Unterpremstaetten, Austria: A reference design developed by AMS shows how a simple current and voltage measurement circuit can produce state of charge (SOC) readings for an electric scooter’s batteries. The company says that electric scooter manufacturers can replace today’s crude voltmeter displays with a fuel gauge while adding only €3 ($3.70) to the bill of materials.
Voltmeter displays typically offer a poor indication of the scooter’s range, since the output voltage at the batteries has a nonlinear relationship with SOC, and varies widely depending on the batteries’ load. According to AMS, its reference design meets the cost requirements of electric scooter manufacturers while delivering accurate voltage and current readings across the charge/discharge cycle, as well as across the battery’s operating temperature range.
The circuit uses the AS8510 sensor interface, which integrates data acquisition and data conversion in one chip. The interface also produces virtually offset-free current and voltage measurements across a wide dynamic range.
Alongside the AS8510 two-channel sensor interface, the reference design incorporates a simple 8-bit microcontroller, LDO and LED driver (driving an LED bar-graph display). It captures simultaneous current and voltage measurements for each of the four batteries at a high sampling rate. Demonstration software implemented in an 8-bit microcontroller converts a combination of open-circuit voltage measurements and coulomb counts into SOC readings.
The reference design supports a simple LED bar-graph display. However, it can also be used to drive a more expensive LCD display that delivers more precise SOC information to the rider.AMS