Table 20: Initial calculation based on 20 hour rating
20 Hour Rating C/20 (Amps) 20 Hour Rating C/20 (Amps) 20 Hour Rating C/20 (Amps)
4.5 Ah 0.225 12.7 Ah 0.635 55 Ah 2.75
5.0 Ah 0.25 18 Ah 0.90 110 Ah 5.5
If either the Standby Current or the Alarm Current is greater than the C/20 current for the initial battery size selected, a Discharge Factor
(DF) must be applied. For example, 1 A load on a 10 Ah battery requires a Discharge Factor of 1.08 (10 Ah / 1 A gives discharge time of 10
hours; DF = 1.08). Use Table 21 to determine Discharge Factor (use the 20 hr value for 24 hr standby).
Table 21: Determining discharge factor
Discharge Time
Discharge
Factor
Discharge
Time
Discharge
Factor
Discharge
Time
Discharge
Factor
Discharge
Time
Discharge
Factor
0.083 hr 5 min 3.85 2 hr 1.43 8 hr 1.10 14 hr 1.03
0.166 hr 10 min 2.78 3 hr 1.30 9 hr 1.09 16 hr 1.02
0.249 hr 15 min 2.27 4 hr 1.22 10 hr 1.08 18 hr 1.01
0.332 hr 20 min 2.08 5 hr 1.18 11 hr 1.06 20 hr 1.00
0.5 hr 30 min 1.96 6 hr 1.14 12 hr 1.05 48 hr 1.00
1 hr 60 min 1.67 7 hr 1.11 13 hr 1.04 60 hr 1.00
Standby Discharge Factor (SDF) = _________ Alarm Discharge Factor (ADF) = _________
Minimum required battery capacity calculation for a final discharge voltage of 20.4V (to account for battery aging, a 1.17 multiplier is
included). Minimum battery capacity in Ah = 1.17 x [(A x C x SDF) + (0.0167 x B x D x ADF)] = _______
Minimum required battery capacity calculation for a final discharge voltage: 23V.
1.32 × [(A × C × SDF) + (0.0167 × B × D × ADF)] = _______
If the battery size initially selected is smaller than the result of step 9 above, repeat the calculations using a larger battery size.
page 59 579-354 Rev. X
4004R Fire Alarm installation, programming, and operating instructions
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