why excessive current draw?

Discussion in 'The Projects Forum' started by Gadersd, Aug 17, 2013.

  1. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    I just connected a 7.4 volt battery to a 50 ohm resister and connected it to my homemade speaker which is a coil of wire on top of a magnet. I noticed that it drawed current well beyond 148 ma. Why would a coil of wire on a magnet draw so much current?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Is the 50 Ohms resistor in series or parallel to the "speaker" coil?
    Can you post a schematic or a photo of the setup?

    Bertus
     
  3. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    As you can see I used two 100 ohm resistors in parallel to get 50 ohms. The resistors are connected to the speaker in series.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    3,235
    Measure the resistance. It must be less than you think.
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Since I = V / R, since your proclaimed I was higher than expected could be one of three things:
    1. "V" is higher than 7.4 V
    2. "R" could be lower than the 50 Ohms
    3. "I" could have been guessed, measured or read improperly.

    I guess it could also be any combination of those three. Double check them all.
     
  6. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    The problem is that I do not own a multimeter, so checking those things is almost impossible.
     
  7. Metalmann

    Active Member

    Dec 8, 2012
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    You can buy a multimeter for less than $10,00 nowadays.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I thought it was mandatory on this site? :p
    Max.
     
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  9. Metalmann

    Active Member

    Dec 8, 2012
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    I just noticed I used a comma instead of a period.:confused: Oh, well.;):D
     
  10. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    What, if any, parts do you have on hand ?

    Do you have a DC supply (Wall Wort) voltage regulator IC, op-amp, comparator IC ? etc...
     
  11. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    I do have a 5v regulator.
     
  12. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I've got a dumb question:

    How did you measure the current ???
     
  13. Gadersd

    Thread Starter Member

    Dec 8, 2012
    98
    1
    I did not actually measure it. I thought the current was high because I saw sparks.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You just want to give the impression of being continental! :p
    Max.
     
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  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,550
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    How many? :eek:
    Max.
     
  16. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    What color were the sparks ?

    Sorry ;)
     
    Last edited: Aug 17, 2013
  17. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    If you dont have a multi-meter, how did you know that the current is well over 148mA?

    [edit] sorry! I didn't read page 2....
     
    Last edited: Aug 17, 2013
  18. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
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    I want to vote this as the thread of the year.
     
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  19. Metalmann

    Active Member

    Dec 8, 2012
    700
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    When I first started out, the sparks did tell a tale of alloys.:D

    Or, not.;)
     
  20. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Hi Gadersd,

    Please don't be offended by a little good-natured ribbing.

    It would help if we new what the final goal of this project is.
    Do you possibly want to build an amplifier for the speaker, or something else ?
     
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