# Cnc vfd problems



## lefleuron (May 22, 2010)

Now I cannot be positive here, but I think you probably have IGBTs instead of SCR's.

The only things I can think of is either the drive is somehow wrong electronically, or...and this is a long shot..there are diodes that shunt motor produced voltage/current around an IGBT when the motor overhauls. If those diodes are not working, the IGBTs will take a pounding and not last.

If the tech finds an exact answer, please let us know. I have heard of one or two go out, but never all 6 at once.

How far above base speed (motor rated RPMs) are you running this?


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## GEORGE D (Apr 2, 2009)

I failed to mention that it wasn't all six, just one of the six. E tech says that it's recommended that when one goes out you change all six(something about the rest get affected). As far as speed goes, I have no idea. Oh and as far as IGBT's go, your probably right right. I've always heard of SCRs in bigger drives but he did say they weren't SCRs but same idea. I'll share everything I encounter come next week, but any help as what to look for is much appreciated, tnx.


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## wdestar (Jul 19, 2008)

One of the problems that I've run into over the years is the flexible raceway tracks provided for the motor conductors. Sometimes the constant bending and/or friction of the insulation rubbing against the raceway proves to be a problem.

Another problem could reside in neither the motor nor the power module, but rather in the control board.


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## lefleuron (May 22, 2010)

If its only one, make sure the tech checks over whatever shunts that feedback voltage from the motor around the IGBTs, and back to the bus. That really sounds like a diode or whatever that maker uses for that purpose.


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## bill4807 (Jan 4, 2013)

Hi there, 

I would first make sure the motor was repaired properly.

Once you verify that if the electronic tech changed the IGBT's ask him if he did a full repair, since the driver circuits for these IGBT's consisting of resistors capacitors and transistors, can cause the power modules to blow again and again. Also check and make sure the motor cables are not shorting out since the cables on the spindle are constantly moving. These are the only ways:
Motor still bad
Not a complete drive repair
Bad cabling
Ask the customer if the drive blew while the motor was in the process of stopping if so the braking discharge circuit in the drive may not be shunting the generated energy from the motor as another post said.

Thank you
Bill


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## Jabberwoky (Sep 2, 2012)

bill4807 said:


> Hi there,
> 
> I would first make sure the motor was repaired properly.
> 
> ...


Hey Bill, The post date on this thread looks a little old.


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## bill4807 (Jan 4, 2013)

Yea you are right. lol i guess i wasn't looking at the date when I replied. Now I am looking at dates. Thanks


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