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