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atx psu power 2 powershot a470 cameras?

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Member - Posts: 2
Member spacespace
Joined: December 04, 2006
Location: United States
Posted: March 10, 2010 at 1:22 PM / IP Logged  
I would like to power my cameras using a PC power supply.
The cameras use 3.15v (two AA) the ATX power supply has 3.3v I was wondering how would be the best way to get the voltage where it needs to be and also not feed the camera to much amp/watt I have both resistors and diodes, I have read that you can use diodes to create a voltage drop. but I still am not sure about the amps/watts
I am also needing to send 5volt pulse to the usb ports of the cameras, this fires the cameras shutter (takes a picture). the computer has 5v, but I think I should drop it to about 4.5v to be safe.. also I would like to make sure I am not sending too much amps/watts here
any recommendations?
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 10, 2010 at 6:37 PM / IP Logged  
You cannot send too many Amps & Watts.
Loads will only accept what they can take for the correct voltage.
And supplying 4.5V to a 5V load may not be safer - it may wreck it (brownout) or cause overheating (constant power load - hence higher current at lower voltage).
V=IR. So I=V/R - ie, the current though a load is the voltage across it divided by its resistance (or impedance).
And P=VI so Power is proportional to current hence inversely proportional to resistance. [from V=IR & P=VI, P=IIR = VV/R)
If the cameras tolerate 3.3V (which they probably do) and the 3.3V supply does not jump above 3.3V (eg if unloaded - some need a load (resistor or lamp) to regulate properly) and it isn't noisy - then it should be fine.
And use 5V for USB, not 4.5V.
And make sure the camera batteries and the USB can share a common ground - they may not be able to. (IE - find more data else test one camera first.)
i am an idiot 
Platinum - Posts: 13,251
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: March 10, 2010 at 7:19 PM / IP Logged  

Running the 3.3 volt supply through a single 6 amp diode should give you very near 3 volts out.  i have never checked to see what kind of current the ATX supply will put out at the 3.3 volt lead.  You will have to research that and also the current consumption of the cameras.  Theoretically there should be 7/10 of a volt dropped across a diode.  It is usually more like 3/10 of a volt. 

Place the diode in the positive wire, band of the diode toward the camera.  Check the voltage with a meter to make sure it is close to 3 volts. 

Member - Posts: 2
Member spacespace
Joined: December 04, 2006
Location: United States
Posted: March 15, 2010 at 12:35 PM / IP Logged  
Just posting to say so far so good.
I have both cameras wired to the 3.3v source and also have the usb remote wired to the 5v source.

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