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The Nitrous Fuel Controller - That's Also a Lot More!

A fantastic little electronics kit that can do lots of things

by Julian Edgar

Click on pics to view larger images

At a glance...

  • Control an extra injector to add fuel to go with nitrous
  • Dim lights
  • Control motor speeds
  • Flash lights or a horn
  • Manually control solenoid flow
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The Nitrous Fuel Controller is a simple electronic kit that can perform lots of functions. Firstly, as the name suggests, it can run an extra injector to add the fuel needed to go along with a shot of nitrous. But with the alteration of just one component, the very same kit can also control the speed of an electric motor – an intercooler pump, for example. And then again, by changing that one component to yet another value, the very same kit can become a light or siren pulser. Or if you want, you can even use the kit to manually control the flow through a pulsed solenoid!

In short, this is an excellent building block for a range of car applications. It’s also cheap (the kit is just AUD$25), easy to make (this is definitely a kit suitable for a beginner), and easy to use.

The Kit

Click for larger image

The Nitrous Fuel Controller consists of a bunch of electronic components that perform three functions. The way these come together is shown in this diagram.

At one end of things we have a device that puts out a frequency – an on/off signal, if you like. By changing the value of a capacitor, this frequency can also be altered. As built, the output frequency is about 60 Hertz (that is, it on/offs 60 times a second).

The next step is to give the user control over duty cycle, that is, how long each pulse is. Duty cycle is controlled by turning a pot. If the duty cycle is set to 50 per cent, the on/off times will be equal in length. If it is set to 90 per cent, the 'on' times will be much longer than the 'off' times.

The final stage in the electronics is a dirty big switching transistor that can handle up to 10 amps (heaps!) There’s also a fuse on the board to protect against short circuits or other overloads... and that’s about it for what makes the device tick.

Building the Kit

Click for larger image

If you are new to building kits, take it all slowly and carefully. You’ll need a fine-tipped soldering iron and to be able to recognise the different components. Look closely at the picture of the built kit as well as the circuit board overlay. So that you get the kit instructions in colour, we suggest that you buy the book that covers all these kits (and also shows in more detail how to build kits), High Performance Electronics for Cars. Many of the components are polarised, that is, they can go onto the board only the one way around. It’s best to use a multimeter to measure the value of the resistors (and capacitors, if your multimeter can measure capacitance) and as always, check, check, check your work.

Testing the Kit

The easiest way of testing that the kit is working is to build it as specified in the instructions, with the 220nF capacitor in place on the far left-hand end of the board. (This is the cap that’s changed to alter the output frequency.) Connect power and earth to the kit (making sure these wires go to the right terminals), then connect a 12V light built between the output and 12V. (Note: the device to be powered always connects between 12V and the output, not between the output and earth.)

Switch on power and turn the on-board pot. If the kit is working as it should, the bulb will be able to be varied in brightness steplessly from fully-on to fully-off. If this isn’t the case, switch-off and check all that you’ve done.

Using the Kit

  • Injector
Click for larger image

In its nitrous fuel injector application, the kit can pulse an injector at whatever duty cycle (ie flow) the user decides. This is changed by simply turning the pot. The injector is oversized for the required fuel flow (more than one injector can also be used) and then wired between the output and 12V. The pot is then used to adjust the fuel flow to suit the nitrous addition.

Note that the fuel flow from this injector does not change with load – it adds a fixed amount of fuel. That suits a nitrous application but does not suit an application where the engine is running lean at high revs through other mods. (In that case use the Digital Pulse Adjuster than can be mapped for the action of an additional injector.)

If the flow through the injector doesn’t vary with duty cycle, the pulsing frequency may be too high – this can be reduced by altering the capacitor value, as covered below.

  • Light Dimming

In its light dimming application, all that’s done is to wire the light(s) between the output and 12V and then adjust the pot as required. Note that it’s easy to use a full-size chassis-mount pot in place of the on-board trimpot – just buy a 100 kilo-ohm pot and wire it to the board with flying leads.

