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
Had a little time on my hands this morning. I used another method to measure converter turn-on current. I inserted a precision 1 ohm, 50W resistor in the "hot" side of the ac power going into the converter. CH1 of scope is measuring incoming ac voltage. CH2 which is inverted measures ac voltage on the other side of the 1 ohm resistor. The scope is set-up so that a third trace adds CH1 & CH2. Since CH2 is inverted, the third trace measures voltage across the resistor. CH1 & CH2 are both at 20V/Div. The third trace is scaled 20V/Div, or 20A/Div. The 10:1 scope probe grounds are connected to ac neutral. The ground connection of the scope's ac power plug is cut off. An isolation transformer also works, but don't have one.
I ran the test about 5 times to try and get a turn-on max current. This occurs when turn-on coincides with the ac voltage is at its peak (170V).
The scope plot shows:
1st cycle max current is about 32A
2nd cycle max current is about 25A
3rd cycle max current is about 17A
4th cycle max current is about 15A
We can also get an approximate ac resistance that limiting the current. At around 150V, 32A are going into the discharged cap bank. The actual turn-on did not start at 170V, but more like 150V.
R = 150V / 32A = 4.7 ohm
Subtracting the 1 ohm current sense resistor and the 2 ohm thermistor, converter input resistance and ac line resistance account for 1.7 ohm.
Sal
I ran the test about 5 times to try and get a turn-on max current. This occurs when turn-on coincides with the ac voltage is at its peak (170V).
The scope plot shows:
1st cycle max current is about 32A
2nd cycle max current is about 25A
3rd cycle max current is about 17A
4th cycle max current is about 15A
We can also get an approximate ac resistance that limiting the current. At around 150V, 32A are going into the discharged cap bank. The actual turn-on did not start at 170V, but more like 150V.
R = 150V / 32A = 4.7 ohm
Subtracting the 1 ohm current sense resistor and the 2 ohm thermistor, converter input resistance and ac line resistance account for 1.7 ohm.
Sal
