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Copper wire problems and strange phenomenon

  1. Dec 4, 2015 #1
    ok so I was creating a connection today and used a 5 v led on a 1.5 v battery. Battery was in a case from radioshack and had insulated leads, full of twisted micro wire. Since there was no way to crimp it or strip the wire without me ruining the twists, I just bundled it to some non twisted wire and crimped it with aluminum foil. So I made an aluminum foil circuit with copper wire. The voltometer measured a steady 1.4 volts. There were a total of 4 aluminum foil crimp terminals, and the voltomer reads were good on all of them, 1.4 volts. (The voltometer completed the open circuit.) So I connected the 5 v led to the last 2 terminals, and the led didn't light. Yet, the LED completed the circuit, I touched the voltometer leads to the LED leads not the aluminum foil terminals. So the led was either defective or did not light at all with 1.5 volts. It was one of those flashing led's. I turned the lights off to verify...no light, a lightbulb did not light either. So I am going to have to buy a led rated at 1.5 volts. But other than that, all and all was good with the circuit, until...

    i then attached a 12 foot long insulated thin copper wire to it. Can't remember the gauge, it was the thinnest I could find though. All of a sudden things went haywire. In order to test it, I stripped some of the insulation, past the 3rd and 4th aluminum foil terminals. I attached the voltometer leads to the 12 foot long wire. Readings were erratic, and the battery started to heat up. Readings fluxed from 0.1 to 0.3 volts. Behavoir exhibited a strange pattern. The further I got from the battery, the more the voltage dropped. The closer I got, the higher the voltage. This was bewildering, because it occured even imbetween the original aluminum foil crimp terminals! It should have short circuited and became like the original model, yet instead of behaving like the original model, where all aluminum foil terminals measured 1.4 volts, this time the 4th and 3rd has less volts because they were further away, and the 2nd and 1st had more volts than the 4th a 3rd terminals, but still not as much volts as directly touching the battery, the voltage behaved as a proximity value. For instance, even at a close range, moving the voltometer leads a few inches closer to the origin would increase the voltage by a high value, the closer it got to the battery. This was bewildering, because it did not behave like a short circuit, which should have reverted its behavoir to the original model. I had to end the experiment short because after adding the 12 foot wire, the battery was heating up and losing voltage at a rapid rate. Does anyone have a explanation for this phenomenon?

    Also, close to the terminal the 12 foot wire was wrapped around a screw about 30 times. No discernible magnetic force was generated, as expected. I will post a picture diagram of the experiment, if need be.
    circuit.png
     
    Last edited: Dec 4, 2015
  2. jcsd
  3. Dec 4, 2015 #2

    meBigGuy

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    Your connections are bad. Strip them (or sand off varnish if magnet wire) before twisting. Forget the foil. Make good connections and retest.

    Measure the drop across your connections if you don't believe me. For example, why does the voltage drop to 0.6, the 0.3 after the connections in #3? The connections should not drop more than the wires.
     
  4. Dec 5, 2015 #3

    CWatters

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    Something is wrong in experiment 1. You can't measure 1.4v between nodes 1 and 3 unless the connection between them is open circuit.
     
  5. Dec 5, 2015 #4

    CWatters

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    A voltmeter should have high impedance so using one to "complete a circuit" doesn't make sense.
     
  6. Dec 5, 2015 #5
    Those were the experiment results. Maybe the connections were bad and it was an open circuit.

    I don't have a solder so I am going to crimp it today and retest the results using crimp connections instead of foil.
     
  7. Dec 5, 2015 #6

    marcusl

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    You can't expect a 5V LED to light up with 1.5V, so you need either a bigger battery (9V, e.g.) or lower voltage LED. You should include a current-limiting resistor as well, unless your light is an assembly that includes one. Use Ohm's law to figure out the appropriate resistance. For instance: if you had a 1.5V LED and a 9V battery, and want to limit current to 20 mA (should be a good starting point), R=V/I or R=(9-1.5)/0.02=375 ohms. A 390 ohm resistor is close enough.
     
  8. Dec 5, 2015 #7
    The battery label does not tell me how much watts or amps they have, so I am just going to guess and say they are 2 watt hours. They are Dollar General brand Heavy Duty AA batteries. http://www.dollargeneral.com/product/index.jsp?productId=12401295

    Is there a way to create an autofunnel limiter that pumps out a steady current regardless of what size battery you put in?
     
  9. Dec 5, 2015 #8

    CWatters

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    The battery might be designed to deliver a certain maximum power (Watts) or current (Amps) but it's typically the circuit that you connect that determines the actual power or current drawn.

    If you already have a 5V LED they usually have an internal resistor to control the current. Try it on three AA batteries in series... 3 * 1.5V = 4.5V.

    Yes it is possible to build a circuit that provides a constant current but I suggest you learn to a bit more before you go down that route.
     
  10. Dec 5, 2015 #9
    So if i hook it up to a 9v battery it wont explode? If I hook it up to a car battery, will the LED catch on fire?

    I would like to learn how to crimp, first and foremost. These foil circuits are aggravating as hell. I went to Radioshack.com but I can't find which crimps are for JTS or not. I looked in youtube and the tutorial was unclear.
     
  11. Dec 5, 2015 #10

    marcusl

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    You can also use wire nuts. The little blue ones are for small wires and would be suitable here.
     
