AEI-e410C Application Note for System Engineers
AP-001 rev1.0

The AEI-e410C provides PoE power to various Power Devices (such as IP Cameras, VoIP phones, etc.) sufficient to operate under the IEEE 802.3AF specification.

Calculating Power Requirements

Virtually all computer power supplies have sufficient characteristics to support current motherboard and peripheral devices, PLUS provide power to support multiple AEI-e410C cards fully populated with Power Devices. 

This article will explain the engineering, and steps you can take to ensure a successful installation.

The AEI-e410C includes onboard power conversion technology that uses the internal Power Supply Unit (or "PSU") +12VDC rail of the Host System, and ramps it up to 48VDC for use on PoE Power Devices. 

It is important for System Engineers to ensure the host system PC Power Supply can support not only present system power requirements, but also the additional Amps/Watts for attached Power Devices (PD). 

First look up the specifications for your current Power Supply Unit (PSU).  You should find something similar to the following:

The electrical current available on +12VDC rail, using the above as an example, is 21Amps maximum. This is calculated by adding +12V1DC to +12V2DC. 

From this figure (21 Amps in this example), you simply subtract the +12VDC current used by the motherboard and other peripherals attached (HDDs, CD-ROMs, etc.).  What is left is available electrical current to power PoE devices.

Mathematical Calculations

The AEI-e410C uses a unique onboard four-phase power transformer that converts and regulates 12VDC source to 48VDC PoE output. This technology provides a current advantage.  Simply, a 1.0 Amp current draw on the 48VDC PoE power output will only draw approximately 1.0 Amps on the 12VDC rail of the Host System PSU.

To start, calculate the following:

  1. Add the wattage from all attached PoE Power Devices. For example, four 9Watt PoE IP Cameras would required (9x4=36 Watts) @ 48VDC.

  2. Convert Watts to Amps  (Watts / Voltage = Amps)

    36W/48V = 0.75 Amps (or 750mA)

In the above example, four 9W IP Cameras would require 750mA of current from the Host System's 12VDC Power Supply.  It's always good practice to add a small buffer, so in this example, we assume a 20% buffer.  Therefore, we assume the four IP Cameras will use 900Amps on the Host System's Power Supply.

Alternative Method

A simplest method to calculate PoE Amp usage is to assume that each AEI-e410C card will have all four ports populated with Power Devices that require the maximum PoE 802.3AF power (minimum specification is 44VDC @ 350mA or 15.4Watts per port). 

Given the IEEE AF standards (350mA x 4 ports x 1.2 buffer = Total 1.68 Amps @ 48VDC Power Output), the AEI-e410C's power conversion technology would require a minimum power input of only +12VDC @ 1.680A from the host system's power supply.