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Plant Configuration Examples
1.
To illustrate the relationships between mirc, abh current drains, the recharge factor, and battery recharge current
for non-redundant and redundant systems, consider the following examples. Note that the QS862A rectifier
provides 25A at 54.5 V
A battery plant is required to provide a load current of 50 amperes, have an 8-hour discharge time (reserve time)
and recharge to 95% of battery capacity in 24 hours. Determine the number of rectifiers required for
non-redundant systems.
From Figure 3-1, the recharge factor is 1.38.
mirc = abh x recharge factor
mirc = 50 x 1.38 = 69 amperes
For low line ac using QS862A 25A (100-120 Vac) rectifiers, three rectifiers (69/25 = 2.76) are required to provide the
minimum installed capacity of 69 amperes for a non- redundant system. If one rectifier fails, the remaining
rectifiers will provide the abh capacity.
2.
An alternate method to calculate the number of rectifiers necessary is to utilize power. In the above example, the
requisite current is 50A. As most battery plant loads are looking into constant-power loads, the 50A would increase
as the battery voltage decreases during battery discharge. Assuming the 50A is the current being drawn from the
load at the plant float voltage of 54.5V, the total power being drawn by the load is 2725W (54.5V x 50A).
We can utilize the recharge factors from Figure 3-1 and use a modified mirc formula,
therefore:
mirc = power x recharge factor
mirc = 2725W x 1.38 = 3761W
In this high line ac example using QS862A 1635W (200-240 Vac) constant power rectifiers, three rectifiers
(3761/1635 = 2.3) are needed to support the load and recharge the batteries within the requisite time.
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Figure 3-1: Recharge Factor vs. Recharge Time
(100-120 V
) and 30A at 54.5 V
dc
ac
Recharge Factor
(200-240V
).
dc
ac
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