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
This failure mode should then happen to all converters when they are toggled on-off-on in a short time period. I can toggle my Parallax or Iota converter without failure.
The energy the thermistor consumes in one cycle is:
E = I^2 * R * t
E = (120Vrms / 5ohm)^2 * 5ohm * 1/60Hz = 9.6 J
If the thermistor is hot and it's at 0.1 ohm, then the energy is 2400J. That would be an incorrect calculation as there's more resistance involved. We got the generator resistance, ac cable resistance, emi filter resistance and capacitor esr.
Sal
The energy the thermistor consumes in one cycle is:
E = I^2 * R * t
E = (120Vrms / 5ohm)^2 * 5ohm * 1/60Hz = 9.6 J
If the thermistor is hot and it's at 0.1 ohm, then the energy is 2400J. That would be an incorrect calculation as there's more resistance involved. We got the generator resistance, ac cable resistance, emi filter resistance and capacitor esr.
Sal
lorelec wrote:Salvo wrote:
The point is, the circuit in question has only 36 J. It takes 300J for the part to fly apart. And it is flying apart. 1/2CV^2 has nothing to do with the failure!
Sal
That 300J rating is probably for a cold thermistor (5 ohms). I assume it's flying apart because the thermistor is hot on start-up, presenting a much shorter time constant for charging those caps. At tens of milliohms, 36J may be too much.
