Electronics gurus: Wiring a fan-off warning light?

Discussion in 'Fox 5.0 Mustang Tech' started by Mustang5L5, Oct 22, 2006.

  1. Tried to figure out how to do this myself but figured i'd get some input.

    I have an SN95 electric fan operating off a Bosch 75A with just a toggle switch turning it on and off.

    WHat i want to do is put a nice bright yellow warning light on my A-pod right next to my water temp gauge. I want to set it up so that anytime the fan is physically not on, the light illuminates. That way I am aware of the times i leave it off (drag strip passes) and if it fails on me at anytime.

    I don't want to wire it to the toggle turning the fan on or off. I want it tapped in somehow to the fan itself so if it every physically fails the light will go on.

    So, how would you do it?
  2. I hope someone figures out how to do this! I spent half an hour trying to think of a way to to do it and came up empty handed...sorry to say. However, I'm definately not an electroics guru, a novice at best. I bet HISSIN or Jrichker will have an idea or two.

    This has me stumped:shrug:
  3. Wouldn't it be easier to wire a light to be on when the fan is on? You could just wire a light inline with the wire going from the toggle switch to the fan, that way when you have the toggle switch on, the light will be on.
  4. I was thinking of doing it in a way that would physically measure the draw going through the wiring to the fan. Then i'd hook up the ammeter to the relay to trigger the light.

    Only negative i can see from this is if the fan shorts internally and still draws power but doesn't spin. That got me thinking that the best way to do this might be something that measures the fan physically moving if i can't figure out a way to do it electrically.
  5. But that doesn't cover the main reason why i want this warning light. If i flip the fan on, the light will go on too. But what happens if the fan motor shorts out and fails? The light will still be on because i'm still powering the relay.

    I want the warning light tied directly to the fan somehow that way if the fan fails for some reason despite the relays working fine, i will know about it.
  6. If your Bosch relay is SPDT, one set of contacts is closed then the fan is on. The other set of contacts is open when the fan is on. When the fan is off the set of contacts that were formally off are now on. Wire the indicator to that set of contacts.

    Wire sizes:
    Fan power feed & Fan ground 10 gauge stranded wire.
    Fan controls, relay & LED's 18 gauge stranded wire.

    Surge Dampner Diode: 1N4003

    Fuse: 30 Amp automotive or circuit breaker
    Green: Radio Shack #276-271
    Red: Radio Shack #276-271

    No external resistor is needed, since the LED's are designed to run on 12 volts.


    Detecting a total fan mechanical failure is possible, but is much too complicated to communicate over the Internet.

    If the fan shorts, it will blow the fuse & neither LED will glow.

    Attached Files:

  7. Unfortunately that's what I want to do. :(

    Any suggestions to make? I'm pretty good with circuits and electonics in general but i'm just blanking on an approach to take for this
  8. You'd probably need a shudder/reluctor type sensor (one part on a fan blade and one fixed on the shroud), and some sort of means of processing the whole event.
    That's where you and Joe would have to chat on the phone and spend some cash to make it work.

    It's something I once considered but never got too far with. I have simple used a panel type light for manual switches and it works well. Generally the temps and volts (system bog, even with a 160 alt) let me know if something didnt kick on or stay on.

    Good luck with engineering something Mike. :nice:
  9. The principal would be to use a hall effect magnetic sensor and then mount a magnet on the fan blades. The rotating magnet would trip the hall effect sensor everytime it came around.

    Use a 555 IC wired as a missing pulse detector with the hall effect sensor to trigger it. The continous triggering of the 555 input would cause the 555 to stay on. Use an inverter IC and you can drive a LED to whatever state you want when the required pluse is missing.

    The major problem to overcome is the mounting of the magnet & hall effect sensor. The electronics are simple stuff.

    See http://home.cogeco.ca/~rpaisley4/LM555.html#22 for information on how to build a missing pluse detector circuit from a simple 555 or 556 timer IC.
  10. Nice, looks like i have some reading and research to do one of these nights. Thanks
  11. Just train one eye to stay on the temp guage... :D ;)
  12. Yeah but then i don't get to have fun designing and building something useful :D
  13. If you didnt want to mount anything on your fan blades a motion detector mounted by your fan would work. It would show other motion tho, but if it was almost constantly on then you know the fan is on.

    The magnet mounted on the fan blade i think is more accurate though.
  14. One question though.

    With the fan off, and the car at speed on the highway, won't the fan blades turn anyway??
  15. Yes. You will need an extra logic gate or relay in line with the display LEDs to take care of that problem.