This is an analysis/reverse engineering review of the Liitokala Lii-500 Engineer 4-slot Li/Ni battery charger/tester.
List of Features
- Voltage Range (Charge): 0-4.2V
- Max Current (Charge): 1A
- 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), >6Hz update rate
Buck Converter (Charger)
Reverse polarity protection is achieved by use of a low-side N-channel MOSFET (LTC8205A) rated for 6A, 20V, 38mOhm at Vgs = 2.5V, up to 0.83W 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 decoupled with a single 220uF/25V electrolytic capacitor. The charger consists of a APM9435 P-channel MOSFET, rated for up to 30V, 5.3A, 90mOhm at Vgs = 4.5V, up to 2.5W power dissipation, switched at 62.5kHz with a 47uH(?) through-hole inductor, through an SS34 didoe, to a 22uF (?) MLCC output capacitor. Current is measured through a 0.3 ohm sense resistor.
Charge is terminated when the current drops below 60mA 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 an FQP30N06 N-channel MOSFET (30A, 60V, 40mOhm at Vgs = 10V, 79W power capability, ~2.16W max dissipation with 40C ambient, equivalent to 0.51A at 4.2V). The PWM rate for the MOSFET is 62.5 kHz, with 62ns PWM resolution (1/(16 MHz)). The peak battery current for a 4.2V Li-Ion battery is approximately 0.8A pulsed.
Discharge termination is when the Li-Ion battery reaches 2.85V at constant current.
The display uses an unmarked LCD Driver Controller/microcontroller.
CCR v1 Performance Evaluation
The Lii-500 uses an unknown microcontroller in 20-SOP packages.
Lii-500 Performance Evaluation
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)|