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Old 08-18-2012, 02:48 PM
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dual electric fans wiring ?

ok i have dual electric fans & i wanted to know is there a way that i can hook up a LED light inside my car so when the fans come on the LED light comes on

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Old 08-18-2012, 07:56 PM
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Use a relay,SPST common 4 pin.
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Old 08-18-2012, 08:56 PM
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Quote:
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Use a relay,SPST common 4 pin.
so ill just have to run the led hot wire to the relay and ground the other wire?
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Old 08-18-2012, 08:59 PM
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You can run a wire from the fan side of the fan relay back to your light..... ground the other side of the light and when the fan fires up so will the light.
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Old 08-18-2012, 09:51 PM
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If you want to use an LED, just wire it in parallel with the fan motor and use a 1/4 watt, ~1,000 ohm resistor in series with the LED. Any value between ~500 ohms and 1,000 ohms will work fine. A lower value will result in a brighter LED, but possibly shorter lived. Alternatively, you can buy LEDs for 12 volts, and they typically include a 470 - 1,000 ohm resistor in series.

The LED is polarity sensitive and the longer lead goes on the + terminal. But if you hook it up backwards it won't do any harm. It just won't come on.
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Old 08-18-2012, 10:08 PM
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coil

The LED should be connected in parallel with the coil of the relay. The circuit that is typically used is as follows.
The coil has a ignition switched and fused source on one of the terminals.
The other terminal of the coil gets connected to the temperature sensor which closes when it reaches it's rated temp. and completes the circuit to ground.
Connecting the LED to the coil is preferred for (3) reasons.
The wire only needs to small (#18) as the load of the coil is very small.
And when the LED is connected to the fan side of the relay the wire will need to be the same as the wire going to the fans or at least fused if the wire is smaller.
And the fans will feedback voltage to the LED as they coast to a stop and sometimes will continue to turn when the car is moving.

vicrod
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Old 08-19-2012, 12:32 PM
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Quote:
Originally Posted by vicrod View Post
Connecting the LED to the coil is preferred for (3) reasons.
The wire only needs to small (#18) as the load of the coil is very small.
And when the LED is connected to the fan side of the relay the wire will need to be the same as the wire going to the fans or at least fused if the wire is smaller.
And the fans will feedback voltage to the LED as they coast to a stop and sometimes will continue to turn when the car is moving.

vicrod
Not if connected directly across the fan motor leads that actually go right to the fan motor.

The wire can be as small as you choose because it only carries about 14 (@ 1,000 ohm) to 28 milliamps (@ 500 ohm) for the LED,

i.e., (13.6 volts - ~1.6 volts for the LED)^2/1,000 ohms = 14 milliamps

No fuse is necessary for just an LED.

The LED is direcly across the fan motor. When the motor stops receiving current, both the fan and LED go out. There is no way that the fan can continue to spin under it's own current produced by the rotation of the motor, though the LED may remain on for a moment after shutdown as the fan winds down.
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Old 08-19-2012, 06:20 PM
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Just a quick quistion,would an LED act like a diode,because it is in a sense it a one way.
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Old 08-19-2012, 07:37 PM
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LED stands for Light Emitting Diode......... It won't take very much current tho
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Old 08-19-2012, 07:38 PM
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Yes it will act like a diode.
It is a diode.
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Old 08-19-2012, 07:52 PM
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hot

The load of an LED is insignificant and not an issue when wire size is concerned. The capacity of the circuit and the protection of that circuit is the factor by which a wire size is selected.
For example a cooling fan could have a 30 amp or larger fuse and #12 or larger wire. Connecting a #18 wire to that circuit is not a good idea when you consider that that #18 wire can become shorted. #18 wire does handle 30 amps well. A very hot wire will result.
That is the point I was trying to make.

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Old 11-01-2012, 06:09 PM
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wiring problem >> need help

ok i got a 12v led light to run to my fans so i no when they come on. i wired the light up to the power wire on my fan & grounded the other inside the car when i did that the led was lit up with the car off / how do i get it to come on only when the fans com on??
im also have a override switch

> this is the led
> the fan controller
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Old 11-01-2012, 06:32 PM
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Quote:
Originally Posted by the82elco View Post
ok i got a 12v led light to run to my fans so i no when they come on. i wired the light up to the power wire on my fan & grounded the other inside the car when i did that the led was lit up with the car off / how do i get it to come on only when the fans com on??
im also have a override switch
The fan controller you have pictured is a Derale 16759. They control the fan by switching the ground on and off rather than by switching the power. So you will need to change the way you have your LED wired. Based on the Derale wiring diagram, I would suggest connecting the LED's positive wire to the controller's yellow, and the LED's negative to the controller's red wire.

Hope this helps....

Joe G.
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Old 01-10-2014, 04:07 AM
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The led bulb that i have wired to my fans comes on when the wind pushes them as im driving how can i fix that problem?
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Old 01-10-2014, 12:28 PM
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It sounds like the rotation of the fan motor is acting as a generator and this is lighting the LED. I think that a properly placed diode in the path could keep this "back emf" from getting to the LED causing it to light but would need to see how it was ultimately wired.

Alternativly, a slightly different wiring scheme may do the trick.

For example, instead of putting the LED across the fan, it could be across the fan's relay activation terminals. Then when the relay is off, thre is no current to these terminals and they are not connected to the fan so receive no back emf.
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