A simple question for confirmation

Discussion in 'General Electronics Chat' started by FND, Apr 2, 2009.

  1. FND

    Thread Starter Member

    Apr 2, 2009
    16
    0
    Hi All,

    I am a new comer in this forum, would appreciate some assistance and please do welcome me. =)

    I'm just testing a simple circuit with 2 9Vs battery which I would require to draw about 1A of current out of it within only miliseconds.

    I was wondering, if i just use a microswitch without relay to complete the circuit, will there be a spark developed at the switch? And would there be any difference if I place the switch before or after the load?

    Help please.. Thank you.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Those little batteries don't have the capacity to supply an amp of current. We might be able to suggest some alternative if you can say what you are trying to do.

    All switches are noisy on opening and closing, although with only 9 or 18 volts applied (you haven't made it clear if the batteries were to be in parallel or series), the spark would be very small. The nature of the load will have a big influence on that.
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    Actually, for a millisecond, they can! Considerably more than that, actually. But I wouldn't give them a steady diet of that. :)

    eric
     
  4. FND

    Thread Starter Member

    Apr 2, 2009
    16
    0
    Thank you both for your reply.

    The batteries I would arrange it in parallel so I would be able to get a high current. I need exactly 0.9A for a period of about 3-5milisecond. I have yet to measure the load's impedence to know how many batteries I need.

    My only concern here is about the developing of spark at the switch. If it's like what you said, the spark would be very small, then I shouldn't worry of getting shock, rite?
     
  5. FND

    Thread Starter Member

    Apr 2, 2009
    16
    0
    Thank you both for your reply.

    The batteries I would arrange it in parallel so I would be able to get a high current. I need exactly 0.9A for a period of about 3-5milisecond. I have yet to measure the load's impedence to know how many batteries I need.

    My only concern here is about the developing of spark at the switch. If it's like what you said, the spark would be very small, then I shouldn't worry of getting shock, rite?
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    A Brand New Energizer 9V Battery has an internal resistance of 1.5 Ohms.

    If you draw 1A from a 9V battery, it will only be at 7.5V. With 2 in parallel, the 1A would be at 8.25V

    A Better solution would be a pack of 7 NiCad batteries in series, along with a 1A current regulator circuit.
     
  7. FND

    Thread Starter Member

    Apr 2, 2009
    16
    0
    Thanks for the info. I will give it a consideration about the current regulator and the 7 NiCad batts.

    At the same time, my plan is to make the circuit as small/compact as possible.
     
  8. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Would a large capacitor overcome the internal resistance problem?
    I would imagine even without using a supercap just using a charged cap would allow 1 amp for .005 seconds.
    I have not done the math, though :)
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    I did something dumb on one of my experiments, and dead shorted a 9V alkaline for a period. They provide 1 amp quite nicely, no voltage, but 1 amp. :rolleyes:
     
  10. wr8y

    Active Member

    Sep 16, 2008
    232
    1
    Energizer makes no claim that their 9 volt batteries will provide an amp.

    http://data.energizer.com/PDFs/522.pdf

    (See page 2)

    You might get close to it with two - but as another poster indicated, it won't be 9 volts. :cool:
     
  11. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
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    Yes it would...I was thinking along the same lines. :)

    eric
     
  12. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Thank you, KL7AJ. It's nice when a post does not just go off into space :)
     
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