As we covered last week in
Intelligent Intercooler Water Spray Controller, Part 1, our new intercooler
water spray controller has sufficient intelligence that it only sprays when it’s
actually needed. That saves a heap of water and provides far better cooling than
a dumb boost switch or a manual dashboard mounted control. In addition, the new
controller has a 10 LED bargraph display of intercooler temp which makes it much
easier to set up.
The genesis for the new design was a Mixture Meter
project completed for Silicon Chip electronics magazine. Also covered in
Smart Mixture Meter, Part 1,
the design used the ten LEDs to display the output of the oxygen sensor. The
project also included an alarm that sounded if the mixtures were lean and
the engine load was high – ie, a lean-out warning.
It was when we were musing about intercooler water
spray controllers that it suddenly occurred: as with the Smart Mixture Meter, a
water spray controller needs a load input with an adjustable switching
threshold. If the oxygen sensor input is connected to a temperature sensing
thermistor, the voltage received at this input can be configured to drop with
increasing temperature. Just as the voltage dropped when the air/fuel ratio was
Therefore, with very little change to the existing
kit, the piezo alarm will sound when the intercooler temp and engine load are
both high. Hmmm, but in that situation we want to operate a spray pump – not
turn on a buzzer. The answer is to replace the buzzer with a heavy duty
automotive relay (protecting the switching transistor with a diode) and then
replace that switching transistor with a Darlington design that will cope with
the new, higher, current demand.
Finally, so that the intercooler water spray won’t
turn off on gear-changes or when the load is fluctuating rapidly, we add a
1-second switch-on delay and a 2-second switch-off delay.
In other words, with just a few simple
modifications to an existing kit, we could have a good water spray controller.
In fact, that approach is the exact one I took to control the intercooler water
spray in my turbo Prius – and it’s been doing an excellent job for the last 12
months or so.
A story was run in Silicon Chip covering
how the Smart Mixture Meter could be modified to be an Intercooler Water Spray
Low-Cost Intercooler Water Spray Controller) -
and then there was another interesting development.
Printed circuit board manufacturer Bob Barnes saw
the article and decided to produce a printed circuit board (PCB) dedicated to
the Intercooler Water Spray function. The PCB is coded SC 05103061 and is
available for AUD$17.05 from the contact listed at the end of this story. In
addition to mounting all the components on the PCB, the new PCB adds a remote
mount LED output to show the driver if the spray is operating. This is a
worthwhile feature as in most cases, the unit will be tucked away out of sight
after it has been appropriately calibrated.
So now we have a PCB with the full functionality
of an intercooler water spray controller. The PCB is available only from RCS,
while you'll need to buy the electronic components from an electronics store
like Jaycar. All are generic, off the shelf components – there are no programmed
PICs or anything like that. (If you want to make things easier, you can get most
of the components in one go by buying the Jaycar Smart Fuel Mixture Display kit
– cat no KC5374.)
So in summary the design uses a 10 LED coloured
bargraph display to show actual intercooler core temperature, as sensed by a
remote mount thermistor. When the intercooler temp exceeds a user-adjustable
level, a monitoring LED comes on. Engine load is sensed by an input from
(usually) the airflow meter. When the airflow meter output signal exceeds a
user-adjustable level, another monitoring LED comes on. When both the
temp and load monitoring LEDs are on, an externally mounted relay is tripped, so
operating the water spray pump. A delay is introduced by a capacitor so that the
pump doesn’t rapidly turn on and off with gear-changes and the like.
Because a complete off the shelf kit of the parts
is not available, this project is best suited to those that have built
electronic kits before. Follow this overlay diagram and the photos for the
component placement. Don’t forget to click on the pics to enlarge them.
The thermistor connects across the ‘thermistor’
inputs and the spray monitoring LED connects between ‘Ext LED’ and GND, with the
flat of the LED going to ground.
The output to the external relay coil is from
these two points – it’s easiest to make the solder connections under the
Note that on-car experience has shown that the
2200uF capacitor might need to be increased in value to provide the best delayed
on-time period, causing the spray to continue to run for a short period after
the load or temperature has dropped. However, initially test the system with the
LEDs 1-10 show intercooler core temperature based
on thermistor input
LED 11 indicates the trip point for intercooler
temperature has been reached and VR4 sets this trip point.
LED 12 indicates the trip point for load has been
reached and VR5 sets this trip point.
Ext LED indicates that the spray relay output has
been turned on (ie both Load and Temperature Trip-Points have been exceeded)
VR1 sets the cold end of the LED bargraph
VR2 sets the hot end of the LED bargraph scale
VR3 sets the night dimmer sensitivity
Connect 12V and ground. Set both VR1 and VR2 to
their centre positions. Remember the LEDs will show sensed intercooler
temperature – green is cool, yellow is warmer, orange is warmer still and red is
At room temperature (~20 degrees C) turn VR1 until
the second from lowest LED (ie LED9 - green) lights, then adjust a little
further anti-clockwise until the lowest LED (LED10 - green) is just lit. Warming
the thermistor with your hand should then move the illuminated LED from LED10 to
LED9. Use a heat-gun to further warm the thermistor. When it is just too hot to
touch (eg 55 degrees C) turn VR2 clockwise until LED1 (the ‘hottest’ LED - red)
lights. Make sure you don’t turn it so far the LED goes out. When the thermistor
is again cold you may need to tweak VR1, as to some extent the pots influence
When calibrated in this manner, the bar-graph
display is configured to show intercooler temperatures over approximately a
20-55 degree C range. (Note that because of the thermistor’s characteristics,
the bar-graph isn’t linear – it needs a bigger change in temperature to move a
LED at the hot end than it does at the cold end.)
