Cooling fan override..

TrickyWicky

Hi gang

I need to override a set of cooling fans that are not working at the mo. They're ECU driven and a two speed unit via 3 relays that are grounded for hi/lo speed. For low they're grounded in series and for hi they're grounded in parallel.

Now the ECU was apparently shot when the coil blew - apparently a known fault with bosch motronic ECUs however the car still starts and runs ok. So what i want to do is build up a controller for the fan unit using an arduino controller, transisters and a couple of diodes to read the engine / rad temp and ground the fan relays.

Problem is I need a good sensor! I can get small thermisters etc from maplin but I don't think any of those are really going to be suitable for car use.

Can anyone recommend me anything? - Or even an entire system for a dual speed unit?

BeenThroughItAll

Bloody hell, talk about over complicated. What's wrong with a switch on the dash that grounds out the relays? Or just fit a thermostatic switch in one of the radiator hoses (available from eBay) and run the fans.

AdrianC

What he said.

Either fix it properly, or just put a switch on the dash.

Stooby2

http://www.demon-tweeks.co.uk/Product.do?method=view&n=1847&p=394088&c=215&utm_source=Google&utm_medium=Base&utm_campaign=Fan%20Controllers%20&%20Thermostats&gclid=CjwKEAjww8eiBRCE7qvK9Z7W_DgSJABfOjf2YJ0LJQf0XnTmRLMWmoBNpoXmc0EJ7IgfroNYqoImIRoCh43w_wcB

Used these a lot on Land Rovers - pretty reliable and easy to fit.

TrickyWicky

BeenThroughItAll wrote: »

What's wrong with a switch on the dash that grounds out the relays?

That would rely on my manually turning them on and that could lead to user error => over heating.

Then there is the holes for wiring etc. No thanks!

I'd rather just put something in that does it all automatically.

Geodark

TrickyWicky wrote: »

That would rely on my manually turning them on and that could lead to user error => over heating.

Then there is the holes for wiring etc. No thanks!

I'd rather just put something in that does it all automatically.

Then why not get it fixed properly instead of some bodge job!

Ectophile

The Kenlowe kits have been used for years. They have a thermostat on them, so you shouldn't need to fiddle around with switches. Just fit and forget.

TrickyWicky

Geodark wrote: »

Then why not get it fixed properly instead of some bodge job!

I will when I have the money for the time being i just need something that will get them working - if thats ok with you? Ok then..

@BeenThroughItAll Thanks for the thermostatic switch reminder, I forgot they existed! Searched ebay and found some that should make life much simpler as I can directly connect them between the ground point and the relays No other bits needed :cool:

Strider590

What's wrong with a bog standard M22 threaded coolant fan switch mounted into an inline coolant hose adaptor.... Like....

http://thmotorsports.com/hasport/hasport_radiator_hose_adapter/egkhafsts/i-150417.aspx

That's ^^ expensive, you can pick them up on eBay for under £10 + £10 for the switch.

TrickyWicky

Strider590 wrote: »

What's wrong with a bog standard M22 threaded coolant fan switch mounted into an inline coolant hose adaptor....

Probably not much other than I doubt it supports dual speed fan units?

I've been on ebay and found these which look like they'll do the job:

http://www.ebay.co.uk/itm/KSD-9700-Temperature-Switch-Thermostat-Thermal-Protectors-40-to-150-degrees-/281469708607?pt=UK_BOI_Industrial_Automation_Control_ET&var=&hash=item4188e6e93f

Upto 150 degrees. That should do me.. one at 90 and one at 120.. both wired directly to the negative terminal and then the ground inputs for both low and hi speed. £2.50 per piece too! Stick them both to the top of the radiator and job done!

Strider590

TrickyWicky wrote: »

Probably not much other than I doubt it supports dual speed fan units?

I've been on ebay and found these which look like they'll do the job:

http://www.ebay.co.uk/itm/KSD-9700-Temperature-Switch-Thermostat-Thermal-Protectors-40-to-150-degrees-/281469708607?pt=UK_BOI_Industrial_Automation_Control_ET&var=&hash=item4188e6e93f

Upto 150 degrees. That should do me.. one at 90 and one at 120.. both wired directly to the negative terminal and then the ground inputs for both low and hi speed. £2.50 per piece too! Stick them both to the top of the radiator and job done!

Problem is they're not in contact with the coolant........ The engine bay of a moving vehicle is like a wind tunnel, the temperature difference between the coolant and the surface you attach them to, could be 20 degrees at standing and 50 degrees when moving.

Do you REALLY need dual speed fans? I don't see the point (aside from noise).....

Also be careful of the current through those, 12A maximum (or 150watts each), will they feed the fans directly?

Finally (and this applies to whatever you do), remember not to take a direct feed from the battery, if you do, you could end up effectively bypassing your ignition switch (depending on whether you leave the old feed in place).