Ambient air sensor and controller

[3Dee]

I know one or two may have done this already, and the current UK heatwave serves to bring this into focus.
Hot air tends to get trapped in the rear clip especially in heavy traffic when slow moving or stationary, and the temps climb rapidly.

Once you are in traffic, then it is rare that you can find a way to get out of it, so rear clip temps can be a worry.

I want to control a fan on the rear clip to exhaust the hot air out the back, but I am struggling to find a suitable thermistor type sensor and variable controller combination that will work in this environment and adjust between say 40 and 80 degrees c.
A post ign off 3 min run would also be useful.

Most I find seem to be mechanical and designed for fluids or coolant/ radiator applications.

Anyone with sources or ideas?

[deadscoob]

Have a word with Mike Rainbird:
http://www.randbmotorsport.co.uk/shop/Details.asp?...

If it can be upgraded to control water injection, can't see why it couldn't do a fan.

[anonymous-user]

Very easy to make with just a normal coolant temp sensor, a comparitor, potentiometer, single transistor and an automotive relay. Power it from the battery, and if post key-0ff temps climb excessively the fan would cut in.
If you want to go flash, and have things like undervoltage battery protection, or post key off running, and hysterisis on the set point, or disable it if the vehicle is above a certain speed, then you'd need a small microcontroller (AVR/PIC etc) to do it. Again, really pretty easy to do

[anonymous-user]

I did i little controller for a similar use (oil cooler on an aircooled engine) a few years back:

[spatz]

since our cars typically get little use electric consumers that are not controlled through a master switch should be avoided, so a mechanicl thermostat is best in my opinion, you should have no problem finding one and run the fan or a relay over it

[spatz]

i use a mechanical adjustable thermostat on the power converters for my solar panels, works flawlessly for years and kicks in at appros 50 degrees of the heat dissapated by the converters that are not fan cooled........
i added fans since in peaknsummer they were running too hot

[anonymous-user]

Finished and snuggled into a nice enclosure:




Operates between 8 and 20V, outputs a 16kHz PWM speed controlled fan driving output, rated at 20A continuous, 40A peak (for 15sec)

Reads in a std automotive air/coolant temp sensor (2.2Kohm@25degC) and drives cooling fans as appropriate. Current output characteristic is as follows:



Also has an external switch input for "override", which turns the fans fully on when switched to ground and drives an external status LED(dash mounted for example), to indicate when the system is running the fans, and also if there is a critical fault (which would stop the system operating).

The device monitors it's own internal temperature, and will automatically derate its output current (to prevent overheating) if it reaches 80degC, and will shut down above 120degC

On power up the unit briefly (15sec) enables the output (at 30% speed) to check the system & Fans are working (handy feedback to the owner that all is working too)

When in "sleep" mode, i.e powered but not operating the fan output (below temp setpoint) the device only consumes 16mA

[bluesatin]

This does the job.

http://www.ebay.co.uk/itm/DC-12V-Digital-Temperatu...

and some more info.

http://www.autospeed.com/cms/A_112617/article.html