Quote Originally Posted by Martinm210 View Post
That's what we heard, but after watching this video, @3:33 it clearly show Voltage as an indicator option.

PWM doesn't operate at lower voltage, so I'm lost... As far as I can tell it's voltage controlled.
Actually PWM does operate @ a lower voltage (not really but bear with me)
what PWM does is either switch it on or off so on the axis of time you have a bunch of 12 states and a bunch of 0 volt states, now if you capacitor filter that output sufficiently Before the capacitor you will see a bunch of 12V states and a bunch of 0V states, but on the other side of the circuit where the filter capacitor is you will see an average voltage that can be anywhere from 0 to 12V.
Let's say the 12V is on 75% of the time hence 0V is on 25% then the voltage after the filter capacitor should be around 9V if you use a filter cap that is too small you will get spikes in that voltage (that's where the humming comes from in some pwm controlled fans). Now let's say 12V is on 66.6% of the time then you'll get about 8V after the filter I think you see where I'm going with this.
So while the PWM circuit IS a 12V circuit because of the charging curve of a capacitor the voltage that is output is lower than 12V, there is also another danger, if you design the filter capacitor to high then it will take a long time for the voltage desired to be reached, however; unless you use one that is way over sized the delay should be no more than a few seconds. There is a way around that though. You measure the voltage after the filter cap and base the on off cycles on this voltage. So it will start basically always on till it reached the desired voltage.
terramir