Solar Powered NAS box

Discussion in 'The Projects Forum' started by Stonekiller, Mar 25, 2011.

  1. Stonekiller

    Thread Starter New Member

    Mar 25, 2011
    3
    0
    I have a D-Link DNS-323 Network Attached Storage box which, according to the specifications sheet has a maximum power draw of 21.04w and a sleep mode power draw of 10.45W. The switch mode PSU it comes with has two voltage outputs, 12v/3A and 5v/3A.

    As it is on all the time (with a duty cycle of around 35-40%) I would like to see if it's possible to run it from two 8W solar panels through a storage battery.

    I have several "yuasa" sealed lead acid batteries and I'm thinking of using a 20AH 12v as the storage battery.

    Given that the duty cycle is less than 50%, using my sketchy mathematics skills I'm assuming that 16W of solar cells should be sufficient to keep the battery charged?

    If this is correct, I assume need to make a circuit that will regulate the charge current for the battery - I have no idea how to do this other than with something like an LM7812 voltage regulator?

    The next thing I need to do is convert the output of the battery into 12v and 5v rails for use with the NAS box. I notice that the 7805 and 7812 regulators have a max current rating of 1A... my concern being that the manufacturer of the NAS box thought it prudent to give both rails a 3A output which exceeds this components maximum rating.

    What other devices are available for such a power converter and is it possible someone could help me out with a circuit diagram?

    Thanks for reading!
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    You will need some switching power supplies for more efficiency.
    A LM7805 at 12 volts will convert the remaining 7 volts * used current into heat.
    So if you draw 1 A from the 12 volts, it will "burn" 7 Volts * 1 Ampere = 7 watts.

    Bertus
     
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  3. Stonekiller

    Thread Starter New Member

    Mar 25, 2011
    3
    0
    Hmmm.. guess thats the LM78xx series out of the question then, I don't have many watts to play with so efficiency is everything.

    I have no idea how to go about making a switching psu though!

    I can however follow a circuit diagram! (hint, hint!)

    lol
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    16 W of solar would almost work if you had 24 hours of high noon sun. 5 X 16 W would be closer, & a larger capacity battery would help, maybe 40 Ah?
     
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  5. russpatterson

    Member

    Feb 1, 2010
    351
    16
    Your battery voltage will fluctuate from around 14V to 12V depending on the state of charge. So if your box is ok with 14V instead of 12 then you just need to buy a charge controller to keep the battery from overcharging, then add some logic to turn off your device if the battery drops below 12V (or 11V or something).

    Lookup buck converter on wikipedia if you want to check out the basics for a switching supply.
     
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  6. Stonekiller

    Thread Starter New Member

    Mar 25, 2011
    3
    0
    Cheers for that, I think I'm going to have to invest in some more panels, luckily I've found a cheap supplier on ebay so I should be able to get a 50W panel together relatively cheaply... I'm guessing because its essentially a computer the voltage is pretty critical, plus it needs a 5v rail too but I'll check out wikipedia as instructed!

    Thanks again!
     
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