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Question about capacity/battery

Discussion in 'Power Electronics' started by ymotion, Jun 3, 2016.

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  1. ymotion

    ymotion

    3
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    Jun 3, 2016
    Hi,
    I'm interested in having an external power for my camera (Sony a7) and would need your advice here.
    The original battery (NP-FW50) has the following specifications: 7.2V (long line and underneath a dotted line), 7.3Wh, 1020 mAh.

    I currently have two options:
    (1) a 95Wh, 14.8V with a regulator (converting to 7.4V) and a dummy battery (size of FW-50)
    http://www.bhphotovideo.com/c/produ..._tools_pd95s_compact_95wh_v_mount_li_ion.html

    (2) 2 x 7.4V 7800mAh. With this option I don't need a regulator - since the voltage is the right one for the camera - so just a dummy.

    I really don't know much about the specifications. Did some research and found out how to convert the mAh to Wh. Option (2) has about 56Wh. Will two of those give me more running time than the 1st option?
    Which option is more efficient and logic? Does is make sense to take a stronger battery with 14.8V and then change it to 7.4V, or is it not very wise? I think it's a good choice to take the 1st option if I have more than just the camera to connect. Is it right? Would be very grateful to hear your opinion here.

    thanks,
     
  2. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    Unless it's a very high frequency you're going to get losses as heat from the inductor so if lucky 90 - 95% with a good switching circuit to step the voltage down and then losses in the switcher ic

    So yeaj stick with 7v battery if you can feed the camera directly
     
    ymotion likes this.
  3. ymotion

    ymotion

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    Jun 3, 2016
    hi cjdelphi, thanks!

    BTW, is there an easy way to know how full is the battery? Some batteries have indication (4 LEDs showing 25-50-75-100%). My battery doesn't have it...
     
  4. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    Yeah use a specialized ic chip like a voltage bargraph or a microcontroller or 4 voltage comparators or even just discrete transistors and voltage dividers
     
    ymotion likes this.
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,474
    2,820
    Jan 21, 2010
    the risk of using a higher voltage battery and a regulator I'd that the camera will no longer be able to detect that the battery is going flat. This can lead to the battery being over discharged and damaged.

    I would recommend using a single higher capacity battery of the same voltage.
     
    ymotion likes this.
  6. ymotion

    ymotion

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    Jun 3, 2016
    Hi cjdelphi and Steve, sorry for the late response - I've been away on a project. Thanks for writing. I went with the 7.4V option :)
     
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