by use of a low-side N-channel MOSFET (STT8205S) rated for 6A, 20V, 38mOhm at Vgs = 2.5V, up to 1.14W power dissipation.
A simplified schematic of the buck converter that charges the battery from a 12V supply is shown in the thumbnail below:
The input is fed through an SS24 schottky diode (2A, 40V, 0.39Vf at 1A) decoupled with a 100uF/16V electrolytic capacitor, plus a 22uF/25V electrolytic capacitor for each cell. The charger consists of a RU30S5H dual P-channel MOSFET, rated for up to 30V, 5A, 56mOhm at Vgs = 4.5V, up to 2W power dissipation, switched at 126kHz with a 47uH inductor and 22uF (?) x 2 MLCC output capacitor. Current is measured through a 0.3 ohm sense resistor.
Charge is terminated when the current drops below 110mA in CV mode. There is no rest period before discharge begins.
A simplified schematic of the circuit that discharges the battery is shown in the thumbnail below:
The battery positive goes through a 0.3 ohm current sense resistor to the drain of a VST012N06HS N-channel MOSFET (55A, 60V, 8.5mOhm at Vgs = 10V, 115W power capability, ~2.7W max dissipation with 40C ambient, equivalent to 0.64A at 4.2V). The PWM rate for the MOSFET is 126 kHz. The peak battery current for a 4.2V Li-Ion battery is approximately 11.6A pulsed, accounting for voltage drops in the FET and current sense resistor.
Discharge termination is when the Li-Ion battery reaches 2.75V at constant current.
The display uses a Holtek HT16C23 RAM Mapping 56*4 LCD Driver Controller.
CCR v1 Performance Evaluation
The Zanflare C4 uses a pair of unknown microcontrollers in 24-SOP packages.
Opus Performance Evaluation
The CCR v2 was assembled 2/15/19 and checked for basic operation cycle testing a Samsung 25R. Charging current is limited to approximately 2A due to power dissipation of the SOIC-8 P-channel MOSFETs. This may improve slightly with proper airflow routing using a 3D printed enclosure. Transient performance and current regulation were measured with a Rigol DS1052E. Discharge shows an overshoot of approximately 18% for 580us, and regulation of +/-3.8% at 1A. Charge shows no overshoot, and regulation of +/-3.9% at 1.5A.
Further investigation showed the MOSFET driver was not able to produce sharp edges, causing higher switching losses at 360 kHz. Changing the code to operate the MOSFETs at 180 kHz allows charging at up to 3.5A.
BOM Cost Estimate
|OPA335 Zero-Drift Amplifier (qty 2)||$2.42||LCSC|
|MCP1402 MOSFET Driver (qty 4)||$1.83||LCSC|
|STM32F103 "Blue Pill"||$1.82||Aliexpress|
|NCS199A1 Current Sense Amplifier (qty 2)||$1.45||LCSC|
|18650 SMT Holder (qty 2)||$1.23||Aliexpress|
|N-channel MOSFET 13A 11.5mOhm SOIC-8 (qty 4)||$0.52||LCSC|
|rBOM (under $0.41)||$4.76||LCSC|
|Assembly||$7.10 - $31.70||PCBgogo|
|100x40x20 Aluminum Heatsink||$3.02||eBay|
|40x40x20 5V Fan||$1.60||eBay|
|Misc HW (Under $0.22)||$0.42||Aliexpress/eBay|
|Total Price||$52.41 (Assembly cost $317, batch qty 10)|