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Electric Fans And Thermostatic Switching


JST
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when the 200 tdi viscous packed up and i had two 12v electric fans lying around i decided to fit these instead. at the moment they are temp wired in to a user controlled switch.

what i would like is a thermostatic control but with user override of needed.

where is a good place to get a thermostat electrical switch from and how much should i expect to pay.

where do these fit into the vehicle? top hose connection?

what sort of temp should i set it to?

and most importantly how do i wire it up? how do you get user on/off function as well as the thermostatic control without blowing the fans?

many thanks in advance.

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James,

I bought a electronic sensor from Demon Tweeks, it does not inpede the flow, not affected by mud like the Facet bulp type and a hell of a lot more accurate !

cost...£45...I think... :unsure:

Fitted in in the top hose.

wiring it comes with a relay and wiring loom, so easy peasy....once its wired as per instuctions to fit an over ride switch run a positive feed to the switch from a Ign contolled source, return wire(switched feed from the switch) to the coil on the relay.

(in parrallel with the stat, if either is "on" the fans will run !)

switch is normally off...if it gets hot...fans don't come on..Ie..sensor duff..switch on and away you go.

settings...

well with all my overheating troubles, mine comes on at 95 degs and switches off at around 85, two fans takes about 3 mins, so the stat is shut again, mybe this is a bit low. but I aint taking any more chances... :P

HTH

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I have the same Demon Tweeks one fited to my 300Tdi (retro fit into what was a TD90). Great piece of kit. Unobtrusive and comes with all the wiring. It's a doddle to fit and IMHO is much better than trying to seal something that's just stuffed inside the top hose (aka Kenlow etc).

Ivan

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thank you for the info, some good food for thought.

just had a look at the demon tweeks site, is it the pacet one at £46 + VAT?, seems alot of cash.

'return wire(switched feed from the switch) to the coil on the relay.'

if i did the above with the wiring would it not then get 24V at the coil if the thermostat was on and then it was also manually switched?

maybe the thermostat fails to work so fans are manually selected, thermo then starts working for what ever reason. unlikely i appreciate but just wondering what would happen. (my electics is like my welding - very poor)

don't suppose you know the internal diameter of hoses do you for 200tdi?

i notice vehicle wiring do a capillary one for around £30 has anyone any exp of this. it looks like the attachment method is simialr to kenlow etc with poking something in the top hose at a jct, something i am keen to avoid.

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Capillery are IMHO.....Pants !

difficult to seal,inaccurate, fill it full of mud, water etc...carp..., my kenlow one had to be WD'd every month just to keep it working ! :angry:

sorry but thats what I think, electronic is a bit more expensive ganted but you will not regret it !

as for the wiring the only way you will get 24 Volts is to fit another battery is series with your exsisting(presuming you only have 12 Volts ?) and not 24 Volt winches/12v vechicle) etc

thinking of it as household electics its similar to a 2 way lighting circuit you can switch it on from 2 places but you only get 240 Volts........

Unless Nige did it then I WOULD expect 415 V.... :blink:

12v plus 12v batterys in parrallel = 12v twice the amps

12v plus 12v in series = 24 volt

I'm rambling sorry.... :ph34r:

or does this help ?

fan-picture3-circuit.jpg

fan-picture4-circuit.jpg

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If you don't mind me elaborating on your Basic diagram Les.

An auto or manually switched fan is easily wired in if you weren't worried about not switching it off for wading:

coolingfan.jpg

(the theory with vehicle electrics is to always pass the earth circuits through the dash wherever possible. If a live wire shorts, it smokes and if the fuse doesn't blow sets fire. If an earth circuit shorts, the item starts working instead, like a fail-safe).

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IIRC....its that Fridge chap ! :unsure:

I tried to keep it simple... :P

two fans wired in series gives both fans running at slow speed,

for fast you switch them to run in parrallel

two stats req or sensor with two temp setttings and more relays.... :rolleyes:

I have two wired through two supplies/relays so if either fails I still have one fan that works...there are loads of ways it can be done...! :blink:

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Les, imspanners

thank you very much for the input. i think i will go for the electric thermostat setup with the additional switch for manual over ride for on.

so as the wading topic has been raised i may as well chase this one well. presumably i can add another switch in the earth from the cooling fan or between the relay and the fan to turn it off as desired irrelevant of the input at that time.

how about internal dia of the hoses, can anyone remember? 45mm???

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I dont like adding joints into radiator hoses uneccesarily.

Visit your local radiator specialist and either get them to fit a treaded boss into the top tank of your radiator, or alternately ask them to supply you with one (last one I got was free!) and solder it into the top tank yourself. Depends how much you trust your soldering as to whether you do it yourself or not!

Then go to your local motor factors a buy the relevant fan switch. The intermotor part numbers are all on Fridgefreezer's website. My local one keep quite a good selection in stock, and they're about £8 each.

