glasgow Posted May 20, 2013 Share Posted May 20, 2013 Hello, all…. Would like to do a fan override switch (K series 2003). Here is the famous circuit by Chris http://farm6.staticflickr.com/5465/8756448121_3a1bf9492a_c.jpg My electricity skill is errmm, let's say “basic” 😬 and I would like to review the shopping/to-do list with you expert guys before I start blowing fuses **** Relay: I am going for this 4pin 30 amp with diode (72714) here is 30 amp ok? **** Switch: Ref: E895 heavy duty 25 Amp) here is 25 amp ok? **** LED LIGHT: Ref: LEDGWL near the bottom here No Amp rating so I take it this “small” LED is OK (correct??) **** Resistor: R1 1K in the circuit? I'm not really sure about this! Do I need it? does the LED light in the above link has a resistor already pre-installed? if i need a separate resistor, any suggestions for one and how to attach it please? **** Connectors: Some piggyback and stationary blades **** Wires: Well, this really looks silly but don’t know which of these thin wall cables I should use ☹️ here **** Would I need these: Relay Sockets (RS or RSI) and terminals **** Fuse: My understanding is I don't need a fuse for this circuit as the circuit will use the fuse already in the fuse box (correct?) Many thanks for your help Ahmed Edited by - glasgow on 20 May 2013 12:03:29 Link to comment Share on other sites More sharing options...
Roger Ford Posted May 20, 2013 Share Posted May 20, 2013 Since you've got a 15A fuse in there, then 30A for the relay should be more than sufficient. The switch doesn't need to be heavy-duty, it's only switching the trigger current for the relay, so only has to handle mA. If you're using a 25A switch, you don't actually need a relay at all. LEDGWL doesn't need a resistor in circuit, that's designed to connect straight into a 12v circuit. And no need for an extra fuse. Wiring - go for the 1mm sq. REF16 - takes 16.5A, so again it's more than the fuse so will be quite sufficient. You don't need a relay socket, you can connect female spade connectors directly to the relay. But a relay socket makes it a little neater and slightly easier to replace the relay if it fails. Edited by - Roger Ford on 20 May 2013 12:13:00 Link to comment Share on other sites More sharing options...
Roger Ford Posted May 20, 2013 Share Posted May 20, 2013 BTW, you shouldn't need the diode version of the relay, although it will have the side effect of preventing engine run-on when you turn off the ignition and the fan is still spinning - but ONLY when the fan is spinning due to the override rather than the temperature switch. Also, that LED is going to light whenever the fan is on. If you only want it to light to remind you that your over-ride is active, then put it in line with the switch instead. Or use "Toggle switch with LED in toggle" from the same page as your switch. Link to comment Share on other sites More sharing options...
myothercarsa2cv Posted May 20, 2013 Share Posted May 20, 2013 And if you don't have a heater, use the heater fan switch already in the dash - keep it neat Link to comment Share on other sites More sharing options...
glasgow Posted May 20, 2013 Author Share Posted May 20, 2013 Thank you Roger and MOC2CV ***** Diode version of the relay: I am not really sure what you meant by: "it will have the SIDE EFFECT of preventing engine run-on when you turn off the ignition and the fan is still spinning - but ONLY when the fan is spinning due to the override rather than the temperature switch." excuse my ignorance ☹️.... My fan currently runs only when the engine is on and doesn't last after I switch off engine, However, after I switch ignition key off, it takes about 3-4 seconds before the engine actually stops.... OK, so in the new circuit, when I turn the engine off while the fan is still spinning due to override, would the Diode version be good or bad? I don't mind paying the extra few quids for the Diode version if there is any (even theoretical) benefit of having it. **** LED: I prefer the light to be on whenever the fan is on, that's a bonus for me. However, your post made me thinking actually of having another LED in the Toggle switch it might be a good idea to show if the switch is on or off. However, here is a quote from Chris W post:...... "some of the illuminated switches have the internal LED wired in such a way that they can blow a fuse when switching off depending on how the positive and negative contacts on the switch"..... I have no idea what this means but I hope it is ok if I use a toggle switch with a built in LED as well as the separte LED And yes I do have a heater so has to put a new switch Link to comment Share on other sites More sharing options...
Colin Cooper Posted May 20, 2013 Share Posted May 20, 2013 This all seems a bit overkill. Just fit a switch in across the terminals of SW1. Or am I missing something? Col Link to comment Share on other sites More sharing options...
