Converter In-Rush Thermistors etc, UPDATE -4

BFL13 wrote:
Getting back to this, where did that 50a come from anyway? (I see the 60 number for part is not a rating just an identity)

If I want to use my 2R thermistor, then if I get my amps to go with the 170 from where that 50 came from, then I would need to use 85a.
Why can't I use 85 instead of 50? If I did, would I get 60 cycles instead of 100 before it failed? Cycles of what anyway?

The 170v comes from peak volts RMS on 120v line voltage, ? , so that means every time you do a cold start, the voltage could be anything from peak to zip which means in rush may be small or great each time.

So whatever thermistor I pick, I could do several starts and it would work every time but that proves nothing, because it may be that I never caught it at peak inrush, but the next time I could and it could blow? So just because it works great after a repair, that proves nothing?

Meanwhile we do see my thermistors blowing but no harm to the diode bridge, or at least not so you would notice. Which brings us back to the spec about handling stress for 100 cycles. A cycle of what? Does that mean you get 100 starts and then anytime after that your diode bridge might fail? Converters are supposed to last years and years so that can't be right.

(I have not forgotten the comments that the production 100amper design for the straight converter version may not work quite right for the same thing used with variable voltage where perhaps higher inrushes might occur. They might need two different designs, no idea. Might hear something about that from them or not. )

LOL and please look at the data sheet link I posted and follow my explanation.

The 60 in the part number is used to identify the maximum or peak recurrent reverse voltage that can be supplied to the diode bridge -> 600 volts peak or 420 volts RMS.

The 50 amps of current I used was an estimate of a safe value of current that can flow for 100 cycles of a 50 Hz sine wave.

This information is found on the graph labeled as Maximum Non-Repetitive Peak Forward Surge Current located at the bottom of sheet 3/4.

As a side note, the current flowing into the capacitor is proportional to the change in voltage across the capacitors terminals in respect to the change in time (dv/dt).

This means maximum instantaneous current will flow into the capacitor when the voltage starts at zero volts (maximum dv/dt)and will end when the capacitor is fully charged at 170 volts (zero dv/dt).

If you use the peak voltage equation to find the current, as in C*170V/4.166ms, you are actually calculating the average value of the current over that period of time, and not the peak current.

The peak current is almost 2 times higher than the average.

If you want the best reliability, use the 5 ohm part and follow the procedures I outlined.

If you want to gamble and possibly cause premature diode bridge failure, or some other series connected part failures, use the 2 ohm part.

I am tired of Salvo's posts and arrogance so I am done posting in this thread.

Take care,

Ken