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Hooking up Relay and Switch

Discussion in 'Electronic Basics' started by Andy, Aug 20, 2003.

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  1. Andy

    Andy Guest

    I am going to do some work in my car. So everything I talk about
    should be ~12 volts. I have some electronics knowledge, but I am no
    expert. I plan to use a relay to switch certain things. Here is how I
    plan to hook up the relay (coil side):

    Battery positive to toggle switch
    Toggle switch to relay coil
    Relay coil to ground
    Ground to battery negative (Of course)

    This will not be a short, will it? (Or do I need some sort of resistor
    in there?) The relays I plan to use can be seen at
    http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=RLY-412&type=store
    The important detail (I think) of the relay is that the coil is 72
    ohm.

    Also, is it safe to use DIP switches? I don't know if they can handle
    the current that will go through the relay coil.
     
  2. Kevin

    Kevin Guest

    Andy, don't forget to fuse both your switch and your supply leads. I
    have been in the auto electronics biz for almost 20 yrs and have seen
    many cars that got burnt because of careless (unfused) wiring. Good
    luck.
     
  3. Si Ballenger

    Si Ballenger Guest

    I can't speak for today's cars, but in years past the coil was
    designed to run on ~9v instead of 12v. The reason for this was
    during cranking the system voltage would drop to around ~9v due
    to the very heavy starter pull on the battery. In the start
    position the battery was fed straight to the coil. When the key
    is released back to the run position, the battery was routed
    through a ballast resistor to drop the now system 12v down to the
    9v for the coil.
     
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