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Nikon DSLR Cameras
General Digital SLR Cameras
Why Not Charge Off USB
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<blockquote data-quote="MrF" data-source="post: 144423" data-attributes="member: 10292"><p>I'd imagine that it's size and weight like Don said, and maybe also heat and complexity. USB spec is 5V and 500mA IIRC. The EN EL-15 in my D7000 is rated at 7V. The charger advertises an output of 8.4V at 1.4A. So, they'd have build in a DC to DC converter to get the 5V USB to 8.4V. Since you're stepping up your voltage by a factor of 1.68, you lose by the same factor in current draw, so the 500mA becomes 298mA. So now you're charging the battery at less than one quarter the current that the wall charger can provide, so it'll take over four times as long to reach a full state of charge. Plus, the small, solid-state converters (essentially just voltage regulators) can only be used to step down voltage. If you want to step up DC voltage it becomes more complex. So, added complexity and cost, only to charge the battery four times as slowly. </p><p></p><p>I would guess that your point and shoots that charge off of USB operate at less than 5V.</p><p></p><p>Just my thoughts; it's been a while since I took EE though.</p></blockquote><p></p>
[QUOTE="MrF, post: 144423, member: 10292"] I'd imagine that it's size and weight like Don said, and maybe also heat and complexity. USB spec is 5V and 500mA IIRC. The EN EL-15 in my D7000 is rated at 7V. The charger advertises an output of 8.4V at 1.4A. So, they'd have build in a DC to DC converter to get the 5V USB to 8.4V. Since you're stepping up your voltage by a factor of 1.68, you lose by the same factor in current draw, so the 500mA becomes 298mA. So now you're charging the battery at less than one quarter the current that the wall charger can provide, so it'll take over four times as long to reach a full state of charge. Plus, the small, solid-state converters (essentially just voltage regulators) can only be used to step down voltage. If you want to step up DC voltage it becomes more complex. So, added complexity and cost, only to charge the battery four times as slowly. I would guess that your point and shoots that charge off of USB operate at less than 5V. Just my thoughts; it's been a while since I took EE though. [/QUOTE]
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Why Not Charge Off USB
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