Ok, so has anyone found it necessary to fit a diode into their radiator feed wire?
I have a switch with a light on, and if the fan is not on and you are driving along the light stays on, because the fan is spinning obviously. Also if
you forget to turn the fan off before you kill the ignition the engine runs on a bit (not particularly good for any of the ignition system).
So what sort of diode should I fit in the rad fan feed? Dont know anything about speccing electronic components, give me a bundle of wires any day!
Cheers,
David
Your gonna need a pretty big diode for this job. I'm no electronics expert though.
I'd imagine you've not got this fan wired through a relay at the moment??? It would cure the problem if it was (IMHO)
Thats what I was thinking. Theres no relay at the moment. Just switched on a 10amp switch. Could add in a relay if its easier than fitting a diode
though. Got to pull my loom apart again to fit my immobiliser anyway.
David
I'm confused...
Radiator fan wiring isn't rocket science. It's a good idea to wire it through a relay, as for any other electric motor of any size.
It's also a good idea to set it up on the non-switched side of the electrics so that it does run on when you switch off the ignition, until the
thermo switch decides that the water is cool enough. This is generally regarded as A Good Thing.
Or have I got hold of the wrong end of the story (again)? 
David
I know its not rocket science... 
The fan is just on a manual switch on the dash, no thermo switch in there at all at the moment. Switched as normal. The wiring in the loom was heavy
enough to do it without a relay, so I didnt bother with one.
I meant that the engine runs on for a second or so when you kill the ignition while the fan is running. Obviously the fan motor takes a while to stop
and so is working as a generator and providing some power to the ignition circuit. By putting a diode in the supply wire you could stop that
happening.
Sounds like I will just fit a relay and be done with it.
David
I would think 10A, 125V PIV (peak inverse voltage) would do it. I threw my Maplin catalogue away just the other day but they should have it. There will be an 0.7 V drop through the diode but that shouldn't worry the fan.
Is it not possible to put the diode on the lower current feed to the ingition circuit on the engine and leave the fan circuit un-restricted...
Im just concerned about relying on a diode when there is so much current involved...at the very least its going to get warm...
Putting a diode in the ignition circuit won't work cos the spurious current from the fan will be flowing in the same direction as the ignition
current.
Just looked at Maplin on line. Diode P600D, code UK60Q would be worth a try at 69P each.
[Edited on 18/3/07 by Macbeast]
If this is indeed the cause of the run on, then I would have thoght the relay would be a better method than a diode.
quote:
Originally posted by ReMan
If this is indeed the cause of the run on, then I would have thoght the relay would be a better method than a diode.
quote:
Originally posted by Macbeast
Putting a diode in the ignition circuit won't work cos the spurious current from the fan will be flowing in the same direction as the ignition current.
Just looked at Maplin on line. Diode P600D, code UK60Q would be worth a try at 69P each.
But if you read the previous post, the suggestion was to put the diode in the ignition feed, not the fan feed as you show.
P600D has higher PIV than 600A and this may be important on switching the inductive motor. Diodes can be paralleled but there is no guarantee of equal
current sharing so usiual procedure would be to put in series resistors but then you get more voltage drop.
[Edited on 19/3/07 by Macbeast]