What is it?

The module disconnects the battery supplying some device if an external power source is inserted. In this way it keeps the battery safe and if the external power source is disconnected, it connects back the battery as main power supply. It can be used also in the case the electrical grid is unstable and there are power outages. In such cases the battery acts as back-up power source.

Why did you make it?

I wanted to design a clock supplied by battery, but having also a connector for external power adapter. I found that simply connecting both : the battery and the power source in parallel can cause problems - even the battery can explode is extremely charged. To prevent such events I designed this module.

What makes it special?

The module allows the joint work of battery and ACDC power adapter, keeping them separated when both exist. When the external power disappears, the module connects the battery automatically to the supply line. The module is able to pass currents around 1.5A (typical USB currents) and works in the voltage range 2.5V-12V. For this module is specific that the battery voltage must be the same or higher then the external. Two LEDs are used to indicate which of the sources is active in the moment. The board is small :30x25mm and has 4 mounting holes.