A rectifier is a group of diodes which allows current in one direction only.like a one way valve. In rectifier there will be two or three Ac terminals and also two Dc terminals.And also there are two diodes from each Ac terminal, and one to each Dc terminal. Which allow flow of charge towards the positive or away from the negative to create a Dc output in the correct direction.
For testing a rectifier we need a multimeter and one rectifier. If you disconnect a rectifier from any circuit carefully disconnect all of the wires from the rectifier, taking care to identify them clearly for reconnection.Now set your multimeter to the diode test position, usually marked with a diode symbol.
Touch the probes to each end of a diode which will give you three possible readings.
1 ) open Circuit : usually indicated by a digit 1 on the left hand side of the display or the letter OL .
2 ) Diode Forward Voltage : usually give a number around 500mV.
3 ) Short Circuit : usually give 0.0 .
Diode in properly functioning condition will give a asymmetrical outcome. open circuit one way and a forward voltage the other way. A short-circuit or an open circuit in both directions indicate a bad diode.
Place the red probe on the positive DC terminal and check with the black probe on each of the AC terminals in turn. You should see open circuit (top right photo). Now try reversing the probes and place black on the positive DC. You should get a number on the display each time you touch the red probe to an AC terminal. Check the negative DC terminal in the same way and you should see the exact opposite (bottom right photo).
If you find a shorted diode or one that is open in both directions, the rectifier needs to be replaced. Consider possible causes, including over current, overheating from poor connections, and lightning surges. Replacing your rectifier with one that is made for higher voltage and current may prevent similar problems from occurring in the future.
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