dear all,

i have wired up a manual over ride for my fan so i can switch it on early if i know i am going to be stuck in traffic, ie once you come off the motorway on the way to Stoneleigh!

The switch has a light on in it to tell me it is on. all works fine and the temp switch still kicks it on at the right temp. My problem is that when driving under normal conditions (fan off) the light is glowing slightly because the fan is spinning with the airflow through the nose.

I understand the principle of the fan motor generating electricity, have i just got something connected the wrong way round?

Any info appreciated.
Col

Is it a bulb or an l.e.d.?. i have the same problem with mine, its an l.e.d. so it takes minimal current to se it off. the solution is to fit a diode (up to 5 amp or whatever your fan can draw) ino the line preceeding the fan, this way only when power is provided directly to the fan does the light come on brightly and reverse current cannot get to your bulb / l.e.d..
Good Luck Sheepy

Sounds like you may have the germ of a radical new speedometer here mate..get the patent in quick!

Serioulsy, I would have thought that if this was an LED (light emmiting diode) then a back current shouild not illuminate it. Diode should fix a glimmy bulb though.
Mind you, I may be talking complete B*ll*cks, it's a long time since I did basic electronics.

[Edited on 11/9/03 by jonti]

Jonti & Sheepy.

I have never done basic electronics so you are both far in advance of myself in this respect.

I can only think it is an LED as the switch is really small and cant envisage shoehorning a bulb into it.

I drove it with the new switch in last night and it was getting brighter as i went faster,

at least it would let me know when i have a tin top hot hatch stuck in the grill cos they wont get out the way!
Col

might be worth just try reversing the wires on the switch

is it possible to wire the light off the switch rather than the fan? This might still leave them linked, if so how about a switch with 4 terminals, like those used on the fog light switch? have 2 circuits switched by the one switch! then the warning light is distinct and seperate from the other circuit that runs the fan.

Hi, hope your investigation is going well. The reason I thought about reverse curent is because of the set-up I've got, I've attached a picture, I know yours is different but it may help. Sheepy

[Edited on 12/9/03 by Sheepy]
Rescued attachment fan wiring.jpg

Sheepys; solution should work for either LED or lamp..I should have drawed it out meself...I wus finkin the LED would be in series with the fan and of course its in parallel (muppet !)

cheers chaps,

where can i purchase the offending 5amp diode then? i am sure it could be bought from maplins or rs or the like but i would look prety daft ordering one diode.

From my limited cdt classes at the age of 15 i remember that i will need a holder for this diode in order to plumb it into the wiring, where too can i get thet from?

Cheers

Colin

Our sierra came with a couple of power diodes in little snap-in holders (not sure what current they're rated at, look like they could take 5A though).

They are in little thin brown cases about the size of a blade fuse, in the middle of a line of relays under the drivers side fascia, which are bolted on in a strip next to what I think is the ABS controller (big aluminium box with wires). Pretty much directly underneath the main engine bay fusebox.

If you can't find a diode you could build a circuit with the LED in series with the fan, using a series resistor and a parallel shunt power resistor across the led and other resistor.. but that's probably just as much if not more hassle than using a diode. If you have a handy power resistor of the right value kicking around though..

Another method would be to use a relay.
The light could be in series or parrallel from switch to relay.
As power to fan is not going through switch there is no danger of back current to light.

Terry

id suggest a bit more than 5a for the diode. Unless you are really sure the fan is less than 50-60 watts. Id use 10a.

if you are really stuck I can probably sort you one out.

A diode can be crimped or soldered into the wire

u2u me if you need one.

atb

steve

ps - there are some tiny bulbs around, so just cos its small doesnt mean its an led....

[Edited on 12/9/03 by stephen_gusterson]

Cheers Steve, i saw the same switches at donny yesterday and they were advertised as LED ones. I will have an ask at work tomorrow to see if anyone has a suitable diode, got some tecchies in the service department!

If not i may take you up on the offer.



Col

Try http:\rswww.com


Look for 1n400? series of diodes.


Hope this helps

RS might be a bit dear try

http:\www.maplin.co.uk

or

Farnell componets ( http:\www.farnell.co.uk ) I think


Andy