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PWM Instructions for Earlier Model

LCD And PWM Controller Instructions

Constant Current PWM (Legacy)

Important Information

Before diving into an installation and operation of your PWM, it is advisable to find out what a PWM is and how it does it's job. There is a simple article on the site that will walk you through the basics of a PWM, and clear up the terms that are used in conjunction with it... Including what "PWM" actually means. You can find it here: What Is A PWM?

Main Components

  1. The LCD Display/Controller module. This device shows you the important readings of your PWM, and also controls the PWM so that it maintains its constant current maximum amperage. This device should be mounted in the passenger compartment of your vehicle so you can see at a glance what is going on with your HHO system.
  2. The PWM enclosed in the box with its switch and cooling fan. This is the actual PWM that does the work of pulsing the power to an HHO cell. This device should be mounted near your cell to minimize the length of any wire runs between your battery and the cell.

Connection Instructions

The LCD display only needs to be connected to the Cat5 cable coming out of the PWM. Plug the Cat5 cable into the receptacle in the Display. It gets its power through this cable. You can then secure the back of the display with the 4 screws provided.

While you are initially setting up your HHO system, it is handy to have the display near your system so you can easily monitor your system when you first start it up. Later, when you have everything working properly, you will want to run the Cat5 cable into your passenger compartment and permanently mount the display where you can see it. Note: to disconnect the Cat5 cable from the Controller's terminal, carefully insert a small screwdriver underneath the cable and press up to disengage the locking tab on the connector.

Connect your PWM to the cell and battery. There are 4 heavy gauge wires coming out of the PWM, and one light gauge wire. Your connector kit has matching connectors. The use of these connectors will allow you to unplug the PWM unit if you should ever need to remove it in the future.

The 4 heavy gauge wires are as follows: Red and Black are for power and ground from your battery. The power lead (red) should be connected to your battery, via a circuit breaker. The black wire should be extended to a good ground, preferably the negative battery terminal.

PWM Connection Diagram



The White and Green wires get extended to your cell or cells. The white wire is the positive lead that goes to your cell. The green wire is the negative lead to your cell. However, don't confuse these with regular power and ground. Once they come out of the PWM they must not be allowed to connect to other power and ground circuits in your vehicle. They must only connect to the terminals of your HHO dry cell.

We use 10 gauge cable for these high current wires for nearly all installations.  But if you anticipate long cable runs or higher amperages, then you should use this chart to calculate the wire gauge you should use.

The small red wire is used to turn on the PWM. We use a small gauge wire to control this function. We recommend attaching this wire to the fuel pump relay circuit. Any gauge wire down to 30 AWG can be used for this purpose. I usually use a larger gauge so that it won't be easily damaged. 24 gauge is fine.

If you have more than one cell then you can extend one cable out to where your cells are, and then split the cable at the cells so that each cell gets both positive and negative connections. Multiple cells are connected in parallel. The diagram shows both series and parallel connections in order to illustrate the difference between the 2 connection methods. But we never connect our cells in series.

You can use 12 gauge wire to connect to any one cell, and this cell should not be run at over 15 amps. If you need more amperage, you should use 10 gauge wire. You can use 10 gauge wire for circuits that run up to 40 amps provided your total wire run is not over 15 feet. For instance if you are using 10 gauge wire from your battery to your PWM and from your PWM to your cells, then the total length of the power wires should not exceed 15 feet. The total length of the ground wires should also not exceed 15 feet.

Multi-stack cells: A stack is defined as 2 hot plates (plates that are connected to the PWM's output white and green wires), with 5 neutral plates between them. A 2-stack cell, or Double Stack Cell can be thought of as 2 adjacent cells. The center hot plate is common to both "cells" on either side of it. It can be either positive (connected to the white PWM output wire), or negative (connected to the green PWM output wire). The other PWM output wire is split to connect to the outside 2 hot plates.

parallel wiring double stack cell

For our 6" and 7" cells, you should not run more than 15 amps per cell, or per stack. See below for a description of multi-stack cells. Our 12" cells can run higher amperages, but are usually not run at over 40 amps and often even less for best efficiency. This information is for understanding PWM installation only. But note that most people use more amperage than they need for best fuels mileage gains. Please see How Much HHO Should I Use? for more information.

