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
ken white wrote:
Unless the 2 thermistors are exactly the same, a matched set, one of them will absorb more energy than the other and very little performance gain, if any, will be achieved - my guess is the tolerance is +- 20%.
That's not true. I agree there won't be perfect sharing, but there will be sharing. It doesn't matter if one of the parts has a 20% higher tolerance. Temperature is the great equalizer in this case. 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.
Edit. The above scenario is for a PTC thermistor. We are dealing with a NTC thermistor. Currents will not share.
If they are matched, the thermal time constant will be reduced and twice the current will flow sooner, which defeats the whole purpose of trying to limit the inrush...
You haven't been listening! It doesn't matter if 5 times the current is flowing. It's still safe. 1 ohm resistance is safe for a 4200uF capacitor bank. The OP only has 2400uF.
The surge limiter is sized to absorb the in-rush created by by the energy stored in the capacitor, which is equal to C times the voltage across the capacitor squared divided by 2.
What does 1/2 * C * V^2 have to do with this?
Sal
The energy is in Joules, which is the specification I stated...