Bricol Posted May 20, 2013 Share Posted May 20, 2013 Why not fit a working rad switch? As per your tin top. Bri Link to comment Share on other sites More sharing options...
glasgow Posted May 20, 2013 Author Share Posted May 20, 2013 Quoting Colin Cooper: This all seems a bit overkill. Just fit a switch in across the terminals of SW1. Or am I missing something? Col because of voltage drop... Lots of talk in the archive about this Link to comment Share on other sites More sharing options...
glasgow Posted May 20, 2013 Author Share Posted May 20, 2013 Quoting Bricol: Why not fit a working rad switch? As per your tin top. Bri I do have a working one but they are known to fail and it is a K series going in summer to spain so don't want to take the chance Link to comment Share on other sites More sharing options...
Ozzy Posted May 20, 2013 Share Posted May 20, 2013 It's not overkill, it's a handy feature. 1. If your rad switch fails, you can easily switch your fan on without lifting the bonnet and bridging the terminals. 2. With the additional light, you get a visual indication when your fan is running. Had it on my car for 8 years or so. Oz. Link to comment Share on other sites More sharing options...
Roger Ford Posted May 20, 2013 Share Posted May 20, 2013 Quoting Glasgow: I am not really sure what you meant by: "it will have the SIDE EFFECT of preventing engine run-on when you turn off the ignition and the fan is still spinning - but ONLY when the fan is spinning due to the override rather than the temperature switch." excuse my ignorance ☹️.... My fan currently runs only when the engine is on and doesn't last after I switch off engine, However, after I switch ignition key off, it takes about 3-4 seconds before the engine actually stops.... OK, so in the new circuit, when I turn the engine off while the fan is still spinning due to override, would the Diode version be good or bad? I don't mind paying the extra few quids for the Diode version if there is any (even theoretical) benefit of having it. If your fan is spinning because of the temperature switch, then when you turn your engine off the fan will become a generator, and feed voltage back through the temperature switch, keeping the engine running until the fan has slowed down. The presence of a diode in the override relay will not affect this, regardless of whether the over-ride is activated or not. If the temperature switch is open circuit (cool, or perhaps broken) and you use your override to turn the fan on, then with a simple relay the same thing will happen. But with a diode relay, the current won't be able to return through the relay, so the engine will stop immediately when switched off. I prefer the light to be on whenever the fan is on, that's a bonus for me. However, your post made me thinking actually of having another LED in the Toggle switch it might be a good idea to show if the switch is on or off. However, here is a quote from Chris W post:...... "some of the illuminated switches have the internal LED wired in such a way that they can blow a fuse when switching off depending on how the positive and negative contacts on the switch"..... I have no idea what this means but I hope it is ok if I use a toggle switch with a built in LED as well as the separte LED I don't understand that either. Can't see any reason why an LED in a switch should blow a fuse unless it's faulty. Note that with an LED switch you'll need an extra 12v supply to feed the LED - it should have IN, EARTH and LED POWER connections. Not sure what you mean about voltage drop if you use a switch rather than a relay - can you link to a post? The switch would be in parallel with the thermo-switch, so wouldn't affect it when open, and I can't see that the extra wiring or the switch itself should introduce much in the way of resistance. Link to comment Share on other sites More sharing options...
glasgow Posted May 20, 2013 Author Share Posted May 20, 2013 Thank you Roger... But with a diode relay, the current won't be able to return through the relay, so the engine will stop immediately when switched off. So it is better to use a relay without diode - right? Note that with an LED switch you'll need an extra 12v supply to feed the LED - it should have IN, EARTH and LED POWER connections. Oops, forgot about this...Will just keep it simple and use a switch without LED can you link to a post? here (also in Page 2, 6 January 2006 15:08 Chris W talks about the problem of LED in a switch Link to comment Share on other sites More sharing options...
Ian B Posted May 20, 2013 Share Posted May 20, 2013 Quoting Roger Ford: If your fan is spinning because of the temperature switch, then when you turn your engine off the fan will become a generator, and feed voltage back through the temperature switch, keeping the engine running until the fan has slowed down. The presence of a diode in the override relay will not affect this, regardless of whether the over-ride is activated or not. If the temperature switch is open circuit (cool, or perhaps broken) and you use your override to turn the fan on, then with a simple relay the same thing will happen. But with a diode relay, the current won't be able to return through the relay, so the engine will stop immediately when switched off. Sorry Roger but I think you're confusing the purpose of the diode. The diode is included to effectively short out any back-emf caused by the relay coil de-energising. It has no effect on the voltage generated by the fan after the engine has been cut, and is still in the same part of the circuit whether the stat or the relay are closed, and won't ground any voltage generated by the fan anyway. To answer Ahmed's question, it's always good practice to fit a diode in reverse across a DC relay coil. In vehicle electrics there is unlikely to be anything sensitive enough to be affected by any back-emf from the relay coil, but it wouldn't do any harm to fit a relay with a diode if it's available. (If it was me, I would). HTH Link to comment Share on other sites More sharing options...
