Print
Category: Hardware
Hits: 15133

Because (nearly) no laptop has a connector for an external WiFi antenna and i couldn't find a 5GHz USB adapter with external antenna connector, i was curious if its possible to power an Ubiquiti Bullet M on the go. After thinking about what battery to use as power source so it fits the PoE specifications, the idea came up to use the laptop-battery, but what in turn would be too much tinkering too. So what connectors are available on a laptop which give at least the power required according to the specs? 

Of Course! USB 2.0 ports give 500mA at 5V. Hopefully this is enough...

Good, back to topic: 802.3af mode B aka "passive PoE"

Wikipedia - Power over Ethernet: Most Passive applications use the pinout of 802.3af mode B - with DC plus on pins 45 and DC minus on 78 (see chart below). Data is then on 12 and 36. This limits operation to 100mb. Gigabit Passive injectors use a transformer on the data pins to allow power and data to share and is typically compatible with 802.3af Mode A. The installer must know the voltage needed by the remote device, and select the power supply correctly. In the common "passive" PoE system the injector does not communicate with the powered device to negotiate its wattage requirements, but merely supplies power at all times. Passive midspan injectors up to 12 ports simplify installations. Devices needing 5 Volts cannot use PoE at 5 V on Ethernet cable beyond about 15 feet (4.6 m) due to IR loss, so a 24 V or 48 V to 5 V DC-DC converter is required at the remote end.[33] 

Well then, according to the Bullet M Specifications:

Power Rating: Up to 24V. Power Method: Passive Power over Ethernet (pairs 4, 5+; 7, 8 return)

So "Up to 24V" seems to tell us that a DC-DC step-down converter is present? And what is the minimum voltage?

Oh, let's just try it! Grab an USB and an Ethernet cable, be careful about the pinout and see if the bullet powers up.

to Bullet:  to Laptop: 

 

 finally connect it:

 

It works! :)

 

Update:

On the web i found shops who sell this cable at incredibly high rates.

It's ridiculous how easy it is to make such a cable... contact me if you need one at a much more cheaper rate (shipping not included, haha).

Item Code: AW-POE-USB

http://www.streakwave.com/itemdesc.asp?ic=AW-POE-USB

http://www.worldeyecam.com/store/aw-poe-usb-usb-power-ethernet-cable.html

 

If you rather would want to power devices with more than 5V, like the Mikrotik RouterBoard SXT 5HPnD i've put in a pot, you might want to read Mobile PoE via USB for devices like Mikrotik Routerboard.