SU3000RMXL3U

[MarkC_apc]

I was cleaning/testing a used SU3000 that I had purchased in unknown condition.  The battery tray was connected with a slight arc (seems typical).  However, when I applied 120 volt AC, there was a definitive "spark" that seemed to originate around the front of the H bridge heat sinks.  I could not see any visible damage, so I continued testing.  The unit started up, ran a 20% and 70% load on batteries  without any problems.  The batteries are charging.  No "events" were logged, and self test passed.

The unit was not extremely dusty/dirty and was gently cleaned with compressed air before any testing was done.  I was certainly surprised that the unit seems to function fully after any arcing around the motherboard.  Any explanation for this "spark" that seemingly did not damage the unit?  I have an oscilloscope - should I check the output wave form?

Any suggestions are appreciated.

[MarkC_apc]

After closer inspection, it is apparent that mosfet Q78 failed as the case is split.  All four heat sinks are fully populated on this unit.  Is it possible to continue using this unit - maybe at a reduced back up load?  Or is it likely that this is the beginning of a chain reaction failure.  The unit was manufactured in 2007.

If I replace this one mosfet, can I expect to have reasonable service out of the unit?

[BillP]

Mark, as I am sure you're aware, Schneider/APC doesn't recommend, condone or otherwise support repair of these units.

I find it amazing that the unit continues to work in spite of the fact that one of the transistors failed (failed open, obviously).  Also speaks to the excellent design of the unit.  Several of those "Q's" must be in parallel to support increased current capabilities and loosing one or more would put added stress on those that remain.  That being said, sure, why not get another one and try and keep the unit working?  You, of all people, should have no problem getting in there and messing around.

Good luck! 

[MarkC_apc · Accepted solution]

Joe;

Yes there are a total of 32 of the mosfets - 8 on each section of the "H".  Fully populated heat sinks.  I'm going to check on some "spare parts units" to see if I can find a similar rated transistor and do a "repair".  Not much to lose on this one.  Everything else looks - so why not!

Thanks, Mark