battery power storage
A custom battery pack should have thermal protection to prevent cell damage or rupture during charging or discharging.
The standard is to use an NTC thermistor 10k 3950. That is, R25°C=10KΩ, and B=3950. B is the sensitivity index constant. Note that 25°C=298.15°K. To calculate temperature from resistance, T = B / (ln(R/r∞)).
An NTC thermistor can also be used for surge protection. It gives a soft start when equipment is first powered up. When powering up the NTC is cold and resistance is high thus limiting current. As the current flows the NTC thermistor will get warmer. This causes resistance to drop which removes the current limiting factor from the circuit.
A PTC resistor may also be used as a thermal fuse to temporarily cut power to or from the cell.
Table of Resistance versus Temperature for M 3950
T(°C) RT/R25 TF% α(%/°C)
-55 99.56 23.2 -7.71 -50 68.95 20.1 -7.42 -45 48.38 17.3 -7.15 -40 34.37 14.8 -6.89 -35 24.71 12.5 -6.64 -30 17.96 10.6 -6.41 -25 13.20 8.8 -6.18 -20 9.803 7.3 -5.97 -15 7.351 5.9 -5.77 -10 5.585 4.7 -5.57 -5 4.251 3.7 -5.39 0 3.275 2.8 -5.21 5 2.544 2.0 -5.04 10 1.992 1.4 -4.88 15 1.572 0.8 -4.73 20 1.249 0.4 -4.58 25 1.0000 0.0 -4.44 30 0.8057 0.4 -4.30 35 0.6534 0.8 -4.17 40 0.5331 1.2 -4.05 45 0.4376 1.7 -3.93 50 0.3612 2.2 -3.81 55 0.2998 2.8 -3.71 60 0.2501 3.4 -3.60 65 0.2097 4.0 -3.50 70 0.1767 4.6 -3.40 75 0.1496 5.3 -3.31 80 0.1272 6.0 -3.22 85 0.1087 6.7 -3.13 90 0.09321 7.4 -3.05 95 0.08027 8.1 -2.97 100 0.06939 8.8 -2.89 105 0.06020 9.5 -2.82 110 0.05243 10.2 -2.75 115 0.04581 11.0 -2.68 120 0.04017 11.7 -2.61 125 0.03533 12.5 -2.55 130 0.03117 13.2 -2.48 135 0.02759 14.0 -2.42 140 0.02449 14.7 -2.37 145 0.02180 15.5 -2.31 150 0.01945 16.2 -2.26