Electric scooters, normally powered by four series-connected 12V lead-acid batteries, are an increasingly popular mode of transport because they are cheap to buy and run, and emit no exhaust fumes. However, the voltmeter dials provided in them offer a poor indication of the scooter”s range, since the output voltage at the batteries has a non-linear relationship with SOC, and varies markedly depending on the load on the batteries.
By implementing this new reference design, electric scooter manufacturers will be able to replace crude voltmeter displays with a fuel gauge, making it more convenient for the rider while not adding to the bill of materials.
The new e-scooter fuel-gauging reference design provides accurate voltage and current readings across the charge/discharge cycle and across the battery”s operating temperature range. This is due to the circuit”s use of the AS8510 sensor interface, which integrates data acquisition and data conversion in a single chip, and which produces virtually offset-free current and voltage measurements across a wide, dynamic range.
The circuit design 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, but it can also be used to drive a more expensive LCD display, providing more precise SOC information to the rider. The software developed by ams is provided at no cost to demonstrate that fuel-gauging can be successfully implemented in the reference hardware design, and to show how accurate and precise voltage and current measurements can be used to produce valid SOC readings.
Bernd Gessner, Vice-President and General Manager of the automotive business unit at ams, said: “Implementing this design enables electric scooter manufacturers to add a huge amount of value to their products while optimising their bill-of-materials cost. With an accurate fuel gauge based on the AS8510, riders of cheap battery-powered scooters will be able to see exactly how much power remains, and can work out easily how far they can ride before needing to recharge.”