stephen grant Posted January 5, 2006 Share Posted January 5, 2006 Has anyone managed to wire up a manual fan switch (to turn the fan on from the dashboard) with a light that confirms that the fan is running, but that doesn't come on simply from the induced current created by the fan idling in the wind created by the car moving forward? If that makes any sense...... stephen Link to comment Share on other sites More sharing options...
dangerous_bryan Posted January 5, 2006 Share Posted January 5, 2006 If you can find a link to oldbutnotsoslow's pictures, he has a wiring diagram on there.....or he did have. Le Mans 05 pictures Building the Dream 2005 Link to comment Share on other sites More sharing options...
DaveMorris Posted January 5, 2006 Share Posted January 5, 2006 Use a relay in the circuit which powers the fan. Then : a/. you'll not get a back feed and b/. you'll not be pulling the fan current through the switch terminals and a long piece of wire, dave Link to comment Share on other sites More sharing options...
Bricol Posted January 5, 2006 Share Posted January 5, 2006 The question is . . why? Has your tin-top, that covers more miles, more miles in traffic jams, more time idling, more. . . got one? Less is more . . . reliability . .. Bri Link to comment Share on other sites More sharing options...
stephen grant Posted January 5, 2006 Author Share Posted January 5, 2006 Yeah, I suppose that is a fair comment.... Link to comment Share on other sites More sharing options...
nickdodo Posted January 5, 2006 Share Posted January 5, 2006 HI, I used a spare Heated Screen switch (not having a heated screen 😬). The switch illuminates when the fan is on - either by switch or thermostat. The light only comes on when powered. Also found a spare wire in the loom to run from switch to the fan if I recall. Seems to work ok... Nick in the (1987) 1700 X Flow... Link to comment Share on other sites More sharing options...
Ozzy Posted January 5, 2006 Share Posted January 5, 2006 Well I've had a failed fan sender already, which resulted in me having to bridge the terminals to get home. That's why I fitted one ❗ If the company tintop blows a gasket, that's one thing. But my own car, different story. Plus they are notoriously unreliable. Oz. Ps: Chris W published excellent easy to follow instructions in low flying. I think it was around June/July 04 Still Shaking 6 speed 1600k Supersport Link to comment Share on other sites More sharing options...
Bricol Posted January 5, 2006 Share Posted January 5, 2006 hmmm - simply fit a decent switch . . . not ever had one go on a tin-top - and it must be the only electrical sensor type device fitted in the Caterham engine bay not to have gone wrong on mine since build in 2001 . . . if you'd of said temp sender, or oil pressure . . . Bri Link to comment Share on other sites More sharing options...
nickdodo Posted January 5, 2006 Share Posted January 5, 2006 Bricol says... '...the only electrical sensor type device fitted in the Caterham engine bay not to have gone wrong on mine since build in 2001...' I see you don't believe fate can be tempted... 😬 Nick in the (1987) 1700 X Flow... Link to comment Share on other sites More sharing options...
Normans_Ghost Posted January 6, 2006 Share Posted January 6, 2006 I've wired up a heavy duty switch (can't remember which and books not out of boxes yet). It's got an LED light and is straight wired using a piggy-back terminal. Light glows at 50, is bright on at 70. Who needs a speedo? Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here You and your seven to The French Blatting Company Limited Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Wiring up a fan switch without using a relay situated adjacent to the fan is not a good idea. The heavy current that would then run all the way from the dashboard switch to the fan will cause a voltage drop in the cable. Even if this were only 10% (one volt say) the fan speed will drop by 20% compared to its normal top speed. (because fan speed is proportional to power applied and power is proportional to volts squared). Further, the force at which the "fanned" air will be delivered to the radiator is proportional to fan speed squared, so based on the figures above, the air delivered may be down to less than 65% of its norm. On a hot day, driving hard, would you want to risk your engine to a fan working this far below its normal capacity? Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 I have posted a circuit diagram for a fan-override switch on my website (click below). Once on the site, it's on page 4 of the photos. This uses a relay and has a dashboard-mounted switch and LED. The LED will come on if the override switch is operated OR if the fan comes on automatically whilst driving along. This is a good indicator therefore that all is well with the temperature switch on the radiator if one spots the LED switching on occasionally. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
