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
BFL13 wrote:
So I have it backwards? Increasing both ratings is the way to go, not dropping the R while increasing the current and energy ratings?
If it's start up related, then dropping zero power R will make the problem worse. The current and energy ratings are easy to choose. You just select based on capacitor bank and max steady state operating current. The R is trickier, as you choose it based on inrush current and the timing you want and the stress you want to impose.
I've seen a table somewhere of what inrush currents to assume based on steady state current, where you don't know the inrush current. IIRC, it told you to assume 100 times steady state current for converters, UPSs, etc. where you are charging a capacitor bank and 30X for lighting, incandescent bulbs, etc. where the low resistance increases as the bulbs get hot. You then plug in the assumed inrush current into a formula for minimum R.
Choosing an R above the minimum is OK. Below the minimum, you risk failure at turn on.
