SFP temperature increase while on PoE - hEX s

Hardware MikroTik hardware general
1

I have noticed that the temperature of the SFP module in my hEX S increases when powered with PoE.

With supplied adapter: 46 degrees celcius
With PoE: 56 degrees celcius (and going up while i write this)

It is within safe limits, but am just wondering why.
Can someone explain why this is?

Sheers, Peter


sfp1 : WAN
ether1: LAN (with VLANS)


Hardware information.

Mikrotik router:
routerboard: yes
board-name: hEX S
model: RB760iGS
serial-number:
firmware-type: mt7621L
factory-firmware: 6.46.3
current-firmware: 7.10.2
upgrade-firmware: 7.10.2

SFP-module: Tsuhan THMPRS-3511-10A rev. A

PoE switch: cisco WS-C2960CX-8PC-L

2

I’d say that what you see is effect of larger voltage drop on step-down converter. The device contents are running on 5V or less and that’s true regardless the supply voltage. So these components don’t produce more heat when device is powered by 48V (or there about). The only difference is the DC-DC step-down converter, the efficiency drops with increasing voltage difference. Since hEX S is passively cooled, one “heater” will cause increase of temperature of all components in the same case, including SFP modules.

3

Thank you for the explenation mkx :smiley: