need help with project

Discussion in 'The Projects Forum' started by andrej33, Sep 9, 2010.

  1. andrej33

    Thread Starter New Member

    Sep 9, 2010
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    Brand new to your forum. Need help with a project. I am a musician and I am building a new rack for my synth gear. I need to save space and weight, so I would like to limit the transformers in my rack. I was thinking of having one 12 volt DC transformer power the top 4 and have a strip with + and - feeds on them and go to each device with the appropriate resistor on the feeds to step down the voltage. Am I thinking correctly? This is what I have in the rack:

    Yamaha VL-70 Center Polarity + 12V DC 700 mA
    Senheiser mic Center Polarity + 12V DC 300 mA
    Roland JV-1010 Center Polarity - 9V DC 1000 mA
    WIDI wireless Center Polarity + 5V DC Doesn’t say how many mA, but it also runs on 2 AA Batteries.

    Alesis Nano Verb 5VA AC Obviously will need it's own transformer.



    Would appreciate any suggestions.
    Thanks!
    Andre
     
  2. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    You will need voltage regulators for the 5 and 9V. Resistors won't work. An LM317 in a TO-220 package would work for the 9V and and a LM78L05 would probably be ok for the 5V. Have a look at the datasheets.
     
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  3. andrej33

    Thread Starter New Member

    Sep 9, 2010
    3
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    Would I use a 12v transformer with these and how many amp transformer should I use? Would I just total the amps for each unit?
    Thanks so much!
    Andre
     
  4. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    Well, a 12V DC power supply, yes. Not a straight transformer. Just add up all the amps and it should be fine. Probably most of the things rarely if ever use their full rating, but go for the total to be on the safe side.
     
  5. andrej33

    Thread Starter New Member

    Sep 9, 2010
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    Thanks so much mark. Curious - if one of these regulators go bad, do they block the current going through them, or do they allow full current? Just don't want to fry anything.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Well, these regulators DON'T generally fail, in my experience, as long as you take care to heatsink them properly and wire them correctly. My hunch is that they would fail to open (no current), but I really can't say.

    In operation these regulators are like "smart" resistors, self adjusting to the load to maintain just the right resistance across themselves to deliver the specified voltage to the load, whatever current that load is drawing. Like any resistor, they will convert the excess voltage to heat. So, in the case of your 9v supply, if your power supply is delivering 13v and you need 1 amp at 9v., the regulator will burn off 4 volts (13-9) at 1 amp, or 4 watts. That'll get hot really fast without a good heat sink. The 12 volt, 1 amp (total) would only generate 1 watt. That might also get too hot without a sink, but is much less waste heat to shed. The 5v. is a big drop from the supply, but probably a low enough current to not need a sink.

    The good news is that your devices probably rarely draw the rated currents.
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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