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> Wiring and Electrical:  Electrical operation and build your own Nitrous Pulse Controller

John WilliamsonElectrical Connections to Nitrous Solenoids, Nitrous Jet Positioning and Pulsed Nitrous "Controllers"

Basically the electrical side of Nitrous Injection Systems is very simple! All you need to do is connect quality cables that will not corrode or fail, to both the Nitrous Solenoid and the Fuel Solenoid. They must be wired in parallel so that they both operate together. You want the fuel and Nitrous Solenoids to work as one!  In a basic system that's it! Cant be simpler.


They Solenoids also need an Arming Switch fitted inside the car somewhere then is easily reached while driving. This does NOT operate the system, but simply allows the power to be switched on ready for when the Throttle operated Micro-Switch or whatever you use, does activate the solenoid valves!

The Throttle operated switch will operate the Nitrous System only when:
a) It is "Armed"
b) It has the Bottle Valve turned on!  If this is off, it is just the same as an empty Nitrous Bottle. You will get the extra enrichment fuel, but no Nitrous! So it will go slower!

If you need to ask how to actually connect up a circuit this simple then I suggest you buy a system it will be safer!

Pulsed Power Controllers - And bad Jet positioning on US based Nitrous Systems

A cars fuel injection works like this. You have a fixed fuel pressure controlled by the regulator. This pressure is sat behind some fuel injectors. The injector is very like a nitrous solenoid in the way that it operates.

A square wave (12vDC) signal opens it for a short time period (short pulse) for low flow rates like idle, and long (say 90 percent) of the cycle for say full power motorway driving. This is known as PWM or Pulse Width Modulation.

The same technique can control the flow of fuel extremely accurately with a fuel solenoid that we will be using with our nitrous system. And to a degree the same applies to the flow of nitrous.

Unless that is you are using an American type system!
These are jetted at the very end of the nitrous delivery pipes, the worst possible place!

If the flow control jet is located DIRECTLY
after the piston/seal/seat in the solenoid valve as mine and HighPower's are then  flow control is almost directly proportional to the pulse width length. Meaning a 50 percent duty cycle (B) will actually give 50 percent of the expected Nitrous Oxide. As will the fuel. Because we are metering Liquid Nitrous Oxide here with no time to change state or turn to a gas in the pipework on the way to the control jets in the foggers like the American systems.

If you fit the Nitrous Flow Control jet at the end of the pipe from the Solenoid as in a "NOS Fogger" type (or other cloned US systems like Holley, Nitrous Express, etc) then you have effectively got a big reservoir in between the Solenoid valve (which has a larger internal cross section than the control jets) and the actual jet!

What then happens is this. At 100 percent you get the correct amount of fuel and Nitrous delivered. But at say 50 percent pulse width, what should be half power is not!

You actually get far more than this because the bore of the Solenoid is much larger than the jet on the end of the pipe, so the solenoid just keeps "topping up" the pipe! The pipe acts as a reservoir. This effect is VERY pronounced when using small jets and/or a large solenoid.

Worse, because the fuel is NOT compressible this stays at 50 percent delivery rate. Meaning that it runs leaner and leaner as the power level is reduced! Bye Bye pistons...

This is one of the MAIN reasons for using a more modern European developed systems.

Remember even on a big US race car, a pulse width controller "start" at low power (weak!) and this begins the heat, pre-ignition, detonation, so when the 100 percent power is used further down the track the detonation which is easy to start but hard to stop will kill your engine...


So, you want to build your OWN Nitrous pulse controller?

A guy called Simon Holland who already has done sent me his circuit diagrams and information to post here.  He is using a DIY Nitrous System with this controller successfully.  Some other members of my Forum are also building and using this.

Here is a copy of his email:


As promised some time ago in return for sending me the circuit diagram, here are some pictures and notes I have got together when building my controller.  It took about two evenings to build and debug the circuit and so far has done three passes up the strip and not fallen to bits yet!

I printed the diagram at work using an expensive CAD thing but have scanned it and saved it as a bitmap so others might find it easier to open.  It is possible to download able graphics manager for a free 30 day period if people want to have a better circuit diagram to work from.

I hope it helps others a little. 

Thanks for all the help and info from your site.


Photo of board


His instructions and how it works below!!! 
A bit beyond me I think...

The MOSFET is what decides how much power the circuit will drive.  The one selected (IRFZ34N) will drive a maximum of 26A if used with a suitable heat-sink.  I mounted the FET to the side of the aluminium box and with no extra heat-sink it seems to cope OK driving both the fuel and nitrous solenoids (I am using Nitrous Works solenoids) If your chosen solenoids are going to draw close to or exceed 26A it may be necessary to substitute this with a more substantial FET.  I would not recommend using a separate FET for fuel and nitrous solenoids as if the fuel FET fails then you will be left with a dangerously over lean condition.

