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Quick electromagnet question

  1. Jan 25, 2009 #1
    Hello all!

    I have created a basic electromagnet using copper wire coiled around a nail. When I hook a DMM in series with the electromagnet and my 12v 3Amp DC power supply, the DMM shows that the amperage fluctuates. It will not come to a certain number or switch between two numbers that are very close together. It is almost like the current from the DC power supply is acting like AC current. Is it normal for the amperage to fluctuate so much? Does this happen because of the coil or is my power supply messed up?

  2. jcsd
  3. Jan 25, 2009 #2
    The more basic DMMs tend to fluctuate and the more basic power supplies give a rectified D.C output but not very well smoothed out.
  4. Jan 25, 2009 #3
    When I hook up my magnet to two C batteries the magnetic pull is much stronger than when I hook it up to my 12v 3 amp dc power supply. What?! The batteries are less amperage so it should be the other way around. Any ideas as to whats going on?

  5. Jan 26, 2009 #4
    What?!.Thats my reaction also.I can only guess.
    1.Perhaps your DMM is faulty or you had a poor connection or you wired it incorrectly.
    2.An electromagnet can draw a large current and most power supplies have a cut out if the current goes too high and you have to wait for them to cool down before they can be reset.Was it possible that you tested your electromagnet when the power was off?The core being a nail and made of steel would have been turned into a permanent magnet by your previous experiments.
    May I make a few suggestions
    1.Try not to use batteries.Your electromagnet draws a lot of power,your batteries will last a short time and this can work out expensive.
    2.Use a soft iron core instead of a steel nail.Soft iron is a temporary magnetic material and loses its magnetism when the power is switched off.I am assuming that your local school would loan you this if you cannot get it otherwise.
    I have just thought of something else.What is the insulation on your copper wire like?If it is coated with varnish or something similar perhaps some of this got scraped off.
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