D40x: charge battery via USB?

Hi,

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

Thanks!

Aaron Fude

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"