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Playing with transformers and resistors....

Discussion in 'General Electronics Discussion' started by Dewald de Bruyn, Jun 14, 2016.

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  1. Dewald de Bruyn

    Dewald de Bruyn

    Jun 14, 2016
    I have watched several "maker" videos on YouTube an i like making stuff myself. The next project I have in mind is simple and in most parts self explanatory, but I do have a few questions. The project is the basic re-purposing of an old PC power supply to make a Desktop power supply. I do however have some alternate ideas. Firstly, i would like supplying a wider spectrum of voltages than the five varieties given by the power supply (-12vDC, -5vDC, 3,3vDC, 5vDC and 12vDC). I know everyone says don't waste power etc. but I don't want to make it complicated so, i'm just gonna use inline resistors. I don't have a multi-meter, and there is no electronics shop around my house in walking distance, so I can't buy one either. if someone can make it easier for me i would appreciate it. I have desoldered many resistors, but I don't know how to calculate their resistance anymore, so pictures or band colour reference would be fine. Here are the resistors I need. 5v reduced to 1,5v, 12v reduced to 9v, 12v reduced to 6v. this will then give me 1,5v, 3,3v, 5v, 6v, 9v, 12v. I will also be using an additional line from each voltage to make charging stations, so that I can recharge batteries for items like flashlights and cameras which of course cannot be connected to the power supply permanently. I have also thought of adding a variable reosthat switch (punctiometer) to make the voltage completely variable, but i'm a little bit unsure as the punciometer has six pins and no markings so I would not know where to connect what. Thanks for your patient answers to my dumb questions, if you're gonna say something nasty, rather just move on to someone else, i'm not that guy...cheers
  2. Minder


    Apr 24, 2015
    If getting into any kind of electronics a meter is pretty much essential, you are not going to confirm any changes you might make or on constructed circuits, if strapped for cash, you can get a cheap meter off ebay for around $8.00 p/p paid.
  3. BobK


    Jan 5, 2010
    Resistors can only be used to reduce voltage when the current is constant. For a general purpose power supply, you need a regulator to reduce voltage. Use and LM317, which is a variable regulator or 78XX which are fixed regulators. Look these up to see what the circuits look like. They are quite simple.

  4. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Welcome to Electronics Point!

    Would you please visit this Google page and tell us which "six pin device and no markings" device you would like to use? If possible, take a picture of it and upload the picture here. Maybe someone can help identify it. It might be a dual potentiometer if it has six pins. These are popular for use as stereo volume controls.

    If you want to do anything in electronics you must have a multi-meter. When I was a teenager, just getting started "playing" with electronics, I saved up my newspaper-route money and bought a mail-order RCA kit Vacuum Tube Volt Meter (VTVM). Best purchase I ever made!


    You have to able to measure AC and DC voltages and resistances to learn anything useful about electronics, and modern digital multi-meters also measure AC and DC currents too. Even the cheapest digital multi-meter is better than no meter at all. Sure, you can farkle around with stuff, hook things up by trial-and-error, maybe even get something that works... but it you truly want to learn electronics, you need test equipment. Start here:

  5. davenn

    davenn Moderator

    Sep 5, 2009
    As Bob suggested, this is a really bad idea and you are going to have absolutely no voltage regulation as a result

    Use proper voltage regulators to get your desired voltages out

    and yes, as minder said ... BUY a meter .... you cant do anything without it

    hevans1944 likes this.
  6. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    You cannot use resistors as you don't know what current will be taken by the item you connect to each of the voltages. If you find a resistor that works for one particular device, the voltage will not be correct when you connect another device to the same output.
    You just need a little technical expertise to add regulators to each of the output.

    I suggest you do a 6 year "Masters of Electronics" and then you will know how to add the regulators and the surrounding components to prevent the regulators going into high-frequency oscillation.
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