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Pulse Width Modulator - PWM


"If it has a Fan on it --- it could be over rated"

Do you really need a PWM? Not really, But without them, the HHO experimenter will be busy observing and maintaining the amperage flow of the HHO electrolyze. And, it is nice to be able to control the output of your hydrogen generator - from your dashboard. During winter months, we need more electrolyte in the water because cold water does not conduct electricity as well. In summer months, we need less electrolyte in the water because hot water conducts electricity much better than cold water. During periods of mixed hot and cold, you are screwed; unless you have a PWM. The PWM allows you to use more electrolyte, but still control the output of the HHO generator.

The purpose of the PWM is to pulse the DC voltage to the cell. Pulsing the voltage turns the current on off on off on off, thus reducing the heat caused by constant current flow. In other words, just as the current starts to flow, it gets stopped. The series of starts and stops happen instantaneously.

In addition, the PWM allows you to regulate the amperage (current). This provides runaway control over the cell. The longer the cell runs on DC, the hotter the water will get, the higher the amps will go. Eventually you will blow a fuse, pop a breaker. The PWM solves that problem.

Some PWM's are self regulating (CC); meaning, they are made to operate at a Constant Current, even as the water gets hotter. You set the maximum output, and forget it.








It is also believed that PWM's help make a higher quality of the HHO. They do so by increasing the % of Ortho-hydrogen and decreasing the % of Para-hydrogen. Ortho-hydrogen is about 3 times more powerful than Para-hydrogen. Ortho-hydrogen is what causes the Pop or loud Snap sound that hurts your ears when HHO bubbles are ignited. Straight DC amperage normally produces 75% Ortho-hydrogen and 25% Para-hydrogen. I am investigating this and will post future information.

Please be advised: A PWM will not increase your HHO output. It will do just the opposite. It will slightly lessen the output; based on what you set it to produce.

PWM Features to look for:

  • Maximum Continuous Amperage Output, not Maximum Amperage. This is the maximum amperage the PWM can be operated at, constantly; long periods, not short operating periods.

  • Automatic Current Limiting, Constant Current (CC). This allows you to set the Amperage Output to a specific amperage. The PWM then will maintain that amperage, regardless of the water temperature.

  • Adjustable Pulse Frequency. This allows you to adjust the time between pulses. Fast pulsing causes more heat than slow pulsing. Pulsing turns the cell on and off rapidly; as rapid as you set the frequency.

  • Duty Cycle Adjustment. The duty cycle reading lets you know if your electrolyte fluids are too weak or too strong as the duty cycle of an automatic current limited PWM will be approximately 70% when the Cell is warmed up (depending on your Cell design). If it is significantly higher, you know you have too little electrolyte and if itís significantly lower, you have too much electrolyte. If the Cell is cold, the current should be at or very close to the set limit (duty cycle will be approximately 100%).

Advanced PWM Features to look for:

  • Alternator Protection. Guards against situations that could over work your alternator and cause it to fail. One side effect of automatic current limited PWMís is that they give the Cell current high priority over every other circuit on your vehicle. To understand this better you need to understand how your electrical system works. If the system voltage drops, every device in your vehicle gets less current because their DC resistance is fixed; this is by design. Lower the voltage across a fixed resistance and less current flows through it; but attach a big load to a automatic current limited PWM and the current going through it will remain fixed as a lower voltage will cause the PWM to increase its duty cycle to maintain the fixed current. The alternators output capability depends on two things, the speed in which it is being driven and by the field current being fed to it through the voltage regulator. The voltage regulator maintains a voltage around 14v, give or take a few tenths of a volt. When the system voltage falls below the regulated voltage, the regulator feeds more current to the field coils of the alternator to get it to produce more current. The higher current in the field coils adds a higher mechanical load to it which slows down the engine. Alternator Protection dials back the duty cycle regardless of what the current limit is set to until the current is again available (when you accelerate). It gives your Cell current the lowest priority in the system; which is exactly what should be done. After all, you really donít need much output when you are idling. So the alternator protection not only prevents your alternator from failing due to overload, but it also helps maintain a smooth idle and prevents you from unnecessarily having to increase your idle. One might think that having the throttle or engine speed control the duty cycle would yield the most optimum results, but it will actually have a negative effect. The reason is due to generator latency. Hydroxy gas is mostly needed when you accelerate and since it takes at least a few seconds for pressure to build after current is increased, there would be a deficiency of gas produced at the time when your engine needs it the most which will negatively affect your results.
  • Charge Sensing Switch. This is what automatically turns the cell on and off. When charge voltage greater than approximately 13.8v is sensed, power is turned on and stays on until the charge voltage drops below approximately 13.2v (when alternator stops generating current). This means that the PWM will only turn on when your alternator is supplying the current. I makes it impossible to leave the cell on, if the engine is not running. You are not required to wire into the ignition circuit.

