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BATTERY CAPACITY CALCULATIONS ( 2V Standby range)
Example
Considerations :System rating : 200 KVA
Inverter efficiency : 96 %
*No of cells : 192 nos. ( 384V DC bus voltage) * In typical
cases, the no. of cells can be arrived at
End cell voltage : 1.75 VPC ,ie., 336 V by dividing the max
charger voltage / max. recommended float volt
Back up required : 30 mins
Operating temp. : 15 DegC
Load pattern : Constant
Capacity calculation for VRLA type (NMST) 2 V cells:
Max. discharge Current = KVA(UPS rating) X 1000 X power
factor
ECV X Inverter Efficiency X No of cells
= 200 X 1000 X 0.8
1.75 X 0.96 X 192
= 496 AmpsCapacty factor for 30mins backup to ECV of 1.75 Volts
= 1.389 ( from capacity factor table )
Hence Calculated capacity = 496 X 1.389
= 689 AH
Final Capacity =((Calculated capacity) x Ktx KD)/A.F
where Kt= Temperature correction factor
KD= Design margin A.F = ageing factor
Kt= 1 + ((27 - op.temp) x CT)/100, where CTis temperature
correction factor at C-10, which is 0.43 for standby range
KD= Design Margin (minimum of 10%)
A.F = Ageing factor of 0.8 ( For Plante' , this is 1)
Hence final capacity = (689 x (1+(12x0.43)/100) x 1.1) / 0.8
= 996.26 Ah
NMST 1000Ah capacity can be recommended
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Capacity calculation for Tubular type 2 V cells:Max discharge
current remains same as above , i.e., 496 Amps
Capacity factor for 30 mins back up to 1.75 end cell voltage =
1.46 (refer capacity factor table)Calculated capacity= 496 X
1.46
= 724 Ah approx.
The Final capacity can eb derived the same way mentioned above
by
applying temperature correction, design margin & ageing
factor.
Capacity calculation for Plante type 2 V cells:
Again the max discharge current is 496 Amps.
Capacity factor for 30 minutes (refer capacity factor table) is
1.16
Hence calculated capacity = 496 X 1.16 = 575 Ah
The Final capacity can eb derived the same way mentioned above
by
applying temperature correction, design margin , except that the
ageing factor.
for plante' should be considered as 1.
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ge.
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BATTERY CAPACITY CALCULATIONS ( 12V monobloc range)
Example
Considerations :System rating : 20 KVA
Inverter efficiency : 96 %
No of cells : 192 nos( 384V DC bus voltage)
End cell voltage : 1.70 VPC
Back up required : 1 hr
Load pattern : Constant
Capacity calculation for VRLA 12 V monobloc (EP -
Powersafe):
Max. discharge Current = KVA(UPS rating) X 1000 X power
factor
ECV X Inverter Efficiency X No of cells
= 20 X 1000 X 0.8
1.70 X 0.96 X 192 = 51.06 Amps
Capacty factor for 1 hr backup to ECV of 1.70 Volts = 1.49 (
from capacity factor table )
So Capacity required = 51.06 X 1.49
= 76.08 Ah
HENCE EP80-12 CAN BE RECOMMENDED
Capacity calculation for vented type 12 V monobloc (EL
tubular):
Max discharge current remains same as above , I.E., 51.06
Amps
Capacty factor for 1 hr backup to ECV of 1.75 Volts = 2 ( from
capacity factor table )
So Capacity required = 51.06 X 2
= 102.12 AH (approximately)
HENCE,nearest type, 6EL100 CAN BE RECOMMENDED
Note: In both the above cases , the temperature correction has
not been considered. It can be
calculated the same way it is shown for 2V standby
batteries.
