[valerun]

Originally Posted by jackbauer

Can you measure Vce sat? Might give you an indication of which one is taking the bulk of the current.

can try. need to read up on that ;-)

Also, after reading through the SEMIKRON doc you posted on the other forum (attached), I realized that my incoming DC connections might not be routed right. Here's what I have:

DC "-", Motor "-"  ========================

                   ========================  DC "+"
                    Q1     D1     Q2     D2 
                   ========================  Motor "+" (or "AC")

So that might be the reason for uneven sharing - when IGBTs (Q1 and Q2) are on, conduction path is from DC "+" through Q1 & Q2 to Motor "+", then through motor, then to Motor "-"/DC "-". Therefore "ON" path is skewed towards Q2 (which is exactly the side that heats more). When IGBTs are off, conduction path is from DC "-" through D1 & D2 to Motor "+", then through the motor back to DC "-"/Motor "-". Therefore "OFF" path is symmetrical.

So I gather that I need to move DC+ cable to the left side.

Am I on the right track?

V