Uninterrupted power supply with SMPS

Discussion in 'General Electronics Chat' started by PlasmaT, Apr 3, 2015.

  1. PlasmaT

    Thread Starter Member

    Feb 19, 2015
    40
    6
    I want to make an uninterrupted power supply system for my (future :)) home automation system.
    Currently I have a 12V 5A SMPS. I plan to use 3.7v Li-ion batteries or lead acid batteries as the backup power source.

    I have looked up many uninterrupted power supply circuit diagrams and they are all meant for a linear power supply system.

    My concern is whether I can use the same circuit diagram with the the SMPS ?.


    The basic system will be as this:
    http://s.eeweb.com/members/circuit_...wer-supply-ups-circuit-diagram-1326212995.gif

    Thanks,
     
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    When you refer to a UPS, what IS the Uniterrupted Supply? 110/220 Volts AC or some DC voltage? What is the Power Required?

    A UPS for an AC supply will have an Invertor ( PWM type in your case ), a Battery and a Switched Mode Battery Charger - all commercially available. You only need to integrate them for your needs.

    Details of your requirement will give you more inputs from other members.
     
  3. PlasmaT

    Thread Starter Member

    Feb 19, 2015
    40
    6
    The uninterrupted supply is for a micro controller, few surveillance devices and and some low power LEDs .
    Power requirement is 12V and maximum 5A. When there is mains power the systems runs on the power supply unit and during power failure it should power up the system from a from a battery pack. Of course I will be adding a separate battery charging module as well.
     
  4. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    You have a few options. You currently have a SMPS is my read:
    Would that be powered by Mains power and what is your normal mains power? For example UK 240 Volts or US 120 Volts? Either way it leaves you open to simply buy a UPS based on your needs. For example a 12 Volt 5 Amp SMPS is a 60 Watt unit and running on 120 VAC will typically draw about 0.5 Amps or running on 240 VAC about 0.250 Amps. I did not take into consideration the inefficiency of the SMPS but for now close enough. To have power for certain things when the mains fail is always very nice. However, you need to determine how long at worst case, you want to have backup power? First we determine how much power will satisfy your needs, then for how long you want that power to last before your battery calls it a day and checks out. :)
    Anyway, a store bought off the shelf UPS will afford you mains type (similar) power to support your existing SMPS assuming it is mains powered, in addition to any other mains powered small utilities in the event of a mains failure.

    Another option is a circuit similar to what you posted. A Google of "battery backup power supply circuit" will bring up a dozen or more circuits similar to what you posted with many including a charger system which will maintain a float charge on your battery. Again, you need to determine the battery size based on how long, worst case, you expect the system to deliver power? Personally looking at your 12 Volt @ 5 Amps as a maximum I would run with a 12 volt lead acid deep discharge battery similar to those used in RV (Recreational Vehicle) and Marine applications.

    What you want or need really isn't all that difficult to build. You just need to figure what the max power demand would be and how long you want power available during a mains failure.

    Ron
     
  5. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Is 12 Volts a Nominal voltage? How high can you go? 14 Volts? Minimum 11.5?
    If yes to both answers, get a 12 volts battery charger with a 15 amps capacity. Simply float a 100 AH battery across the 12 volts. A 100 AH battery will comfortably support 20 hours backup. This is the simplest solution.

    You can opt for a more sophisticated solution with a Float and Boost Charger that monitors the battery status independently for a longer battery life - may not be required in your case.
     
    PlasmaT likes this.
  6. PlasmaT

    Thread Starter Member

    Feb 19, 2015
    40
    6
    Thanks Ramussons and Ron. The SMPS I got is 12V, so I guess I cannot go high, or Can I?, or may be I should use a boost converter right?

    At worst case, the backup power should last for 2 to 3 day or so. In case I am out of the house, I might want to switch off the mains, but still keep the surveillance system running. It may be put on standby, so I can keep the average current consumption to less than 0.5Amp, so that means 36Ah capacity for 3 days.

    Anyway, my main question still remains, "can I use the SMPS instead of the Linear PS as indicated int the circuit"

    Since SMPS regulates using the feedback from the output, with the battery connected will the SMPS give up and let the battery carry on although the mains power is available? I am a bit reluctant to practically try this :rolleyes: I don't want to blow things up.

    Thanks,
     
  7. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Yes! :)

    You can use your SMPS it won't matter. Just make sure you have a large enough capacity battery. The circuit you posted would work fine using your SMPS just fine or any like circuit.

    Ron
     
    PlasmaT likes this.
  8. PlasmaT

    Thread Starter Member

    Feb 19, 2015
    40
    6
    Thanks Ron for giving me the confidence.:)
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    is your 12 volt smps 12 out, 12 in, or both? you cant run a 120 volt input smps on 12 and expect it to output `anything.
     
  10. PlasmaT

    Thread Starter Member

    Feb 19, 2015
    40
    6
    Well... The PS I got is the same as this [​IMG]power supply. I ll be using it on a 220V AC mains.
     
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