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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