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

Abstract

This manuscript describes a novel cross-needle analogmeter whose scale reads out voltage, current, and time remaining to reach full charge. The design is inspired by cross-needle Standing Wave Ratio(SWR) meters that read forward and reverse 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 a single 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 remaining to fully charge a Lithium-Ion single cell battery.