AC/DC ADAPTER and Battery

Discussion in 'General Electronics Chat' started by superway, Sep 26, 2013.

  1. superway

    Thread Starter Active Member

    Oct 19, 2009
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    0
    Hello,
    I would like to ask a question.

    I have AC/DC adapter Class 2 Transformer 12Vdc 1000mA, and a battery 12V 4.5Ah. Can I connect them in parallel to apply 12vdc to my DUT or UUT? If there is no AC outlet near by, so I can use battery to power up my DUT, If the AC outlet isr near by, so I can power up both adapter and battery. I am not sure shoud it work or not?
    If not working that way, I can install 2 circuit breakers to control battery and AC/DC adapter.
    Please help

    Thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,034
    Are you hoping to charge the battery with the transformer? Does your load require a regulated voltage?

    The simple way to OR power supplies together is to just put a diode on each one to prevent reverse current. But diodes reduce voltage and waste a bit of power as a result.

    The wall wart likely has a bridge rectifier internally and would not require an additional diode - you'd just need one on the battery. That would prevent charging.
     
  3. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    My Device Under test is drawn about 450mA when turning on. I don't think the wall wart is a good device for recharge battery, and it has very small wire( Awg#22) on output side, I rule out the charging. So can put a 1N4001 in series with postive cable on battery?
    Thanks
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    An unregulated 12v wall wart can output nearly 17v. Make sure your device can tolerate the maximum output from your transformer. Otherwise, use a voltage regulator.
     
  5. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    When I used wall wart to power up 1 unit, the inrush current goes up to 1.1Adc about 3 sec., then drops down to 200mA. If I applied 2 units at the same time, the inrush current will be double while my wall wart is rated only 1000mA. Can it handle over current in 3 seconds?
    Thanks
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    3 seconds is a pretty long time. I assume you don't have any specs for you adapter, and so there is no way to know.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,100
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    You can get away with it but it's not good practice.
     
  8. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    Yes, 3 seconds is a pretty long time to load about 2 amps, but after that the current drops down to 400mA. It is not good practice, but I just want to turn 2 units on for demo.

    Thanks
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,034
    A proper adapter would cost very little and remove all concern.
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Its a bad idea, but if you already made up your mind you don't need my advice. Take care.
     
  11. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    I don't think the adapter will survive 100% overload (for 3 seconds) more than a few times. Try it. If it smokes, you will know you were wrong and end up buying the right adapter.
     
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