Cross-Needle Analog Meter to Monitor Charge Time for Lithium-Ion Single Cell

Hiroshi Mohri and Jonathan Scott

This manuscript describes a novel cross-needle analogmeter whose scale reads out voltage, current, and timeremaining to reach full charge. The design is inspired by crossneedleStanding Wave Ratio(SWR) meters that read forward andreverse power. Voltage is displayed on an offset-zero linear scale,and current on a logarithmic scale from 1 mA to 10 A. Thisleads to a wide range of perceptible charge times and pleasantcharge-time contour lines. The prototype is implemented on asingle PCB using a cheap PIC micro controller. It is scaled formonitoring a single 18650 lithium cell charged by a small solarpanel. The Novel contribution of this paper is the use of a crossneedleanalog meter with a third scale to measure time remainingto fully charge a Lithium-Ion single cell battery.