FETs for 1000w Grid-Tie Inverter...

Discussion in 'The Projects Forum' started by 2dbit, Mar 18, 2013.

  1. 2dbit

    Thread Starter New Member

    Feb 13, 2013
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    Hmm. Trying to find an alternate FET for this inverter... I have 6 blown IXFP110N15T2 FETs, I was hoping to upgrade them to something more rugged to avoid future failure, but at 110A, I think it'll be hard to beat in a TO-220 package! Even just to replace them with identical units, they're difficult to source...

    Anyone have a good resource for FET interchangeability?
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    http://www.digikey.com/product-detail/en/FDP075N15A/FDP075N15A-ND/3163343

    http://www.digikey.com/product-detail/en/IPP075N15N3%20G/IPP075N15N3%20G-ND/2081152

    (Try to find them on findchips.com)

    First of all 110A would be at 25°C. Your inverter will not run at 25°C.

    Then, AFAIK most manufacturers put a small (almost invisible note on their datasheets saying that the package limit of the TO220 is 75A, regardless of the theoretical limit)

    You should ask yourself why they fail. Maybe 150V isn't enough? Maybe they overheat? Maybe some snubbers around them are damaged and don't fulfill their function?

    From my experience it is easier to kill FETs with overvoltage than overcurrent, especially because most control circuits employ some kind of current limit.
     
  3. 2dbit

    Thread Starter New Member

    Feb 13, 2013
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    I'm willing to bet the cause of failure was due to engineering... I'll get some pictures and load them soon. This board is a disaster.... It's a fleabay inverter, and likely was only robust enough for light duty.

    Heat was definitely a factor. The unit was operating outdoors in AZ, temps over 100deg F....
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    TO-220s also have another problem. When mounted on a heatsink and using thermal pads to isolate them electrically from heatsink they can actually cut through the thermal pad when excessive force is used. I would only trust TO220 with thermal pads if they are fixed with a clip, not with a screw.
     
  5. 2dbit

    Thread Starter New Member

    Feb 13, 2013
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    Well, at least I know the insulator pads weren't the issue. Cleaned them all, and found no punctures... I'll have to look closer at the boards though... Looks to be a couple of burned smd caps
     
  6. 2dbit

    Thread Starter New Member

    Feb 13, 2013
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    Here are some pictures from the underside of the board, pretty ugly...[​IMG][​IMG][​IMG][​IMG][​IMG][​IMG]
     
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