Ali King Posted March 29, 2022 Report Share Posted March 29, 2022 (edited) Hi All, I have an electric cooling fan and thermostatic switch fitted as per attached diagram (TR4A). I am considering fitting a warning light (to show when the fan is on) and perhaps an override switch to turn it on when I want. I know it's not really required, but just humour me (I have a whole in the dash that needs filling with something!). I just wanted to check: For the warning light, is it as simple as fitting a wire from the fan live feed to a standard Lucas type warning light, which then goes to earth? For an override switch, can I just take a live feed from somewhere to a switch, then on to connect to the live feed to the fan (bypassing the thermostat)? I think I would prefer this switch to enable me to turn the fan on even with the ignition off. Should I fit additional fuses anywhere, and what size of wire? Thanks, Ali. Edited March 29, 2022 by Ali King Quote Link to post Share on other sites
RogerH Posted March 29, 2022 Report Share Posted March 29, 2022 (edited) Hi Ali, your circuit diagram is not the best solution. The thermo switch is taking the full Fan motor current (10 - 20 amps ) If you place the Thermo switch exactly where the fuse is then it will be controlling the relay coil (100Ma) The manual switch could go in Parallel with the thermo switch The warning light can feed off the output f the relay to fan . I'm sure somebody will post a decent circuit diagram shortly. Roger Rad Fan xx.docx Edited March 29, 2022 by RogerH Quote Link to post Share on other sites
RobH Posted March 29, 2022 Report Share Posted March 29, 2022 As Roger says, with your circuit the relay protects the ignition switch from high current but should also do that for the thermal switch and override if configured correctly; also your fuse doesn't protect the high current circuit at all. If you simply fit the lamp in parallel with the motor as you suggest in your question, you may find the lamp comes on at speed because the fan will 'windmill' and act as a generator. There are a number of ways to re-arrange the circuit, this is just one way to do it. The terminal numbers are for a modern relay. The brown unswitched supply and fan earth wires need to be large enough to take the fan current (say 3 mm^2.) The others can be low-current (say 0.65 mm^2.) It's probably best to use a 30A fuse - the motor will have a considerable inrush current on start-up. Quote Link to post Share on other sites
John Morrison Posted March 29, 2022 Report Share Posted March 29, 2022 3 hours ago, Ali King said: Hi All, I have an electric cooling fan and thermostatic switch fitted as per attached diagram (TR4A). I am considering fitting a warning light (to show when the fan is on) and perhaps an override switch to turn it on when I want. I know it's not really required, but just humour me (I have a whole in the dash that needs filling with something!). I just wanted to check: For the warning light, is it as simple as fitting a wire from the fan live feed to a standard Lucas type warning light, which then goes to earth? For an override switch, can I just take a live feed from somewhere to a switch, then on to connect to the live feed to the fan (bypassing the thermostat)? I think I would prefer this switch to enable me to turn the fan on even with the ignition off. Should I fit additional fuses anywhere, and what size of wire? Thanks, Ali. Ali, a manual overide switch is a really good idea. Lets you anticpate your car getting hot say when approaching traffic jams, or climbing hills, pop the switch on to keep the car cool, better than letting it get hot, and then the thermo switch coming in to pull the temp back down again. John. Quote Link to post Share on other sites
Ian Vincent Posted March 29, 2022 Report Share Posted March 29, 2022 I have my cooling fan wired with an override switch in parallel with the thermo switch and fed from a relay but the power supply to the relay is unswitched. The indicator light is just fed from terminal 87 on the relay and terminal 85 is jumpered to terminal 30. It means that whenever the fan is running the indicator light is on whereas with Rob's layout it looks to me as if when the ignition is off the indicator light goes out even if the fan is still running, (as mine does frequently after a hard drive when I turn the engine off and the water stops circulating). Rgds Ian Quote Link to post Share on other sites
RobH Posted March 29, 2022 Report Share Posted March 29, 2022 (edited) 6 hours ago, Ian Vincent said: Rob's layout it looks to me as if when the ignition is off the indicator light goes out even if the fan is still running, No Ian, with the arrangement shown the fan stops when the ignition is switched off. I'm not sure whether having an overrun arrangement is a good idea if there is an override switch - you could end up with a flat battery if you forget, though there are ways round that by adding more complication of course. Here is the circuit modified to give cooling overrun and 'safe' override which won't flatten the battery with ignition off. The diodes are needed to prevent current flowing between the switched and unswitched circuits. As shown it is for negative earth - reverse the diodes for positive earth. Edited March 29, 2022 by RobH added note on diode polarity Quote Link to post Share on other sites
