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(Topic ID: 155307)

Increasing the power to a coil, remove more windings?


By jodini

4 years ago



Topic Stats

  • 16 posts
  • 11 Pinsiders participating
  • Latest reply 28 days ago by MarkG
  • Topic is favorited by 1 Pinsider

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    #1 4 years ago

    My daughter the other day was asking for help with her science (4th grader) and the question was, "Which is one way to increase the strength of an electromagnet?" I told her it was a trick question and to answer "C: Remove some coils of wire" Because what do we do when want to increase the power to a coil in the EM world....remove windings. I know, not too many....but I know it works. My daughter gets her paper back with a big RED check mark and says "WRONG"!

    So can someone please explain to me "why"? It does make sense if I want to create a magnetic nail, that I would increase the windings, but in our EM world we remove?

    #2 4 years ago

    Doesn't seem to make sense....following this logic, wouldn't it then mean that removing all the windings entirely increases the power infinitely? Which obviously isn't possible.

    #3 4 years ago

    More current = more magnetic pull

    Ohm's Law ... I = V/R where,
    ...I = Current
    ...V = Voltage
    ...R = Resistance

    Holding voltage constant, reducing resistance (with fewer windings), increases current.
    There are tradeoffs.

    I'm sure a bonafide EE can chime in.
    --
    Chris Hibler - CARGPB #31
    http://ChrisHiblerPinball.com/contact/
    http://webpages.charter.net/chibler/Pinball/index.htm
    http://www.PinWiki.com - The Place to go for Pinball Repair Info

    #4 4 years ago

    This explains some:
    http://www.pinrepair.com/em/index3.htm#low

    Science fair is coming up and I would love to create a project for my daughter that proves her answer right! You guys have any suggestions how I can make a experiment using some DC voltage (that way I'm not shocking my kid)!

    #5 4 years ago

    ""The less turns of wire, the more powerful it will be" rule is only good up to a point. That is, if the resistance of a coil goes below about 2.0 ohms, it becomes essentially a dead short. This means the coil will not work correctly, and may blow fuses too. Also a coil with too little wire (or shorted wire) can have an inadequate magnetic field."

    And this is the exact reason your daughters paper was correct, and marked wrong.

    The person grading it or the collateral they were reading did not include all ways to increase or decrease coil power. They were probably only thinking that increasing voltage and wire gauge was the only way.

    Anyone working on pins knows that stripping a few windings is sometimes the easiest way to skin that cat.

    So way to prove it, take two exact same coils using the exact same power source and remove some windings from one. Maybe even use a couple fully built but not attached to a pin flipper assemblies.

    Maybe a left and right flipper mounted on plywood.

    #6 4 years ago

    A magnetic nail only has a few windings of wire on it which makes the resistance negligible so increasing the number of windings increases the magnetic strength. If you kept putting more wire on there, eventually the resistance would cause the field to decrease due to the reduction in current flow. A good experiment might be to find the number of turns of wire that maximize the magnetic field and then to show the curve. Also another cool demonstration would be to put some iron filings on it to show the actual size of the field for the different scenarios.

    #7 4 years ago

    This is great folks! fattdirk...I like your thinking!

    Just a disclaimer: I've fixed over 100 games I would say and have only used the removing windings trick three times. Once on a pitch n bat with the curveball....wanted more pull, on a Genco Basketball when after replacing the bridge rectifier I still not have enough power on the bell, and once on a Superstar that had a weak coil on the knockout holes. All problems could of been fixed by some other means, I really resort to this fix ONLY if I've tried everything else (even replacing coils). So I hope this topic does not turn into a "never remove windings from a coil" topic!

    I'm going to try a few experinements and see what I come up with. Just very interesting!
    Thanks all and keep your inputs coming!
    Joe

    #8 4 years ago

    Just show the current has increased by using an amp meter. Even a dead short will draw amperage for a period of time.
    You could also prove her answer is right by using Oms law.

    #9 4 years ago

    The easiest demonstration would be to power two WMS coils side by side, powered from the same source, and devise a method to test magnetic pull. Perhaps ability to hold a paper clip attached to a string in mid air. The -1200 will be able to hold it at a longer distance.

