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
BFL
If I read correctly, it sounds like you are have the converter running Open circuit then connect a discharged battery as a heavy load.
More than likely the designed "Normal" operation would be starting the converter while connected to a load (battery or otherwise) and the ouput current rising to supply the load.
Without schematics it's hard (well, impossible) to determine exactly what is happening, but with no load on the converter running for minutes it's possible that the thermistor is in a relatively high resistance state. current draw with no load is probably very very low. Connecting a low battery is going to be almost an "impulse" function to the converter, likely much higher instantaneous current demand from the converter than any other load would be.
A sudden high load on the output will drive up input current, maybe causing the converter to go "open loop" and for whatever reason causing the thermistor to blow.
Switching power supplies can behave (misbehave might be a better description!!) in very unusual ways when they see load conditions they weren't anticipated to see.!!
It could be a design flaw/oversight not accounting for this use case, or an indication that at some time with this use case something else has failed resulting in thermistor overload under this use case.
Might be worth giving the vendor a call and describing the exact use sequence and see what they may say.
In the meantime I'd advocate connecting the converter to the battery BEFORE applying power to the converter. This will allow the converter to ramp up the current to the battery keeping the converter functioning as designed.
If I read correctly, it sounds like you are have the converter running Open circuit then connect a discharged battery as a heavy load.
More than likely the designed "Normal" operation would be starting the converter while connected to a load (battery or otherwise) and the ouput current rising to supply the load.
Without schematics it's hard (well, impossible) to determine exactly what is happening, but with no load on the converter running for minutes it's possible that the thermistor is in a relatively high resistance state. current draw with no load is probably very very low. Connecting a low battery is going to be almost an "impulse" function to the converter, likely much higher instantaneous current demand from the converter than any other load would be.
A sudden high load on the output will drive up input current, maybe causing the converter to go "open loop" and for whatever reason causing the thermistor to blow.
Switching power supplies can behave (misbehave might be a better description!!) in very unusual ways when they see load conditions they weren't anticipated to see.!!
It could be a design flaw/oversight not accounting for this use case, or an indication that at some time with this use case something else has failed resulting in thermistor overload under this use case.
Might be worth giving the vendor a call and describing the exact use sequence and see what they may say.
In the meantime I'd advocate connecting the converter to the battery BEFORE applying power to the converter. This will allow the converter to ramp up the current to the battery keeping the converter functioning as designed.
