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  1. #1
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    I was wondering... If you have a wire with 12v flowing through it and you put a tiny 3v LED onto the wire, does that mean that you will have only 9v after the LED or will it still be 12v?

    And if it's still 12v doesn't that mean that I could put 50 3v LED's on a 12v wire and have them all work?


    The purpose of this question is this: I've had some trouble with the wiring in my old car and so I'd like to put some LED's are important wires so that I can easily see where power is and where it is not.

    Take for example the wire that runs to my fuel pump. When working correctly it has 12v going through it. If I put a 3v LED on it, will the pump still work?


    kthxbye!

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  3. #2
    Senior Member filburt1's Avatar
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    It means that you'll blow out the LED. You can put several 3V LEDs on a 3V circuit.
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  4. #3
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    Oh really? So then to use an LED I need to find a 12v LED?

    Hmm... I kind of thought that wouldn't happen only because there doesn't seem to be much of a difference. But then again I know just as much about electricity as I do about ... hmm... well I guess something that I don't know much about.

  5. #4
    Senior Member Brak's Avatar
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    Theoretically... you can put infinate amount on their.. that's assuming there's 0 resistance in the wiring and LED's... which there is. Eventually the current will be diminshed, but no.. not how you were originally thinking. Putting a 3V LED may not blow it out since LEDs are pretty sturdy.
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  6. #5
    Senior Member filburt1's Avatar
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    Put more simply, LEDs are by definition diodes, not resistors. Only the resistance of the wiring and the circuitry will resist the electricity as Brak said.

    LEDs tend to have a high tolerance in my experience, but I did once blow out an LED once. Just a pop and a puff of smoke.
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  7. #6
    WDF Staff smoseley's Avatar
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    it won't decrease the voltage, but it will decrease the amperage. The only way to increase or decrease voltage is with a transformer.

    12V won't blow out a 3V LED, but it will make it shine REALLY bright.

  8. #7
    Senior Member mossoi's Avatar
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    12Volts will seriously damage the LED's life expectancy if it doesn't execute it immediately.

    Current is going to be your main concern here though - 12V from a car battery is not the same as 12V from a PC or stereo. If you short the terminals of a car battery you get some impressive sparks.

    I would completely forget the idea of sticking an LED on a car battery. It's akin to putting a slot racing car on a subway track!

    Your best bet would be to use car bulbs and wire them in parallel to the circuit you are testing. If you wire in parallel you get a decrease in current, in series you get a decrease in voltage.

    Remember V(voltage) = I(current) x R(resistance) That's all you need to work out what'll happen when you wire things up.

    If you wanna be really swish you can use a relay to close a connection on a less beefy circuit to power the LED's. That way the effects of you testing the circuit are not have any impact on the circuit itself.

  9. #8
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    thanks mossoi. that helped me out a whole lot!

    i guess it was sort of a bad idea. when i was at fry's (looking for parts to rebuild the wiring harness in my car) i thought "golly. it would be really cool to have little green and red led's on some of the wires." but alas...


    thanks again.

  10. #9
    Senior Member justlivyalife's Avatar
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    Never mind

    Check out http://www.elexp.com/opt_3330.htm - they have some info on LEDs - they also sell 12V LEDs...

    The LED wont reduce the power to your fuel pump either.
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  11. #10
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    It's not the voltage thats really the problem, it's the current.... the low resistance in the LED's and negligable amount in the wires means a relatively high current (relatively as in for an LED) is flowing which is likely to nuke something.

    And depending upon cell type will determine the danger - Car battery lead acid cells have nearly no internal resistance and rigged up to a sufficient coil can easily administer lethal currents so be careful what you rig up to the terminals. However if it were say, a bank of regular nickel cadmium cells then you'd probably be alright using your tongue to bridge any gaps in the wiring!


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