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LED light question?

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LED light question?

Unread postAuthor: wangpushups » Tue Oct 09, 2007 12:59 am

I'm using a 12V fan operating it with a 9V battery and I have a green LED light that I want to install so I can tell when the fan is on. Do I need to have resistors or anything for this or do I have to connect it to another battery? Maybe I have no clue what I'm talking about, I don't know... Is there some kind of diagram showing how to install the LED that I don't know about.
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Unread postAuthor: Orpackrat » Tue Oct 09, 2007 1:09 am

Just connect a 1/4 watt 470 OHM or 560 OHM resistor to the LED. Then you can operate it on 9-12 volts without a problem
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Unread postAuthor: wangpushups » Tue Oct 09, 2007 1:18 am

So the 560 OHM resistor, the green LED, 9v battery, 12v fan, and the switch can all be in the same circut with no problems?
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Unread postAuthor: mark.f » Tue Oct 09, 2007 5:45 am

If you wire the resistor inline before the fan, you will limit the voltage to the fan as well.

Install the LED after the fan, (negative side).
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Unread postAuthor: Hotwired » Tue Oct 09, 2007 6:32 am

:?:

Having the resistor in series with the fan anywhere will slow it down.

Have the resistor and LED in parallel.
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Unread postAuthor: paaiyan » Tue Oct 09, 2007 6:54 am

I agree with hotwired, have it in parallel. Then you can either wire in a resistor with the LED, or you can get one that has it built in.
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Unread postAuthor: jimmy101 » Tue Oct 09, 2007 12:21 pm

This is how to do it
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9V battery, switch, resistor, LED and fan circuit
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Unread postAuthor: wangpushups » Tue Oct 09, 2007 12:55 pm

Thanks jimmy the help is much appreciated.
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Unread postAuthor: mark.f » Tue Oct 09, 2007 5:14 pm

Heh, I don't know what I was thinking. There's no excuse this time, I'm just a dumbass. I will say that I'm not an electrician, though. 8)
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Unread postAuthor: miskaman » Tue Oct 09, 2007 5:34 pm

jimmy101 wrote:This is how to do it


That's not gonna work, sorry. Electricity takes the shortest path ALWAYS. I'm not an experienced electrician, but I do know that is not going to work. The LED will light up, the fan just won't work.
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Unread postAuthor: Lentamentalisk » Tue Oct 09, 2007 5:40 pm

miskaman wrote:That's not gonna work, sorry. Electricity takes the shortest path ALWAYS. I'm not an experienced electrician, but I do know that is not going to work. The LED will light up, the fan just won't work.


wrong. not much more to be said.

btw, saying LED light is repetitive and redundant, LED stands for Light Emitting Diode.
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Unread postAuthor: iPaintball » Tue Oct 09, 2007 5:47 pm

Your right, you're not an experienced electrician. Its called wiring in parallel.
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Unread postAuthor: Lentamentalisk » Tue Oct 09, 2007 6:39 pm

think of it like this:
the power plant sends out its electricity, at bazillions of times the voltage and watage that comes out your wall. the electricity does not instantly turn the first house it comes to into a gigantic fireball, the house takes what it needs, and then the rest continues on to the next house, otherwise we would all need our own power plant, and that would just not be economically possible...
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Unread postAuthor: jimmy101 » Wed Oct 10, 2007 12:33 pm

miskaman wrote:
jimmy101 wrote:This is how to do it


That's not gonna work, sorry. Electricity takes the shortest path ALWAYS. I'm not an experienced electrician, but I do know that is not going to work. The LED will light up, the fan just won't work.


sigh

Yep, you are not only not an experienced electrician but apparently you know little about physics.

Electricity does not take the shortest path. If it did, every 120V outlet in your house would have a big ass arc jumping from the hot plug to the common and/or ground plug. That is the shortest path. Why would the electricity bother running down the wires to an appliance when it can take the "shortest path ALWAYS" and just arc through the air?

Electricity takes the lowest resistance path, which may or may not be the shortest physical path.

If the power supply can supply sufficient power, then all parallel paths will carry current. This is almost always the case in a real world circuit. In my drawing the current through the LED is limited by the resistor. The current through the fan is limited by the internal resistance of the fan. The power supply can supply more than the sum of those two currents.

Every light bulb in your house, along with the fridge, computer, TV … are wired in parallel exactly as in my drawing.
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Unread postAuthor: mark.f » Wed Oct 10, 2007 6:29 pm

Come on miskaman, even I could admit I was wrong. :wink:
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