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

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One of the more common problemsseen in ourVariable Frequency Drive (VFD) repair division is the failure oftheIGBT (Insulated Gate Bi-polar Transistor)power section modules.

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

A digital voltmetertest cantellifa short existsfrom the input side of yourIGBT power section modulesto the output side without having to take the wholeVFD apart to inspect them.An alternative, more costlytest 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 againfor$100.00 fuses.The digital voltmetertest could savemoney, fusesand the embarrassment of aVFD blowing up in your face.

Digital Voltmeter on Diode Test:

Every ACVariable Frequency Drive (VFD) has a sectioncalled theDC buss. This section is the output oftheIGBT‘s.The terminals are oftenlabeledDC+ and a DC-. The preliminary requirements to the Digital Voltmetertest include:

  1. Locating the DC+ and DC-terminals ontheVFD. 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 theVFD because this will effect the readings on your meter.

Now thatthe right terminals have been located, proceed with the following steps totest theIGBT power section:

  1. Turnthe voltmetersettings toDiode check. It looks like this ->I-
  2. Takethe positive lead on the voltmeter and put iton the DC- terminal of theVFD.
  3. Now takethe negative lead and put it on each input and outputterminal of theVFD one at a time.
  4. If a terminal is good,it should returnanywhere from a0.299 volt to a 0.675 volt reading onthe meter.
  5. Nowrepeat the sameprocess the opposite way.
  6. Takethe negative lead and put it on the DC+ terminal.
  7. Now takethe positive lead and put it on each input and output terminal of theVFD.
  8. Again,one shouldexpect the same readings as in step 4.
  9. Ifthe meter returnsa reading of 0.000 – 0.100,theIGBT is shorted and needs changed.These readings could result in blown fuses or even morecostly damages.
  10. Ifthe meter returns a readingof more than 0.750, it is possiblethe contact is open or there could be other devices with issuesbetween theIGBT andtheterminal. 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 withVariable Frequency Drives (VFDs). The failure of theIGBTpower 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 beforeyou called. This can result in less cost to you and less diagnostics work for them.