How to Test a Common Mode Choke

I was recently hired as an intern at Wurth Electronics. At Wurth I am responsible for testing common mode chokes, which are used to clean up the signals in anything from power lines to the circuitry in your house. In this essay I will go over how I use a schematic from Wurth’s website to find the correct pins, solder longer leads on, orientate it correctly in the testing enclosure, run the test, and use the results to plug into an Excel spreadsheet.

The first order of action is to find a new part and use the part’s number to look up its own schematic on Wurth’s website. Most common mode chokes are wrapped up in bubble wrap with a label stickered on it. Once a component is selected use the part number on the label to look up the schematic on WE-Online.com in the search bar. Open the PDF file and print the schematic.

Next is to solder longer leads onto the pins usually located on the bottom of the common mode choke. The longer leads help when you wire the choke to the testing enclosure. turn on the solder box and fix the heat to 800 degrees. While the soldering iron is heating up, cut four separate pieces of wire about two inches long. Clamp the wires using the stand and orientate the fixture so the wire lines up with the pin. Use soldering wire and the iron to solder the four wires onto the four pins of the common mode choke. You are now ready to wire the choke into the enclosure.

Use the schematic to locate pins one through four. This is important because if the common mode choke is connected incorrectly during testing it could cause catastrophic damage to the Electrical Fast Transient Generator. Use the lead from pin one and place it into the red positive line voltage screw-down. Wire the three other leads into their corresponding screw-downs. You are now ready to run a test on the common mode choke.

To start a test, you must first make sure that the oscilloscope and test receiver are connected to the testing enclosure with a BCD cable. After that is ready, set the Electrical Fast Transient Generator for 4000 volts. This means that 4000 volts AC (alternating current) will pulse through the common mode choke continuously for about three minutes. Start the test and use the oscilloscope and test receiver to find the waveform being produced. Save the waveform on the oscilloscope and test receiver and name it as the part number and name of the test. This test is called “common mode” for how it is wired in the enclosure. For example, a saved test should be named something like “7448052001_cm_4kv”.

Now that you have completed the test and saved the results, use a USB flash drive to move the files from the oscilloscope and test receiver to a computer. Once you transport the results to the computer open the pre-made Excel spreadsheet for plugging in the test results. After that open the results from the oscilloscope and test receiver in excel and use ctrl + shift+ down arrow to highlight all of the test points of that test. Next press ctrl + c to copy the numbers. Now go to the spreadsheet and paste in the oscilloscope results in the oscilloscope tab and the test receiver results in the test receiver tab.