Fan Tell Tale LED Issue - Fans as generators

[Johno]

OK, I know, I was being thick. I just forgot !

So the question is, given the LED is being illuminated on the voltage generated by the fans' windmilling' is it possible to introduce resistance into the circuit to prevent it happening until the ECU switches the fan on.

This is through an Emerald set up, so not via otter switch etc.

I was thinking that by measuring the voltage generated when 'windmilling', by intriducing resistance I could stop it illuminating the LED until fully switched with 12 volts. . .

Any thoughts. . . .

[chrispitman]

Use a small relay to switch the led as these will require more current than an led.

[nicktowe]

Johno said:

OK, I know, I was being thick. I just forgot !

So the question is, given the LED is being illuminated on the voltage generated by the fans' windmilling' is it possible to introduce resistance into the circuit to prevent it happening until the ECU switches the fan on.

This is through an Emerald set up, so not via otter switch etc.

I was thinking that by measuring the voltage generated when 'windmilling', by intriducing resistance I could stop it illuminating the LED until fully switched with 12 volts. . .

Any thoughts. . . .

Ithought Diodes only allow the current to flow in one direction, so I am a little syrprised that windmilling fans light up the LED. Time to look out those electronice text books. Maybe a diode wired between the fans and the LED would sort it.

[shpub]

The LED is a diode... hence Light emitting Diode..

The diode lights because the fan is acting as a generatot and will be generating sufficient voltage to turn the LED on.
Not totally sure how they have been wired up but the normal practice is to use the ECU to switch a relay that turns on the fans and then conmnect the LED to the ECU relay connection. That way the windmilling fan will not illuminate the LED.

[Johno]

Cheers all, think i should go with the switched relay route, not going to be as easy as you imagine with a total integrated loom, but we'll give it a go . .

Cheers

[spend]

Mini relay & diodes powered from the fan relays, which switched the led ground was my final solution, but I use tri-led for independent fans (common ground)....