IMPORTANT SAFETY RELATED INFORMATION: The final wire on the PWM is the control wire. This is the small red wire (18 gauge). This wire must have 12 volts on it in order for the PWM to turn on. This is used as a safety measure so that the PWM will only run when the engine is running. This wire should be connected to the fuel pump relay circuit, or similar. The fuel pump relay circuit powers up briefly when the car is turned on to charge the system, but after that will only be on when the engine is actually running. Since this is the only time we want HHO to be produced, we use this circuit for the source of our control voltage. This will ensure that the PWM is not running when the ACC switch is on, but the engine is not actually running. Be sure to test this circuit carefully to make sure it is only on when the engine is running. If your HHO system is producing HHO while you are sitting in the car listening to the stereo, you can have HHO build up under your hood, and this can explode when you start your engine. So this point is important.

Important Notes For 24 Volt Systems

There are 2 modifications to the PWM installation instructions when working with 24 volt systems. They are quite simple, but quite important:

1. The PWM control wire must receive 12 volts. The control wire is the small gauge red wire. It is an 18 gauge wire, whereas the current carrying wires colored red, black, white and green are all much larger. Power must be supplied to this wire for the system to be able to turn on. This circuit draws negligible power - about .35 amps. To be clear, the PWM can control 24 volts on its heavy gauge wires. But must be controlled with 12 volts to the small gauge red wire on the PWM. Using 24 volts on this control wire will damage the LCD Controller.

There are 2 methods of supplying this 12 volts to the PWM:

  • 1) DC to DC Converter. Take a wire from your fuel pump relay to the "24 Volts + In" on the voltage converter. Also provide a ground wire to the converter. Then connect the "12 Volts + Out" terminal to the small gauge red wire on your PWM.
  • 2) Relay. If you have a source of 12 volt power available, you can use a relay. Note that if you use 2 - 12 volt batteries to supply your 24 volt ignition power, you can get 12 volts from the connection between the 2 batteries. You would control the relay with your system voltage (24 volts), and it would switch the 12 volts which you would route to the 18 gauge red trigger wire on the PWM.

If you have an EFIE or a MAP Enhancer that also needs 12 volts, you can use this source to power them. These devices take about 50 milliamps (.05 amps).

2. Use 11 neutral plates. While we're powering the PWM and controller ciccuitry with 12 volts, we're still powering the cell itself with your system voltage of 24 volts. The 10 gauge red wire coming out of the EFIE gets connected to your 24 volt system voltage, via a circuit breaker as per the instructions. The black cable gets connected to ground. With this arrangement the PWM will output 24 volt pulses on it white and green cables. Since the pulses have twice as much voltage, we need to connect them to the cell differently than with a 12 volt system.

On 12 volt systems we use 5 neutral plates. With 24 volt systems we use 11 neutral plates, and with 32 volt systems 23 use 15 neutral plates. A neutral plate is a plate that has no wire from the PWM connected to it. Below is a diagram of a 24 volt system connected to the cell. Notice that there is a center tab that would have a wire connected to it on a 12 volt system, but on a 24 volt system that center tab becomes a neutral plate. If you count the plates between the green and white wires, you'll see that there are 11 neutral plates. This arrangement ensures that we get the proper voltage between adjacent plates for efficient HHO production.

Double Stack

These are the only 2 changes required for 24 volt systems. Otherwise, just follow the instructions for 12 volt systems.


The instructions for the Display/Controller are the same as for our other versions of the PWM. Go to the following link and scroll down to the bottom half of the page: Constant Current PWM Instructions

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