A useful little project for those that require battery backup for mains powered equipment. It started out as an investigation into applications of Smart Diodes. In essence, these are diodes which have an almost negligible forward voltage drop.

BiPower uses a pair of smart diodes to provide reverse polarity protection and battery backup to equipment driven from 12V mains power supplies. Load current is drawn from whichever power supply has the higher voltage. The intended use is for a 13.8V mains PSU to be one of the inputs and a lead acid battery to be the back up input. The 13.8V supply will deliver current until it fails when the 12V battery will take over.