Converter In-Rush Thermistors etc, UPDATE -4
UPDATE on 17 Nov, Update 2 on 22 Nov, Update 3 on 16 Jan 14, Update 4 on 19 Oct 14. --------------- In a recent thread there was mention of how you can wreck your gizmo (in my case a converter) ...
Forum Discussion
Let's say all the current goes through the thermistor with the lower resistance. This part will heat up and as a result, its resistance increases to that of the other part. Now the parts have equal resistance and they will share. One of the parts will just have a little higher temperature.
These thermistors (designed for inrush current limiting) are NTC components. NTC is negative thermal coefficient, which means that as the temperature goes up, the resistance goes the other way - down. For most materials, electrical resistivity will increase with increasing temperature, they have a PTC.
The result is that with two NTC thermistors in parallel, the one that has the lower resistance draws more current, gets hotter and its resistance goes down even more, making it even hotter. You end up with one thermistor of near zero resistance and one that's close to its zero power resistance of a few ohms. All the current flows through the low resistance thermistor, and none through the one that has a few ohms. They won't share and the one with the least current initially gets less and less current over time. For PTC components in parallel, they will share, but thermistors, like this, are specially built with the NTC property specifically because you want high resistance at startup and low resistance during operation.
