945 seat motor fire

Discussion in 'Volvo 940' started by Howard Nelson, Apr 4, 2005.

  1. Today while my daughter was driving our 1993 945T began to release smoke
    from under the drivers seat (memory power seat). Pulled over, shut down
    engine and got out. Smoke continued and then flames rose over the front edge
    of the seat. Fire was put out with extinguisher and on examination all the
    electronics (motor, controller, wiring) under the seat was fried and the
    carpet and seat upholsetery burnt.

    I can understand electrical shorts and the resultant heat but the 30A fuse
    controlling the seat had blown so why did the motor/controller burn up and
    start a fire? The problem was the seat motor and not the seat heater. No
    other fuses blew.
    Anyone had something like this happen to them? Any thoughts why burning
    continued to the point of flames when fuse had blown (oil from motor?)? Any
    source for replacement parts or seat (nothing good on ebay at this time).
    Thanks for any information you can provide.
    Howard
     
    Howard Nelson, Apr 4, 2005
    #1
  2. Howard Nelson

    Glenn Klein Guest

    Contact Volvo Customer Service & tell them what happened as this is a
    issue that I have not run in to yet. Do not know what help they may or
    may not offer you but it can not hurt to go on record with them about this
    Glenn

    --
    "*-344-*Never Forgotten"
    Is for the New York City Firemen who lost their lives on September 11,2001.
    The official count is 343, but there was also a volunteer who lost his life
    aiding in the initial rescue efforts. And I will never forget them as
    long as I live,
    nor should any American.
     
    Glenn Klein, Apr 5, 2005
    #2
  3. Howard Nelson

    James Sweet Guest

    Yikes! Can you tell where the fire started? Was it the motor itself or the
    wiring? It's entirely possible that a wire chafed, grounded out, and had
    enough resistance that it didn't blow the fuse before heating up hot enough
    to burn the insulation off, though it does surprise me that it actually
    caught fire, that's kinda scary.

    Best I can suggest for parts is a wrecking yard, or see if you can file an
    insurance claim and get the parts from Volvo, but a wrecking yard is sure to
    be far cheaper, even a nicer one with newer cars.
     
    James Sweet, Apr 5, 2005
    #3
  4. What probably happened is that the seat heater overheated and shorted to
    the motor and burned out the motor fuse but continued to burn the seat.
    That explains why when the fuse burned out it didn't stop the fire, it
    was the wrong fuse. The seat heater can cause a fire and does when the
    thermostat fails.
     
    Stephen Henning, Apr 5, 2005
    #4
  5. Seat heater is fine. Fire under seat centered at motor and controller unit.

    Howard
     
    Howard Nelson, Apr 5, 2005
    #5
  6. Howard Nelson

    James Sweet Guest

    It was probably the wire, or maybe a connector that overheated. I've shorted
    a couple wires connected to high current 12v sources before and it's
    shocking how quickly the insulation practically vaporizes, though I haven't
    yet had one actually catch fire.
     
    James Sweet, Apr 6, 2005
    #6
  7. What is there to burn in a motor? The control unit is the biggest
    candidate. I had a smoke detector that started a fire. Control
    circuitry can start fires easily. When I was a physicist at AT&T, one
    of my jobs was designing electronic components so they were not
    flammable. The plastic parts are very flammable and once the fire is
    started the fire continues even after the fuse blows. We solved the
    problem by making all components connected to the power source
    non-flammable. They were made of flammable resins but were designed so
    they would always fail safely by cracking before they ignited. This
    always prevented a fire.
     
    Stephen Henning, Apr 6, 2005
    #7
  8. The fuse is to keep the wire from catching on fire. The way to prevent
    fires is to have a smaller section of bare wire that melts before the
    insulation catches on fire (i.e., a fuse or fusible link). When I did
    this type of work I had a 200 amp power supply and could make just about
    anything catch on fire.
     
    Stephen Henning, Apr 6, 2005
    #8
  9. Howard Nelson

    James Sweet Guest


    Reminds me that I should really get fire extinguishers to keep in my cars,
    I've seen enough cars of all makes burned to a crisp in junkyards and heard
    just enough stories that a $20 compact extiguisher is cheap insurance.
     
    James Sweet, Apr 9, 2005
    #9
  10. Howard Nelson

    James Sweet Guest

    In an ideal world the fuse would always blow to prevent a fire, but it's
    entirely possible for a connector to corrode enough to limit the current
    just enough to burn up the wire without actually blowing the fuse.
     
    James Sweet, Apr 9, 2005
    #10
  11. This I don't believe. I spent a lot of time flame testing wires and
    only wire smaller than 20 gauge would burn at less than 20 Amps. The
    rating on wire is not for flammability, but voltage drop. At their
    rated currents they don't even get warm.
     
    Stephen Henning, Apr 9, 2005
    #11
  12. Howard Nelson

    Mike F Guest

    I've seen heat damage in a circuit where the fuse doesn't blow, but it's
    always been at some sort of connection, where I guess resistance from
    poor contact can create enough heat to cause melting and fires.

    --
    Mike F.
    Thornhill (near Toronto), Ont.

    Replace tt with t (twice!) and remove parentheses to email me directly.
    (But I check the newsgroup more often than this email address.)
     
    Mike F, Apr 11, 2005
    #12
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.