What is a PoE Power Budget?
Updated at Nov 21st 20241 min read
A budget typically balances income against expenses over a set period. Similarly, in industrial networking, a PoE power budget represents the allocation of power rather than money.
In industrial environments, Power over Ethernet (PoE) technology is essential, employing industrial PoE switches, PoE injectors, and PoE media converters as Power Sourcing Equipment (PSE). These devices supply electricity to Powered Devices (PDs) such as IP cameras, wireless access points (WAPs), VoIP phones, and sensors. The total wattage required by connected PDs must not exceed the maximum wattage supplied by the PSE. Insufficient power can prevent devices from booting or may cause them to malfunction, leading to intermittent power cycles or device failures.
Thus, understanding the PoE power budget is crucial. It refers to the total power that the PSE can supply to its connected PDs. Miscalculating this budget can result in unavailable or damaged devices, production downtimes, or network outages.
PoE Types
How Many Watts Can PoE Provide?
Before diving into PoE power budget, let’s briefly explore the different IEEE standards for PoE:
Type 1 (PoE): 802.3af supplies up to 15.4W per port, delivering a minimum of 12.95W over two pairs.
Type 2 (PoE+): 802.3at supplies up to 30W per port, delivering a minimum of 25W over two pairs.
Type 3 (PoE++): 802.3bt supplies up to 60W per port, delivering a minimum of 51W over two or four pairs.
Type 4 (“High Power PoE”): 802.3bt supplies up to 100W per port, delivering a minimum of 71-90W over four pairs.
Note: The power loss during transmission is due to heat generated along the Ethernet cable.
It's essential to choose rugged PoE switches that comply with IEEE standards, ensuring safe and efficient power delivery. Non-standard PoE switches may provide constant power, risking damage to connected devices.
Maximum Power Consumption
Even if a PD supports a PoE standard, it may not utilize its full power capacity. For instance, a wireless access point compliant with IEEE 802.3af might only require 5W instead of the full 15.4W. To determine a PD's actual power requirements, check the manufacturer’s specifications for “Maximum Power Consumption.” If this value is significantly lower than the port’s full capacity, administrators should consider configuring the “Port Limit” to avoid overloading.
When calculating your PoE budget, sum up the Maximum Power Consumption of all PDs connected to a hardened PoE switch, rounding up to provide a safety buffer. For example, if your application involves four 9-megapixel 360° outdoor cameras, each with a Maximum Power Consumption of 12.5W, you would need 12.5W x 4 devices = 50W.
What is a Total Power Budget?
A total power budget refers to the maximum power available for a specific system or application, defined by the power supply used. It encompasses the power consumption of all components within the system, including processors, memory, and network interfaces. Exceeding this budget can lead to system malfunctions, making it vital for designers to balance power requirements carefully.
How Do You Calculate the PoE Budget?
To determine your PoE power budget, start with an 802.3af Ethernet 4-port switch that supplies 15.4W per port. The switch’s PoE budget is calculated by multiplying the number of ports by the wattage per port: 15.4W x 4 ports = 61.6W. While this seems sufficient, real-world conditions often reduce the actual wattage delivered to devices.
To illustrate this calculation in a practical context, let’s consider the TSN3220-10S-U, a managed 10-Port Gigabit Ethernet L2 Industrial PoE++ switch. This industrial PoE switch features 8 PoE++ ports with a total power budget of 360W, along with 2 SFP+ ports for high-speed connectivity. The switch can deliver up to 60W per PoE++ port, allowing it to power demanding devices efficiently.
If all 8 ports are fully utilized, the maximum power consumption would be 60W x 8 = 480W. However, given the total power budget of 360W, the switch can effectively power up to 6 devices at their maximum capacity (60W each), totaling exactly 360W (60W x 6 = 360W). This ensures optimal performance while remaining within the power budget. Additionally, the TSN3220-10S-U operates reliably in extreme conditions, with an operating temperature range of -40°C to 75°C, making it an ideal choice for industrial applications.
Network administrators typically prefer to have spare ports for diagnostics or future expansion. Moreover, an effective PoE strategy includes selecting a higher-power switch, such as those provided by FS, which can deliver greater total wattage and reduce the need for future upgrades.
Another consideration is that powered devices may increase their power draw after initial installation. For instance, adding a heater to an outdoor camera can elevate its power requirements significantly, potentially exceeding the industrial PoE switch capacity.
Additionally, environmental conditions can impact power delivery. In extreme temperatures, power delivery can diminish by up to 40%. Opting for FS industrial PoE switches, which are engineered to operate in harsh conditions, ensures reliable power delivery.
Conclusion
Developing a well-calculated PoE power budget is essential for the reliability and efficiency of your industrial network. By carefully assessing the power needs of your devices and selecting the right equipment, such as industrial PoE switches from FS, you can avoid costly downtime and ensure seamless operation.