  12. Dec 5, 2015 #11

    marcusl

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    You can connect to a car battery if you use a current limiting resistor as I suggested.
     
  13. Dec 5, 2015 #12

    Averagesupernova

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    I think for this experiment if you are starting with clean non-corroded wires just twisting them together will be satisfactory. You want to avoid a lot of movement as this will loosen the connection. Also, this sort of connection is not suitable for higher currents but just the few milliamps needed to light an LED should be fine.
     
  14. Dec 5, 2015 #13

    meBigGuy

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    I repeat --- the connections are bad --- the connections are bad ---- the connections are bad. See picture three measurement from 1 to 2.
    It's also possible (in addition) that the LED burnt out when you first connected it, or that it is connected backwards (in addition to the voltage being too low).
    So many things are wrong. Fix the connections, increase the voltage for the LED, and provide a current limiting resistor.

    And, as explained above, a voltmeter is like a very high impedance resistor, >10Mohms probably, so it's effect on the circuit is minimal. If you set it to measure current, then it is a very low (but not zero) impedance.
     
  15. Dec 5, 2015 #14

    CWatters

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    Tell us where you got the 5V led?

    Ordinary LEDs need a resistor to limit the current and stop them burning up.

    However most "5V leds" are designed to work on 5V (4.5V is close enough) without a resistor because they have one inside already.
     
  16. Dec 6, 2015 #15
    First - I want to say I am glad to see that your ARE playing with this, the 1.5 V battery keeps it very safe and you lean a lot by just trying to do something and then figuring out (or asking ) why are the outcomes not what I expected!!

    Next - when possible simplify. You seem to have a lot going on just to light an LED. Start as simple as possible and then make it more complex.

    Aside from crimps - you can get a terminal strip at RS - or a breadboard. The breadboard will need solid wire.

    Keep "playing" - as long as you are using the small batteries.

    And lastly - Jiff of course....
     
  17. Dec 6, 2015 #16
    Got it at RS. The package was delightfully vague. I dont believe the package told me about any resistor. It says the maximum ratings are 5VDC, 80mA forward current, reverse voltage 0.4VDC.
    However, I should have looked at the "supply voltage" stat more carefully before I bought it. I bought it on clearance for 67 cents and I just assumed it would run on only 1.5 volts. The supply voltage says 2.5-5 volts DC though. the other stats are luminous intensity (1.2mcd typ at 3V) peak wave length 697 nanometers, and blinkrate 0.5-3.0 hz (2.0 hz) type. THose were unimportant but Id figured Id mention them because I hate when companies and labels leave out the stats.

    I chose the organic because Jif Has partially hydrogenated oil. I dont think my RS has any terminal strips but I will call and double check. I still think you need crimps to plug into the terminals. I think a breadboard is the way to go but I dont know if I just plug in the JST wire or I need to crimp it or else it will be loose. Small batteries are always the way to go. I need a lady who wanted to make a coil gun, she used large batteries. I havent heard from her since.
     
  18. Dec 7, 2015 #17

    sophiecentaur

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    If you are suggesting the use of a car battery then you should also recommend that he uses a FUSE in series with the circuit. A current limiting resistor will drop volts, according to the load and that can interfere with the experiment and introduce confusion in your results. A car battery can easily land you with a metre of red hot wire, which is not nice to play with. Limit the current to just a few amps with an in-line fuse and have several spare fuses with you. (And spares for all the other components)
     
  19. Dec 7, 2015 #18

    marcusl

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    Agreed, a 9V battery is far safer for experimentation.
     
  20. Dec 8, 2015 #19

    sophiecentaur

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    An LED is probably less useful, as a method of measuring Volts or current than a small filament bulb (pea bulb) because a pea bulb will vary its brightness and colour over a big range of volts. It can be quite an effective 'meter' when a DVM is not available. Very cheap too. An LED just does nothing with low volts across it.
     
  21. Dec 8, 2015 #20

    Merlin3189

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    Resistors are conductors and conductors are resistors. A "short" is a relative concept - a resistance much lower than the source or conductance much higher than the load.
    I can't understand how a "short" would make it like the original model, where you had an "open" circuit (a LED below its threshold voltage.)

    So you have a battery in series with a chain of resistances. The voltage drops over each resistance. You measure the biggest voltage at the battery terminals and lower voltages further away as the voltage drops through each bit of resistance.
    Acircuit.png

    The battery has internal resistance. When it supplies current to an external resistance, both the external resistance and the internal resistance heat up according to P=I2R.
    12' of wire may loose heat faster than a small battery, so you may notice only the heat in the battery.

    The internal resistance causes a voltage drop proportional to the current V=IR, so the battery voltage is always lower when supplying current.
    What you are probably noticing here, is chemical changes. As a battery looses energy, its voltage drops, which is why it goes "flat" after long use. But if you load it heavily, short term chemical changes (polarisation) can reduce its voltage quickly, even before it goes flat. After a period of no (or low) current draw the battery is depolarised by other chemical reactions and its voltage may recover.

    This is the only surprising finding! I guess the magnetism was just to small for you to notice. Did you try putting a small compass near the coil? (If you do, it would probably work better without the nail. Just wrap the wire round the compass perpendicular to the natural lay of the needle.)
     
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