Solar Energy Charger Question

There are several ways of going about it.

One thing to remember is that the voltage delivered by a solar panel varies greatly depending in the amount of current it's delivering. Panels for charging of 12-volt batteries usually have an "open circuit" voltage output of 15-18 volts. However, this voltage drops quite a lot when you're drawing current approaching the panel's maximum output... if you short-circuit the panel's output leads, you end up with essentially 0 volts output, and a maximum amount of current flowing through the panel and the short (and all of the power thereby turning into heat and IR in the panel and wiring).

Small, simple solar "trickle chargers" have a low maximum current output. Chargers of this sort often have no voltage regulation at all... they're simply connected to the battery through an anti-reversal diode (and some even omit the diode!). The idea here is that the battery's terminal voltage (which rises as the battery charges) never actually rises all that high... the panel's current output is low enough that it just counteracts the battery's charging loss and self-discharge, without overcharging the battery enough to cause it to start electrolyzing away its precious bodily fluids.

Lower-cost chargers with larger panels (ones which deliver enough current to actually recharge the battery in reasonable time, and thus possibly capable of overcharging the battery) tend to use some form of linear voltage regulator. They may use a "series" regulator (perhaps something like an LM317), which sits between the panel and the battery and limits the current flow through the regulator so that the battery terminal voltage doesn't rise too high. Some use a "shunt" regulator (something like a large zener diode) which sits in parallel with the battery, "clamping" the voltage and dissipating any excess power from the panel as heat. The shunt regulator generates more waste heat when the battery is fully charged (or disconnected), but has little or no waste when the battery is low and is actively being charged by the panel. The series regulator is the other way around... it generates relatively little heat when the battery is not being charged, but can waste a good deal of power during active charging (depending on its design).

The most sophisticated charge controllers I've seen are "switching" regulators, which can accept a wide range of panel voltages and deliver a well-regulated voltage to the battery with relatively little power loss in the regulator itself. These regulators can even transform down the power delivered by the panel, to a lower voltage at a higher current, thus leading to greater charging efficiency than you'd get if you use a linear regulator or let the panel limit itself under heavy load. These switching controllers are the sort that you'll usually seen used in large "off the grid" solar panel applications.

Thanks EC

"Dave Platt" ëúá áäåãòä: snipped-for-privacy@radagast.org...