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
ktmrfs wrote:
"And consider this. As long as the thermistor can handle the inrush current (joules spec) and the power at max steady state current, a higher than "optimal" thermistor initial resistance within reason, really will not hurt anything and has upsides. inrush current will be lower (good), time for the caps to fully charge will be longer, but only by a few cycles, not noticeable. No real downsides."
I don't have the answer but one thing seems to be overlooked here. All the talk here is about the capacitor inrush current and steady state current. This is an important part of the design but not the only thing.
The thermistor must be hot, in the low resistance state, when the inverter starts to provide the high current output to the battery. If it is not hot enough there will be large power dissipated in the thermistor. This was the case with connecting the battery after the converter was turned on. So it may be argued that using a smaller thermistor close to the ratings is best, but don't turn it on and then connect the battery!
As you can see there is no simple answer as all design is a trade off. Getting it correct is often a matter of trial, measure, and rethink it. With this inverter a range of thermistor values should work as long as it is used in a manner that it was designed to, that is do not turn it on and then connect the battery.
"And consider this. As long as the thermistor can handle the inrush current (joules spec) and the power at max steady state current, a higher than "optimal" thermistor initial resistance within reason, really will not hurt anything and has upsides. inrush current will be lower (good), time for the caps to fully charge will be longer, but only by a few cycles, not noticeable. No real downsides."
I don't have the answer but one thing seems to be overlooked here. All the talk here is about the capacitor inrush current and steady state current. This is an important part of the design but not the only thing.
The thermistor must be hot, in the low resistance state, when the inverter starts to provide the high current output to the battery. If it is not hot enough there will be large power dissipated in the thermistor. This was the case with connecting the battery after the converter was turned on. So it may be argued that using a smaller thermistor close to the ratings is best, but don't turn it on and then connect the battery!
As you can see there is no simple answer as all design is a trade off. Getting it correct is often a matter of trial, measure, and rethink it. With this inverter a range of thermistor values should work as long as it is used in a manner that it was designed to, that is do not turn it on and then connect the battery.
