Overload protection circuit for small motor - consists of measuring resistor with level detector and time delay operating trip contact

摘要

The application is typically to drives in motor vehicles, eg for fans or windscreen wipers. A measuring resistor(12) is placed in series with the motor(10), and the voltage across it fed to a level detector(16). A time delay element(18) actuates the trip contact(14) in the motor circuit when the level detector gives an output. The circuit is more versatile than a fuse in its ability to discriminate between a permitted overcurrent and a fault. Typically the time delay resets if the level detector output is not maintained for the whole time delay period.