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Getting high current from AA batteries

  1. Apr 5, 2013 #1
    I am trying to increase the strength of my electromagnet, at the moment by increasing the amperage. I have been using an old 12V motorcycle battery, but also tried with 10 AA batteries.

    I was wondering how I could connect the AA batteries to get a high current, so hopefully a stronger magnetic field. I have a very basic knowledge of electronics - I know that connecting batteries in series adds their voltage together. Would this then increase the amperage in the same way?

    I have also heard that having batteries in parallel reduces the power drawn from the individual batteries, but are there other advantages of this.

    So what I am looking for is a high current from AA batteries - I have about 30 of them. Also, at what point does it become quite dangerous to handle?

    Thanks for any help.
     
  2. jcsd
  3. Apr 5, 2013 #2
    To get the maximum strength out of your magnet it should be U shaped like a horseshoe magnet. That way the magnetic flux will not have to go through air.
    Also how to best connect the batteries depends on the resistance of the coil. Can you change the number of windings? If you have more windings you need less current.
     
  4. Apr 5, 2013 #3
    Oh sorry, I forgot to mention it has an iron rail road spike for the core.

    I am hopefully getting more wire today, so I can have more windings, but I'm not sure how much resistance it will then have - I forgot what gauge the wire was... If the resistance becomes too high, then I'll need more voltage, won't I?
     
  5. Apr 5, 2013 #4

    Drakkith

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    Staff: Mentor

    Each battery applies a certain voltage to the circuit. This voltage, when divided by the resistance of the circuit gives you the amount of current. However, batteries themselves have internal resistance that isn't usually given. Hence why you cannot put a small wire from one end of the battery to the other and get a thousand+ amps. The battery simply cannot put out that much current thanks to internal resistance.

    Putting them in series will increase the voltage, and thus the current through the circuit, but you must be VERY careful that you do not put too many together, as too much current flowing through the batteries may heat them up and cause them to explode.

    Now, what you CAN do, is find the voltage you need for your circuit and put several series of batteries in parallel. (AKA put 4 batteries in series. Then put another 4 in another series. Then take those two series and put them in parallel with each other.) The voltage remains the same as if you only had one set of batteries in series, but the current flow through each series of batteries is split in half.

    At the point where you no longer know if it is dangerous to handle. :wink:
     
  6. Apr 5, 2013 #5

    Drakkith

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    Staff: Mentor

    Yes, as your resistance increases, current decreases and you need more voltage to keep your current where you want it.
     
  7. Apr 5, 2013 #6
    Ok, so for the 2 sets of 4 batteries in series, there would be a total of 1.5*4 = 6V. So the current isn't doubled, but is just split between the batteries? Is that just to prevent too much current going through one set of batteries?

    Would that then mean that I would need 2X as many batteries to achieve the same voltage as all of them in series, but it reduces the risk of damaging the batteries?
     
  8. Apr 5, 2013 #7

    Drakkith

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    Staff: Mentor

    Four batteries in series is 6 volts. Add another set of four in parallel and the voltage is still 6 volts. There is no change in current because there is no change in voltage. However, each set of batteries will provide half the current.

    I'm not an expert, but I believe that is correct. I don't know how many batteries you can put in series before it becomes a problem, but I can almost guarantee you that it does become a problem at some point.
     
  9. Apr 6, 2013 #8
    It is generally not a good idea to connect batteries in parallel. If they are not identical (and they almost certainly will not be) then current will flow from one battery through the other, even if no external circuit is connected.
    You could possibly try something with batteries in parallel and use a diode in each arm to isolate batteries from each other.
     
    Last edited: Apr 6, 2013
  10. Apr 6, 2013 #9
    Thankyou both for your replies. I will experiment a bit, and see how it goes.
     
  11. Apr 6, 2013 #10
    If the batteries are zinc carbon or alkaline putting them in parallel is no problem because the internal resistance is high enough to keep it safe. Rechargable batteries however should never be connected in parallel.
    Also the only problem you can get when you put alot of batteries in series is that the voltage becomes dangerous i.e. it can give you a nasty shock.
    The combined voltage of your batteries devided by the resistance of the coil equals the current. Current times the number of windings determines the strength of the magnet. So if you double the number of windings and keep the voltage the same the current will drop to half it's previous value but the strength of the magnet will not change.
     
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