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:
I see you found the diode.
It has a peak surge rating of 350A.
Your thermistor needs to be larger than 170V/350A = 0.49 ohm.
I haven't heard any rational reasoning for going greater than 2 ohm.
Note, the surge current is for an extremely short time; 4 ms max. The charging pulses that follow the initial pulse have significantly less current.
Just to review:
1. The desired resistance of the thermistor has nothing to do with the size of the capacitor bank.
2. If this is your standard peak-charge circuit, the diode bridge is the weakest link and may need inrush current surge protection.
3. The energy the thermistor consumes during turn-on is equal to 1/2CV^2. It doesn't matter if the thermistor has 1 ohm or 5 ohm, they will consume equal energy.
4. The size of the capacitor bank determines the minimum energy spec for the thermistor.
Sal
So you are not concerned about saturating the core of the transformer, or its kVA rating, when allowing 350 amps to flow?
If saturated, the surge current will flow longer than 1/4 cycle and will persist for more cycles too...
