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Power Supply Calculations
7.3 Calculating the System Current Draw
7.3.1 Overview
The control panel must be able to power all internal and external devices continuously during the
non-fire alarm condition. To calculate the non-fire alarm load on the system power supply when
primary power is applied, use Calculation Column 1 in Table 7.3 on page 137. The control panel
must support a larger load current during a fire alarm condition. To calculate the fire alarm load on
the power supply, use Calculation Column 2 in Table 7.3 on page 137. The secondary power
source (batteries) must be able to power the system during a primary power loss. To calculate the
non-fire alarm load on the secondary power source, use Calculation Column 3 in Table 7.3 on page
137.
When calculating current draw and the battery size, note the following:
•
'Primary' refers to the main power source for the control panel
•
'Secondary' refers to the control panel's backup batteries
•
All currents are given in amperes (A). Section 7.2 shows how to convert milliamperes and
microamperes to full amperes.
To convert...
Milliamperes (mA) to
amperes (A)
µ
Microamperes (
A) to
amperes (A)
7.3.2 How to Use Table 7.3 on page 137 to Calculate System
Current Draw
Use Table 7.3 on page 137 to calculate current draws as follows:
1.
Enter the quantity of devices in all three columns
2.
Enter the current draw where required. Refer to the Device Compatibility Document for
compatible devices and their current draw
3.
Calculate the current draws for each in all columns
4.
Sum the total current for each column
5.
Copy the totals from Column 2 and Column 3 to Table 7.4 on page 138
Following are the types of current that can be entered into Table 7.3 on page 137:
Calculation Column 1 - The primary supply current load that the control panel must
support during a non-fire alarm condition, with AC power applied.
Calculation Column 2 - The primary supply current load that the control panel must
support during a fire alarm condition, with AC power applied.
Calculation Column 3 - The standby current drawn from the batteries in a non-fire alarm
condition during a loss of AC power.
136
Multiply
mA x 0.001
µ
A x 0.000001
Table 7.2 Converting to Full Amperes
SFP-5UD & SFP-10UD Series Manual— P/N 52879:C2 1/24/2012
Calculating the System Current Draw
Example
3 mA x 0.001 = 0.003A
µ
300
A x 0.000001 = 0.0003 A
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