  • Short Circuit Protection. This is not generic like a fuse; it is specially optimized for a Cell. Fuses are designed to open from the heat generated by the short circuit. They need to be flexible enough to work with motors and other inductive loads which generate current spikes that would open the fuse if this was not so; the same is true with generic circuit breakers. Fuses can take up to 100 milliseconds to open after exceeding their rated amperage; thatís a tenth of a second. It may be quick enough for a motor winding, but not for a semiconductor. A typical PWM relying on fuse protection may survive several times after a short circuit, but the heat that the fuse sees is also the heat that the MOSFETís see. This means that every time a fuse pops, there is at least some damage happening to the MOSFETís due to the current spike in a typical PWM.

  • Over Current Protection:  prevents you from dialing in currents significantly higher than thePWM recommends.

  • Disable Terminal: allows you to hook up as many turn off devices as your application requires. These devices are essential to bullet‐proof your system. Any connection to chassis ground will disable the PWM output. You may use this for safetydevices, such as temperature, water level, pressure switches on your Cell and/or just a simple toggle switch for when you donít want your Cell to operate.


When you purchase a PWM, pay close attention to the output rating. Most sellers do not tell you the "Continuous" Output. If they say it is a 30 amp PWM, in most cases that is a Peak or Maximum output rating. You can not operate at maximum very long. If you want or need a constant 30 amp output - make sure the PWM you purchase can withstand that output continuously. It is better to have too much PWM, than not enough; the output is adjustable.


KZX1250  Smart 50 Amp Continuous - Automatic On/Off Sensing & Adjusting (very reliable)
  • Automatic Power on/off when you start your car
  • Automatic Current Limiting (set it and forget it)
  • Alternator Power Protection Shut-down
  • Short Circuit Protection
  • Thermal Protection
  • Built in Display for Amps, Duty cycle and Frequency
  • Adjustable Frequency, 300hz to over 3khz
  • Disable Terminal (Optionally attach toggle, water pressure, water temperature, water level switches to your car to disable your cell on a fault condition)
  • Easy three wire installation
  • No Power Relay needed
  • Go-no-Go switch is built-in to start and stop the HHO electrolyzer when the engine is operating or not operating.

     This PWM is no longer available

Smart PWM - 40 amps Continuous Output
  • Automatic On/Off voltage sensing capability
  • Constant Current Adjustment
  • Frequency Adjustment
  • Low/High Voltage Setting
  • Error Codes
  • Water Level Indicator capability



100 Amp Smart PWM

This item comes complete with everything you need to run the PWM.  It includes the PWM, the Liquid Crystal Display/Contrller and a 25' cat5 cable to connect the controller to the PWM.




40 Amp CC PWM

  Hydrogen Boost Now




Constant Current PWM, and Remote
 ( Experimenters are Reviewing this PWM's reliability)
  • Continuous 50, 70, 90 Amp Models (not recommended for under 10 amps)
  • 12 to 48 vdc
  • Frequency = 500 HZ
  • Remote for on/off, amperage adjust, and built-in amp gauge
  • No Fan, and 50 A model does not have a heat sink.
  • Heavy Duty Electronics
  • Constant Current only maintains +/- 10% (not so good)

Available at Green Fuel H2O web site
Installation Video

  • Several Models Available
  • 12 volts to 72 volts
  • Up to 600 amps continuous

  AXE web site

Bob Boyce PWM3G Controller

A pulsed square wave DC circuit, with 3 frequency adjustments & 3 wave length adjustments. To be used with electrolysis, to break the 1825 Faraday's law of electrolysis; up to 4x's with a ortho spin state of H and O.

  Information available at Hydrogen Garage


PWM - Cell Mounting Hardware

Any time you use a PWM to power your Cells, you are going to have to keep the PWM negative ground from touching the vehicle frame or chassis (which is grounded to the battery). If they touch, the PWM will not Pulse the DC voltage. The PWM ground must be isolated. A good way to keep them from touching is to use Nylon Shoulder Washers.
Nylon Shoulder Washers

Use these to insulate your Cell and mounting bolts from touching the chassis or frame ground. It may be necessary to use 2; 1 top and 1 bottom of each bolt. 
  • The Cell electrodes must not touch the frame ground.

  Size information



  Duplicates Bob Boyce circuit  


Page Last Edited - 04/03/2022

    Copyright © 2003   All rights reserved.   Revised: 04/03/22.                                             Web Author, David Biggs
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