nickdodo Posted January 6, 2006 Share Posted January 6, 2006 Chris, The normal supply (without a switch) runs from the fuse box to the Fan thermostat. The Voltage drop here is going to be no different than the Voltage drop from a dash switch to the fan thermostat. I really don't see what the issue is - and would most certainly dispute a reduction of 65% that you calculate if wired as follows 1) Fuse Box -> thermostat side A -> thermostat side B -> Fan (original wiring) 2) Fuse Box -> Switch -> Thermostat Side B (additional wiring) This effectively puts the switch and thermostat in p//l and should cause no more V drop to the fan - with either connected. I would notice a 65% difference - there is no discernable difference in the Fan operation - thermostat or dash switched. Nick in the (1987) 1700 X Flow... Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Hey Nick You pays yer money and takes yer choice. Firstly, there IS definitely a reduction in fan speed if wired from a straight dashboard switch because there IS an additional volts drop in the additional wiring needed. (Note the 65% figure I used refers to air pressure - not sure how you measured that). Secondly, the dashboard switch, if wired sans relay, will need to be a beefy affair to cope with the fan current, whereas, using a relay, the dashboard switch can be a small low-current model. Thirdly, why would you not want to use a relay? It's good engineering practice where larger currents are concerned and only adds about £3 to the cost? So I'm not sure what point you are making. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Normans_Ghost Posted January 6, 2006 Share Posted January 6, 2006 I agree with Chris. However as my fan will bring the temprature down from an indicated 100 to below 80 in a matter of minutes (stationary) then even with the voltage drop (I get 12.8 at fan and 13.6 at battery) it is efficient enough to work well. I have chosen to wire it this way as I have rewired the whole car to be lightweight and simple. None of the original relays or fusebox are fitted. Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here You and your seven to The French Blatting Company Limited Link to comment Share on other sites More sharing options...
nickdodo Posted January 6, 2006 Share Posted January 6, 2006 Chris, You could well be right that a relay is good engineering practice, however the original supply does not run through a relay. It runs from the fuse box with a 20 Amp fuse (if I recall correctly). I guess caterham didn't feel the need for a relay. Nick in the (1987) 1700 X Flow... Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted January 6, 2006 Support Team Share Posted January 6, 2006 The other advantage to using a relay is that should you purchase an Emerald ECU, you can control the fan with the ECU and set it to come on and off at whatever temperatures you like. Yellow SL #32 Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Nick That's because they didn't run a heavy current all the way TO the dashboard and then all the way FROM the dashboard back to the fan. Where they do have to do this, for example, in the case of the Headlights and the Horn, they do use a relay. Chris 2003 1.8K SV 140hp see it here Edited by - Chris W on 6 Jan 2006 14:08:29 Link to comment Share on other sites More sharing options...
stephen grant Posted January 6, 2006 Author Share Posted January 6, 2006 Chris - thanks for the circuit diagram, that's exactly what I wanted. I'm going to give it a go. stephen Link to comment Share on other sites More sharing options...
nickdodo Posted January 6, 2006 Share Posted January 6, 2006 Chris, Fair point, but in my old 1987 xflow the fuse box is positioned such that the extra wire to go to via a switch on the dash rather than direct to the thermostat only makes it about 6 inches longer. Perhaps there is more distance in to travel in an SV... maybe things are positioned differently. Mine has fuse box to left of centre on the bulkhead under the dash, the loom runs across the car to exit in to the engine compartment near the steering column. Thus a small diversion to a switch... Not sure I'll ever have an ECU in this car. I guess it depends on the car and the configuration. Nick Nick in the (1987) 1700 X Flow... Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Nick Yawn. You do it your way, I'll stick to my way. Don't forget to fit a very heavy duty switch in your dashboard if you don't use a relay. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Stephen One tip............. use a separate LED on the dashboard rather than a switch containing an LED. Some of these illuminated switches have the internal LED wired in such a way that they can blow a fuse when switching off depending on how you wire the positive and negative contacts on the switch. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
stephen grant Posted January 6, 2006 Author Share Posted January 6, 2006 Ta. I was thinking along those lines anyway, since it would be a bit wierd for the switch to light up even when not on (due to the fan cutting in "normally"). I take it that a spare relay of the type plugged into the fuse box will be suitable? stephen Link to comment Share on other sites More sharing options...
Chris W Posted January 6, 2006 Share Posted January 6, 2006 Stephen Correct re the relay. Maplin do them at about £2 each here Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
stephen grant Posted January 6, 2006 Author Share Posted January 6, 2006 Cheers - I bought a few from CC a while back after the car got soaked and the electrics went mad, so I'll just use one of them stephen Link to comment Share on other sites More sharing options...
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