NTC Thermistor resistance (Li-Ion Charging) - Page 1
Forum section: electronics / projects

author: SenSeS
author_rank: Contributor
timestamp: November 03, 2015, 10:45:08 am
content: I'm charging a 7.2V Lithium Ion battery back with the TI bq2057. In the datasheet of the battery pack it says that a 10k NST thermistor is included for temperature sensing. To connect this to the bq2057 I need to know both the cold and hot temperature resistance of the thermistor however and these are not listed in the datasheet. Are these standard values for a 10k NTC thermistor or how can I find these?Datasheet battery pack:http://www.farnell.com/datasheets/1806913.pdfDatasheet bq2057 charge IC:http://www.ti.com/lit/ds/symlink/bq2057.pdf(see pages 12-13 for thermistor connection)

author: prasimix
author_rank: Unknown
timestamp: November 03, 2015, 11:56:35 am
content: http://www.electro-tech-online.com/tools/thermistor-resistance-calculator.php10K NTC usually has 3977K Thermistor Beta Value

author: eneuro
author_rank: Super Contributor
timestamp: November 11, 2015, 10:44:26 pm
content: Quote from: prasimix on November 03, 2015, 11:56:35 amIt looks like it depends sometimes on manufacturer parts number like those ones 10kNTC Thermistor by muRata (page 9 10k Betas )- there is for B25-100 something close to this you posted 3944 K, but another 10kr part has 3455K from the same manufacturerLooking for datasheet for NTC 10k 1% made by SR Passives to find A,B,C,D parameters and implement (compute) in my MPU this way for fastMeasuring Temperature using an NTC Thermistor using an Abbreviated Lookup Table, but look up table will be stored in flash program memory rather than EEPROMI've made look up table based on A,B,C,D method linked above as well as B value computation using thisNTC parameter calculatorso it will be interesting to see which will be more accurate in real testsUpdate: I've found that for example this NTC made by SR Passives NTCM-HP-10K-1% -55÷125°C; 50mW has B constant 3380 K ,so as expected it depends on manufacturer, part number, etc...However, for battery protection probably high accuracy not needed to estimate when it gets hot...

author: crazy horse
author_rank: Contributor
timestamp: November 12, 2015, 12:16:06 am
content: Measure at 25 deg. Put in oven and heat up to 45deg and measure. Put in fridge and cool down to 3deg (or however cold it is) and measure.Obviously need decent thermometer.And it will take a while for the temperature to stabilise. Soak at the temperature for 2 hours at least.

author: eneuro
author_rank: Super Contributor
timestamp: November 12, 2015, 11:18:58 pm
content: Quote from: crazy horse on November 12, 2015, 12:16:06 amIn the case of 1% NTC I've shown above, it looks like its 3380K given by manufacturer is fine, since measured 11300 Ohm at measured ~22 Celcius with China multimeter, so NTC temperature sensor should give similar temperature when look up table will be used on MPU based on ADC value 543 in this caseSo, it confirms B constant can differ between NTC sensors of course, so if we do not know its value lets make a few measurements and calculate, than with look table if possible it can be very fast temperature readings while we do not need make those complicated calculations.BTW: I've found Arduino sketch, where someone used floating point operations with C log() math function for NTC calculation-I wonder how much MPU clocks they needed to convert ADC reading to temperature in Celcius this way?

author: gcgrant
author_rank: Contributor
timestamp: February 19, 2021, 12:22:57 am
content: Thermistor Selection Guide for Texas InstrumentsAdvanced Fuel Gaugeshttps://www.ti.com.cn/cn/lit/an/slua621/slua621.pdfThermistor Coefficient Calculator for TI Advanced FuelGaugeshttps://www.ti.com/lit/an/slua398/slua398.pdf