Electromagnets for uncoupling

canoemaker Sep 2, 2013

  1. canoemaker

    canoemaker New Member

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    Does anyone use electromagnets for uncoupling rather than permanent magnets? If so, have you found a way to control them with dcc decoders?
     
  2. DCESharkman

    DCESharkman TrainBoard Member

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    Electro-Magnets can be made by wrapping many loops of wire around a nail. Depending on the winding density, or turns ratio, and the resistivity of the wire, DCC control may or may not be available. This becomes a question of the amount of current needed to setup the proper magnetic field to control the coupling/decoupling. At worst case, you can use a push-button switch, or you may need to use a stationary decoder set for HO or O gauge power to handle the current spike needed. You would also want to decide is you want a North or South pole. This is determined by the direction of the winding. Counter Clockwise turns will give you a North Pole while Clockwise turns will give you a South Pole. ( By convention of the old Right Hand Rule)

    Now the issue is whether either pole will provide the field density to trip the couplers. If not then you may need to use a staple shape where the wire is wrapped around the flat top of the staple. In either case, the magnet needs to be offset from center slightly, because it is the difference in the magnetic field strength that that creates the energy differential to move the pin on the coupler. If you center the electromagnet, the magnetic power on one side is canceled out by the magnetic power on the other side.

    So from a DCC standpoint, you only need the short term spike, so a stationary decoder would be the best bet. But if you are really looking to couple and decouple in an operating mode, then you may just be better off using spring loaded contact push button switch than any DCC device.
     
  3. canoemaker

    canoemaker New Member

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    Thanks for the reply, David
    I purchased a couple dozen electromagnets from an electronics surplus store (either all-electronics or electronic goldmine) several years ago. They are 24v magnets from brakes on disk drives. I removed the brake pad/spring assembly and experimented with a few of them. When I mount them under the rails (removing ties), they work great. I prefer the electromagnets to permanent magnets. The latter seem to provide me with unexpected uncouplings, such as when I'm pushing a decoupled car to a resting spot and another set of couplers happens to come to rest over the magnet.
    I plan to use toggles for uncoupling in my yard, but would like to have a few in remote places on the layout that I could activate as I walk around. If I provide the 24v power via external power supply, would decoders be able to pass the power to the magnets without damage? Would I need to switch to 12v magnets? I'm thinking the decoder would act as a relay. I would leave the magnet activated as long as it took to uncouple, then deactivate it. Any other thoughts and comments are welcome and appreciated.
    Tim
     
  4. RT_Coker

    RT_Coker TrainBoard Supporter

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    Tim,
    I would try your existing magnets at 12v before buying new ones.
    Bob
     
  5. markwr

    markwr TrainBoard Member

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    Clockwise turns give you both a north and a south pole as do counter-clockwise turns. Mono-poles are theoretically possible but making one will probably win you the Nobel prize for physics.
     
  6. DCESharkman

    DCESharkman TrainBoard Member

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    It has essentially been done already in the sub-atomic particle physics world.

    The point I was trying to make was the pole under the track can be controlled, the other end of the nail would be the other pole.
     
  7. markwr

    markwr TrainBoard Member

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    I think you'll find that the electromagnet needs to be positioned with the axis of the core perpendicular to the track. The north pole under one rail and the south under the other. It doesn't matter which side is which pole.
     
  8. markwr

    markwr TrainBoard Member

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  9. canoemaker

    canoemaker New Member

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    I have tried them at lower voltages, and they don't work well. They actually work fine with 28-30 volts. Can that kind of voltage pass through a DS64 as an external power supply for the electromagnets?
    Tim
     
  10. DCESharkman

    DCESharkman TrainBoard Member

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    Again there are several ways to "Skin the Cat". By offsetting the wire wrapped nail from the centerline of the track you will have the same capability. It is the differential magnetic field that causes the trip pins to move.
     
  11. Josta

    Josta TrainBoard Supporter

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    Is there an electromagnet powerful enough to uncouple HO scale cars when mounted under the plywood for those of us who didn't plan ahead good enough? So, it would have to reach through the plywood, cork roadbed, and ties to do so.

    John
     
  12. canoemaker

    canoemaker New Member

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    John,
    It wouldn't be difficult to use a large Forstner bit, say 1-1/2", to drill from below until you reached the cork roadbed. Then you could glue your electromagnet in place without any trouble.
     
  13. DCESharkman

    DCESharkman TrainBoard Member

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    The strength of an Electro magnet is related too the number of turns on the wire and the amount of amperage passing through it.
     

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