VFD inrush current

[xoom]

Hi, have to fix VFD007L21E. Found that inrush current limiting resistor is almost burned.. when meassuring it shows ~900ohm. And by size its like 2W resistor.. Why its burned and what better nominal to put? btw there is relay across it so its active control.. after caps are charged it should short out that resistos.. tested that relay and its working..

[jmelson]

OK, I assume this is a variable frequency drive (not vacuum fluorescent display).

If it has a resistor to slow-charge the capacitor bank, and a relay to short the resistor before starting operation, then either the relay was not operating, or there is an excessive load on the DC side.
These things usually have some kind of voltage sensing circuit that decides when to switch on the relay.  If there is an unexpected load on the DC side, the cap bank voltage may never rise to the level where the relay turns on.  That will smoke the resistor for sure.  Possibly there is a shorted transistor in the inverter section.

When you say you tested the relay, do you mean you tested it alone?  Then the circuit that controls the relay may be bad, or as I say above, the caps may never charge to the required voltage.

Jon

[Paul Moir]

Happen to be repairing one right now that looks the same.  One motor phase had a short and so the inrush resistor exploded (which was a little surprising!).  The identical unit has a 120 ohm inrush limiter.  I'll be trying out STGP10NC60KD to replace the original, obsolete Fuji Electric 1MB05D-060 IGBTs.  This is the first time I've tried to match up an IGBT so it may not be successful.

Can you post a pic so we can make sure we're working on the same thing?

EDIT:  I guess I can too.  CR1 is where the resistor was. 

[jmelson]

If the IGBTs popped, it likely took out the gate driver chip, too.  From experience, I'd replace the driver for both transistors of that phase, and both transistors of the popped phase, too.

Jon

[Paul Moir]

Yes, fortunately it's easily available:  IR2112.  Mine seem healthy but I ordered one anyway.
EDIT:  Just dropping a note that the repair was successful.  The IR2112 turned out to be fine as did the other phases IGBTs.  I also had to get some new 0.3mm insulating thermal pad covers for the to220 packages.  My version is the Automation Direct GS1-10P5.  I didn't realize how inexpensive the drive was before I ordered the parts.  It certainly doesn't look that cheap on the inside:  nice parts and nice workmanship.  But probably not worth fixing (~$10/phase for IGBTs & driver + $5 for the silpads).