What the PWM is?

Do you know the Vamo? Or other "budget" mods? For sure yes...
If we look at the voltage shape of such mods we will see something like that:

For comparison, let's look at the ProVari voltage shape:

So, looking at the PV voltage shape everything is OK - the voltage is smooth, stable at 4V, and that's it. But what is going on with the Vamo? Why the voltage reaches 6V and oscillates to zero volt?

This is how the PWM works. PWM means the Pulse-Width Modulation which actually is a modulated square wave with 3 basic parameters:
* voltage - amplitude of square wave,
* clock cycle - frequency of square wave,
* duty cycle - the percentage of the positive state compared to the period of the signal.

I tried to show them below:

 As we can see the most important parameter for us is DUTY CYCLE because it has a direct impact on resultant voltage of mod. In other words the area under the positive state of wave determines the "total" voltage. In case of square wave we can calculate it in very easy way: multiplying the voltage by percent of the fill (as shown in picture).

But what if we have more complex signal? Not regular square wave? In this case we have to use RMS value:

The root mean square (abbreviated RMS or rms) is the square root of the arithmetic mean of the squares of the values, or the square of the function that defines the continuous waveform.

WIKIPEDIA

It sounds complicated but really isn't. We have to sample the signal within a given period of time and just "averaged" it. By use the square root of the arithmetic mean of the squares, blah blah blah :-) It would be better to show it in practice:

As we can see in both pictures the main conclusion is that in the case of modulated signals is usually a BIG difference between the maximum and REAL value of effective voltage generated by mod.

What I tried to show I hope clearly ;-)