    The 26-1500 and 26-1200 would work well since both use the same gauge wire and the same size bobbin.
    --
    Chris Hibler - CARGPB #31
    http://ChrisHiblerPinball.com/contact/
    http://webpages.charter.net/chibler/Pinball/index.htm
    http://www.PinWiki.com - The Place to go for Pinball Repair Info

    #10 4 years ago

    I like your idea Electrocute (I like your icon "Dodge City" too...one of my favorites)!

    I'll see what I can dig up in my coil bin Chris....mostly gottlieb coils...however I did strip out a Bally bingo game...gotta be a bunch of coils in there I can test.
    The problem I have with this is how to make this safe. Don't really want to use DC current, but I also don't want to have to keep replacing batteries for her project.

    #11 4 years ago

    The way I was taught was to think of electricity like a river where
    The width of the river = voltage
    The speed of the river = amperage
    The amount of water flowing = Watts

    #12 4 years ago
    Quoted from Electrocute:

    The way I was taught was to think of electricity like a river where
    The width of the river = voltage
    The speed of the river = amperage
    The amount of water flowing = Watts

    And the current of the river = current.

    #13 4 years ago

    This is somewhat complex to explain. The magnetic field is based on two main factors... amount of current flowing, and distance from the wire. Removing coils from the outside of a large coil (where the field impact on the core is less than coils near the center) has less reduction on the magnetic pickup capability. Removing any wire will reduce the resistance, and increase the current... but not very much unless the wire is very fine. Wire has a pretty small amount of resistance.

    So, when you remove the coils, did you decrease the resistance enough to increase the current enough to create more magnetic field across all of the coils given some reduction in field from the coils that you removed.

    Make sense?

    For the class exercise, you would probably get more increased field coupling by adding windings because the wire size is large enough that the added resistance is negligible.

    Mac

    #14 4 years ago

    You might also try using a DC wall wart, and a variable resistor in line with the coil.
    dial it up, and the coil gets stronger, dial it down, and it gets weaker.
    use some small washers to see the amount of hold the coil has.
    you can add washers in line and count them.

    1 year later
    #15 2 years ago
    Quoted from jodini:

    My daughter the other day was asking for help with her science (4th grader) and the question was, "Which is one way to increase the strength of an electromagnet?" I told her it was a trick question and to answer "C: Remove some coils of wire" Because what do we do when want to increase the power to a coil in the EM world....remove windings. I know, not too many....but I know it works. My daughter gets her paper back with a big RED check mark and says "WRONG"!
    So can someone please explain to me "why"? It does make sense if I want to create a magnetic nail, that I would increase the windings, but in our EM world we remove?

    A year later I know, but here you go.... there are two ways to increase the electromagnetic force.

    1.) Increase the voltage which will increase the current going through the same resistance (Ohm's Law). Be aware that coil resistance will change as the wire heats up and will affect the current.

    2.) Increase the number of turns (number of times the coil is wrapped around the core) up to a point where diminishing returns make it ineffective because the coil becomes to far aware from the core to add much to the field.

    Removing windings (reducing the number of turns) will reduce the electromagnetic force. However, you are also reducing the resistance when you remove windings, so you are increasing the current (assuming voltage remains constant and you don't fry the coil). As a result, there is a trade off. There is the possibility that removing some of the turns that are the furthest from the core may have a small net benefit in force if the current increases more than the # turns are reduced. The may be why the "EM world" trick of removing windings could work up to a point before it starts to reduce the force.

    ----------------------------------------------------------------------------------

    Calculate the force by writing the equation:

    F = (n x i)2 x magnetic constant x a / (2 x g2)

    Where, F = force, i = current, g = length of the gap between the solenoid and a piece of metal, a = Area, n = number of turns in the solenoid, and the magnetic constant = 4 x PI x 10-7.

    Analyze your electromagnet to determine its dimensions and the amount of current you will be running through it. For example, imagine you have a magnet with 1,000 turns and a cross-sectional area of 0.5 neters that you will operate with 10 amperes of current, 1.5 meters from a piece of metal. Therefore:

    N = 1,000, I = 10, A = 0.5 meters, g = 1.5 m

    Plug the numbers into the equation to compute the force that will act on the piece of metal.

    Force = ((1,000 x 10)2 x 4 x pi x 10-7 x 0.5) / (2 x 1.52) = 14 Newtons (N).

    2 years later
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