Lii500

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This is an analysis/reverse engineering review of the Liitokala Lii-500 Engineer 4-slot Li/Ni battery charger/tester.

Fully functional v1 CCR prototype in regenerative configuration, testing Re-volt and Samsung 2600mAH cells.

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

Electronics

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:

Simplified buck circuit schematic for the CCR v2.0.

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.

FET Discharger

A simplified schematic of the circuit that discharges the battery is shown in the thumbnail below:

Simplified boost circuit schematic for the CCR v2.0.

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.

LCD

The display uses an unmarked LCD Driver Controller/microcontroller.

CCR v1 Performance Evaluation

Buck (charging)/Boost (discharging) converter efficiency for the CCR v1.0.
Boost (discharging) mode operation at 1.5A, showing peak external transistor temperature of 57.8 C.

Microcontroller

The Lii-500 uses an unknown microcontroller in 20-SOP packages.

Lii-500 Performance Evaluation

File:X.png
Charging mode ramp from 0 to 1A (CC).

...

BOM Cost Estimate

EE Component Cost Source
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
PCB $2.00 JLCPCB
Assembly $7.10 - $31.70 PCBgogo
HW Component Cost Source
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)