ams reference design provides blueprint for battery fuel gauging in electric scooters

Date
07/30/2012

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Circuit uses AS8510 sensor interface to sense simultaneously the voltage and current of four series-connected 12-V batteries

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The ams AS8510-based battery-monitor reference design captures simultaneous current and voltage measurements for each of the four batteries at a high sampling rate. Application software that runs on an inexpensive 8-bit microcontroller computes the battery's state of charge.

ams has announced a reference design that shows how a simple current and voltage measurement circuit can produce SOC (state-of-charge) readings for electric scooter batteries. The reference design uses the AS8510 sensor interface from ams, a two-channel battery sensor interface, together with a simple 8-bit microcontroller, an LDO, and an LED driver and bar-graph display. The bill-of-materials cost for these active components is around $3.70. By implementing this design, electric scooter manufacturers can replace today's crude voltmeter displays with a fuel gauge, thus making the vehicle more useful and convenient to the rider while adding little to its cost. Normally, four series-connected 12 V lead-acid batteries power electric scooters, which are an increasingly popular mode of transportation because they are cheap to buy and run, and emit no exhaust fumes. The voltmeters their manufacturers provide 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. The new e-scooter fuel-gauging reference design from ams succeeds in meeting electric-scooter-manufacturers tight cost requirements while delivering accurate voltage and current readings across the charge-discharge cycle and across the battery's operating temperature range. This is due in large part to the circuit's use of the AS8510 sensor interface, which integrates data acquisition and data conversion in a single chip, and which produces low-offset current and voltage measurements across a wide dynamic range. The ams circuit design captures simultaneous current and voltage measurements for each of the four batteries at a high sampling rate. Demonstration software ams 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 can also drive a more expensive LCD display, providing more precise SOC information to the rider. ams provides the software at no cost to demonstrate that scooter manufacturers can successfully implement fuel gauging in the reference design hardware, and to show how they can use accurate voltage and current measurements to produce valid SOC readings. Bernd Gessner, Vice-President and General Manager of the automotive business unit at ams, said: "Implementing this innovative design from ams enables electric scooter manufacturers to add a huge amount of value to their products while optimizing 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." ams product deep link application deep link

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