Solderless Breadboard + Wall Wart?

Discussion in 'General Electronics Chat' started by UncleDarryl, Feb 5, 2007.

  1. UncleDarryl

    Thread Starter New Member

    Feb 5, 2007
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    0
    Hello - I'm completely new to electronics, and bought a solderless breadboard kit to tinker around with. It came with a proprietary +5v power supply kit (which will be my first attempt at soldering) that requires a wall transformer. I asked if there was a suggested or limit current on the wall wart, and was told to stay under 250 mA without a heat sink.

    The problem is, after quite a bit of searching, I can't find a 5vdc wall transformer under 500 mA that has the right connector (2.1mm center positive). I'm not sure if these are really this hard to find, or if I just don't have my facts straight. If I use a 5vdc 1A transformer, is that going to overheat and melt everything? Any advice?

    Thank you
     
  2. kender

    Senior Member

    Jan 17, 2007
    263
    0
    It depends on the circuit that you have on the breadboard. If it doesn't have shorts, nothing should melt. For example, the battery in a cell phone can deliver a few amps of current, but the phone uses only 100mA without melting away.

    You can get wall wart with a higher current rating and a correct connector and splice a fuse holder into one of the leads. Then you can limit the current with a 250mA fuse.

    You could get a wall wart with a sufficiently low current rating, cut off it's connector, strip off the wires and solder them to you proprietary power supply module. You could also splice a switch and a fuse into the cable.
     
  3. UncleDarryl

    Thread Starter New Member

    Feb 5, 2007
    6
    0
    Thanks for the reply. So far the best I can find is 750 mA, so I guess I'll try that. I know the breadboard can handle an amp or two, but I was more concerned about damaging the power supply.

    Incidentally, is there something odd about 5vdc wall transformers? It seems like they're relatively uncommon. I've found a lot of 4.5- and 6-volt transformers, but few 5's.
     
  4. kender

    Senior Member

    Jan 17, 2007
    263
    0
    IMHO: Often there is a linear regulator (e.g. LM317, LM7805, which are a staple for the hobby projects) or a low dropout linear regulator (LDO, e.g. LM2937) after the wall wart. Digital circuits usually run on +3.3V or +5V. Linear regulators require some "head room". In other words, if you give +5V to a linear regulator, you will not be able to get regulated +5V. Linear regulators can work with large input voltage (Vin) relative to the output voltage (Vout). But the bigger the difference between Vin and Vout the more heat the regulator will need to dissipate. So, wall +4.5V wall wart suits well for a system that runs on +3.3V internally, and +6V transformer suits well for a system that runs on +5V internally.

    I guess, I’m leading towards a suggestion: don’t use a proprietary power supply - use linear regulators instead. They cost about $1.00. They are not proprietary. They are easy to understand. If you fry your proprietary power supply, consider this suggestion.
     
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