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Battery current

  1. Jun 11, 2008 #1
    im trying to figue out how much current comes from a 12 volt car battery? i know that the starter pulls atleast 200 amps so does that mean anything that is hooked to it will get a very high current ? what would happen if i hooked up a 15 amp 20 volt transistor to it? would it short out the transistor? ive search the internet and cant find anything that answers this question. any answers would be a big help. thanks
  2. jcsd
  3. Jun 11, 2008 #2


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    What you connect to the battery determines the current supplied by a battery.
    Try reading up on ohms law.

    Depends on how you hook the transitor up.
  4. Jun 11, 2008 #3


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    The limit for the current you can pull from a bettery depends on the internal resistance of the battery.
    Picture it as a perfect 12V source with a series resistor inside.
    Typical internal resistance for a lead acid battery is a few 10mR, so if you pull 200amps you will lose at least 2V accross the internal resistor. Once you lose all 12V accross the internal resistor you can't get any more current out and will damage the battery.

    In reality it also depends on how quickly you take the current and for how long since the internal resistance depends on temperature andtaking current heats the battery.
  5. Jun 11, 2008 #4
    No offense, but, maybe you should study the fundamentals before connecting anything to a battery. A car battery contains sulfuric acid which, if the battery should explode, could result in severe burns and even blindness. If one is in the learning stage, they should use current-limited bench top power supplies. I'm just looking out for you.
  6. Jun 14, 2008 #5
    Jearls74, the current that comes form it is dependent on the consumer that you attach to it. That's why it says on it a number of Ah.
    What would happen to the transistor would depend on the way you connect it.
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