D40x: charge battery via USB?

Discussion in 'Digital Photography' started by aaronfude@gmail.com, Jul 11, 2007.

  1. Guest

    Hi,

    Is it possible to charge the battery by connecting the camera to your
    computer via USB?

    Thanks!

    Aaron Fude
     
    , Jul 11, 2007
    #1
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  2. SMS Guest

    wrote:
    > Hi,
    >
    > Is it possible to charge the battery by connecting the camera to your
    > computer via USB?


    No.

    Most compact and D-SLR cameras use 7.4V Li-Ion batteries (2 cells), so
    it's not as easy to do a USB charger (either external or internal) as it
    is with smaller devices (such as cell phones) that use a single cell
    (3.7V). A USB port puts out 5V at 500mA (guaranteed, even though there
    is quite a bit of margin built in on most systems). You'd have to do a
    DC-DC boost converter, which would boost the voltage while lowering the
    current, and these converters are only about 85% efficient, so you'd
    convert some of the energy to heat in the conversion.

    For sub-compact cameras they could do USB chargers if they wanted, but
    it'd be slow, and add complexity to the camera. There are some
    sub-compact cameras that do USB charging internally, but most don't.
    Canon used to have in-camera charging on some compact cameras (G series)
    but they dropped it. It was actually quite convenient to plug directly
    into the camera without removing the battery.

    I added a section on _USB Current Limits_ to the charger page at
    "http://nordicgroup.us/chargers" that explains how all this works (in
    terms of charging NiMH batteries from USB and why it isn't practical to
    charge Li-Ion batteries from USB). Click on "Explanation of USB Current
    Limits" at the top of the page.

    A lot of D-SLRs have optional battery grips that can use six AA cells,
    so that would be a workaround to USB charging, but the D40x does not
    have a battery grip available.

    Steve
    "http://batterydata.com"
    "http://nordicgroup.us/chargers"
     
    SMS, Jul 11, 2007
    #2
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