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Use Power from the PC's USB port, instead from AC/DC adapter....??

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Offline rtiz_rtiz_rtiz

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Use Power from the PC's USB port, instead from AC/DC adapter....??
« on: 02 / February / 2009, 06:42:56 »
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I have this idea, to make power cable, which recieves power from the USB port, as far as i know, USB is 5v, Powershot A720 and other similar models use 3.15v.

Will it be ok to use the 5V form the USB or should i better scale them down somehow to 3.15V?

Will it be ok to use Flash from USB power? Is there a chance that the flash charging can fry my USB port...?


any ideas?
« Last Edit: 02 / February / 2009, 11:50:10 by rtiz_rtiz_rtiz »
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Offline barret

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #1 on: 02 / February / 2009, 07:14:50 »
hmmm... it would be nice to power camera via standard usb cable, but i'm not sure if that's possible without any hardware modifications, especially knowing that camera have separate power source connector. maybe cable which connects usb from computer and power supply socket would do? with scaling down from 5 to 3.15V?

btw: a550 also uses 3.15V, so i'm also interested.
« Last Edit: 02 / February / 2009, 07:17:02 by barret »
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Offline rtiz_rtiz_rtiz

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #2 on: 02 / February / 2009, 07:47:59 »
Yes yes, that what i was thinking of, ie cable that is [USB plug] un one end and [Canon power plug] on other end. That would look like:

[PC or MAC]<<[USB plug]=================[Canon power plug]>>[Your Canon Axxx camera Power Hole]

Eventualy, whe could integrate all this in one Y-form USB/Power cable for USB data and power, that would look like:

[PC or MAC]<<[USB plug]=====|============[Canon power plug]>>[Your Canon Axxx camera Power Hole]
                                                      |============[Canon power plug]>>[Your Canon Axxx camera USB Hole]

All this is easy from soldering point of view, but i am concerned about Voltages, 5v > 3.15v and Flash charging from USB power frying the USB chip in my PC.

.....
« Last Edit: 02 / February / 2009, 07:53:26 by rtiz_rtiz_rtiz »
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Offline barret

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #3 on: 02 / February / 2009, 08:02:54 »
i'm not concerned about frying anything. what concerns me more is electric current: canon a550 requires about 1A for operation. can usb handle this?

btw: those cable ideas above: great & simple :)
« Last Edit: 02 / February / 2009, 08:09:41 by barret »
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Offline rtiz_rtiz_rtiz

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #4 on: 02 / February / 2009, 08:16:46 »
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databoy

Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #5 on: 02 / February / 2009, 09:10:27 »
As a qualified electrical professional who earns his income from servicing electrical/electronic equipment I will say one thing.

Servicing professionals DO NOT post technical servicing information on Wikipedia.

Regardless of what is printed and the specifications, there is a reason why manufacturer's provide a separate power socket and not derive power input from a USB connector. If you do not have an electrical circuit for your camera DO NOT deviate from the manufacturer's specifications.
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Offline barret

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #6 on: 02 / February / 2009, 09:44:00 »
Quote
there is a reason why manufacturer's provide a separate power socket and not derive power input from a USB connector
yes, we know that, so we don't want to power camera via camera's USB socket, but instead power camera from computer's USB socket to camera's power socket.

anyway, thanks for your input.
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Offline rtiz_rtiz_rtiz

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Re: Use Power from USB port, instead from AC/DC adapter....??
« Reply #7 on: 02 / February / 2009, 11:47:40 »
Quote
Regardless of what is printed and the specifications, there is a reason why manufacturer's provide a separate power socket and not derive power input from a USB connector.

they do that to charge $$$$ from us for the power adapter  :D

anyway, acording to the wikipedia article mentioned earlier:
Quote
A unit load is defined as 100mA in USB 2.0, and was raised to 150mA in USB 3.0. A maximum of 5 unit loads can be drawn from a port in USB 2.0, and was raised to 6 in USB 3.0. There are two types of devices: low-power and high-power. Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4V in USB 2.0, and 4V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard. All devices default as low-power but the device's software may request high-power as long as the power is available on the providing bus.

that means, USB2.0 hub can suport Maximum of 5 units, at the same time one unit load is defined as 100mA, that makes:
Code: [Select]
5 * 100mA = 500mA = 0.5A


Which, as i understand, unfortunately, means that there is not enough power to obtain from USB hub to run the Axxx Camera, which requires 1A.  :'(

any coments  :blink:


« Last Edit: 02 / February / 2009, 11:50:46 by rtiz_rtiz_rtiz »
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Offline rtiz_rtiz_rtiz

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Re: Use Power from the PC's USB port, instead from AC/DC adapter....??
« Reply #8 on: 02 / February / 2009, 14:12:36 »
ok, i could no resist, i made the cable, connected the camera
 - camera turned on in play mode, showed some white garbage on screen, when i tried to swich to record mode, it briefly showed some white stuff on screen, then turned itself off. retrying this gave the same results.  :(

so i am stuck with the Canon power adapter.

btw, my camera is still working with bateries, no damage done.  8)
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Offline fudgey

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Re: Use Power from the PC's USB port, instead from AC/DC adapter....??
« Reply #9 on: 02 / February / 2009, 14:43:28 »
Yep, USB will not give you enough current to work zoom. Even if you stepped 5 V down to 2.5 V  with 100% efficiency (yes, 2.5 V works, there's just less room for cable and connector drops) you'd only get 1 A from USB's 500 mA @ 5 V port without exceeding it's spec (and that's on a good day... USB may actually supply less than 5 V).

A huge capacitance would help with temporary motor current drain, but USB specs 10 uF max between the supply rails and you'll need about a million times more (something that probably damages your PC unless you're lucky).

I don't know how USB ports in PCs are typically built for real, but I find it quite likely that many supply their 5 V rail to USB with little series impedance, so it's possible a PC exists from which you can draw a lot more than the USB spec allows. But you won't find anyone who's going to recommend for you to try that and the USB spec is very strict about requiring devices to report their power needs before they draw more than a little bit of current. Some OSes (recent Linux kernels to name the only one I know of) even forbid total port currents in excess of 500 mA to protect hardware.
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