ianc Posted March 29, 2022 Report Share Posted March 29, 2022 It has always concerned me to hear stationary cars with their electric fan(s) running. Even more so with modern cars which cannot be bump started when the battery is almost flat. When I park my TR, I isolate all the electrics so as not to have such worries. Manual override and indicator lamp are very sensible additions. On my dashboard, I still have the original 1970 Kenlowe chrome bracket with switch & lamp, although the fan is now a Revotec sucker bolted to the radiator, rather than the Kenlowe pusher. Ian Cornish Quote Link to post Share on other sites
Hamish Posted March 29, 2022 Report Share Posted March 29, 2022 My fan runs on if hot without ignition. often wondered the merit in this as it will only cool the rad coolant and not the engine. Quote Link to post Share on other sites
RogerH Posted March 29, 2022 Report Share Posted March 29, 2022 20 minutes ago, Hamish said: My fan runs on if hot without ignition. often wondered the merit in this as it will only cool the rad coolant and not the engine. Hi Hamish, it will also help cool the block - as the water in the rad cools it draws in new hotter water from the block. Roger. Quote Link to post Share on other sites
Hamish Posted March 29, 2022 Report Share Posted March 29, 2022 Glad it’s not wasted then Quote Link to post Share on other sites
PodOne Posted March 29, 2022 Report Share Posted March 29, 2022 6 hours ago, RobH said: As Roger says, with your circuit the relay protects the ignition switch from high current but should also do that for the thermal switch and override if configured correctly; also your fuse doesn't protect the high current circuit at all. If you simply fit the lamp in parallel with the motor as you suggest in your question, you may find the lamp comes on at speed because the fan will 'windmill' and act as a generator. There are a number of ways to re-arrange the circuit, this is just one way to do it. The terminal numbers are for a modern relay. The brown unswitched supply and fan earth wires need to be large enough to take the fan current (say 3 mm^2.) The others can be low-current (say 0.65 mm^2.) It's probably best to use a 30A fuse - the motor will have a considerable inrush current on start-up. Hi Rob Yet to rewire my TR6 I guess this circuit will work equally as well for me. Thanks Andy Quote Link to post Share on other sites
Quicksilver Posted March 29, 2022 Report Share Posted March 29, 2022 (edited) this type of (override) switch, it has a control led build in..On-off toggle switch + LED green - 12V - 20 amp Dimensions in mm: Outer: 30 x 17 Drill: 11,8 Lenght: 63. Edited March 29, 2022 by Quicksilver Quote Link to post Share on other sites
RobH Posted March 29, 2022 Report Share Posted March 29, 2022 12 minutes ago, Quicksilver said: this type of (override) switch, it has a control led build in.. It has, but it won't work in all circuits because one end of the LED is permanently connected to one of the switch terminals. Being an LED you have to be careful with the polarity - as per the markings on the switch. It is awkward to use it on a positive earth car. Quote Link to post Share on other sites
Ali King Posted March 30, 2022 Author Report Share Posted March 30, 2022 Thanks everyone for your replies. As always, there are a few more things to think about than I originally envisaged. Rob, I think I may go with your diagrams (or version thereof), thanks. But I have a couple of additional questions now: - Rob: if I read it correctly your second circuit will allow the fan to continue with the ignition off until the thermostat cuts it out? I had originally thought I wanted to control whether it continues by using the manual overide after the ignition is turned off. I think this could be achieved by simply swapping the thermo and override switches around in your second diagram? I would usually use my battery isolator if leaving the car, so even if I inadvertantly left the override on it would just get the extra cooling while I faf about before leaving the car, then be isolated. The switch posted by Quicksilver looks appealing (as I only have one hole to fill in the dash) - is there a way of wiring this type of switch so that the inbuilt led would come on whenever the fan is on, whether by override or thermo? (mine's a negative earth car). It also dawns on me that the warning light is only going to indicate that power is going to the fan, not that it's actually working - any easy way of doing that? (but I suppose that's what the temperature gauge is for). One more thing - I've no idea how to physically wire a diode into the circuit: solder? crimp? connector block? Thanks, Ali. Quote Link to post Share on other sites
RogerH Posted March 30, 2022 Report Share Posted March 30, 2022 Hi Ali, the simple answer to your ' is the fan actually running' is as you state look at the temo gauge. It gets more complicated if you want to 'see' that it is actually running. You need to measure/detect the current flowing. This could be simple(ish) of complex. I have a simple circuit for monitoring the brake lights if you are interested to use it for your fan. Roger Quote Link to post Share on other sites
