Electromagnet Solenoid Project

Discussion in 'The Projects Forum' started by jsvwx, Mar 17, 2014.

  1. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    0
    Hi,

    I'm looking to add this 88 LB (40kg) Magnet Electromagnet Solenoid to hold together this gate for a bike project. When magnetized, the electromagnet will hold the steel plate on the gate and when de-energized the gate will drop flat onto the ground.

    I'm looking for a circuit diagram to wire this. Aside from a 12VDC battery source, a switch and the electromagnet, what else would I need? I'm guessing a relay, cap and diode maybe? Someone who I met once and had built one of these circuits gave me a 16VDC 33000uF cap to use, but I just want to verify this. Any help preferable with a circuit schematic will be appreciated. Also if you can provide the specs of the parts needed to make sure I buy the correct parts.

    Thanks!

    $_57 (1).JPG

    startgate3.jpg

    startgate1.jpg
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    I don't know what the cap would be used for.

    Just use an on/off switch. A diode across the switch will make it last longer.

    Is this something that will be energized for long periods?

    Seems a solenoid released latch would make more sense.:confused:
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,145
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    +1
    You could still use the same solenoid, just have it pull on a latch that then allows the door to drop. You only need to pulse the coil for a second.
     
  4. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    Thanks for the quick reply. Basically a rider balances at the gate for up to 30 seconds. When ready I would hit the switch, which would open the circuit and drop the gate, so that he would ride off. So to answer your question, I would keep the magnet energized for 30 seconds up to 1 minute maybe.

    I've seen the solenoid releases, but I've never seen them used for these gates. The magnet has to be strong enough to hold the rider and his bike on the ramp, so maybe it's a better solution - IDK?. Maybe the cap was recommended to store a charge for a quicker release?
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,173
    397
    What is the trigger source?
    Coil resistance?
    Current or watts?
    If just switch, or relay activated, then maybe just a diode across coil to prevent switch point welding.
     
  6. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    So to make sure I'm understanding you, I wouldn't use the electromagnet anymore and just use a plunger-type solenoid to release the gate sort of like a door lock?
     
  7. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    Right now I don't have any parts yet. I want to verify exactly what parts I will need to buy to built this circuit. What do you recommend?
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
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    For short times you may be on the right track.

    The mechanical release designs can be tricky. You don't want it sticky.

    You're way is foolproof if you don't lose power.

    With the right design, a latch would be stronger. But it must be leveraged to allow quick release under load.
     
  9. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    So if I stick with the original eletromagnet, what else do I need?
     
  10. wayneh

    Expert

    Sep 9, 2010
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    You might want to look at an existing commercial product.

    The slow part of the process will be the falling of the gate. My idea was a mechanical latch to hold it closed, with your magnet pulling that latch out of the way. The magnet doesn't have to be strong enough to hold the gate and it only needs to be active very briefly. Someone must have solved the mechanical latch issue, so that the latch moves easily even if there is pressure on the gate. I tried to find an example but only found the link above so far. Otherwise inwo's caution is relevant.
     
  11. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315

    Just a switch and a diode.
    The diode is connected across the coil to protect the switch.
    Technically not needed if the switch is heavy enough.

    Or use a bosch relay or starter solenoid from an atv, if the magnet draws over 10 amps or so.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    I was surprised to learn that horse racing gates use your active-on strategy, in part because it allows the gate to open if a horse hits it with enough force to overcome the magnet. Prevents injuries, and that could be relevant in your application as well.

    The gate opens when the power is cut.
     
  13. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
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    That's a good thought.

    I'm concerned that It might not release instantly unless there is considerable force against it.

    Maybe that's why the capacitor was recommended. For forced commutation.:confused:

    I've no luck finding a suitable release mechanism.

    Here's one I made for a 2000lb parasail release.:D Not adaptable for this though.
     
  14. jsvwx

    Thread Starter New Member

    Sep 9, 2012
    11
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    To release the gate quickly, I'll add a bungee cord like the one in my original post to help pull the gate down once the magnet releases. Does the cap help? If so does it get wired in series between the relay and the electromagnet and will the 16V 33000uF cap work that I already have?

    How does this schematic and parts list look:

    12VDC 10W 88 lbs. Electromagnet
    http://www.ebay.com/itm/88-LB-40kg-...993?pt=LH_DefaultDomain_0&hash=item27be44a7d1

    12VDC 7200mAh lantern battery
    http://www.batterymart.com/p-rayovac-926-12-volt-lantern-battery.html

    12VDC/3A DPDT Plug-In Relay & Socket
    http://www.radioshack.com/product/index.jsp?productId=2049720

    NO and NC momentary switches
    http://www.radioshack.com/product/index.jsp?productId=2062541



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  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
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    That type of magnet is often used in material lift operations and once energized with the metal surface in contact with the magnet, not only is there residual magnetism that helps attraction once the power is removed, but it also requires much less current through the magnet when it is in the holding condition, IOW the power can be reduced, usually there is, and often has to be in place, a reverse shot to release the object being attracted by the magnet.
    Also you might want to look at GellCell batteries for recharge and economy.
    Max.
     
  16. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    What's involved in the reverse shot you mention - in getting the object to release? Is that where the cap comes into play?
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Probably the cap was used for that in conjunction with a couple of relays.
    Just as in a lift and drop circuit.
    Max.
     
  18. jsvwx

    Thread Starter New Member

    Sep 9, 2012
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    0
    Does the capacitor get wired in series between the bottom relay switch and the EM? If yes, then would the + polarity of the cap face the relay and the - face the EM? The way I'm looking at it, the cap gets charged once the start button is pressed, which would also turn on the relay and energized the magnet. Once current to the relay is cut, the cap will quickly discharge and quickly releases the EM...am I on the right track here?

    What's the purpose of additional relays? Anyway to attach some type of schematic?
     
  19. inwo

    Well-Known Member

    Nov 7, 2013
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    No. Adding the cap across the coil will slow the release.

    Use a second set (DP n.o.) of contacts to route power to the capacitor charging it while magnet is "on".

    When the release button is pressed, the relay opens and the capacitor is connected thru nc contacts to the magnet coil. Polarity reversed.

    That may not be needed. Or just connecting the discharged cap to the coil may be enough.

    Max may have a standard diagram. I'd have to draw one as google didn't find one.
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have done design work on scrap yard Loco cranes (100amp/240vdc magnet).
    I could post a modified relay control circuit if you need it?
    Max.
     
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