Voltage Source - Phone AC to DC Adapters

Discussion in 'The Projects Forum' started by pradsy90, Dec 27, 2015.

  1. pradsy90

    Thread Starter New Member

    Nov 4, 2013
    Hi -

    I have just started experimenting with this hobby. I typically buy phone chargers from Goodwill and use them for my power source. I clip the ends and attach them to the alligator clips and start using them. But I find that very often literally within two or three days they give way. They just stop working. I assume its because I wire my circuits wrong and so it shorts it or whatever. But I am going through a lot of these. I am about 4 weeks into this hobby and so I have a lot of learning to do and mistakes to learn from.

    So, what would be your suggestions?

    1. Just get a better more robust power source from RadioShack which is obviously an easier option?

    2. Is there anything I can do within my circuits to avoid the shorting go back and corrupt the power source?

    Thanks in advance for your time.

    Pradhip. S
  2. ebeowulf17

    Active Member

    Aug 12, 2014
    Well, if you're at the stage where you're regularly smoking power supplies, this may be over your head, but if you could build a simple current-limiter circuit, it would prevent your short-circuits from drawing enough current to smoke your supplies.

    This thread includes a few different approaches that would work:

    The lm317 voltage regulator is a popular choice. Its data sheet includes a simplified schematic showing how to configure it as a current limiter:
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    If your using 3V, 5v and 12V, use an old atx computer psu as a bench power unit, cheap as chips... and lots of power.
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
    If you are smoking them that fast obviously you are trying to pull way more current from them than they are designed to produce.

    As others mentioned using a old computer power supply could be one option but unfortunately very few of them handle an actual short circuit very well which is a common occurrence when first starting out with electronics.

    On the option of buying one I would spend the money on a online purchase from Amazon or eBay or such before I would go to RadioShack for one. For the money you can likely find something way bigger and better. ;)
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012

    Look at the power supply carefully. There is a voltage rating and a current rating. The voltage is what it is. It cannot be changed. The current limit is a warning to you that you must consider in your design. For example, if you have a 5 volt supply that says, 500 mA, then you have to make sure that you always have at least 10 ohms of resistance between the power leads. 5V / 10 ohms = 0.5 amps (or 500 mA). If you have less than 10 ohms, then your power supply will crap out.

    Many older cell phone chargers were only 100 or 200 mA, meaning that a load with even higher resistance is needed. Use ohms law to calculate every circuit's current draw.
    Last edited: Dec 27, 2015
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