How the heck does a Solenoid work? Diagram anyone?

Discussion in '40- & 55-Series Tech' started by sonoranfun, Jul 21, 2005.

  1. sonoranfun

    sonoranfun

    Messages:
    572
    Likes Received:
    0
    Joined:
    Apr 17, 2005
    Location:
    Tucson, AZ
    Okay, got a 35amp switch and I quickly see that my electric fan blows that out so I knew a solenoid would get the job done and have many other uses but I'm clueless on how they work. I assume like a big relay? It's a four post Ford solenoid and I would guess the two larger ones get 12v with the one getting it only when 12v is supplied to either one of the smaller two? Is this correct, could you tell me how they work or do you have a diagram?

    THANKS A LOT!!!
     
  2. dfmorse

    dfmorse

    Messages:
    1,518
    Likes Received:
    2
    Joined:
    Jul 7, 2004
    Location:
    EVERGREEN, CO, USA
    This might help a little:

    http://web.appliance411.com/faq/test-solenoid.shtml

    And yes, its like a relay. Two contacts attach to the coil, when 12 volts from a battery is applied, pulls an armature, a steel pin into the electromagnet thus pulling two larger contacts together with loud clack. These two larger contacts will usually handle very large currents, depending on design..

    David in Denver
     
  3. sonoranfun

    sonoranfun

    Messages:
    572
    Likes Received:
    0
    Joined:
    Apr 17, 2005
    Location:
    Tucson, AZ
    Okay, I know how that type would work for say a shaved door kit but it's this one that I don't get. I assume I can hook the fan up to one of the larger contacts then the battery up to the other but what are the other two for? Do they both just open or close the circut or is one for somehting else?
     
  4. honk

    honk

    Messages:
    3,413
    Media:
    10
    Likes Received:
    367
    Joined:
    Nov 14, 2004
    Location:
    PNW
    I think that what you want to use is a relay, not a solenoid. Although there are solenoids made for long duration apply modes most of them will burn up if they're energized for long because they are a set of points that arc when first connected by energizing their coils. You don't need arcing and no fan needs the kind of current a solenoid can carry. Leave them for starters.

    A relay does what you've described. It is activated by your low current wiring from a switch and when activated it passes direct high current to a high use device like headlights or a fan. Although they really do the same thing they do it without the initial high current blast that makes sparks. Just get a relay rated for the current draw of the fan or a little higher. It'll have "12V - 40A" in the hard to read stuff on the little square plastic case.
     
  5. theo

    theo

    Messages:
    1,432
    Likes Received:
    2
    Joined:
    Feb 19, 2002
    Also, some relays are normally open, some are normally closed, some can do both.

    Terminals:
    30 - constant +12V (hi amp)
    87 - load (normally open)
    87a - load (normally closed)
    86 - switched +12 (lo amp)
    85 - grnd

    You can reverse 30 with 87 and 87a and you can reverse 85 and 86. Not sensitive to current direction.

    You're correct on wiring the big posts. For the 2 little posts, run switched power to either one, ground the other.

    Honk is right about using a starter solenoid. I wouldn't either. You could use a continuous duty solenoid. A few thousand of us are using them in our dual battery setups, but again, it's overkill for a fan ;)
     
  6. CruisinGA

    CruisinGA

    Messages:
    6,168
    Likes Received:
    16
    Joined:
    Mar 27, 2003
    Location:
    Georgia Tech
    check waytekwire.com for a large selection of quality Bosch relays and matching plugs...
     
  7. RHINO

    RHINO

    Messages:
    3,764
    Likes Received:
    4
    Joined:
    Dec 23, 2003
    Location:
    valley of the sunstroke, AZ
    i dont have a diagram but i assume you have a ford starter solenoid??

    the two big posts are 12v in and out, one from batt+ and the other goes to the starter motor (or fan). of the two little ones you will only use one, on the same side as the power supply. that is your switched power source, the fourth is simply a 12v jumper post that would go right to the coil to ensure it gets 12v when starting. you dont need to use the fourth post but you could if you wanted another small 12v power supply. however you DO NOT want to use the solenoid in your application. as mentioned it it designed for momentary and short term use, you will burn it out quickly if used as a relay.

    go down to the auto house and get yerself a relay, simple inexpensive plastic box with four posts, BATT in and out, switch and ground. relays are good.
     
  8. Pin_Head

    Pin_Head

    Messages:
    14,530
    Likes Received:
    2,168
    Joined:
    Feb 6, 2002
    Location:
    OC, CA
    A solenoid is a more general term for an electromechanical consisting of an electroagnet with an iron core that moves inward in response to energizing the coil. When a solenoid mechanical motion is coupled to activate an electrical switch is is called a relay.

    If it is like a Ford starter relay, one big lug is 12+ input, the other one is 12V+ output and one of the little ones is the switch control wire (12V). The other little one is either switched 12V accessory output or a ground if the case is not a ground.
     
  9. theo

    theo

    Messages:
    1,432
    Likes Received:
    2
    Joined:
    Feb 19, 2002
    Geez, I get tired of the taste of my own feet. If you have a starter solenoid you can't run the 2nd "little post" to ground unless you're having a BBQ. Thanks again fellas. :eek:

    At least I'm probablay right about common automotive relays. :rolleyes:
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.