Spatial Orientation of Conductive Material

Discussion in 'The Projects Forum' started by tshanno, Apr 6, 2013.

  1. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Hello all:

    I want to pass a current through a copper disc using a variable dc power supply. The disc measures 52.5 millimeters broadside and ~0.75 millimeters thick. It's like a big, flattened penny.

    My first question is whether or not the placement of the alligator clips / electrodes changes the resistance.

    My second question is if there is any way I can use the known mass of the conductor (the copper disc) to guesstimate my initial voltage and amperage settings. I just bought the thing (the power supply) and I don't want to wreck it, at least not on the first day I have it. ;)

    Any and all insight greatly highly appreciated.

    Signed,

    'lectric newb
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Sure it does... if you drive the current front to back you have a much shorter path, and hence a lower resistance, then if you run the current across the face side to side.

    What settings could these be?

    Anyway, it may not matter. If this is an adjustable power supply with current limiting just turn it down to zero, connect it, then turn it up slowly and observe what happens. The current limit keeps the supply safe from most things you can connect it to.

    Exceptions to being safe are connecting to things like other power supplies.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Unless the copper is a special kind of copper, that we don't know of, the scenario your talking about is called a short circuit. And will effect your power supply. You need a series between on alligator clip and the power supply.
     
  4. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Thank you.

    0-30 volts, 0-5 amps.

    My power source is a Precision Variable DC Power Supply. The manufacturers blurb says it has "Short Circuit & Over Load Protection" but I would rather not rely on that.

    Is it correct to say that there is an energetic threshold above which a circuit becomes a short-circuit?

    It's just copper. Nothing exotic. Because I can vary the power output, I don't think I'll need to put anything else in the circuit.

    Rather, I can just add less energy to the circuit?
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Even a flashlight battery will short out if connected with a copper wire. But, hey, it's your power supply so go for it. :)
     
  6. #12

    Expert

    Nov 30, 2010
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    Precision Power Supplies are not designed to heat flattened pennys. You will only be at a few millivolts when the current limit is reached. Thus you WILL be depending on the settings to defend the power supply from melting.
     
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  7. ErnieM

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    Apr 24, 2011
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    "Short Circuit & Over Load Protection" means someone spent a lot of time designing a circuit that is nearly impossible to kill. It's designed to drive a short circuit like a big copper disk.

    Now I have some personal mental reservations about slamming a short circuit on to these myself, so when driving a short I'll turn both voltage and current to zero, connect the short, then turn V and I up to what I want.

    However, there is no reason for that. You can safely bang a short on them when set to the max... I'm just stressing them a but less.

    Ummm... I'm not sure what that means.
     
  8. patricktoday

    Member

    Feb 12, 2013
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    Yes. The threshold would be the point when resistance becomes 0 across the terminals of the circuit's power supply; but, colloquially, it's also the term used to describe the phenomenon of replacing a normal circuit load with a large metal disc.
     
  9. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Yes. I've never seen a 9v battery casing bend open and heat up to over 40deg C. Not once. Not me. Never.

    Okay, got it.

    Okay.

    The power supply in question is a bottom-end, no-name brand. Its owner is a tinkering newbie hack. Hmmm... I forsee absolutely no potential problems here. Especially if the box the power supply came in says "Short Circuit & Over Load Protection" on it!

    I'm being a smart-*ss; my point is, I don't want to find out if this power supply unit can protect itself or not.

    Ah, I get it. For some reason I was thinking the large metal disc made for a large resistance, but my big penny is offering a *small* resistance.

    Let's say I employ a voltimeter at the alligator clips. I postulate that as long as there is a voltage drop, my power supply is safe. True or false?
     
  10. patricktoday

    Member

    Feb 12, 2013
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    So are you just connecting the item directly across your power supply? Perhaps you can add one resistor in series like this:
    (+) terminal ----> 100 Ω resistor ----> magic orb ----> (-) terminal

    If the resistance level between the terminals is within normal range, there should be a full voltage drop across the load; the supply voltage shouldn't change when you attach your load.
     
    Last edited: Apr 8, 2013
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  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    The only question remaining is, why would you want to pass some current through a large copper disk? The only thing you will achieve will be generating some heat.
     
  12. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Okay, I will do that. I think this is what shortbus was getting at as well.

    Does the above series indicate a resistor between the magic orb and the alligator clip with the little plus sign stamped on it?

    So a voltimeter should read zero across the load?
     
  13. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Say, my power supply, cranked, goes up to 30V and 5 amps. That equates to 6 Ohms? Wouldn't a 100 Ohm resistor be out of the ballpark here?
     
  14. patricktoday

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    Feb 12, 2013
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    1st question: yes

    2nd question: no. Let me restate it. If you put a voltmeter across the power supply and there's nothing attached at all, it will read a certain voltage, right? Say 12V. If you attach anything, whether resistors, orbs, or any other circuitry, it should still read 12V; if the voltage drops that means the supply cannot sustain the current it's putting out.

    Sounds like 6Ω is the minimum resistance your power supply can handle. Any resistance above that is fine. If the orb is less than 6Ω and then you attach it alone then, zap, current overload is happening; if you add another resistor the supply will see XΩ + OrbΩ in series.
     
  15. ErnieM

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    Apr 24, 2011
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    Not if you turn the voltage down.

    Use 5 volts and 100 ohms limits the current to .05 amps even into a short circuit.
     
  16. tshanno

    Thread Starter New Member

    Apr 6, 2013
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    Okay.

    I think I'm good to go.

    Thank you all very much for your all your help!!!
     
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