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
DryCamper11 wrote:Salvo wrote:
Tell me again why do you want 5 ohm?
I gave my answer above.
1) It reduces inrush current max.
Not an issue. Turn on energy is 35J. The part is stressing out at 300J. Turn-on resistance is not the problem. Can't you see that?
2) It reduces di/dt on inductive components (which are unknown).
Your arguments are sounding like the boy who keeps crying wolf. We're talking about a 4 ms transient! Tell me what's supposed to happen to the emi filter that you're afraid of?
3) It reduces dv/dt on capacitive components (which are unknown).
Again cry wolf. We're talking electrolytic caps. I've never heard that dV/dt is an issue. Nippon Chemi-Con, a major manufacturer of electrolytics doesn't mention dV/dt problems. Ripple current is the biggest issue with these caps.
Al electrolytics
The pdf does mention inrush current. They say it can be 100 times greater than typical operation, but due to the short transient time period, they're harmless.
4) We don't know the minimum resistance since we don't know much about the circuit, but given that there is no "maximum resistance" calculation for thermistors, it's better to increase resistance than decrease it when faced with a failing thermistor.
:h I fail to see that logic. If the part is blowing up, then it's better to give the next part even more resistance???
I would rather conduct an analysis why it's failing. We know it's not getting overstressed at turn-on. 35J won't overstress the device. Where does that leave us? The only thing that's left is continuous operation. The converter is pulling 13Arms. Power dissipation of our thermistor is P = I^2 * R. The greater the thermistor resistance the greater the power dissipation. A 2 ohm thermistor will have a lower resistance and subsequent lower power dissipation than the 5 ohm part.
I would turn this around and ask what benefit you think there is by reducing the resistance? I listed the possible benefits that I'm aware of from such a reduction, and why I think those benefits aren't as great as the benefits from increased resistance.
I haven't seen any benefits list. You got a cry wolf list. Iota doesn't have a thermistor. Are their emi inductors failing? Are their cap banks failing? Come on, lets get real!
I've produced to the diode bridge spec and shown the actual max surge current requirement. Please do that to your list.
Sal
