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Chapter 22 Use it to control an extra injector for the nitrous fuel supply or even just to vary pump or fan speeds! Nitrous Fuel Controller A NITROUS SYSTEM consists of   a supply of nitrous oxide and an additional fuel supply. Traditionally, the fuel and the nitrous have both been added through the one assembly (eg, a “fogger” nozzle), where the fuel stream is atomised by the force of the nitrous flow impacting it. These “wet” systems use solenoids on both the nitrous and fuel lines – when the nitrous is activated, both solenoids simultaneously open. In “dry” systems, the extra fuel is added by increasing the fuel pressure to the standard fuel injectors, so that more fuel flows through them for a given duty cycle. However, this gets tricky to set up, because what’s really needed is a constant flow of fuel to go with the constant flow of nitrous – rather than a fuel supply that increases with engine load. What this kit allows you to do is replace the specialised fuel solenoid and fuel jet(s) with a conventional injector. This new injector is pulsed by the Nitrous Fuel Controller. This saves you having to shell out for a fuel solenoid (and they’re often nearly as expensive as the nitrous solenoid!), gives you a well-atomised spray and allows you to fine-tune the air/fuel ratios when on nitrous. To keep costs down, you can even run multiple extra injectors – you don’t need to source a single monster injector. Tuning the on-nitrous air/fuel ratio is possible because the duty cycle of the new injector can be varied by turning a pot. So after the new injector(s) have been (over)sized for the nitrous flow, testing on the dyno can be carried out with the new injectors initially running at 100% (ie, flat out) and then gradually pulled back in duty cycle until the air/fuel ratio is correct. Note that the Nitrous Fuel Controller shouldn’t be used to control an extra injector that’s been added because the normal mixtures are too lean. If the fuel supply is inadequate in normal operation, run the extra injector using the Digital Pulse Adjuster described in Chapter 16. Specifications Maximum solenoid load ........................................................10A (1.5Ω load) Duty cycle......................................................... nominally 0-100% adjustable Output signal.................................. switch to ground to drive injector solenoid siliconchip.com.au Main Uses •  Drive the fuel injector in a nitrous system •  Vary electric water pump or fan speeds •  Dim filament light bulbs If you’re not interested in running nitrous, the Nitrous Fuel Controller can control the speed of pumps and fans, up to a maximum rating of 10A. For example, if you’re running a water/ air intercooler system, you can use it to slow the pump speed when you’re off boost. Fig.4 shows how to do this. Compared with using a simple dropping resistor, you benefit in terms of heat management (the dropping resistor would need to be a very high power one, often with a large heatsink) and the “off boost” speed can be very easily adjusted. If you want, you can even replace the trimpot on the PC board with a dash-mounted pot, allowing you to easily dial-up the fan or pump speed you want in any situation. Construction The Nitrous Fuel Controller is a very simple kit to build. However, when assembling the PC board make sure that you insert the polarised comPERFORMANCE ELECTRONICS FOR CARS 149 Parts List 1 PC board coded 05car111, 79 x 47mm 2 2-way PC-mount screw terminals 1 TO-220 mini heatsink 19 x 19 x 10mm 2 M205 PC fuse clips 1 10A M205 fast blow fuse 2 M3 x 6mm screws 2 M3 nuts 1 50mm length of 0.8mm tinned copper wire 1 100kΩ horizontal trimpot (VR1) Fig.1: this overlay diagram shows where each of the components is placed on the PC board. RESISTOR COLOUR CODES Semiconductors 1 7555 timer (IC1) 1 BC337 NPN transistor (Q1) 1 BC327 PNP transistor (Q2) 1 MTP3055 Mosfet (Q3) 1 12V 1W zener diode (ZD1) 1 16V 1W zener diode (ZD2) 1 1N4004 1A diode (D1) 1 MUR1560 15A 600V diode (D2) 2 1N4148 diodes (D3,D4) Capacitors 1 10µF 16V PC electrolytic 1 1µF 25V PC electrolytic 1 220nF MKT polyester (used when controlling an injector) (code 224 or 220n) 2 100nF MKT polyester (code 104 or 100n) 1 56nF MKT polyester (used when controlling a motor) (code 563 or 56n) 1 10nF MKT polyester (code 103 or 10n) Resistors (0.25W, 1%) 1 1kΩ 1 100Ω 1 10Ω Value 4-Band Code (1%) 5-Band Code (1%) 1kΩ 100Ω 10Ω brown black red brown brown black brown brown brown black black brown brown black black brown brown brown black black black brown brown black black gold brown ponents the correct way around – ie, the IC, diodes, transistors and electrolytic capacitors. During construction, look at the photos