Dc to Dc UPS for router

Discussion in 'The Projects Forum' started by spooge, Jun 25, 2011.

  1. spooge

    Thread Starter New Member

    Apr 13, 2009
    2
    0
    Hi I tried searching for similar projects. but wasn't able to find a suitable one.
    I want to make a UPS for my Router/modem so when the power goes out i can still use it with my laptop. power outage occurs 2, 3 hrs per day where i live. I found a schematic which i believe will be right for the job but i need to make sure what changes needs to be made keeping following in mind.

    1. It should have Battery overcharge protection.
    2. I can use an after market ac to dc power adapter. what voltage/amps will be right for it.
    3. keep it as simple as possible.

    I don't have extensive knowledge in this area so please help me.


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  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    What voltage do you expect? What current?
     
  3. spooge

    Thread Starter New Member

    Apr 13, 2009
    2
    0
    The router is 12V (1 amp).
    I think U1 (LM7805c) and C3 1.0u can be removed from the circuit, yes? as its not useful in this situation.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    You will still need some regulation for the high rail, as the battery voltage can be as high as 14.4V. A 12Vac transformer should be ok. Try to search the net for some simple battery charger.
     
  5. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    I'd move the 7805 to the left and make a float charger out of it. This is a variation of what kubeek said. A transformer only charger can drive a battery crazy because of power line voltage changes. Decide on a float voltage that suits your exact battery and set the 7805 at that voltage. This will insure a good lifetime for the battery. Then you can decide if you need another 7805 (or similar) to set the output voltage to 12.00 volts.

    I doubt that the output voltage is very sensitive because routers usually run from wall warts. If your original wall wart for the router was a common, unregulated, POS, the router will get along fine with 13 or 14 volts.

    Be sure to check other people's opinions. I might be wrong!
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If your router needs 12v @ 1A, and your power goes out for 2 or 3 hours per day, you'll probably need a battery rated for 1A*3hr/.3 = 10AH or more in order to not kill it in a short period of time. If the battery becomes discharged past 70% of full charge, its' life will be relatively short; the deeper the discharge, the shorter the life.

    Your power adapter will need to be able to supply enough power to both charge the battery AND power the router at the same time; so you'll probably need a 2A supply for both supplying the router and recharging the battery. This also means that the 1N400x diodes you've shown will not be adequate; as they are rated for 1A continuous.

    Charging/discharging a lead-acid battery is a "lossy" process, for every 1AH you put in, you get about 0.75AH back; most of the rest of the power is dissipated as heat in the chemical reactions that occur.

    Efficiency should be a big issue for you. Your power company has outages because the infrastructure is not sufficient to handle loads 24 hours a day. If you add a UPS that has a low efficiency, you make the problem worse instead of better. Unfortunately, linear regulators are not very efficient.
     
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