help with multi-camera power supply

Discussion in 'The Projects Forum' started by santoshaha, Sep 10, 2013.

  1. santoshaha

    Thread Starter New Member

    Sep 10, 2013
    1
    0
    Hi there, I'm trying to design and make a circuit to power a multi-camera array. I have 60 Canon Powershot A640 cameras which can each be powered by an adaptor which supplies 4.3 Vdc and 1.5 Amps. I have bought 3 bench power supplies which each output a fixed 13.8 Vdc and 40 Amps. I am hoping that I will be able to create a working circuit from these which will not destroy the cameras.
    I am a newbie so I do need help to navigate any pitfalls . I am thinking of creating a circuit of 8 sets (in parallel) of 3 cameras (in series). I am thinking that 3 cameras in series would receive 13.8/3 = 4.6Vdc each and that the 40 Amps output would be enough for the 24 cameras (as 24*1.5 = 36).
    I could create this setup but what are the dangers here?
    I have thought that if the resistance of the cameras varied depending on whether they are on or off then that could expose the other cameras in the series to too much voltage .. is it possible to test this?
    Also 4.6 VDC is 0.3VDC higher than the manufacturers adaptor. Is this very bad and could some resistance be added to the series to bring the Voltage down to 4.3 VDC ?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    no..no..no

    The "smartest" thing for you to do is simply use all 60 of the adapters that come with the cameras and create a big mains power strip.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    You cannot put the cameras is series. If they were lightbulbs (purely resistive, consistent loads), this could work. But they are not. For instance when charging the flash capacitor after a discharge, they might draw a LOT of current compared to when they are sitting there "idle". Since you cannot ensure they are all doing exactly the same thing at the same time, their current loads will vary. This means that the series arrangement cannot maintain the safe voltage across each camera in the string.

    So they need to all be in parallel. This could be accomplished with a single power supply rated to, say >25% more current than the sum of all the cameras. In theory, the 1.5A rating is plenty of safety factor, so you'd need a 4.3V, 90A supply. That's only 387 watts but I think it may be pretty tough to find. Maybe a welder?

    On the other hand, the adapter is sized to charge the battery in the camera, right? So maybe you need much less current to actually RUN the camera. [update] I checked the specs and it looks like the camera only draws about 100mA in playback mode. That gets you down to only ~6A, which is very much easier. I think you can find an old computer PSU that has that much 5V capacity, and then just use a single diode in series with each camera, to drop the voltage by 0.7V.
     
    Last edited: Sep 10, 2013
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