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FAQ :: VFDs | How Do I Test The IGBT Power Section On My Drive?

One of the more common problems seen in our Variable Frequency Drive (VFD) repair division is the failure of the IGBT (Insulated Gate Bi-polar Transistor) power section modules.

If the Variable Frequency Drive (VFD) is blowing fuses, or the VFD simply is not turning on, the following test may aid you in finding the root of the problem.

A digital voltmeter test can tell if a short exists from the input side of your IGBT power section modules to the output side without having to take the whole VFD apart to inspect them.  An alternative, more costly test is done by simply replacing the fuses that have blown, then turning the power on.  This is costly because if the short exists, after turning on the power you can expect a boom that will hit you yet again for $100.00 fuses. The digital voltmeter test could save money, fuses and the embarrassment of aVFD blowing up in your face.

Digital Voltmeter on Diode Test:

Every AC Variable Frequency Drive (VFD) has a section called the DC buss. This section is the output of the IGBT‘s. The terminals are often labeled DC+ and a DC-. The preliminary requirements to the Digital Voltmeter test include:

  1. Locating the DC+ and DC- terminals on the VFD. They are usually located near the input and output terminals.
  2. Locating your input and output terminals, and if you located your buss already you have found these terminals.
  3. Make sure that there are no input or output leads connected to the VFD because this will effect the readings on your meter.

Now that the right terminals have been located, proceed with the following steps to test the IGBT power section:

  1. Turn the voltmeter settings to Diode check. It looks like this  ->I-
  2. Take the positive lead on the voltmeter and put it on the DC- terminal of the VFD.
  3. Now take the negative lead and put it on each input and output terminal of the VFD one at a time.
  4. If a terminal is good, it should return anywhere from a 0.299 volt to a 0.675 volt reading on the meter.
  5. Now repeat the same process the opposite way.
  6. Take the negative lead and put it on the DC+ terminal.
  7. Now take the positive lead and put it on each input and output terminal of the VFD.
  8. Again, one should expect the same readings as in step 4.
  9. If the meter returns a reading of 0.000 – 0.100, the IGBT is shorted and needs changed.  These readings could result in blown fuses or even more costly damages.
  10. If the meter returns a reading of more than 0.750, it is possible the contact is open or there could be other devices with issues between the IGBT and the terminal. If this is the case one should contact their local electronics repair shop or contact us during our store hours to resolve the issue.

There are many things that can go wrong with Variable Frequency Drives (VFDs).  The failure of the IGBT power section is one of the most common.  Educating yourself and understanding how the technology works is the first step in saving both you and your company money.  Often times, you will find the electronics repair shop who does work for you will appreciate the preliminary troubleshooting you have done before you called.  This can result in less cost to you and less diagnostics work for them.

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