will this wiring set up work?

[mollydog]

I have the rad fan of my car set up so it can be switched on if in traffic-jam and the coolant temp starts rising


on the rad, the wire I can cut in to (easy option) is a negative feed and where I have the on/off switch there is a posative feed so I use a relay to swap the posative trigger in to a negative trigger, thats all OK and works fine, like this:



so no problem with this setup, but would like to improve on it

my next step/plan is to insert a delay off relay between the on/off switch and the negative output relay, so once I press the switch (on the time delay relay) it will feed the fan for the set duration then cut the power, this way I can power the rad fan of the car and can forget about having to switch it off very time I power the fan manually


will my setup in this diagram work, the way shown?



or if you can point me in the right direction, where I'm going wrong please?


Power from the battery is already fused from the fuse box but haven't shown it on the diagram (error)





many thanks

 

[telectrix]

surely there is a temperature switch on the radiator for this very purpose. the water gets hotter when you are stationary and this kicks the fan in.

 

[Richard Burns]

I cannot see how the first set up works because you would have no positive supply unless the fan is already on. The thermostat will switch on the positive supply to the fan and the only thing you could do with the negative would be to stop the fan by disconnecting it.

Therefore the second scenario would also not work.
If you were using the second relay arrangement to supply a positive input to the positive side of the fan then this would work as a manual override and if using a pulse time delay relay (if such a thing is available for cars) would also work so long as you used a press to make switch.

 

[plugsandsparks]

Not partial to the timer wiring set up but it looks like com should have a 12V feed from battery not earthed

 

[R G]

If there is a temperature switch , which I would have thought there is , I would wire the relay in parallel with the switch so that both the temperature switch and the relay can bring on the fan ,,,


Come to think of it, the existing temperature switch usually brings on a relay anyway , so all you need is switch in parallel with the temperature switch ,,,,

 

[mollydog]

Thank you all so much for your help

This further explanation might explain better

The car is a Lotus Elise and on one of the user groups, people have made a fan override switch by cutting in to the negative wire as I have done, I can only think the Elise fan works on a negative feed.

I did ask these same questions I’m asking here, on the Elise forum but few are electrical minded so no answers came back

The fan will come on if the temp gets to 104c - 106c, but in the four years I’ve had the car the fan only came on once, when I left the engine running for a good 20 to 30 minutes to see if the fan ever came on and it did at 104c -106c, but on many occasions while driving it to Italy and being in stationary traffic jams for 4 or 5 minutes the coolant temp reached 100c / 102c and the fan not kick in, reason some owners have made an override switch, in this way try to keep a constant coolant temperature as possible

Just switching off the engine is not the solution and there is nothing worse than switching off a very hot engine with hot coolant round the head, it will produce head gasket failure hence the fan override switch,

I could get a lower coolant sensor but now I have the wiring all working, I’d like just to add a delay off to it so when I use it I can forget about having to switching it off

The fist diagram is how I have my override set up at present, the relay in my first diagram is to convert a live feed in to a negative feed to the negative wire leading to the rad and it works fine, I would like to add a time off delay to the circuit and this is where I am lost

will something like this work? That is the actual relay/timer I have



As the coolant can and will get up to 100c to 102c when stationary, it’s handy to be able to override the fan sensor occasionally

 

[itselectric]

The way I see it you need to remove your red between common and plus 12v, and put a connection from common to earth.
I'm not an auto electrician.

 

[telectrix]

sealed cooling systems are designed to run up to a water temp. of 110deg.C, so why worry.

 

[clydey]

last diagram is wrong
positive battery supply through in line fuse to common of relay
operating momentary contacts sends the positive voltage through the n.o. contacts to ecu/fan junction marked 12v negative.
this will blow the in line fuse and could damage the ecu.
if in fact the circuit is physically working you have mixed up the positive and negative markings on the drawing at the fan
cheers

 

[mollydog]

you can tell I'm stumped with this,

what I do have working right now is whats on the first diagram:



all works as it should but would improve its use if I could add a delay off to it.

reason for the relay is that the fan needs a negative feed, so I'm converting a positive feed to negative feed, power from the 12V + (battery) this feed is is fused but not shown in the diagram.

what I would like to add to this circuit/diagram is a delay off relay/timer, by pressing a momentary switch a delay off is activated

maybe using what I already have, one of these:






if I have to use another type of relay I can do that too, just need to know how,



am I somewhere near with this circuitry?:




many thanks for taking time to reply to me, its much appreciated

 

[Richard Burns]

From your description and diagrams, I cannot see how the first modification works, so there must be something different in the wiring.
You are not converting a negative feed to a positive feed, you show you are connecting negative to negative which should have no effect.

These diagrams show how I would approach it assuming I have the original correct, however the description you give of your override working does not match with my expected original.

 

[clydey]

remove earth from com of timer relay completely then bridge com to pos+ of timer relay
it appears fan is negatively switched with permanent pos+ supply

 

[itselectric]

Going back to post 1#, second diagram, remove cable from common to earth, and loop from 12v positive to common

 

[plugsandsparks]

See post 4 and above. If this fan is brought in by the ECU, typically ECUs have semiconductor switches that switch the negative side only. This is very common. It is unlikely the ECU is switching the fan directly but via a relay (although its possible) You could leave it just as a switch provided the switch is rated high enough, suspect the fan would take around 10 amps depends on size. A 20A relay is a common component on cars and easily available. Use your diagram in your last post , fit a fuse, 3A would be more than enough after battery and connect direct to +ve of timer AND com of the relay contacts of the timer, remove the earth wire you currently have on com.Thats IT

 

[guest119]

I had the same issues with a car a couple of years back. I had to rev it quite a bit when sitting in traffic. Or put the heater on and open all the windows.
Turned out to be just the water pump had lost some of its efficiency.

Your temp gauge is telling you the engine temp not the radiator temp.

Boydy

 

[mollydog]

with my circuitry, I'm bypassing both the temp sensor and the ECU, I am making my connection on the wire coming out of the OEM's relay to the fan.

I managed to copy the wiring diagram for the Elise rad fan ( I re drew it):




hope this is further help


@ Richard, thanks for this diagram, if I don't have to switch from pos to neg, I rather not have the switch over relay

have I got this right? sorry for being a bit dumb when it comes to scemetics

 

[mollydog]

Have I got it right

like this?





is the feed from the NO (normally open) a neg feed?

 

[mollydog]

yes clydey , it look that way as I connect to the neg feeding the rad fan

 

[plugsandsparks]

@itselectric

like this?

@ mollydog I give up ! - good luck

 

[mollydog]

@plugsandsparks

I know, I really wish I could follow these instructions, thank you for trying to put me right, I really do appreciate it very much all the effort people on here are making for me