Power Supply Requirements
Calculating the System Current Draw
38
FCPS-24FS PN 51883:B 12/04/02
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 39. The power supply 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 6.3 on page 39. 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 39.
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 39 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 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 6.3 on page 39
Following are the types of current that can be entered into Table 6.3 on page 39
✓
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
Table 6.2 Converting to Full Amperes
To convert...
Multiply
Example
Milliamperes (mA) to
amperes (A)
mA x 0.001
3 mA x 0.001 - 0.003 A
Microamperes (
µ
A) to
amperes (A)
µ
A x 0.000001
300
µ
A x 0.000001 = 0.0003 A
