A simple charge controller suitable for wind or solar applications. Uses a TL-084 Op Amp, automotive spotlight relay and a handful of other components. The same circuit could also be used as a low voltage cut off to disconnect your battery before its fully discharged. Suitable for 12 and 24v operation.
The controller uses two trimpots to set a low and high switching voltage. When the applied voltage ( battery ) exceeds the high voltage setting, a relay is turned on. The relay will remain on until the applied voltage drops below the low voltage setting.
Wind or Solar Charge Controller - [Link]