Fire-Lite FCPS Series Field Charger/Power Supply - Manual (Page 39)

FCPS-24FS Series Instruction Manual — P/N 51883-L8:J1 8/30/13 39
Calculating the System Current Draw Power Supply Requirements
6.3 Calculating the System Current Draw
6.3.1 Overview
The power supply 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 power supply when primary
power is applied, use Calculation Column 1 in Table 6.3 on page 40. The power supply must sup-
port 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 6.3 on page 40. 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 6.3 on page 40.
When calculating current draw and the battery size, note the following:
• Primary refers to the main power source for the power supply.
• Secondary refers to the power supply’s backup batteries.
• All currents are given in amperes (A). Table 6.2 shows how to convert milliamperes and
microamperes to full amperes.
6.3.2 How to Calculate System Current Draw
Use Table 6.3 on page 40 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 Fire-Lite Device Compatibility Document
for compatible devices and their current draws.
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 6.3 on page 40.
Following are the types of current that can be entered into Table 6.3 on page 40.
 Calculation Column 1 - The primary supply current load that the power supply must
support during a non-fire alarm condition, with AC power applied
 Calculation Column 2 - The primary supply current load the power supply 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
To convert... Multiply Example
Milliamperes (mA) to
amperes (A) mA x 0.001 3 mA x 0.001 = 0.003 A
Microamperes ( μA) to
amperes (A)
μA x 0.000001 300 μA x 0.000001 = 0.0003 A
Table 6.2 Converting to Full Amperes