Page 60 - Battery Reference Book

Effect of discharge rate on performance characteristics 1/45

Table 1.19 Effect of discharge rate on energy density and other parameters
lh 1 min
discharge discharge

1. Duration of discharge (min) 60 1
2. Voltage, E (V) 1.7 1.2
3. Capacity (A h) 20 8
4. Discharge current (A) 20 480
5. Coulombs delivered during discharge 72 OOOh 28 800/min
6. Volt coulombs 122 400 34 560
7. Watts (E x A) delivered during discharge 34h 576/min
8. Watts delivered per second 0.009 44 9.6
9. Watt hours delivered during discharge 34 9.6
10. Practical energy density (W h/kg) 34 9.6
11. Ohmic (Joule) heating during discharge (cal) 29 282h 8268/min
E x A x seconds
J=--
4.18
A2 x 17 x seconds
-~
-
4.18
12. Internal resistance, E/A (Q) 0.085 0.0025
13. Heat content change of cell reaction during
discharge (negative sign = heat evolved)
-75 053h -52 890/min

(see Equation 1.20) (assuming
dEldP = 0,000 25, n = 2, F = 96 500 C,
T = 25°C ((298 K))
14. Total heat evolution during discharge,
.I + AH cal 104 335h 60 390/min
15. Heat evolution (cal/s) 29 1006

Table 1.20 Disc.harges of 2V lead-acid battery at different rates-basic data
t (min) 30 20 10 4 2 I
E (VI 1.6 1.59 1.56 1.51 1.41 I .26
Capacity (Ah) 30 30 25 20 16 10
Current (A) 60 90.09 149.70 299.85 480.48 602.41
Coulombs 108 000 108 108 89 820 71 964 57 658 36 144
Volt coulombs 172 800 171 892 140 119 108 666 81 298 45 541
Watts 96.0 143.2 233.5 452.8 677.4 759.6)
Wattskcond 0.0533 0.1193 0.3892 1.8867 5.6450 1.2650
Watt hours 48.00 47.72 38.92 30.18 22.58 12.66
Energy density (W Nkg) 48.00 47.72 38.92 30.18 22.58 12.66
Joule (ohmic) heating 41 340 41 110 33 517 25 998 19447 10 895
AH=- -3600 C ~-T(Z)J
R = E/A(Q) 0.0267 0.0176 0.0104 0.005 03 0.002 93 0.002 09
4.18 -39415 -39 157 -31982 - -24 722 -18400 - 10 208
Joule + AH 80 755 80 267 65 499 50 720 37 847 21 103
Heatlsecond
Total 44.86 66.90 109.16 211.33 315.39 351.71
Joule 22.97 34.25 55.86 108.32 162.06 181.58
AH 21.89 32.63 53.30 103.00 153.3 170.13
AH as % of total 48.8 48.8 48.8 48.7 48.6 48.4
Joule as 9% of total 51.2 51.2 51.2 51.3 51.4 51.6