Much nicer doing it this way - it looks professional, is cheaper, and is the way many cars from the factory!

As to the switching, I've got mine wired via a 3 way switch such that i have, off, auto and on to choose from. Auto being via the thermostat, and on being a manual on. The ability to turn it off is also useful when wading. I've also got warning lights to show when the thermostat has cut in, and also a fan running light, which is great for letting me known the fuse has gone (my poxy kenlowe eats fuses!)

HTH

Jon

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Good Thread James,, I was going to ask the same,won't bother now,,

I have the same job to do, now I know why your fans were running all the time last Thursday,, same as me, one switch,, on or off, and remember to switch on when that little gauge is near the red bit :)

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How do you connect to one of the spare warning lights we all have [eg the Llama cab tip-up warning]so you know when the fan has cut in?

Better than looking under the bonnet when you're driving.

Neil

Neil,

connect feed to the lamp togeher with the fan either at the fan or at the relay and up to the dash and earth the other side of the lamp, so when the fans run either via the stat or the override switch the lamp comes on !

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I have Ian's (Bull Bar Cowboy's) design of twin fans switched through a two stage temp sensor mounted in the top hose.

You get half speed at the lowert temp and full speed at the upper temp with manual cut off for wading. The sensors are about a tenner each and all you need is to braze a fitting up to fit into the top hose

Recognisethis-copy.jpg

I have a word doc somewhere with the wiring diagram and description......... I'll see if I can dig it out as Ian said he was more than happy for the wealth to be shared!

The fans I have came from a V6 mondeo with aircon and fit the RR radiator perfectly.

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You mean this article? B)

I second the vote that capillary stats are pants with sick on, my kenlow one packed up really quick. I believe the MG Owners Club sell those solid-state fan switches but not sure if they're any better than Demon Thieves on price.

The electronics in it are pennies, if anyone could be bothered to work out the circuit and pot it into a box it'd be a very robust solution and probably come in under £10.

And no, I can't be bothered to work out the circuit as my ECU will run fans already :rolleyes:

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I second what Jon says about joining hoses; best to avoid if possible.

Even though I have been slated for using a Kenlowe, I fitted it to a new hose with no leaks and so far is working :P . If, or or more likely when it fails, I'd look to fitting a boss in the radiator to take a thermostatic switch or thermostat; first problem is to find the suitable fitment - any idaeas?

The latter is not an on/off switch but with some simple electronics, a comparator with adjustment, perhaps can be made for a fraction of the price; AFAIK most thermostatic switches are set to switch at a certain temp?

The circuit that was shown before is as below; it has LED lamp to show when fan is on,. Uses a Lucas 3 way switch wired to give: Fan on, Fan off and Fan switched by thermostat. I rang Kenlowe to confirmn no damage is caused to thermostat by the wiring -they basically said they do an override switch to connect in the same way (there is nothing more than some bellows and contact inside the thermostat).

DSC01052.jpg

and how it should look when fitted.

DSC01050.jpg

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double post .... :unsure:

I prefer the on light to be from the relay/fan so you know that their running not just power out of the switch etc.

all the lamp on your drawing does it tell you if the stat is calling for the fans to be on...not if there running/power to them !

which still means nothing if your fans duff of course....hence why I run two !

Pedant mode off... :ph34r:

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double post .... :unsure:

all the lamp on your drawing does it tell you if the stat is calling for the fans to be on...not if there running/power to them !

which still means nothing if your fans duff of course....hence why I run two !

Pedant mode off... :ph34r:

the lamp shows that power is going to the relay coil. Granted if there is a problem with the coil or the contacts that provide power to the fans, the lamp becomes meaningless.

If the lamp is connected across the fan, then all it tells you there is power to the fan, it does not necessary mean the fan is running e.g. fan motor has burnt out or fan earth has come lose (ok, depends on where the earth or the lamp is fitted). It is better in that it tkaes the relay out of the picure. (I may have wired it that way, not sure now :( )

It may be possible to fit the lamp in series with the fan, you'd need a shunt for the main current to the fan. Although better is some ways, again this is not fail safe, you can guard against o.c. for the fan but the fan could be drawing current and still not be turning, say if a badger was wedged in the fins.

For me the lamp is there for manual override indication although the important condition I should be guarding against is when the fan is turned off and have a reminder to put the fan to auto. I also have water temp guage that is read often.

I suppose the only sure way would be a motion senser to detect the fan blade rotation.

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how about internal dia of the hoses, can anyone remember? 45mm???

Can I repeat James' question, as I bought what looked like a good sytem [like Pacets], made by Revotec, from Scrapiron's tent at Billing.....the hose link is made from a bomb-proof looking cast alloy.

However, they assured me that the top hose ID for a TDi was 38mm...mmmm, have I been rooked?

Neil

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