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
Salvo wrote:
The reason for looking at the smaller thermistor is because it has no, or very little ceramic material surrounding it. The thermistor that we're dealing with has a time constant of 134 s. It's slower due to the attached mass. Still, the small bead thermistor has a sizable time constant.
I could go on with this discussion, but it's really a moot point that we're arguing. The turn-on surge current is not the problem! Regardless if we're using a 2 ohm or 5 ohm device, the energy dissipated in the thermistor is only 35J. The part fails at 1200J. It isn't failing during turn-on. Your argument that the 5 ohm part is better during turn-on is not valid. That is not the problem.
Sal
the 134 second time constant is how long it takes to COOL to 50% of initial resistance with no current flow in free air. I has a very limited relationship to how fast the thermistor heats up. that is an entirely different time constant and is dependent on current and the mw/C thermal impedance. Proper choice of thermistor and it will heat up to the near 200c expected operating temperature in way less than 134seconds. Probably in seconds or less.
