VFD beginner question. 1

[fabiosm]

Hello,

I'd like to know which measureaments are necessary to verify the rectifier module, capacitors and IGBT's of a VFD.

Thanks.

 

[itsmoked]

Just the classic measurements to test those type components. Google it/them.

If it's a VFD under a few hp - just run it. If it has a problem with the IGBTs it will probably tell you. Use a clamp-on to see if the three phases supplying the drive are pretty close together. If they're not, but the voltages are the same, you have a bad rectifier.

You can do the same test with the outputs. The actual amp numbers will be complete and utter garbage but they should be very similar.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[fabiosm]

Thanks Keith.

I posted this thread because I came across a case this week of a VFD displaying a short circuit fault message. When I replaced the output IGBTs, the drive stopped displaying this message and started working perfectly again.
The problem is that, when I measured them, they didn't appear to have anything uncommon. The test that i made was using a multimeter in diode scale.

Thanks,

Fabio Melo

 

[DickDV]

An output short circuit fault with the motor leads disconnected is usually a shorted IGBT. They will generally short when they fail but, in your case, they didn't.

Sometimes, at a test voltage of 1.5V, the short will not appear where, at operating voltage of 660VDC, it will. That's probably what happened with your drive. You did the right thing.

 

[jraef]

LPS for Dick. Too often people trust that little battery in their DMM for everything.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[ScottyUK]

Completely correct Dick.

Many modern meters deliberately test resistance at less than 0.6V to avoid forward-biasing any semiconductors. It is very easy to be misled - you need to understand the capabilities of the instruments.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Often when set to their highest resistance scale they change to supplying substantially more voltage, like 9V or the reference voltage.

Keith Cress
kcress -

http://www.flaminsystems.com