If you want the pulsing to occur more quickly, use a smaller value of capacitor. If you want the pulsing to occur more slowly, use a larger value capacitor.

  • Motor Speed Control
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To control a motor, it’s likely that the frequency will need to be higher than standard. As the box above suggests, this is achieved by using a lower value capacitor in place of the 220nF one mounted at the left-hand end of the board. For example, a 56nF capacitor will give a more appropriate output frequency of 270Hz, operating the motor more smoothly.

Any DC electric motor can be smoothly speed controlled, including water/air intercooler pumps, intercooler spray pumps, radiator fans and fuel pumps. Remember that the max current draw is 10 amps, so with big radiator fans and pumps it’s important that you use a multimeter to measure their current draw (especially at start-up) before hooking them up to the controller.

To alter motor speed anywhere from fully off to fully on, just rotate the pot.

Using this module to dim lights or vary motor speeds has two main advantages over the use of a dropping resistor. Firstly, the amount of heat that needs to be dissipated by the module is far less than needs to be dissipated by a resistor. Translation: it stays heaps cooler. And secondly, motors work really well with the high-speed bursts of power coming from the controller – far better than they perform with just a series voltage-dropping resistor.

  • Pulsing
Click for larger image

Pulsing a light or horn is simply a case of slowing right down the frequency output of the controller. This is achieved by fitting a higher value capacitor in place of the 220nF one at the left-hand edge of the board. However, there’s a trick – once you get up to about 1uF in capacitor size, the cap design that’s used is polarised – ie it must go in the right way around. When the board is orientated as shown in the instructions, the negative lead of the capacitor goes to the bottom track of the board. (You can easily trace this track around to the ground terminal to confirm that this is the case.)

So what’s a good value of capacitor to use? As with each of the frequency changing capacitor selections, that depends on what you want to achieve. A value of 10uF will give a fast flash rate of about 2Hz. (The exact output frequency will vary a little from board to board as the tolerance value of other components will affect the outcome.)

In this situation the pot will allow precise adjustment of the ‘on’ time of each pulse. This is really useful because if you want only a very short-duration flash (say of an alarm LED or high powered shift-light), you can adjust the duty cycle downwards.

Again, before pulsing a high-powered horn, make sure that the current drawn is not greater than 10 amps.

  • Manual Solenoid Control
Click for larger image

The kit can also be used to control flow through a solenoid. For example, if you want to have variable control over a simple bleed-type boost control system (eg Project EXA - Part 3 - DIY Boost Control. ), just replace the needle valve with a boost control solenoid that you then pulse with the kit. Replace the on-board pot with a chassis-mount pot and you can have a boost control knob on the dashboard!

Most boost control solenoids will work happily when pulsed at about 10Hz, which a cap value of about 1.5uF will give. But remember, the exact output frequency will depend on other component tolerances, so you might need to try a few values until you find you can control solenoid flow over a wide range. This is easy to check – just blow through the solenoid while adjusting its duty cycle with the pot.


The Nitrous Fuel Controller kit is a very versatile design. It’s also an excellent beginner’s kit, not only because of the ease of building and its uses, but also because it quickly brings you up to speed with concepts like variable frequency and duty cycle.

The Background Story

So how did this kit come about?

The Nitrous Fuel Controller was developed and designed by Silicon Chip [] electronics magazine. The kit, along with many others, is covered in the Silicon Chip publication, High Performance Electronics for Cars. The book is a must-have for DIY modifiers. The kit for the Nitrous Fuel Controller is available from Jaycar Electronics [] or through the AutoSpeed shop .

The electronics design and development of the Nitrous Fuel Controller was carried out by electronics engineer John Clarke, while I came up with the concept and did all the on-car development. (During this period I wore a different hat to an AutoSpeed contributor, working for Silicon Chip Publications as a freelance contributor to High Performance Electronics for Cars.)

So by no means should the Nitrous Fuel Controller be seen as an AutoSpeed-developed project, but at the same time I am happy that AutoSpeed endorses it and promotes it.

Julian Edgar

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