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
I don't believe the thermister was at fault, nor do I believe the cause of the converter failure is due to not being connected to the battery.
The thermister blew because one of the Al capacitors shorted. The cap shorted because of poor quality parts as well as a bad design (I'm speculating). The converter is under greatest stress when outputting 100A. At 100A, the Al caps see the greatest ripple voltage and ripple current. The combination of the capacitor's ESR (internal resistance) and ripple current heat the capacitors. They get hot and the electrolyte dries out. At some point in time they will short.
What's the rated voltage stamped on those caps, 200V or 250V? If they are rated 200V, then there's little margin since the working voltage is 170V. I worked in very high reliability electronic designs. We always derated capacitor voltage by 50%. If working voltage is 170V, then cap voltage must be greater than 2 * 170V = 340V.
I also suspect ripple current is too high because there's not enough capacitance. The rule of thumb for the front end caps is greater than 1.5 uF/Watt. This converter has a 1600W rating. That means the capacitance should be greater than:
C = 1.5uF/Watt * 1600Watt = 2400 uF
Take a look inside to verify cap voltage rating and capacitance.
Sal
The thermister blew because one of the Al capacitors shorted. The cap shorted because of poor quality parts as well as a bad design (I'm speculating). The converter is under greatest stress when outputting 100A. At 100A, the Al caps see the greatest ripple voltage and ripple current. The combination of the capacitor's ESR (internal resistance) and ripple current heat the capacitors. They get hot and the electrolyte dries out. At some point in time they will short.
What's the rated voltage stamped on those caps, 200V or 250V? If they are rated 200V, then there's little margin since the working voltage is 170V. I worked in very high reliability electronic designs. We always derated capacitor voltage by 50%. If working voltage is 170V, then cap voltage must be greater than 2 * 170V = 340V.
I also suspect ripple current is too high because there's not enough capacitance. The rule of thumb for the front end caps is greater than 1.5 uF/Watt. This converter has a 1600W rating. That means the capacitance should be greater than:
C = 1.5uF/Watt * 1600Watt = 2400 uF
Take a look inside to verify cap voltage rating and capacitance.
Sal