For remote installation, the thermistor should be
soldered to some twin-core flex and the joins insulated with heatshrink. The
thermistor should then be pushed well into the fins of the intercooler,
inserting it from the rear of the core. This location will give the best
indication of intercooler temperature. The thermistor may need to be held in
place with a dob of silicone.
The load input for the Intercooler Water Spray
Controller can be taken from the airflow meter or MAP sensor outputs, or where
these are not available, from the throttle position sensor. This can be done at
the ECU or the sensor itself. Use the workshop manual wiring diagram to find the
load sensor output and then use your multimeter to check that it’s correct. The
measured voltage on the load sensor output should rise with engine load. (Some
cars use a frequency output on the airflow meter – in that case, use the
throttle position sensor output.)
The intercooler water spray pump relay is best
located under the bonnet, near to the pump. The relay is wired to operate the
Test that when VR4 and VR5 are adjusted so that
their adjacent LEDs are on, the pump turns on and the water spray operates.
Install an assistant in the car and then drive the
car and monitor the displayed temperature on the bar-graph. The lit LED should
move up and down the display with the variation in intercooler temperature.
Adjust VR4 until its adjoining LED lights when the intercooler is becoming warm.
Then adjust VR5 until its adjoining LED lights when the car is coming onto
Drive the car so that the intercooler gets warm
and the car is under load and check that both LED11 (intercooler temp) and LED12
(load) light. When both have been lit for more than about a second, the water
spray will operate, as shown by Ext LED.
After monitoring the displayed intercooler
temperature, you may decide that you want to make further adjustments to the
load or temperature trip points. Another important aspect to keep in mind when
setting these thresholds is water consumption – check this over a few weeks to
make sure that you haven’t got the system tripping too early.
The Intercooler Water Spray Controller can be
mounted so that the bar-graph LEDs can be seen by the driver, or alternatively,
the whole device can be located out of sight.
Intercooler water sprays are a very effective and
cheap way of upgrading intercooler capabilities. However, using just a ‘dumb’
system to trigger the spray often results in the need for frequent water
top-ups. Compared with such an approach, the Intercooler Water Spray Controller
is likely to reduce water consumption by up to two-thirds with no loss in
Over the 12 months that we’ve been using the
system we’ve been enormously impressed with its operation. With the spray set to
come on at about half full load and the temperature trip set at about 35 degrees
C, in winter the spray will stay off for months at a time. But then, as soon as
the days start warming-up, on it comes. Driving through a series of steep hills
and valleys on a country road on a hot day, you can clearly see the actual
intercooler temp getting lower after the spray has been working – the system
trips less after the core has been well soaked, even when climbing a subsequent
hill on boost. Furthermore, if it’s raining (it rains in hot weather here), the
cooling effect of the evaporating rain can clearly be seen - the spray doesn’t
trip in these conditions.
In short it’s proved to be a set and forget
controller. All you do is keep an eye on the ‘spray-on’ LED and when you see
it’s often working, don’t forget to fill the tank!
RCS Design – +612 9738-0330 www.rcsradio.com.au
Jaycar Electronics –
As stated in the main text, because it is not available as an off the shelf kit,
this is a project for those experienced in electronic construction. We will not
be providing technical advice on fault-finding.
1x single pole single throw (SPST) 30A automotive
relay (Jaycar Cat. SY-4068 or equivalent)
3x PC mount 2-way screw terminals with 5mm pin
1x Light Dependent Resistor (Jaycar RD3485 or
1x 100mm length of 0.8mm tinned copper wire
1x LM3914 LED bargraph driver (IC1)
1x LM358 dual op amp (IC2)
1x BD682 PNP Darlington transistor (Q2)
1x BC327 PNP transistor (Q1)
3x 16V 1W zener diodes (ZD1-ZD3)
1x 5.6V 400mW zener diode (ZD4)
2x 1N4004 1A diodes (D1)
2x 1N914 diodes (D2, D3)
3x green, 4x yellow, 2x orange, 1x red 5mm
1x 470uF 16VW PC electrolytic
2x 10nF MKT polyester
1x 2200ìF 16V electrolytic capacitor
Resistors (0.25W, 1%)
1x 220kohm horizontal trim pot (VR3)
2x 100kohm horizontal trim pots (VR4, VR5)
2x 5kohm horizontal trim pot (VR1, VR2)
1x 4.7kohm 0.25W resistor
1x1.8kohm 0.25W resistor
1x 4.7kohm thermistor (Jaycar RN3438)