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DIY battery pack capacity

  1. Oct 2, 2016 #1
    Hi,

    I am a university student in the Netherlands and I just got the assignment of building a robot on a budget. Because of this budget I would like to make the battery pack that powers the 2 servo motors and 2 electric motors myself.

    I did some research and found out it would be best to connect multiple AA Alkaline (1.5 V 2700 mAh) batteries. I know my basic physics as the current will stay the same and voltage adds up, though what about the capacity? I understand how this battery works but now my question was if I connect for example two batteries do I get a battery pack that can deliver 3.0 V with 5400 mAh, or just the 3.0 V with again a capacity of 2700 mAh.

    Thanks in advance!
     
    Last edited: Oct 2, 2016
  2. jcsd
  3. Oct 2, 2016 #2

    Bystander

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    Think about it ... a little bit more and you will have answered your own question.:rolleyes::wink:
     
  4. Oct 2, 2016 #3
    You sound like my physics tutors haha! I calculated the amount of Watts and think it is silly to assume that both the capacity and the voltage gets doubled. So from this I will assume that the battery pack would have a 8.1 W output with the 3.0 V and 2700 mAh!

    Thanks
     
  5. Oct 2, 2016 #4

    Bystander

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    Ta-da.
     
  6. Oct 2, 2016 #5

    jim hardy

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    See ? You new all along !
     
  7. Oct 4, 2016 #6
    That's a pretty common source of confusion. Charge capacity in terms of Amp-hours does not change with the number of series cells, but energy capacity in terms of Watt-hours multiplies with the number of series cells. For a load that consumes a constant amount of power run time will double, for an ohmic load where power consumption goes up with voltage run time will not increase.
     
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