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zl4dk's picture
I want to run my nanostation from a battery supply for portable use. I see from the documentation that it uses passive POE and should be happy with 10.5 through to 25Vdc at the port, so as long as the ethernet lead is short I should be able to poke 12v up the right wires and all should work. I wonder if there is a preferred way to do this more elegantly. Is a current limiting circuit recommended? or is a 1A fuse protection enough? I wonder what others have done and are there any good or more importantly bad experiences with this.

WU2S's picture
Do not exceed 24 VDC
Do not exceed 24 VDC at the Ethernet port. There are a great variety of passive POE injectors in use. You can find them in eBay,Amazon and from the major vendor like Streakwave, Flytec Computers and many others. Some are short pigatails about 6 inches long and another type is the small plastci block with 2 Ethernet ports and a barrel jack for power input. Some of the later come with multiple in/out Ethernet ports in mltiples of 4, 6 and 8.
I have used a variety of these injectors with success at 12 VDC over Ethernet cables as long as 125 feet.
kg9dw's picture
yes do fuse!
Hi David -

Yes, you want to put a fuse in the circuit. I'm running other gear at my solar/battery site so I have 10 amp fuses. 

battery -> fuse -> wire to passive POE injector -> outdoor, shielded CAT5 to device

I've used these from eBay:

Good luck! MB
K6OQK's picture

A 10 Amp fuse at the battery to the main 12 Volt feeder may be fine, but I'd suggest a much smaller fuse, maybe 1 or 1.5 Amp at the individual POE injector input.  I'm pretty new to the Ubiquity world, but as I understand, they draw about 800 ma or less, depending on power.  Hopefully someone more knowledgeable than I will chime in on this.

Burt, K6OQK

kg9dw's picture
My experience has been that they draw less than an amp. (400mA if memory serves with a 5GHz nanobridge at max power)

You have to ask what you're protecting with the fuse. You aren't protecting the equipment. You can't "force" too much current into the radio. The purpose of the fuse is to protect the wiring and to keep the battery from blowing up. 
We1btv's picture
Not just the battery. Especially the cables behind the fuse. You don’t want to replace a fried cable in the mast during bad weather. As an electrical maintenance engineer I have seen people making this mistake more then once, using fuses to big... Not just on AWG 24 but also on AWG 4/0 and bigger. :-)

kg9dw's picture
Sure. That's why in my post I
Sure. That's why in my post I said the wiring and the battery. 
That's correct, I measured
That's correct, I measured about 350mA being pulled from a 2S Lipo(7.4V). So even a 1/2 amp fuse should work.
k1ky's picture
I have measured 480ma on AirRouters @ 5 Volts
I have measured around 480 ma on AirRouters @ 5 Volts - general rule of thumb fuse at double the average current draw for low current. 1/2 amp on the above situation may be a bit low as you don't know what the startup current needs might be.
zl4dk's picture
Thanks for the comments. Those injectors look good. I have managed to find a source with free shipping so have ordered a couple.


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