"If it has a Fan on it --- it
could be over rated"
Do you really need a PWM? Not really, but 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
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; meaning, they are made to
operate at a constant amperage, even as the water gets hotter. You set the
maximum output, and forget it.
Please be advised: A PWM will not increase your Hydrogen
Generators HHO output. It will do just the opposite. It will restrict 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
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
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 utilize 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. Thisis 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. Thisis 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.
If 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.
This is rated at 30 Amps Maximum. I would
not operate it over 15 amps.
Variable adjustment for amperage
Variable adjustment for frequency; up to 6Khz
Schematics and Parts Lists
Several Models Available
12 volts to 72 volts
135 amps to 250 amps continuous
AXE web site
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
The Cell electrodes must not touch the frame ground.