Battery in paralle with circuit for uniterrupted power supply.

Discussion in 'General Electronics Chat' started by Makis Germ, Oct 25, 2016.

  1. Makis Germ

    Thread Starter New Member

    Sep 7, 2015
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    Hello! I have a simple (maybe stupid) question. Can i just connect a recheargable battery in parallel with my 5V dc circuit in order to supply it for a very short period of time, in case of a power failure? Will this work? Why not? Is a more complex power circuit needed?
     
  2. Makis Germ

    Thread Starter New Member

    Sep 7, 2015
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    Guys? Anybody?
     
  3. tcmtech

    Distinguished Member

    Nov 4, 2013
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    Only if you can keep you battery at 5 volts +- a few tenths of a volt for full charge to discharge.
     
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  4. Ramussons

    Well-Known Member

    May 3, 2013
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    There is no 5 Volt Battery.

    Almost all the "5 Volt" equipment actually have a 3.6 Volt (1.2 Volt x 3 cells in Series) for normal working.
    Since the AC power unit delivers 5 Volts, you just cannot connect the "battery" across the supply in a Floating mode - you will need to control the charging current..... etc.

    Having said that, If you need a simple short term backup, you can use a Low Voltage Drop Diode to isolate the battery from the Normal 5 Volt supply (to avoid the 5 Volt charging the battery), and charge the batteries separately as and when needed.

    This should work IF your 5 Volt equipment can work on 3.6 Volts (or 4.4 Volts in case of 2 Lead Acid Cells)
     
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  5. tcmtech

    Distinguished Member

    Nov 4, 2013
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    4 nicads or NiMH cells will float at 5 volts well enough but at some point they would need to be kicked up to ~5.8 - 6 volts to recharge properly.

    It's a poor power backup system but it would allow most 5 volt USB powered devices to run well enough being they are by design some of the more forgiving 5 volt powered devices around.
     
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