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Electromagnetic effects, DC

  1. Dec 28, 2016 #1
    I know there have been discussions on electromagnets, but I think my question here is specific and hopefully quite different. Using DC power only, what amount of pull might I expect from, let's say, 48v of decent lead acid battery or batteries? It occurs to me that one could use an ebike battery of 48v? In case it is required information, let's say that pull is being exerted on a ton and a half weight from, say, 20ft? By all means hit me with clarification needs! I'm new here and not overly scientifically minded. Inventive yes, genius not so much
     
  2. jcsd
  3. Dec 28, 2016 #2

    berkeman

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    Welcome to the PF.

    At 20 feet, not much. At something like one foot of separation, you will get a pretty substantial force. But that force is not going to accelerate 1.5 tons very quickly (even with zero friction to overcome). What is the application?

    https://en.wikipedia.org/wiki/Electromagnet
     
  4. Dec 28, 2016 #3
    Your question may lack some specifics but in general, the "pull" that you mention I take that it means "power" or how much work can be done given a specific time.
    Battery power can be measured in how much current it can discharge. For example, if the 48V battery can discharge 10A at any given time, then it can do 48V * 10A = 480W or it can do 480 Joules/sec. My basic physics a bit hazy so I guess you can find an equation to calculate how fast you can accelerate a 1.5Ton object with 480W of power. But guess there are other factors such as frictions, gearing, ... that not specified in your questions.
     
  5. Dec 28, 2016 #4

    berkeman

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    That's not a good approach, IMO. Who cares if the coil around the electromagnet dissipates 480W through resistive losses? That has nothing to do with any attractive force and the work done via it.
     
  6. Dec 28, 2016 #5
    Hm... I thought the OP was asking how much his 1.5Ton object can be "pull" by using a 48V pack. I am not sure what you referred to in your post such as electromagnetic and resistive losses had anything to do with my post? I was simply trying to refer how much his 1.5Ton can be pulled by the power of a 48V pack.
     
  7. Dec 28, 2016 #6

    berkeman

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    Have you read through the wi,kipedia link that I posted on this topic for the OP?

    How much experience to you have with force and work done by electromagnets? We appreciate you trying to help with questions here. Please be sure to do the research before replying. Thanks.
     
  8. Dec 28, 2016 #7
    oops, sorry, I was trying to answer a different question. I mean the OP could be more specific by saying he is trying to calculate the electromagnetic force induced by using a solenoid (at least I think that is the intent of the question). I thought he was asking about how fast a car with 1.5T weight can be accelerate using 48V battery pack. That's why I mention fiction and gearing.
     
  9. Dec 28, 2016 #8
    Seems good value in the answers of both you and Sleepdeprived. Given my notion that an ebike lead acid battery could be the pwer source, I don't see why seventytwo volt battery couldn't be the power for the electromagnet. If so, could the pull on a ton and a half object not be reasonable at, say, ten feet? Sorry I can't yet entirely give away the reasons for my queries
     
  10. Dec 28, 2016 #9
    Does it make any difference that I am looking to decelerate the object rather than accelerate. To pull said object toward the electromagnet. I thought that was the usual intent?
     
  11. Dec 28, 2016 #10
    I have to say that is a very odd question. What is it that you're trying to pull? By what mechanism -- I assume some type of electromagnetic force but could you be more specific? Based on your description, I mean it could be anything. Sorry if I am being a bit blunt. I am not quite as polish as some of the participants here.
     
  12. Dec 28, 2016 #11

    berkeman

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    No way. Did you read the wikipedia link that I posted?
     
  13. Dec 28, 2016 #12
    Yes, indeed I looked up the Wikipedia link you posted. That confirmed for certain that I'm no scientist! It appeared that much of the data was written with the notion that the reader would be making ones own electromagnet. Hell may freeze over before that happens, but I assume there are myriad electromagnets available that one can purchase, once an understanding of the unit's ability for my application is established. Fortunately, it seems many here have ideas about electromagnets ability - voltage, pull etc. Given my aim, any and all info appreciated
     
    Last edited by a moderator: Dec 29, 2016
  14. Dec 29, 2016 #13

    berkeman

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    And the quantitative section of that wikipedia article did not help you in your calculations?

    Maybe your focus on Homeopathy mentioned in your Profile page is hindering your quantitative analysis...
     
  15. Dec 29, 2016 #14
    Surely, the voltage, the amps, play a large part n the ability to decelerate a ton and a half weight, of steel I might add. I am just trying to figure why you said No way. As. I say, I did read your Wikipedia link. But yes, it was heavy going for me.
     
  16. Dec 29, 2016 #15
    No bloody way. Why shouldn't I add quantitative analysis and simply electromagnetic study to my life? My questions are not burn of minor amusement, rather intense interest in a new topic in my life, and plan to use what I learn for a serious purpose.
     
  17. Dec 29, 2016 #16

    berkeman

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    Well, when you watch YouTube videos of practical working electromagnets that lift cars off the ground using thousands of amps and much more power than your question involves, what is the typical distance that is used to start the lifts...?
     
  18. Dec 31, 2016 #17

    davenn

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    yep ... I was thinking of asking the same thing with the huge electromagnets in scrap metal yards

    Dave
     
  19. Dec 31, 2016 #18

    Baluncore

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    The magnetic field will prefer to pass a few feet through the air between the electromagnet's poles, rather than 20 feet to the steel and then 20 feet back again. Once a magnetic circuit is formed, the attraction results in the field lines shortening. The fundamental problem here is that the 1.5 tonnes of steel will need to get across, or between the poles of the magnet, or it will not become part of the magnetic circuit.
     
  20. Dec 31, 2016 #19
    Fair point, reflects the fact I am no physics expert. But what I lean toward is that scrap metal yards surely get past this issue, but how? And with what wattage/amperage? Either way, my application has to be DC powered.
     
  21. Dec 31, 2016 #20

    berkeman

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    One of the ways that they maximize the magnetic "pulling/lifting" force is to keep the magnetic path length (thorough the air) short, as Baluncore said. If you look at the lifting electromagnets in those high-force applications, you'll see magnet structures like coaxial cylinders. So the two poles of the magnet are coaxial and the faces are close together. That makes for a very small magnetic path through the air to capture the load and lift it.

    A horseshoe magnet is similar -- the distance from one pole to the other is small magnetically when the two tips of the horseshoe are brought close to the ferrous metal target (car or scrap metal or whatever).

    https://s-media-cache-ak0.pinimg.com/originals/59/3e/76/593e76d79b7dcb43c8065d5a1535413a.jpg
    593e76d79b7dcb43c8065d5a1535413a.jpg
     
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