Drop Out Relay Circuit

Discussion in 'The Projects Forum' started by Oxbo Rene, Jul 6, 2009.

  1. Oxbo Rene

    Thread Starter Active Member

    Feb 20, 2009
    Years ago (DOS-5, 286mhz days) I had my first computer running along nice and smoothly, then, in a lightning storm the power went out, and, just a second or two later it came back on.
    However, my computer went dead.
    Called up a friend who was quite fluent in computer mechanics, and asked him what could've gone wrong.
    He zips over to take a look, says that when one cuts off computer the head/heads, go to "park" position. Says that possible scenario is that when heads went to park, and, power came back on, heads returned to original position, but, apparently wiped out the FAT table as it returned (something like that).
    He gave me a circuit for a drop-Out-Relay that would keep the computer off if/when the situation ever occured again.
    I realize I could mess with the switches to be a little better, but, never have. I made this circuit and it has performed perfectly for years now. And, it has been utilized many times.
    What this does for me is to eliminate having to buy/maintain one of those battery deals that
    Keep power on till ya save and cut system off, etc, etc.
    Ain't never had one and never seemed to need one with this setup.
    Yep, computer cuts off unexpectantly but have "NEVER" had it mess up, lost a few documents/e-mails in the process but, never a machine malfunction.
    The relay was a heavy duty plug-in type I got out of an old welding machine.
    I just thought I'd share this with ya'll if anyone doesn't want to put out the bucks for a battery thingy (I can't think of the name for those things at the moment) but would like a way to prevent HD failure due to PWR going out.......
    I did send in my faulty HD and got a new one....
    Have a nice day,
    Last edited: Jul 6, 2009
  2. Wendy


    Mar 24, 2008
    Your schematic seems flawed, unless you push S1 and S2 at the same time. Neither S1 or S2 will energize the relay by itself, both have to be pushed to give the relay coil power.

    S1 could be across S2, or you could eliminate S2 altogether. What switches S2? If it is part of the relay then it wouldn't switch separately as shown.
  3. eblc1388

    Senior Member

    Nov 28, 2008
    S2 is the main ON/OFF switch. It is needed to turn off the power.

    I would, however, place it as the very first part of the circuit though. The circuit then become:

    1. a ON/OFF switch as the first control element
    2. a relay self hold circuit *After* this ON/OFF switch to switch power to the output sockets.
  4. Oxbo Rene

    Thread Starter Active Member

    Feb 20, 2009
    Mornin ya'll;
    Yeah, as I said, if I took the time I could improve it (switch functions).
    But, I made it a long time ago and it has always worked as is, so, just never got around re-rigging it.
    I was digging around in my Electronics projects file last night and ran across it and thought I'd throw it up here on the forum, etc.
    It does offer a sort of security system for the computer as one has to push the on/off switch (located on the front of the unit box) then reach to the back of the unit box and push the other button in order to activate the unit, then, one can cut the computer on.
    This keeps curious visitors (kids) from messing with it, even though I really don't know if anyone has deftly tried to turn on the computer when I'm not here anyway, and then, they'd have to get the password correct, etc.
    Improvements are certainly welcome.........
    (Bill, that ckt explanation for drawing #1 is misleading, S2 is just a regular SPST switch).
    Last edited: Jul 7, 2009