Bricol Posted May 20, 2013 Share Posted May 20, 2013 I still have a working original fan switch on my 13yr old Caterham - used and abused for all that time in all temps, all sorts of traffic from Scotland to South of France, down into Italy etc. I check it every so often - much as I do with the tin top one. With the additional light, you get an indication the light is working, not necessarily the fan Had one fan of a pair seize in a Stratos replica a good few years ago - switch was switching, but fan wasn't too bothered about rotating until serviced. Bri Bri Link to comment Share on other sites More sharing options...
Roger Ford Posted May 21, 2013 Share Posted May 21, 2013 The diode is included to effectively short out any back-emf caused by the relay coil de-energising. It has no effect on the voltage generated by the fan after the engine has been cut, Ah, so the diode goes to earth? I assumed it was in series with the high-current side. In that case, yes, ignore everything I said on the topic of diode relays. Can anyone think of a reason not to put a diode in series with the fan itself? Wouldn't this stop the "engine run-on" problem? Link to comment Share on other sites More sharing options...
richy Posted May 21, 2013 Share Posted May 21, 2013 *confused*Wouldn't it just be better to carry a spare switch? Link to comment Share on other sites More sharing options...
glasgow Posted May 21, 2013 Author Share Posted May 21, 2013 Quoting richy: *confused*Wouldn't it just be better to carry a spare switch? On more than one occasion in a heavy summer traffic I wished i could override the fan as the temp was creeping up despite the fan was working on/off as it should. Link to comment Share on other sites More sharing options...
Ian B Posted May 21, 2013 Share Posted May 21, 2013 Quoting Roger Ford: The diode is included to effectively short out any back-emf caused by the relay coil de-energising. It has no effect on the voltage generated by the fan after the engine has been cut, Ah, so the diode goes to earth? Well sort of; the anode of the diode goes to earth and the cathode to the supply - other way around it would just short the supply to earth Can anyone think of a reason not to put a diode in series with the fan itself? Wouldn't this stop the "engine run-on" problem? Yes, a diode in series with the supply feed to the fan (cathode towards the fan) would stop the fan back-feeding to the ECU and causing the engine to run on. One thing to consider would be the diode would need to be meaty enough to handle the fan current, and you'll also lose about 0.5 volt drive to the fan as that'll be dropped across the diode (shouldn't be an issue). Link to comment Share on other sites More sharing options...
johnv Posted May 21, 2013 Share Posted May 21, 2013 do you have a link to the correct relay to use (and the wiring diagram wou;d be good)? I have always had an override switch but just direct .. I think I'd better put a relay in after reading this thread thanks Link to comment Share on other sites More sharing options...
Roger Ford Posted May 21, 2013 Share Posted May 21, 2013 I really don't think there's any issue with using just a switch rather than a relay. OK, there are wires going to the switch. But are they significantly longer than the wires going to the relay? If you're putting the relay behind the dash with the other relays, then no. If the wires are decent and the switch is good quality, I can't see why there should be significantly more resistance with a direct switch rather than a relay. And worst case, your fan is going to run a bit slower WHEN you have to override the temperature switch. If you're doing this from scratch, fitting a relay might be good practice but I wouldn't worry if your current override doesn't have one. Link to comment Share on other sites More sharing options...
Ian B Posted May 21, 2013 Share Posted May 21, 2013 Direct switch is fine, as long as the wires are appropriately sized for the length of run - and no relay is one less thing to fail Link to comment Share on other sites More sharing options...
johnv Posted May 21, 2013 Share Posted May 21, 2013 I'll leave it as it is then! thanks Link to comment Share on other sites More sharing options...
charlie_pank Posted May 21, 2013 Share Posted May 21, 2013 Quoting Glasgow: On more than one occasion in a heavy summer traffic I wished i could override the fan as the temp was creeping up despite the fan was working on/off as it should. Presumably you know this because you see the temperature creeping up on the gauge. This must mean that the radiator temperature is significantly different from the engine temperature. Perhaps it might be more effective then to link the fan to the indicated temperature on the gauge rather than the radiator temperature? Although the counter-argument might be that if the radiator temperature is not high enough to trigger the fan, while the engine temperature is what you judge to be too high, then artificially triggering the fan will cause even colder water to arrive in the engine from the radiator leading to thermal shock? C Link to comment Share on other sites More sharing options...
glasgow Posted May 21, 2013 Author Share Posted May 21, 2013 Oh, Bloody hell... I hate this word (Thermal shock).... But this is getting too technical to me again.. I'll just do the fan override switch and keep reving the engine in the traffic jam 😬 Link to comment Share on other sites More sharing options...
combine Posted May 21, 2013 Share Posted May 21, 2013 I just wired straight from the fan switch back to a dash mounted switch , works fine , probably don't need it but nice to have one in emergency ! 😬 Link to comment Share on other sites More sharing options...
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