Over the years we’ve covered quite a few temperature switches. We’ve salvaged
them from frypans and heaters, we’ve got them out of hot water systems and
dishwashers. However, all those stories have typically required a bit of
do-it-yourself electrical work (eg adding a relay) or have needed the sourcing
of secondhand bits.
But here’s a cheap temperature switch that doesn’t require that you do
anything except order it! It’s perfect for triggering an intercooler fan or
intercooler water spray, or for turning on and off an amplifier cooling fan. The
design is rated up to 16 amps, is normally open (that is, it closes when the
threshold temp is reached) - and best of all, clicks over at just 38 degrees
C!
The AutoSpeed shop has made a special purchase of the switches and has
available a limited number available at AUD$8 each.
The Switch
The switch uses a snap-action design. That is, it cannot chatter around the
switch-on and switch off points – it’s either open or closed.
The difference between the closing temperature and opening temperature is
about 10 -15 degrees C. In other words, if the switch trips at 38 degrees C, it
won’t go off again until the temp is below about 23-28 degrees C. This
hysteresis (the diff between the switch-on and switch-off temps) means that the
switch isn’t suitable for tightly regulating the temperature of something – to
do that, you need a switch with (say) 2 degrees of hysteresis.
However, it’s ideal where you want to control something that is switched on
whenever the device is warm. Let’s look at an example – running a cooling fan on
an amplifier that’s mounted in the boot.
The overnight temperature’s been 10 degrees C and since the car has been
parked outside, that’s the temperature of the whole car. You jump in to go to
work, crank up the sound system and join the daily commute. The amplifier fan
stays off until the amplifier reaches 38 degrees C, whereupon the switch
triggers and the fan comes on. The fan’s a big one and with the cool air in the
rest of the boot, it’s no drama to bring the amplifier temp down by 10 or 15
degrees – so the fan then switches off.
However, the drive home is a different story. This time the day has warmed up
so there’s no way the amp temp is going to drop so low – even with the fan
tripped and running. The result? The fan stays on until you’ve parked and turned
off the car.
In short, this switch is ideal for switching on something once the
temperature is warm to touch. So how do you use it?
Triggering Intercooler Fans
The switch can be used to trigger an intercooler fan, but how you do it will
depend a lot on the location of the intercooler, how hard the intercooler works,
and the climate where you live.
For example, if you have an underbonnet intercooler, and you mount the switch
on the core, the switch will trip (and stay tripped) once the engine has warmed
up. However, if you have a front-mount intercooler and you place the switch on
the front face of the cold-side tank, the switch will trip only when the
intercooler outlet temp is above 38 degrees C. Or alternatively, you might
decide to mount the switch so that it measures just the temperature of the air
above the road (eg by placing it in a brake duct). That way, the fan will come
on only when the day is a hot one.
The small size of the switch and its low trip point gives you a lot of
flexibility in approach.
Note: while the switch is rated for high power, some really big intercooler
fans will take even more than 16 amps. In that case, you should wire in a heavy
duty relay.
Triggering Intercooler Water
Sprays
Everything said above about triggering intercooler fans also applies to
triggering intercooler water sprays – except you also need to use a throttle
position or manifold pressure switch.
In this case, you wire the temp switch and pressure (or throttle) switch in
series, so that both the temp switch and the pressure (throttle) switch need to
be activated to trigger the spray pump.
Adding the temp switch has the potential to save a lot of wasted water – the
spray will be enabled only when the temperature of the day (or temp of the
intercooler) is above 38 degrees C, with the triggering then occurring through
the action of the other switch.
Amplifier Fans
The switch is ideal for triggering cooling fans in electronic equipment. It’s
not confined to car sound amplifiers, either. Any in-car electronic equipment
can be cooled, including ECUs, DVD players, PCs, etc.
The switch should be attached to the standard heatsink and wired in series
with the cooling fan. Easy, huh?
Power Source
When using the temp switch, the power should come from an ignition-switched
source. That is, the power supply switches off whenever the car is stopped and
the ignition key removed. This prevents the fan (or other switched device)
continuing to run, even if the monitored temp is above 38 degrees C.
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Conclusion
How many times have you wanted to trip a cooling device when something gets
warm? Yeah, me too. (Come to think of it, the switch would be ideal in my home
stereo amp which has a big fan running continuously!). This switch lets you do
just that, in most cases without needing to use a relay or any extra
circuitry.
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