The prices and RS stock numbers shown were correct when I built my circuit but they are subject to change without notice.  Check before placing your order. 

Due to minimum order quantities you may have to order more than you need (resistors for example come in lots of 10) but the price is not affected much and you will have some bits left over for your next project!

Some hints from CBTS (Another guy on my forum who I think designed this circuit and who supplied the circuit diagram)

To set up , measure frequency at the lm393 pin 2 , adjust pot for 20Hz.
activate throttle switch , wait till pulsing is at max , then use the 'full on cal ' to set the output so it just turns completely on.

Then set start ,build and max to approx positions required , range of start is about 10-40% , max is about 50-100% , build time is 0.1 to 5 seconds over pot range.

The frequency can be adjusted if required and if the solenoids will respond , the higher -the smoother the delivery , but the less of a progressive range will be achieved. The lower will give a wider progressive range , but a more 'jerky' power delivery.

if you try and pulse too fast , if a little too fast - the solenoid will not start opening until 50-60% or so , if much too fast - the coil will 'buzz' , get hot and the solenoid will not open at all.
If testing this make sure you have full pressure on the valves as with no pressure any solenoid will able to pulse much faster!

I had some problems with the build up time, CBTS's answer was:

look on the positive terninal of the 47Uf capacitor. With throttle off check the voltage and see if it changes with the start level pot . set it to around 1v . then activate throttle - see if it starts to rise to 6-7V.
If the start voltage is 6-7V the BC337 is permently on or something is wrong around the start pot , if the voltage is low but doesn't rise, then either the BC337 is not turning on , or something is wrong around the build pot and associated BC557.
If the voltage rises OK , the problem is around the max level pot.

Cable colours used for potentiometers

Yellow wires to VR3 Start up Power level

Blue wires to VR2 Running Frequency

White wires to VR1 Build up time

Green Wires to VR4 Maximum power Level

Disclaimer:  This circuit worked for my application.  It was tested on a closed race circuit.  It is the individualís responsibility to ensure the suitability of this circuit for use in their own application. Remember to check your circuit thoroughly before connecting your solenoids and again with solenoids before running your engine.  Solenoids are best tested with pressure on them.  The author can-not be held responsible in anyway for any damage or injury caused in using any information supplied or inferred in this or any related document.

IE Donít blame me if it all goes horribly wrong, people should start to accept responsibility for their own actions!


        RS Components - part number and description

Current Unit


122-3513 Capacitor, electrolytic, 63V, 1uF



192-828 IC, Transient Voltage Suppressor, 1500W, 20.5V, 1.5KE 24CA



298-6990 IC, Voltage Regulator, 3 terminal, 1A, KA7808TU



434-217 PCB, stripboard, breadboard, Veroboard, SRBP, hole pitch 0.1in, 112x177x1.6mm



148-427 Resistor, metal film, 0.25W, 1%, 470R



148-506 Resistor, metal film, 0.25W, 1%, 1k



148-376 Resistor, metal film, 0.25W, 1%, 300R £0.035


148-629 Resistor, metal film, 0.25W, 1%, 3k3 £0.035


148-540 Resistor, metal film, 0.25W, 1%, 1k5 £0.035


148-815 Resistor, metal film, 0.25W, 1%, 22k £0.035


148-663 Resistor, metal film, 0.25W, 1%, 4k7 £0.035


148-269 Resistor, metal film, 0.25W, 1%, 100R £0.035


148-736 Resistor, metal film, 0.25W, 1%, 10k £0.035


148-972 Resistor, metal film, 0.25W, 1%, 100k £0.035


261-154 Diode, Rectifier, 1N4002 £0.07


446-8551 Diode, Signal, Barrier, Schottky, Silicon Diffused, 1N4148(1N914) £0.051


302-413 IC, Amplifier, Comparator, dual, LM393N



131-1036 Transistor, Bipolar, PNP, BC557



348-9406 Transistor, Bipolar, NPN, BC547C



249-9121 Potentiometer, 9mm, PCB mount, r/a, lin, 10k



162-798 Potentiometer, panel mount, lin, Cermet, 2W, 470R



374-935 Potentiometer, Cermet, 1 turn, top adj, 3362P, 1k



122-4386 Capacitor, electrolytic, 25V, 1000uF



122-4342 Capacitor, electrolytic, 25V, 47uF



122-3557 Capacitor, electrolytic, 63V, 10uF



343-9580 Enclosure aluminium



217-1182 MOSFET IRFZ34N































OK so this box could be prettier!  But hey, its experimental!

It works OK!  Some comments from the Forum:

I built this circuit today.
Gave up on my own design...
Worked first time exactly as described with the adjustments.
All fitted, pick up a full 10lb bottle of N2O tomorrow.
Fingers crossed.
Thanks everyone.

Yes its cbts's circuit i have built.
works fine

Excellent work mate :-]
I've built the same circuit and it seems to work well. Just have to test it under pressure to set it up now!



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