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Charging current?

  1. Dec 6, 2006 #1
    Charging current??

    i have a question that says a generator is charging a normal battery the internal resistance of the generator and battery are given, and i must calculate the charging current how might this be done?

    generator is 30v with 4 ohm internal resistance.
    battery is 24v with a internal resistance of 2 ohms.

    thanks in advance
  2. jcsd
  3. Dec 6, 2006 #2
    This, at it's most simple, is just ohm's law.
    You know the potential difference in the circuit and the resistance in the circuit therefore you can calculate the current flow.

    Redraw the circuit lumping all the voltage sources together and resistances together and you should see how to work it out.

    Or were you wanting it a chemical level?
  4. Dec 6, 2006 #3
    no chemical level, its just a generator pointing up with a resistance on top of it, and on the right side a resistor on top and a battery at the bottom (with the positive side facing up) and its all connected in series. and its asking 4 the charging current so i thought it may be asking the exact current needed for a 30v generator to charge a 24v battery. i was thinking of using kirchoffs 2nd law and i got the equation 30-24 = 2I + I (not sure if its right). can i use this or if your method best?
  5. Dec 6, 2006 #4


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    You're making this too complicated, nemesis24. Draw a picture. It'll contain two voltage sources (one 30V, one 24V), with a total of six ohms of resistance between them.

    That's six volts dropped across six ohms... use Ohm's law to find the current.

    - Warren
  6. Dec 6, 2006 #5
    so i take it that the two voltages would be substracked as it is the charging current. or would it add to give the total voltage?
  7. Dec 6, 2006 #6


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    You're thinking about it too much, still.

    One one side of this combined six ohm resistor, you have 30V. On the other side, you have 24V. There is, thus, 6V across the resistor. 6V across a 6 ohm resistor gives....

    - Warren
  8. Dec 13, 2006 #7


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    Actually you are on the right track here, using Kirchoffs Voltage Law (The total voltage around a closed path equals zero). Except you have an error in your equation 30-24 = 2I + I [hint: What did you say was the internal resistance (Rs) on the generator? ]
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