EnerSys PowerSafe Data Safe - Appendix - Hydrogen Evolution Calculation

Page 46
www.enersys.com Publication No. US-FL-IOM-002 January 2007
APPENDIX
HYDROGEN EVOLUTION CALCULATION
Significant amounts of hydrogen are evolved only as the battery approaches full charge. The
maximum hydrogen evolution rate is 0.000267 cubic feet (7.56 x 10
-6
cubic meters) per minute
per charging ampere per cell at 77
o
F (25
o
C).
To calculate the amount of hydrogen produced, consider an antimony alloy type (flat plate or
tubular) battery at a point where it is nearing end of life, or equalize charge at 2.33 VPC.
Float Current demand of
fully charged stationary lead-acid cells.
Milliamperes per 100 Ah @ 8-hr. rate
Charge Voltage Antimony Calcium
NEW – OLD
2.15 vpc
15 – 60
—
2.17 vpc
19 – 80
4
2.20 vpc
26 – 105
6
2.23 vpc
37 – 150
8
2.25 vpc
45 – 185
11
2.27 vpc
60 – 230
12
2.33 vpc
120 – 450
24
2.37 vpc
195 – 700
38
2.41 vpc
300 – 1100
58
NOTE: The above values apply when the electrolyte temperature is 77
o
F (25
o
C).
The values will double for every 15
o
F (8
o
C) of temperature rise. If the
temperature drops, the current value will be halved for every 15
o
F (8
o
C)
decrease. Antimony ranges indicate current increases due to cell aging.