use ac-dc adaptor instead of 4 c batteries

Discussion in 'General Electronics Chat' started by lionfly, Mar 4, 2005.

  1. lionfly

    Thread Starter New Member

    Mar 4, 2005
    5
    0
    I have a toy "activity center", which uses 4 c batteries. As the baby grows, the batteries exhaust quicker and quicker. I want to buy a 6v ac-dc adaptor, and connect the wires to the toy, instead of using 4 c batteries. I know many people will say it is not safe, but of course I will keep the wires and the DIY work safe for my baby.

    My question is: how many mA output should I buy, to drive the toy making sounds as 4 c batteries? 300mA? 500mA? 1000mA?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The capacity of the wall transformer is not too critical, as long as it will supply enough current. The 500 ma unit should do - C cells are not capable of much current.

    The output voltage is safe - there's not enough voltage to make it dangerous for a small child. If you don't have a connector on the activity center for external voltage, you might just want to lead in the wires through a small hole and attach to the battery contacts. Knot the wires to prevent them from pulling out of the hole. For best performance, place a 100 - 220 microfarad capacitor across the wires inside the case. Wall transformers are recitfied, but not regulated or filtered. Make sure the polarity is correct, too.
     
  3. lionfly

    Thread Starter New Member

    Mar 4, 2005
    5
    0
    Hi, beenthere,

    Thanks for the information.

    I saw the "Masterplug 1200mA Multi Voltage Adaptor", and not sure whether the 1200mA means the output current will burn the toy. Someone says the 1200mA is "MAXIMUM output" for the toy to use, not push the 1200mA to the toy. How do you think?

    and I am not sure whether the 1200mA is for every voltage (3, 4, 5, 6, 7.5, 9 or 12V), or only for the 3v or 12v. If it is for 3v, then when I use for 6v, does it mean the (maximum?) current will be 600mA. If it is for 12v, does it mean the (maximum?) current is 2400mA on 6v ?

    (by the way, why can the capacitor improve performance?)

    Sorry for so many questions.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi Lionfly,

    Wall transformers are pretty simple - they use one diode and perhaps one small cap. The multi-voltage one you have has multiple taps on the transformer for the different voltages. It's no better than 5% accurate. The 1200 mills (1.2 amps) is overkill for the application, but the transformer will run nice and cool.

    Loads don't use more current than they need, so all you need be concernd with is the voltage applied. The added cap inside the activity center will smooth the DC and perhaps make the circuit happier.

    You might want to tape over the voltage selector switch so inquiring hands don't push it up to a level where bad things will happen in the activity center. Kids seem to know how to do stuff like that. I once found an 18 month old kid who had found out how to pop the welds on 5 1/4" diskettes and peel them open.
     
  5. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    Problem with most batteries is they tell you the voltage and thats it. A much better value to know is the Ampere-Hours within the battery. i.e., how many hours of operation does the battery have if it outputs 1 Amp. From knowing this and the amount of time it takes for your batteries to go dead, you can see how much juice you actually need.

    Since the batteries are in series, you only count 1 battery's life for the entire system., and if I remember correcly, a C battery is around 600-800 mA-hours. So if your system dies in say, 5 hours of use, then you need your supply to dish out 700/5 = 150mA.
     
  6. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi lionfly,

    your wall adaptor is designed to give out 1200ma maximum it cannot go beyond that. since your batteries supplies 6v then use the 6v in you adaptor. if you will measure the voltage output at 6v tap you will notice that you have a rectified output of of about 8.48v unloaded. once you connect the load, it will drop to about 6.2v to 6.8v. :)
     
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