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Old 11-08-2006
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Wiring a LED to my e-fan

I bought an e-fan from Jusnes Modified and installed it a few months ago. My truck is a bit loud and I can never hear the efan in the cab, so I have been wanting to install a LED so I know when the cooling fan comes on and goes off. Yesterday I finally did it, I installed a LED to the power wire and ground wire of the e-fan. I blew the LED within a few seconds of the fan running.

After reading up on it today, I found that the fan runs at a high amperage. Can anybody tell me what I would have to do to run a LED in the setup, so I can tell when the fan is on or not? I was thinking I could run a resistor to the LED, but I'm not sure of what size I would have to use.
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Old 11-08-2006
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Nice....that's pretty cool. I can't help ya but it would be great if you could post up how you did it cause I wouldn't mind doing that.
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Old 11-08-2006
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You just need the right LED. Get a 12 VOLT LED. Connect the + side the fan's positive power wire. Connect the ground to any ground. That all you need to do.

I did this and took it a few steps further. I have three LED's:
* AC Compressor Demand
* Fan Power
* Fan Manual Disable (switched off)

This way I always know what it is doing and what it should be doing.
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Old 11-08-2006
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Quote:
Originally Posted by FireRanger
You just need the right LED. Get a 12 VOLT LED. Connect the + side the fan's positive power wire. Connect the ground to any ground. That all you need to do.

I did this and took it a few steps further. I have three LED's:
* AC Compressor Demand
* Fan Power
* Fan Manual Disable (switched off)

This way I always know what it is doing and what it should be doing.
That, or some simple calculations will show you what resistor you need so you don't need to pay $5 for a "12 volt" LED (which is just an LED + internal resistor anyway).

LEDs light/blow because of current, not voltage. I used this same technique with my shift **** mod and it's working fine. Simple eletronics:

Voltage = Current * Resistance

Figure out what typical voltage is running for the wire you will be monitoring. Let's say it's 12 volts as it would be in this case.

Now look at the specs for the LED you bought. There should be a forward voltage drop and a current rating. The voltage drop shows you basically how many volts are "lost" to the diode in the LED (I am not an EE, maybe someone else around here can explain that one better). Just understand that your target voltage is your source voltage MINUS the voltage drop. EG:

12 volts and 2.2 volt drop = 12 - 2.2 = 9.8 volts

From here, look at the current rating of the LED. Should be something like 20 milliamps (ma). Now apply it to the formula:

V = IR
12 - 2.2 = 0.02 * R

(Note that current (I) is expressed in whole amps, hence the decimal). Now you can figure out how many ohms of resistance you need to safely drive that LED:

9.8 / 0.02 = 490 ohms

So find a 490 ohm or higher resistor and you should be set. Note that I used a 1K ohm resistor in my shift **** because I wanted to dim the LED more (it was a superbright green LED). I usually round up a bit as a safety factor (what happens when the circuit is 14V? A car power supply is NOT the most steady thing in the world)

Depends on how hands-on you are with electronics. May be easier for you to find and buy a 12V LED... I just mention this as an option.
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Old 11-08-2006
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Yes, you could do that. Or you could save yourself the hassle and just buy a package of 12v LED's. There is no functional cost difference in the first place... plus you don't have then buy resistors and solder.
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Old 11-08-2006
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Quote:
Originally Posted by FireRanger
You just need the right LED. Get a 12 VOLT LED. Connect the + side the fan's positive power wire. Connect the ground to any ground. That all you need to do.

I did this and took it a few steps further. I have three LED's:
* AC Compressor Demand
* Fan Power
* Fan Manual Disable (switched off)

This way I always know what it is doing and what it should be doing.

Thats correct.

I have an LED (green) and it is on when the fan turns on. I also have an "off/auto" switch. It allows me to let the fan run in auto (controller) mode, or turn it completely off (for water holes, etc).

I have the LED wired to the positive on my fan, the ground was behind my radio bezel. I wired the switch to interrupt the fan positive, it works great!

I bought my LED and switch at radio shack for under $5
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Old 11-08-2006
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Thanks for the info guys, I remember, VI=R from school (many moons ago). I will look into the 12v LED though, so that I don't have to do all the soldering, etc.

Unfortunately the LEDs that I have are all old ones that I've had for a while, and I don't have any of the packaging.
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Old 11-09-2006
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Quote:
Originally Posted by FireRanger
Yes, you could do that. Or you could save yourself the hassle and just buy a package of 12v LED's. There is no functional cost difference in the first place... plus you don't have then buy resistors and solder.
To each his own I guess. I've just found it easier to find LEDs in a larger variety with the "normal" voltage vs. 12V. Maybe I havn't looked hard enough though.

Whichever you end up using, post a pic of the final setup. Would be interested in how you style the indicator lights (I assume on the dash).
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Old 11-09-2006
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Quote:
Originally Posted by winks
Thanks for the info guys, I remember, VI=R from school (many moons ago). I will look into the 12v LED though, so that I don't have to do all the soldering, etc.

Unfortunately the LEDs that I have are all old ones that I've had for a while, and I don't have any of the packaging.
it is actually v=IR....lol...

i have one on my fan.....the fan from Jusnes you need to tie it into the blue wire that goes from the fan to the controller........
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Old 11-09-2006
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Twinkle twinkle little star v is equal to IR up above the world so high p is equal to VI. Ok I will stop now. At least I got good grades in physics
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  #11  
Old 11-10-2006
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Oh yeah, brain fart, lol. Thank you for pointing out the error of my ways so many times.

The light and my new switches are actually near my shifter. I should have a resistor in there next week, and I will post pics.
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  #12  
Old 11-10-2006
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if you got 12v LED's then you dont need any resistors........
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  #13  
Old 11-10-2006
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Well, apparently what I have are not 12v LEDs, so John is going to give me a resistor this Saturday when we meet.
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  #14  
Old 11-10-2006
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Quote:
Originally Posted by winks
Well, apparently what I have are not 12v LEDs, so John is going to give me a resistor this Saturday when we meet.
at least you are getting it from someone who knows about them......
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Old 11-10-2006
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Lol, I have a hunch that he just does alot of guess work and trial and error.
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Old 11-10-2006
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yea probably...
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