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Capacity Calculations for multiple load pattern
Assumptions
Battery required = VRLACut-off voltage = 1.85Vpc
Load Pattern
Current A I3= 60A
I1= 40A
t1= 30 min Time t
t3= 30 min
Operating Temp = 20 Deg CDesign Margin required = 20%
A.F = Ageing factor (0.8 for VRLA)
Capacity =(( I1x F1 + (I2-I1) x F2 + (I3- I2) x F3) x Ktx KD) /
A.F
Where
T1= t1+ t2+ t3/ T2= t2+ t3/ T3= t3
F1 = Cap factor for T1/ F2 = Cap factor for T2/ F3 = Cap factor
for T3
Kt= 1 + ((27 - 20) x CT)/100, where CTis temperature correction
factor at C-10, which is 0.43
KD= Design Margin of 10%
t2= 120 min
I2= 20A
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Capacity factor for VRLA 2V type
Final volt 1 min 5 mins 15 mins 30 mins 60 mins 90 mins 2 hrs 3
hrs 4 hrs 5 hrs 6 hrs 8 hrs 10 hrs
v/cell
1.85 1.490 1.760 2.110 2.703 3.195 4.219 5.181 6.173 7.194 9.009
10.753
1.80 1.241 1.499 1.812 2.342 2.809 3.731 4.630 5.556 6.494 8.197
10.000
1.75 0.417 0.625 1.110 1.389 1.661 2.179 2.653 3.521 4.386 5.319
6.173 7.937 9.615
1.70 0.412 0.609 1.020 1.311 1.570 2.070 2.538 3.401 4.237 5.128
5.952 7.692 9.259
1.65 0.408 0.592 0.960 1.258 1.511 2.008 2.457 3.268 4.132 4.975
5.814 7.463 9.091
1.60 0.398 0.572 0.920 1.225 1.471 1.969 2.398 3.185 4.000 4.831
5.650 7.299 8.929
Capacity factor for Vented 2V tubular type (NDP)
Final volt 1 min 5 mins 15 mins 20 mins 30 mins 45 mins 1 hr 2
hrs 3 hrs 4 hrs 5 hrs 6 hrs 7 hrs 8 hrs 9 hrs 10 hrs
v/cell
1.85 1.60 1.65 1.95 2.10 2.35 2.50 2.85 3.55 4.50 5.25 6.10 6.85
7.80 8.55 9.30 10.00
1.80 1.10 1.20 1.34 1.54 1.74 2.02 2.31 3.25 4.18
1.75 0.86 0.95 1.09 1.30 1.46 1.77 2.00
1.70 0.68 0.77 1.03 1.12 1.28 1.61
1.65 0.58 0.67 0.91 1.00 1.17 1.50
1.60 0.53 0.60 0.72 0.92 1.10 1.44
Capacity factor for Vented 2V tubular type (HDP)
Final volt 1 min 5 mins 10 mins 20 mins 30 mins 45 mins 1 hr 2
hrs 3 hrs 4 hrs 5 hrs 6 hrs 7 hrs 8 hrs 9 hrs 10 hrs
v/cell
1.85 1.38 1.44 1.54 1.74 2.04 2.12 2.50 3.30 4.15 5.05 5.92 6.75
7.70 8.48 9.25 10.00
1.80 0.96 1.04 1.16 1.34 1.62 1.87 2.02 2.81 3.70
1.75 0.74 0.82 0.96 1.13 1.37 1.65 1.67
1.70 0.60 0.68 0.80 0.98 1.20 1.51
1.65 0.51 0.58 0.70 0.87 1.10 1.41
1.60 0.46 0.52 0.63 0.80 1.03 1.35
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Capacity factor for Vented 2V Plante type cells
Final volt 1 min 5 mins 10 mins 15 mins 20 mins 30 mins 45 mins
1 hr 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs 7 hrs 8 hrs 9 hrs
v/cell
1.85 1.18 1.28 1.30 1.38 1.48 1.62 1.74 1.80 2.80 3.80 4.65 5.60
6.50 7.45 8.25 9.10
1.80 0.94 1.00 1.04 1.10 1.20 1.34 1.48 1.60 2.67 3.59
1.75 0.75 0.82 0.86 0.92 1.00 1.16 1.32 1.54
1.70 0.63 0.68 0.72 0.80 0.86 1.04 1.22
1.65 0.52 0.58 0.63 0.70 0.77 0.94 1.15
1.60 0.46 0.50 0.56 0.64 0.72 0.88 1.10
Capacity factor for VRLA 12 Volt monobloc.
Final volt 30 secs 1 min 2 mins 3 mins 4 mins 5 mins 7 mins 10
mins 15 mins 20 mins 30 mins 1 Hr 90 mins 2 Hrs
v/cell
1.80 0.25 0.26 0.26 0.27 0.29 0.31 0.36 0.43 0.56 0.67 0.91 1.56
2.38 2.78
1.70 0.18 0.20 0.20 0.23 0.25 0.28 0.33 0.40 0.53 0.63 0.87 1.49
2.08 2.50
1.65 0.15 0.17 0.19 0.22 0.24 0.26 0.31 0.37 0.50 0.61 0.83 1.45
2.00 2.44
1.60 0.13 0.15 0.18 0.20 0.23 0.25 0.30 0.36 0.48 0.59 0.80 1.43
1.96 2.38
Capacity factor for Tubular 12 Volt monobloc.
Final volt 1 hr 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs 7 hrs 8 hrs 9 hrs
10 hrsv/cell
1.8 3.16 4.14 5.13 6.02 6.82 7.61 8.42 9.18 10
1.75 2
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10 hrs
10.00
