tegwin
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| posted on 27/3/07 at 09:42 AM |
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Complicated fan system
To save money and effort im going to use a dashboard mounted swtich to activate the fan.
My plan is to have it so you cant turn on the fan unless the ignition is on, but the fan will continue running after the ignition is switched off.
I have drawn this schematic...can someone have a look at it and just make sure that i havnt made a silly booboo...
In an ideal world the fan would stay on for say five mins after the ignition was turned off and then switch itself off....but I dont feel like going
into the design of a timer circuit...
[Edited on 27/3/07 by tegwin]
 
Rescued attachment Fan latching switch.JPG
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RazMan
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| posted on 27/3/07 at 09:46 AM |
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You don't appear to have a thermal switch involved, or have I missed something? You could simplify even more by just wiring a thermal switch to
a permanent feed - the fan will always switch off when the temperature drops below 90 degrees or so.
[Edited on 27-3-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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tegwin
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| posted on 27/3/07 at 09:49 AM |
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I dont have a thermal switch, because the cheapest thermal switch and mounting that would go in the water hose was £30...Would be nice to have one,
but for that money is it worth it...
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RazMan
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| posted on 27/3/07 at 09:51 AM |
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But surely your circuit will just switch the fan off when the ignition is switched off.
I can't see why you have a diode in there really.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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tegwin
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| posted on 27/3/07 at 09:59 AM |
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My logic is that once the fan switch is switched on it passes a +ve ignition feed into the relay coil. As soon as the relay closes the fan comes on
and the supply to the fanswitch/relay gets switched to +ve perminant supply....If you turn off the ignition the fan switch is still powered so the fan
will remain running...
If you turn off the fan switch with the ignition off the rlay will open and there will no longer be a supply to the switch so the fan cant be
reactivated until the ignition is back on....
The diode is there to prevent the +ve perminant supply feeding back into the ignition circuit when the ignition is off causing engine overrun....
Complicated, but I think it should work?
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Mr Whippy
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| posted on 27/3/07 at 10:08 AM |
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Pah, just wire a normal fan thermo switch in then that to a relay for the fan and then make it permanently live. No need at all for a manual over ride
at all.
Fame is when your old car is plastered all over the internet
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RazMan
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| posted on 27/3/07 at 10:09 AM |
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Ahhh I see it now! My brain is a bit slow this morning (due to strong pain killers).
Ingenious and quite simple really .... especially if you cant fit a thermal switch.
 I think you can get latching relays which do a similar job.
[Edited on 27-3-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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dilley
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| posted on 27/3/07 at 10:11 AM |
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I always prefer a manual switch for the an and no rad switch, when its on its on!!
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tegwin
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| posted on 27/3/07 at 10:13 AM |
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Tis ok...there is something about ciruits like that that confuse me aswell!
Just out of interest, what aftermarket thermo switches are most people using and where do they get them from?
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RazMan
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| posted on 27/3/07 at 10:25 AM |
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In my case I used a Polo rad with a built in switch (it might be worth looking in the scrappy if you don't fancy a new one) but I think Vauxhall
ones are commonly used.
TBH I have never seen the point of a manual overide switch - that's what the thermal switch is there for 
[Edited on 27-3-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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tegwin
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| posted on 27/3/07 at 10:31 AM |
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I have a really weird rad...not sure what its from...but it actually fits in the car...It doesnt have a rad temp swich on it....
If I do have a thermo switch its going to have to be an inline pipe jobby....
Where is the cheapest place to get one?
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James
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| posted on 27/3/07 at 10:58 AM |
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Used a Golf (v' similar to Polo) rad and Golf switch on mine.
Having seen Merlin seize his engine on the way to SVA as he was in traffic and forgot to look at the temp' gauge I really would advise you fit a
thermo' switch!
If you can't fit a switch into the rad then weld a threaded boss to a piece of pipe and fit a cheap thermo switch in there (fiver from motor
factors).
HTH,
James
------------------------------------------------------------------------------------------------------------
"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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omega 24 v6
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| posted on 27/3/07 at 11:40 AM |
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quote:
Complicated, but I think it should work?
But the fan will run forever if you leave the relay energised!!!!!!!!!!! and flatten ythe battery.
Sorry if I'm stating the obvious here but I agree with the others fit a temp switch and be done with it.
If it looks wrong it probably is wrong.
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caber
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| posted on 27/3/07 at 12:55 PM |
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Cheap thermo switch
The cheap solution, find a busted Polo Radiator, take the fan switch out then hacksaw into the rad header and you will find a brass nut that the
switch threads into. Go to plumbers merchant get a 28mm equal tee saw the T leg down and solder the nut to the stub, its easier if you file the
corners of half the nut so it locates in the tube!
Here is one I did earlier, the hose fits nicely onto the plumbing bit and the solder ring holds the jubilee clip nicely!
Caber
 
Rescued attachment Photo_022407_001.jpg
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BenB
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| posted on 27/3/07 at 01:31 PM |
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Yup. I'd certainly go to the effort of having a thermo switch. Whether you bother with a manual overide or not is up to you.....
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Hellfire
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| posted on 27/3/07 at 02:40 PM |
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We have a Micra Rad fitted with it's own thermo-switch - wreckers £15.
We also mounted a dashboard override for trackdays...
Steve
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MikeRJ
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| posted on 27/3/07 at 03:23 PM |
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This won't work unfortunately, there are two fatal flaws:
1) The fan will run as soon as you switch the igntion on via the diode.
2) There's no way to stop the fan once it's running!
Adding a second diode in the wire running from the fan to the switch would solve the first issue, but not the second. To switch it off you would have
to break the circuit somewere (with e.g. a normaly closed relay) in order to break the latched action of your relay.
The cost of a thermo switch is trival in comparision to the consequences if you forget to switch a manual one on...
[Edited on 27/3/07 by MikeRJ]
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tks
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| posted on 27/3/07 at 04:06 PM |
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yeah
with mike on this one!
infact a normal diode wont work because the fan is quite some amps..
anyway before the fan fit the thermoswitch
and feed the thermoswitch true a Fuse direct to barrery +
then if igntion is off and engine temp is higer as fan switch for example a (92 / 97)
(ITS HIGHER THEN 97degrees!!) then it will switch on the fan..it will switch off when 92degrees is reached..
the manual button will need to be connected to the motor terminal (just as the terminal switch) and to a ignition feed)
and that case its never a problem to switch on the fan below 97degrees (if its off) and you cant forget to let it stay on when ign is off
Sow from Ign live to switch from switch to motor terminal (behind the th switch)
from fuse box to fuse from duse to TH switch from th switch to motor..
Easy really and no diode involved..
Tks
The above comments are always meant to be from the above persons perspective.
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suparuss
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| posted on 27/3/07 at 04:45 PM |
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i got my adjustabe thermo switch free with my fan. all the PACET - Clovafan Club Range come with them on rally design.
but you need to buy a fan though.
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