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A 'trip' switch, looking for anwsers

Discussion in 'General Electronics Discussion' started by Kentos123, Jun 9, 2013.

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  1. Kentos123

    Kentos123

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    Jun 9, 2013
    I have been getting into the hobby of building small electronics recently and admittidly im not very informed on certain aspects of how circuits are built precisely.

    With this in mind, being a rookie, I pose a question.

    I am looking for a way to close/open a power circuit to an electromagnet. I need this to be autonomous ( not needing my direct input or control beyond turning the whole thing on ). Basically, I am playing around with magnetic coils, electric motors ( brushless DC) and a few other small projects. I have sifted through many tutorials online and have not come to a satisfactory way to perform, in an automatic way, switching power on and off, although I have recently been looking into IR LED + recievers I am at loss off how to make this a 'trip' switch. Im pretty sure I have either bought the wrong receiver or am lacking the understanding of how to use it.

    My general assumption was that it would itself, operate in either a normally open or normally closed state with an IR LED on. However I believe I have missed an important step as im finding out that this type of receiver has a carrier pin, and looking into it more this would be along the lines of something needing a programmed controller board and generally used for remote IR commands ( like a small tv remote or something similar ).

    The basic issue i am looking to solve is how to automatically pulse the electromagnet. Perhaps with a way to decrease the intervals between consecutive on states.
     
  2. duke37

    duke37

    5,364
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    Jan 9, 2011
    You need to be much more specific.

    1. What is the power supply?
    2. What is the resistance of the electromagnet?
    3. How long should the magnet be energised?
    4. What is the time between energising?
    5. Should this automatically cycle on and off?
    6. Any more useful information.

    I know nothing about coded controllers.
     
  3. poor mystic

    poor mystic

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    Apr 8, 2011
    :)
    It's easy enough to wire a relay to switch a magnetic load. If you have a signal you want to control the relay, you can feed that signal into a transistor which will operate your relay. So if your receiver produces a steady signal when the IR LED is lit, you have something to work with.

    But!
    You need to know that switching an electromagnet off causes a high voltage to appear on the terminals of the magnet. (This voltage is usually called "back emf.) That's why I recommend a relay. Even the relay needs protection - the voltage goes briefly into the hundreds of kilovolts, without a compensating load... spelled out so there's no mistake! The resulting currents destroy relay contacts fast and transistors can have very high mortality. This all means you'll need to design a snubber circuit for the switch; this is the compensating load I mentioned.

    I don't know any way to use an IR receiver to generate a pulse, and I have only an unconvincing-even-to-myself guess as to why you want to do it.
    Pulse generation will need to be done separately - you could use the pulses you somehow generate to power the LED, and with care you'll be able to achieve isolation of both your pulse generator, and yourself, from the magnet circuit.

    Mark

    PS When you're ready, ask about snubbers. It's too much for one thread.
     
    Last edited: Jun 9, 2013
  4. Kentos123

    Kentos123

    5
    0
    Jun 9, 2013
    The power supply can be one of many i have lying around, from 1.5v batteries, 3.7v lithium ion batteries ( 3.7v @ 670 mAh ), or any number of them wired series/parallel.

    No idea what sort of resistance on the coil will be, i have hand turned a coil and it is using 18awg magnetic wiring. probably a few feet in length ( un-coiled) with 2 layers of around 15 turns.

    The electromagnet should be energized long enough to pull on a static magnet, but not so long as to act in opposition to the direction of the turning. I'd imagine this would be a very small fraction of a second as 600 RPM would be a very slow rotational speed for my purposes.

    The time between energizing is very small, im trying to get the gap as short as possible but accurate enough to properly function as an electric motor.

    Automatically cycling the on and off is what im trying to find a solution for, an IR led/reciever combo seems like it would be the best option from what I've read as far as automatically turning the power on or off ( say, as the arm passes between the receiver and IR LED, it would shut off, and then perhaps with a plactic tab or some such object only let the light pass to the reciever when the next arm is closer to the magnet then the previous arm [ such as with a single electro magnet] .

    I am open to other suggestions and I have a lot of small electronic parts and various types that I could make use of except for the IR receiver.

    I know nothing about coded controllers either, so that is where I believe i made the mistake with the IR receiver, as it has a carrier pin that is generally used to pass bits of data depending on the signal.

    To note as well. I am not specifically looking for 'should i use a 4.7k resistor or a 2uF capacitor' type of q&a, im curious to know how to build a functioning brushless DC motor, or learn enough about how it is done to make sense of the general idea of how to controll the electromagnets in a way that spins the motor instead of locking it in place ( due to the electro magnet not powering off as the magnet nears the center alignment ).
     
  5. Kentos123

    Kentos123

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    0
    Jun 9, 2013
    My apologies if my working knowledge of electronics is sub-par. I just find myself at a loss of how the rotation of an electric motor is controlled, preferably at high speeds. I understand the principle behind power to the magnetic coil to pull on the magnet, till it almost reaches the center, then cutting the power so that it can continue in the same direction, and when the next or same magnet gets close to the electromagnet power is put through the coil again and then shut off at the same point. I dont understand what it takes to actually do this with out manually trying to turn it on and off at the right time using a push button switch or the like.
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    A DC motor with brushes has an armature with several coils. The minimum is three but there can be many more. The coils are connected to a commutator which the brushes rub on so the appropriate coils are connected to make the motor turn. The magnet (permanent or electro) is on the outside of the motor.

    A brushless motor is inside out, the magnet (permanent) is rotating and the coils are switched at the appropriate time. In order to do this it is necessary to determine the rotor position. You will need at least three coils to make a motor which will start.

    Depending on your engineering skills and construction, there are various methods of finding the location. You can use an led source and sensor with a flag to stop the signal or a reed switch controlled by the magnet or a Hall effect device. Getting this to work reliably would be the difficult part.

    If you are content to start the motor by hand or to set it to the correct starting position then you may be able to get away with one coil.
     
  7. Kentos123

    Kentos123

    5
    0
    Jun 9, 2013
    Thank you, I would prefer not to have to set the motor position to start. I had looked into reed relay or switch. Although im not entirely clear how that sort of switch would work.
    I am not limited to use one coil, but i had though for very basic testing this might be able to be used in a pulse type electric motor, but I can easily wind two more coils if it would produce an over all better and less hands on type of motor.

    My engineering skills would be low, but learning the basics of an brush-less DC motor is something I am pursuing to learn more about how electronics work, and with some time perhaps make small gadgets ( like this one ) for personal use.

    Any help on the basics needed for this would be great, I think an LED sensor will be fairly easy to obtain or even a reed switch ( though im not sure how to implement one ).
     
  8. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Reed relays are slow.
    Optocoupled inerrupted beams are fast, and cheap. You can buy optocouplers with slots in the chip, and a slotted disc on the motor shaft can be set to pass through the slot.
    Look at the search results for "slotted optocoupler" and you'll see what I mean.
     
  9. Kentos123

    Kentos123

    5
    0
    Jun 9, 2013
    This looks like precisely the type of thing I could make use of. Thank you for the suggestion.
     
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