and overlay diagram closely to avoid making mistakes. If you intend controlling an injector with this project, build it exactly as shown by the overlay diagram (Fig.1). However, if you want to control an electric motor (eg, a pump or fan), replace the 220nF capacitor (on far lefthand side of the PC board as shown in Fig.1 and the photo) with the supplied 56nF capacitor. This component change smooths the action of the motor. Testing Testing is easy – and you don’t need to use a fuel injector or motor. Start by connecting +12V power and earth leads to the board, then wire a low wattage 12V lamp between one of the “out” terminals and +12V. When the power is switched on, you should be able to adjust the lamp brightness from fully on to fully off using VR1. Fitting It’s beyond the scope of this article to go into detail on setting up a nitrous system but, in brief, you need to select injectors that have sufficient flow capacity. For example, a 50HP nitrous system will need at least a 50HP injector. Oversize the injector(s) so that you can run them at a relatively low duty Fig.2: here’s how the Nitrous Fuel Controller is wired into the rest of the system. When the “safing” (master on/off) and throttle switches are both closed, the new fuel injector is brought into action by the relay which also activates the nitrous solenoid. 150 PERFORMANCE ELECTRONICS FOR CARS siliconchip.com.au D1 100Ω K 5 7 A 8 4 IC1 7555 3 2 6 D3, D4: 1N4148 A K E Q1 BC337 E B VR1 100k C Q2 BC327 ZD2 16V 1W 220nF BC327, BC337 SC 2004 GND FUSE1 10A E D G K 1k S OUT1 Q3 MTP3055 OUT2 MTP3055 A MUR1560 D DIODES, ZENERS B NO 2 FUEL CONTROL 1 µF 25V 100nF A A K +12V D2 K MUR1560 10Ω D4 D3 1 C B A 1N4004 ZD1 12V 1W 10 µF 16V 100nF 10nF K A C G K D S K A Fig.3: the circuit is essentially a variable duty cycle pulse driver which can be used to control the opening times of a nitrous injector. Or it can be used to control the speed of pumps or fans siliconchip.com.au injector’s solenoid is switched off. The 100nF and 1µF capacitors across the supply at this point prevent the transient from being propagated on the supply line. Fuse F1 is used to protect the Mosfet should there be a short from the output to the +12V supply rail. Power for the circuit is derived from the switched +12V ignition supply via diode D1 and a 100Ω resistor. Zener diode ZD1 provides regulation to 12V, supplying IC1 with a relatively stable voltage so that the duty cycle is maintained at the set value. +12V CHASSIS (0V) VIA IGN. NITROUS FUEL CONTROLLER PC BOARD 1 1 1ra c 6 0 L ORT N O C LEUF SU ORTI N + + 21+ +12V GND OUT1 +12V VIA IGN. TU O 1k DNG ADJUST VR1 1N 4148 cycle to reduce the margin for error when you are tuning the system. Fig.2 shows how to connect the system. Power for the PC board is derived from the switched +12V ignition supply, while the new injector(s) are wired between the ignition supply and the output of the controller. The minimum total injector resistance is 1.5Ω. If you use multiple injectors wired in parallel, their paralleled resistance must be greater than this. If you are controlling the speed of a fan or pump, the device is again wired between the output and +12V. The PC board fits straight into a 130 x 68 x 42mm jiffy box, so when the system is working correctly, the board can be inserted into the box and n tucked out of sight. discharged with the same amount of resistance via VR1 and so the output at pin 3 will be a true square wave (ie, a 50% duty cycle). Adjusting VR1 will allow the pulse duty cycle to be set from fully high (100%) to fully low (0%), or to any duty cycle in between. Pin 3 of IC1 drives a complementary transistor buffer comprising Q1 and Q2 and these drive the gate of Mosfet Q3 via a 10Ω resistor. This in turn drives the new injector. Diode D2 clamps the transient voltage that occurs when the 1N 4148 IC1 is a CMOS 555 timer connected to provide a continuous square-wave output. Diodes D3 and D4 are used in conjunction with trimpot VR1 to obtain a variable duty cycle. The 220nF capacitor is charged up when IC1’s output at pin 3 goes high, via diode D3 and the resistance between the cathode (K) side of the diode and VR1’s wiper. Similarly, it is discharged via D4 and the resistance between D4’s anode and VR1’s wiper when pin 3 goes low. If VR1’s wiper is centred, then the capacitor will be charged and NORMALLY OPEN PRESSURE SWITCH PUMP CHASSIS (0V) Fig.4: the controller can be used to slow the action of a water/air intercooler pump when off boost. The normally-open boost pressure switch bypasses the controller, causing the pump to run at full speed when on boost. Off boost, the pump speed is set by the controller. This off-boost speed can easily be adjusted by turning the on-board pot. PERFORMANCE ELECTRONICS FOR CARS 151