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activating reed switch

Discussion in 'Electronic Basics' started by lerameur, Jul 26, 2008.

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  1. lerameur

    lerameur Guest

    Hello,

    I made myself a small electromagnet to activate a reed switch using a
    6v supply. The problem is that I am pulling 3 amps, I do not want the
    electromagnet to be bigger by making more turns, I believe there are
    such electromagnet on the market that can activate a reed switch with
    current in the milliamps. anybody know such device, I looked at
    digikey and mouse but I did not find anything under electro magnet.

    thanks

    ken
     
  2. You could also try a capacitor and resistor in parallel to drive a quick
    surge of 3 amps to activate the reed relay, and the resistor to provide
    just enough current to keep it activated. I have done this to operate AC
    relay coils using DC.

    Paul
     
  3. Bob Eld

    Bob Eld Guest

    Yes they have reed relays that draw 10mA at 6 volts. Three amps means you
    don't have nearly enough turns and, of course, the wire you are using is a
    1000 times too fat.

    If you are serious about it you'll have to wind them with AWG 44 or thinner
    wire. Good luck finding that. Good luck winding that with 10,000 turns. Not
    a job for the timid.

    Look for reed relays under relays. Jameco has them.
     
  4. That brings up what the original poster is wanting to use this for.

    I was going to say "well can't you buy coils to activate them" and then
    I realized standalone reed switches are mostly activated by a permanent
    magnet.

    So there either has to be a better way, or the poster needs a different
    method.

    Figure out a mechanical system to move the permanent magnet in close
    to activate the switch.

    Take apart an existing relay for the coil, and use that.

    Or figure out why a normal relay can't be used; there may be
    reasons, such as the reed switch has a more direct contact for
    RF use, but there really should be a good reason to do it this
    way rather than a "normal" relay.

    At this point, I'm even willing to believe that the original
    poster is unaware of regular relays.

    Michael
     
  5. ehsjr

    ehsjr Guest

    I'm wondering if the op isn't envisioning something like this:

    reed
    ---====---
    (||)
    (||)
    (||)
    +_(||)_-

    Coil around a core, core at 90 degrees to the reed,
    with maybe a bolt or nail as the core.

    Ed
     
  6. Zagan

    Zagan Guest

    Ken,

    I use to work for a company that made pneumatic and hydraulic cylinders
    (with rods coming out of one or both ends). We used reed switches and
    electronic magnetic sensitive sensors to detect the rod(s) extension (see:
    http://www.fabco-air.com/products/sensors/sensors.html). Since I was the
    only engineer there that knew one end of a battery from the other, I was in
    charge of designing these magnetic sensors. We used a magnet ring mounted
    around the piston heads of our cylinders and the end user could place the
    sensors wherever alone the length of the cylinder to detect the extension(s)
    of the rod(s) and send that signal to a PLC or whatever.

    Anyway, my point here is that perhaps you could use a solenoid or similar
    device to move a permanent magnet back and forth to activate/deactivate the
    reed switch. Magnets are cheap as are most low-power solenoids. There is no
    need to make your own electromagnet to operate the reed switch. And 3 amps
    is certainly excessive when some current in the milliamp range would do the
    trick as described above. Look up solenoid at digikey, etc.

    Hope this helps,

    // Jim
    http://members.atlantic.net/~jcd/
    http://www.writingservicesunlimited.com/
     
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