It can be powered by the same source being measured. It doesn't require external shunt, it have built-in shunt. With input connection-reverse protection. Super wide range of working voltage . Easy install. Product Name Digital amp meter Power supply DC4v-30V Measuring Range DC0A-20A Display blue 0.56"LED Measuring Accuracy ± (1%+2 byte) Operating Temperature -10 ~65 Cut-Size 45.5mm*26.5mm Dimensions 48mm*29mm*21mm For use Is widely used in equipment and electromechanical device. Cars, boats, planes etc. for measuring current.

Digital LED blue DC 0-20A Amp Meter For 12v Car auto Boat Solar Built-In Shunt