Connect with us

MOSFETs heat sinked to case power inverter safety.

Discussion in 'Troubleshooting and Repair' started by Magicsmokemaker, Feb 20, 2016.

Scroll to continue with content
  1. Magicsmokemaker

    Magicsmokemaker

    5
    0
    Feb 20, 2016
    Hi all my first post on any site ever! I am fixing a cheap Chinese power inverter 12v DC to 220~240AC it blew a MOSFET on the 240v output side. Now here's the problem the output MOSFETs are heatsinked directly to the aluminium case they are K15A50D by Toshiba in a 220f case i.e. the drain is insulated. I don't have any to hand and they are £10 each from ebay ! I want to swap all 4 output MOSFETs for cheaper alternatives which will be in 220 cases I.e. the drain is connected to the metal mounting tab. Is it safe to use some of that grey coloured rubbery sheet to insulate the MOSFETs from the case?
     
  2. Anon_LG

    Anon_LG

    453
    117
    Jun 24, 2014
    Please elaborate.
     
  3. Magicsmokemaker

    Magicsmokemaker

    5
    0
    Feb 20, 2016
    I believe it is a good thermal conductor and electrical insulator often sandwiched between a heat source and heatsink grey in colour and often smeared with a white greasy compound. I don't know what it's called and found it twice in power inverters and once on a radio controlled electronic speed controller.
     
  4. Anon_LG

    Anon_LG

    453
    117
    Jun 24, 2014
    From what I have read, this is a good thermal conductor and a good electrical insulator. So yes, this will be fine for electrical insulation, I was merely unsure whether you were referring to generic grey foam sheet, this would not have worked. Read here, this is where I checked.

    I hope this helps,
     
  5. Magicsmokemaker

    Magicsmokemaker

    5
    0
    Feb 20, 2016
     
  6. Magicsmokemaker

    Magicsmokemaker

    5
    0
    Feb 20, 2016
    Thanks for the speedy reply could I earth the case somehow in case of insulation breakdown? The case currently has no connection to anything electrically its in mid air so to speak.
     
  7. Anon_LG

    Anon_LG

    453
    117
    Jun 24, 2014
    Grounding, this is usually best left to the advice of an electrician, rather than an electronics hobbyist.

    I assume that you are familiar with the purpose of an earth return? To enable a more conductive path to earth should the device become hot and the body is touched, ie, an internal short electrifies the metal body with 240 volts RMS relative to neutral, the neutral is connected to earth at the breaker box. A person touching the box should be more resistive than the copper wire going to earth, rendering the device saf(er).

    Does the device have any connection to mains? If so it MUST be earthed asap. Whatever you do with earth, I do not think it will protect the FETs. Without the drains connected to the box (the insulator being intact) will the drains be connected to anything?

    Is it definetly the drains and not the bodies that are connected tab?
     
  8. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    Refine your search (select international sellers)
     

    Attached Files:

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-