Temperature Controlled PWM

Feb 07, 2011

Some HHO PWM vendors are selling a PWM that is controlled by the temperature of your cell. With such a system you would install a temperature sensor on your Electrolyzer. The PWM would run at 100% duty cycle until the temperature rose to a predetermined temperature and then adjust to keep the temperature from rising further or falling; thus keeping the system running at full potential without thermal runaway.

While having such a system means the user doesn't have to determine what current the cell needs to run at, the problem is that it's not fail safe. For instance, what happens when the sensor fails and tells the computer that the generator is cold, even when it is boiling hot? Obviously, the PWM will remain at 100% and the generator will be subject to a meltdown. The odds of a sensor failing are much higher when the sensor is soldered directly to wires and then attached to the generator. All it takes is one of the connections to break and the sensor will report a false temperature. Of course it is possible for the controller to determine when there is an open circuit, but the functionality has to be implimented. The sensor could also loosen its mechanical connection to the generator or even fall off altogether. This is why using such methodology to control pulse width is unreliable.

Sensing the temperature is not without merit though. While using the cell temperature to exclusively control the pulse width is unreliable, using cell temperature to shut down the PWM due to overheating is not. It makes a good extra safety measure just in case you didn't choose the correct cell current or the water level dropped.

The KZX1250 has a disable line which allows you to digitally gate off the current using a ground signal. You can use a temperature sensor with a pre-defined temperature set point to give you a ground signal when the temperature is reached. The temperature can be selected to be above what you would consider normal operating temperature. This signal can then be attached directly to the disable line on the KZX1250; thereby shutting down the generator in an event that the generator overheated.

It's always a good idea to plan for the worst. Some ideas are sometimes better used as an extra precaution, instead of the main controller. Understanding the faults of such ideas and what those ideas are better suited for is important to create a robust system that you can be confident using in your vehicle.

- Regards, FreeMindResearch

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