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Power over Ethernet Hub
This document describes a very rudimentary change to an ordinary hub in order to allow for very simple PowerOverEthernet (PoE) use.
Note that this method is NOT according to the (still in draft) 803.11af specification as power is applied regardless of what is plugged in. The specification dictates that one should measure first and establish if the device is PoE capable prior to applying the power. The hack below does not do that.
This means that plugging in a non PoE device may damage either that device, your hub or blow up your hubs power supply. This is in particular the case for any 'proper' 802.11 device; which has the mandated resistor terminating pin 4,5,7 and 8. When plugged into this hub there will be a current through the terminator; which quite possibly is harmful; especially when applied over longer periods of time. The low cost ethernet cards (and hubs) do typically not have those terminators.
This disclaimer and license applies to the information which follows. So do not complain if this blows up your house, computer or sets fire to your desk. The author however does use this method to power several soekris net4521 boxes while they are being configured.
Essentially almost all low cost Hubs and Switches for 10Mbit and 10/100Mbit have nothing connected to pin 4,5 and 7,8; the PoE pins. If your hub is of this type; and its power supply is rated at 7.5 volt DC or more; you are in luck. You may/will propably also need to connect a bigger adaptor; as it will need to provide a few extra watts (5-7 watt for the soekris).
Take the hub apart. It should look somewhat like this:
Next verify that for each of the UTP sockets pin 4,5,7 and 8 are not connected to anything. You will need an ohm meter for this.
When this is not the case; solder some wires to pin 4,5 and 7,8; crossconnecting each (refer to this diagram if needed.
Then solder these wires to a convenient place. In this case we take the 48Volt elco which sits atop the power supply and after the fuse. The elco also has a convenient polarity marking; and the fuse will now also protect our PoE setup. Do note that with the PoE device your hub will draw several watts more than normal. The fuse may not be able to handle that.
And that is it.
This is NOT, repeat, NOT, a 803.11af compliant power supply; but instead a simple hack which will directly apply a voltage to pin 4,5,7 and 8. Unlike a compliant power supply this method may well blow up any non PoE device you plug into it.
And although the information containted herein is under this license and provided AS-IS with no warranty whatsoever - please do contact firstname.lastname@example.org if you have *any* addition or find any faults in the above. As it may prevent some one else their equipment from blowing up.