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The tiny droplet size resulting from the use of the
“espresso” pump and a Spraying Systems nozzle can
be seen here. In this case, the nozzle is aimed forwards
and the car drives into the cloud of water droplets.
These very effectively cool a front-mounted intercooler
and as a bonus also help cool the other radiators!
By JULIAN EDGAR
Low-Cost Intercooler
Water Spray Controller
A cheap but sophisticated way of controlling a
turbo car intercooler water spray
M
OST TURBOCHARGED petrol
and diesel car engines use intercoolers – radiators that cool the air
after it has been compressed by the
turbo. An intercooler has twin benefits
of providing more power (the intake
charge is cooler and therefore denser)
and in the case of petrol engines, reducing the chance of detonation.
In many cases though, the intercooler is too small for best performance
– especially in a hot country like Australia. This can be greatly improved
by adding a water spray – the small
droplets evaporate on the core, lowering its temperature.
How do you trigger the spray? Many
people use a boost pressure switch –
but this wastes lots of water because
the spray operates even when the
38 Silicon Chip
intercooler is cool. Another approach
is to use a temperature switch but
this also wastes a huge amount of
water because it doesn’t take into
account heat-soak (eg, when the car
is stopped for a long time in traffic),
where a simple temperature switch
can continue to run the spray until
the tank is emptied. Also, both types
of switch cannot easily be adjusted for
their switch-on points.
Possibly the best way to trigger the
water spray is on the basis of measured
intercooler temperature and engine
load; when both are high, the spray is
switched on. This wastes very little
water because the spray operates only
when it is really needed.
So now we know what we want –
but how to get it? The answer is that
the Smart Mixture Meter project (described in both the “High Performance
Electronics for Cars” book and in the
April 2005 issue of SILICON CHIP) provides nearly all that we need. In fact,
it provides even more features, with a
colour LED bargraph that can be used
to show intercooler temperature!
To transform it into its new function
we need add only a handful of components and make some simple changes
to the PC board, none of which require
cutting tracks.
That makes it one very cheap and
easy to build Intercooler Water Spray
Controller!
Smart Mixture Meter
The Smart Mixture Meter was designed to monitor the output of the
siliconchip.com.au
Fig.1: the circuit is virtually identical to the Smart Mixture Meter, described in Performance Electronics For Cars.
An LM3914 IC drives the display LEDs, while op amp IC2b, transistor Q2 and Relay 1 control the water spray.
oxygen sensor which indicates the
rich/lean status of the air/fuel ratio.
Two inputs were provided – one from
the oxygen sensor (with its output
shown on a LED bargraph) and the
other from a load sensor, such as the
airflow meter. When the load was
above a set threshold and the output
of the oxygen sensor showed that
the fuel mixtures was lean, a piezo
alarm sounded, to give a “lean-out”
warning.
We have adapted the Smart Mixture
Meter to control a water spray controlsiliconchip.com.au
ler. It needs a load input with an adjustable switching threshold, while the
oxygen sensor input is connected to a
thermistor, with its output configured
to drop with increasing temperature.
Therefore, with very little change to
the existing kit, the piezo alarm will
sound when the intercooler temperature and engine load are both high. But
instead of operating a piezo buzzer,
the circuit now operates heavy-duty
automotive relay, to switch a spray
pump.
Finally, so that the intercooler water
New Par t s Required
1 BD682 PNP Darlington
transistor (Q2)
1 1N4004 silicon diode D4
1 single pole single throw (SPST)
30A automotive relay (Jaycar
Cat. SY-4068 or equivalent)
1 2200mF 16V electrolytic
capacitor
1 4.7kW 0.25W resistor
11.8kW 0.25W resistor
1 4.7kW thermistor (Jaycar
RN3438)
March 2006 39
Fig.2: this is the modified PC board layout for the Intercooler Water Spray Controller. Alternatively,
you can build the Smart Mixture Meter exactly as detailed in the kit instructions, verify that it is all
working correctly and then modify it by following the step-by-step instructions in the article. Don’t
forget the 4.7kW resistor that’s fitted on the copper side of the board (shown in red) – it should be
insulated from the tracks using heatshrink sleeving – see text.
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.
Changing The Mixture Meter
The Intercooler Water Spray Controller can be built in two ways. The
first way – best if you’re a kit beginner – is to build the Smart Mixture
Meter exactly as per the original kit
instructions. That way, you can test
the final result and be sure that the
device is working before undertaking
the modifications that turn it into the
Intercooler Water Spray Controller.
The other way is to build the kit
from scratch as the Intercooler Water
Spray Controller, incorporating the
modifications as you proceed. Here
are the modifications:
THERMISTOR INPUT: as indicated earlier, a
thermistor is used to sense intercooler
core temperature – the resistance of the
thermistor decreases with increasing
temperature. So that the voltage signal
received from the thermistor never
drops to near zero (which would cause
all the bargraph LEDs to be off), a 1.8kW
resistor is wired in series with it. It’s
easiest to solder the resistor in-line
with the cable going to the thermistor
and then cover the lot with heatshrink
sleeving.
The thermistor/resistor assembly is
then wired between the original Oxygen Sensor input (now the Thermistor
Input!) and the ground connection.
In order that it acts as a voltage
divider, power needs to be supplied
to the thermistor. This is achieved by
wiring a 4.7kW resistor between pin 7
of IC1 and the thermistor input. The
new resistor and its connecting wiring
are most easily soldered into place
under the PC board, with the additions
insulated with heatshrink sleeving.
As with all the PC board changes,
Fig.2 shows where this resistor goes.
If you have built the Smart Mixture
Meter and want to test the modifications as you go along, you can now
power up the board and check that
when you heat the thermistor, the illuminated LED moves along the scale.
DARLINGTON TRANSISTOR: Q2, the BC327
transistor, is not up to the task of supplying enough power to run a heavyduty relay and so needs to be replaced.
Why Measure Intercooler Temperature?
At first glance it would seem that rather than measuring intercooler core temperature, it would be better to monitor actual intake air temperature. However,
this is not so. Intake air temperature can rise substantially when the vehicle is
stopped, for example, at traffic lights.
However, if the stop is a short one, the intercooler will remain relatively cool.
If intake air temperature was being monitored to trigger the spray, the spray
would come on when the car was driven off under high load. But the intercooler
would in fact still be cool – so water would have been wasted.
40 Silicon Chip
A simple pump/reservoir combination
for an intercooler water spray
can be cheaply obtained by using
a late model Holden Commodore
windscreen washer reservoir and
pump.
siliconchip.com.au
The Intercooler Water Spray Controller is based on the
Smart Mixture Meter, previously published in SILICON CHIP.
Seven new components are needed and the modifications
are straightforward. The Water Spray Controller operates
an intercooler spray whenever engine load and intercooler
temperature are both above preset levels.
The replacement is a BD682 Darlington transistor. Note that the pin-outs
of this transistor are not the same as
the original BC327, so care should be
taken in following the overlay diagram
(Fig.2) and the photographs when
installing this device.
At this stage, remove the 680W resistor that is positioned on the PC board
directly above diode ZD4. Now, with
the new transistor in place the board
should work as it did previously. That
is, by appropriately setting trimpots
VR4 and VR5, LEDs 11 and 12 should
be able to be switched on and when
they are both illuminated, the piezo
buzzer should sound.
DIODE AND RELAY: the relay and the
transistor protection diode replace
the piezo buzzer. The 1N4004 diode
is placed so that its cathode (the
white band) is towards the top of the
PC board. Again, check the overlay
diagram and photos.
When you have inserted and soldered this diode in place, don’t cut the
leads off short. Instead, leave enough
of each lead protruding through the
siliconchip.com.au
ABOVE: two changes are made on
the back of the PC board: (1) a 4.7kW
resistor is used to link pin 7 of IC1
with the thermistor input (here the
resistor is covered in heatshrink); and
(2) two flying leads are added, one to
each side of the diode that’s installed
in place of the piezo buzzer. These
flying leads connect to the relay coil.
RIGHT: transistor Q2 is now a BD682.
Its pinouts are not the same as the
original BC327: the new transistor
must be installed as shown here.
March 2006 41
show that when LEDs 11 & 12 are on,
there is a short delay before the relay
pulls in. Also, when one or both LEDs
switch off, there should be a longer
delay before the relay drops out.
If you want to increase the length
of these delays, increase the value of
the capacitor – say by adding another
2200mF 16V capacitor in parallel. If
you want to decrease the length of
the delays, reduce the value of the
capacitor.
Note that because this capacitor
provides an anti-chatter function, the
lowest value that should be used is
1000mF.
OPTIONS: if you wish to, you can alter
The nozzle (circled) sprays a fine mist of water over the intercooler to improve
performance. A spray is especially beneficial when the intercooler is mounted
under the bonnet.
board to allow flying leads to be easily
soldered to them. Connect these flying
leads to the relay’s coil contacts. We
suggest you use a heavy-duty automotive type relay, in which case these
leads will connect to terminals 85 and
86 on the relay.
If you’re checking things as you go
along, power up the board and confirm
that the relay pulls in with an audible
click whenever LEDs 11 and 12 are
both illuminated.