RobH Posted March 30, 2022 Report Share Posted March 30, 2022 (edited) 1 hour ago, Ali King said: Rob: if I read it correctly your second circuit will allow the fan to continue with the ignition off until the thermostat cuts it out? I had originally thought I wanted to control whether it continues by using the manual overide after the ignition is turned off. I think this could be achieved by simply swapping the thermo and override switches around in your second diagram? If you do that the thermal switch will only operate when the ignition is on but the manual override will always work. Since you are going to rely on the battery master switch you might as well just leave both switches in parallel and forget about the diodes, like this, which will give automatic overrun. The light will come on if either switch closes. Its pretty obvious from the noise, when the fan is running and the ignition is off : Sorry if the diagram is getting. bit scrappy looking - I'm doing quick mods to the original to save time in replying. Edited March 30, 2022 by RobH Quote Link to post Share on other sites
Ali King Posted March 30, 2022 Author Report Share Posted March 30, 2022 After some thought ... I want the thermal switch to only work when the ignition is on. I want the manual switch to work anytime. I want the warning light to come on whenever the fan is powered. Rob, I think your second diagram does that for me if I swap the thermal and override switches around, and I think I still have to use the diodes in that scenario as per diagram. (please correct me if I am wrong!) So, I am going to put the warning light in the existing hole in the dashboard. I am going to drill new 12mm holes for two new matching switches: one simple toggle switch for the fan override and one 'On-On 3PDT' for hazard warning lights following Bob's instructions recently posted on Pete's 'That was the year that was' post (Thanks Bob and Pete). Thanks to all, as always what a great forum. Ali. Quote Link to post Share on other sites
Lebro Posted March 30, 2022 Report Share Posted March 30, 2022 Ali. What indicator bulbs do you have fitted ? If normal bulbs & the original style flasher unit then my circuit will make the flash rate drop considerably. To use my circuit you would need to have a flasher unit which does not care how many bulbs are connected to it, eg: https://www.classiccarleds.co.uk/collections/indicator-relays-electronic/products/12v-electronic-indicator-flasher-relay-classic-car-with-oe-click-x-l-p-2-3-pin This will work with any bulbs, but is really intended for LED types. Bob Quote Link to post Share on other sites
RogerH Posted March 30, 2022 Report Share Posted March 30, 2022 Hi Bob, your recent post is about the indicator flasher. The OP is interested about an electric rad fan. Or am I missing something Roger Quote Link to post Share on other sites
Lebro Posted March 30, 2022 Report Share Posted March 30, 2022 Yes, you are ! read last para of Ali's latest post Bob Quote Link to post Share on other sites
Ali King Posted March 30, 2022 Author Report Share Posted March 30, 2022 Bob, I have also followed your recommendations for LED lights (not headlights for the time being), so hopefully I'll be OK. Roger, I meant to say thanks for the offer of fan/brake light monitoring wiring, but that's probably a step too far for me at the moment. I need to see if I can actually accomplish what I have set out here first! Ali. Quote Link to post Share on other sites
RobH Posted March 30, 2022 Report Share Posted March 30, 2022 (edited) 1 hour ago, Ali King said: Rob, I think your second diagram does that for me if I swap the thermal and override switches around, and I think I still have to use the diodes in that scenario as per diagram. (please correct me if I am wrong!) You are right but if you want the illuminated switch to light for both then it needs a change in the position of the diodes like this. The diodes shown are a reasonable size with thick-ish leads. It is easy to crop the leads to length then solder (or crimp) one end to a spade terminal and solder a wire to the other, or just solder into a wire on both ends. Then cover with heatshrink sleeve for insulation . Edited March 30, 2022 by RobH Quote Link to post Share on other sites
Ali King Posted March 30, 2022 Author Report Share Posted March 30, 2022 What can I say? A customised wiring diagram for my idiosyncratic needs, plus wiring instructions - thanks Rob. Just a minor point, I'm not going for the combined switch/warning light after all, but separate items. In that case, does it matter which side of the manual switch the diode is on? Quote Link to post Share on other sites
RobH Posted March 30, 2022 Report Share Posted March 30, 2022 (edited) 32 minutes ago, Ali King said: does it matter which side of the manual switch the diode is on? No - as long as the lamp is directly connected to the relay coil on pin 85. The second circuit with the switches swapped is what you want. Edited March 30, 2022 by RobH Quote Link to post Share on other sites
Quicksilver Posted April 4, 2022 Report Share Posted April 4, 2022 (edited) On 3/29/2022 at 11:13 PM, RobH said: It has, but it won't work in all circuits because one end of the LED is permanently connected to one of the switch terminals. Being an LED you have to be careful with the polarity - as per the markings on the switch. It is awkward to use it on a positive earth car. you are right, my TR4 has been converted to + is positive. If the switch is in the off position, but the thermal switch comes on (fan turns on), the light will come on. Easy control. It also works the other way around, check if the fan still works, turn on the switch... Marcel p.s. I'm not sure if the switch I mounted is an LED (was installed about 10 years ago) Edited April 4, 2022 by Quicksilver tekst Quote Link to post Share on other sites
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