DELAY: the switch-on and switch-off de-
lays are provided by a 2200mF capacitor wired in where the 680W resistor
previously resided. This won’t fit on
the board so should be wired in place
with flying leads and then glued to the
inside of the box or placed horizontally
over the new diode. When viewed as
shown in the overlay and photos, the
capacitor should be wired with its
negative lead to the right.
Testing of the finished design should
Quick Guide To The LEDs & Trimpots
The kit instructions for the Smart Mixture Meter explain how the circuit works
and lists in more detail the function of each LED and pot. But here’s a quick
reference guide for when the circuit is being used as an Intercooler Water Spray
Controller:
• LEDs1-10: show temperature based on thermistor input, LED1 (red) indicating
hottest and LED10 (yellow) indicating coldest
• LED11: “on” indicates the trip point for temperature has been reached
• LED12 “on” indicates the trip point for load has been reached
• VR1 sets the cold end of the scale
• VR2 sets the hot end of the scale
• VR3 sets the night dimmer sensitivity
• VR4 sets the temperature trip point
• VR5 sets the load trip point
42 Silicon Chip
the position of the LEDs to better
indicate the rise in intercooler temperature. For example, you can swap
the position of the green and yellow
LEDs so that as temperature rises, the
illuminated LED alters from green
through to yellow and then red. Or you
can replace some of the green LEDs
with yellow LEDs, etc.
Bench Calibration
Now for the calibration. First, set
both trimpots VR1 and VR2 to their
centre positions. That done, ensure
that the thermistor is at room temp
erature (~20°C), then rotate VR1 until
LED9 (yellow) lights. When it does,
adjust VR1 a little further anticlockwise until LED10 is just lit.
Warming the thermistor with your
hand should then move the illuminated LED from LED10 to LED9.
Now use a heat-gun to further warm
the thermistor. When it is just too hot
to touch (eg, 55°C), rotate VR2 clockwise until LED1 (the “hottest” LED)
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 the pots interact with
each other to some extent.
When calibrated in this manner, the
bargraph display is then configured to
show intercooler temperatures over
approximately a 20-55°C range. Note
that because of the thermistor’s characteristics, the bargraph 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.
Installation
For remote installation, the thermistor should be soldered to some twincore flex and the joins insulated with
siliconchip.com.au
This Ulka solenoid pump is capable of extremely high
pressure, resulting in a very finely atomised intercooler
spray. The pump is normally used in espresso coffee
machines and requires a small 12V DC to 240VAC inverter
to run in car applications.
heatshrink sleeving. 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 adhesive.
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.
Note, however, that 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,
close to the pump. Test that when
trimpots VR4 and VR5 are adjusted
so that their adjacent LEDs are on, the
pump turns on and the water spray
operates.
Driving Tests
With an assistant in the car, drive
the car and monitor the displayed temperature on the bargraph. 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
siliconchip.com.au
This Spraying Systems brass nozzle incorporates a filter
and non-drip check-valve. This nozzle gives far better
results than the small garden irrigation nozzles that are
widely used in intercooler spray applications. Spraying
Systems can be contacted in Australia on (03) 9318 0511.
until its adjoining LED lights when the
car is coming onto boost.
Drive the car so that the intercooler
gets warm and the car is under load
and check that both LED11 (intercooler
temperature) and LED12 (load) light.
When both have been lit for more
than about a second, the water spray
will operate. (If you want an on-dash
indication that the water spray pump
is running, wire a 12V pilot light in
parallel with the pump.)
After monitoring the displayed
inter
cooler 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 bargraph LEDs can be seen by the driver
or alternatively, the whole device can
be located out of sight.
Conclusion
Intercooler water sprays are a very
effective and cheap way of upgrading
intercooler performance. However,
using 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
SC
cooling efficiency.
Water Spray Pumps And Nozzles
The cheapest and simplest pump and nozzle combination is to use a windscreen washer pump and reservoir and a miniature garden irrigation spray
nozzle. Late model Holden Commodores use good quality pumps and large,
box-shaped reservoirs.
A dramatic improvement in spray quality can be gained by using brass nozzle
assemblies from US company, Spraying Systems. These incorporate a mesh
filter and check valve and provide much smaller droplet size than can be achieved
with the garden nozzle. Spraying Systems can be contacted in Australia on
(03) 9318 0511. These nozzles can be used with windscreen washer pumps.
However, if you want an intercooler spray of almost unbelievable efficiency,
use the Spraying Systems nozzle with an Ulka solenoid pump, as used in cappuccino coffee machines. These 240VAC pumps develop extremely high pressures, are designed to flow water, are light and small, and are quiet-running.
In car applications, a small 12V DC to 240VAC inverter can be used to power
them. Jumbo Coffee (02 9666 6114) sell these pumps.
March 2006 43
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