hello guys

i've got a vivotek FD6121V ip camera and would like to power it with POE

so i went onto ebay and bought a linksys 12v poe splitter but now know that i need an injector as well to be able to make this work

problem is guys that i'm baffled as the injectors i've seen all say they supply 48v output but the camera only needs 12v so i'm scared i'll frazzle it with one of these injectors

i'm new to POE and cctv in general and just need a bit of info on the correct injector to buy

any help appreciated

thanks lads

Gary

The PoE spec is 48 volts. The vivoteks will handle it just fine.

many thanks Thomas


cheers for taking time out to reply

all the best

Gary

There are 5v, 12v and 48v IP cameras. I know some Axis do 5V and Arecont for example 48V. So If you have camera that needs 12v you need POE 12V Kit or 12V splitter if you power is coming out from PoE Ethernet switch(its 48V).

Most modern PoE equipment will do a handshake to determine what voltage is actually needed. You generally do not need extra equipment.

So, it means that PoE switch will check and supply exactly needed voltage to camera??

No. POE starts off with 48 VDC at the powering end in order to maximize power with minimal losses due to wire resistance. 48 V is chosen based on what is acceptable to apply to this class of wiring.

The recipient of the power at the other end needs to convert whatever voltage is left (after cable losses at the current used) to whatever voltage it needs, up to a max of 13 watts.

If that device is a POE-compatible camera such as an Arecont it will deal with that internally without any user intervention.

If your powered device is not equipped with POE (as per the original post) then you need to use a "power splitter" to extract the power out of the cable and convert it to the exact voltage required by the end use. That's why there is a choice of 5, 12, etc, with a max of 13 watts.

The device supplying power has no idea what you are doing with it, but it will limit its output to 15.4 watts.

If camera is PoE, then you can power it from PoE 48V Switch even camera needs only 12v, it wont damage it. But if device is not PoE, you need splitter to cut off extra and supply exactly 12V.

Am I correct in my understanding? :?:

Yes, the thinking is correct, the exact wording less so.

Voltage is not "cut off," power is converted with minimal losses to the voltage needed at the circuit level. So if the POE can supply 48V at 100mA then the camera may convert that to 5V at up to a bit less than the ideal 960mA. This is the "wonder" of switch-mode power electronics!

A POE camera *not* powered with POE may, or may not, have a wide tolerance for voltage at the separate terminals provided. You have to check the docs.

But, as an example, I think the Arecont 3130 as an example can take anything from 12 to 48 V at the "separate" power input terminals.

So, i can plug 48v PoE switch stright into lets say 12v PoE camera ?

"you have to check docs"

What exactly I should be looking at ?



Is it "Classification" step which checks what voltage needs to be supplied to camera?

I am not trying to confuse any one but this is a good place to post this.


AXIS just came out with some high power midspans and splitters which are rated a 2A @ 12V and 1A @ 24V. So you can now power heaters, blowers, and PTZs with POE.

http://www.axis.com/files/datasheet/ds_high_poe_32463_en_0809_lo.pdf

Absolutely, it doesn't matter what "voltage" the camera uses IF you are using the POE to power it. It knows what to do, it's an IEEE standard.


As I said, only if *not* using the POE. How did you find out it was a "12V" camera? - you checked the docs!

The table you posted are the details of how the POE injector (midspan or POE switch) internally figures out if its safe to apply voltage to the cable. You don't need to worry about that stuff. It's the job of the POE camera to figure out how to power itself off whatever appears on the line.

One thing to note, it's a nitpick, but not all injectors follow the IEEE standard. Almost all of the switches and other hardware will, but there are a number of cheap PoE injectors that do not follow the standard. Easy way to spot them is if they use a pair of injectors, one for power in, and one with a DC cord out.

IEEE placed a standard on PoE. 802.3af and soon 802.3at. With in this standard the medium voltage is 48vdc, with a max of 450mA of power. 802.3at ( PoE Plus) max of 700mA ( which is being debated on).

Also long as the device is a IEEE-802.3af compliant there is no issues wtih power.

A side note, numerous low end PoE switches are not providing enough power to all their ports. Normally a 4 port would need 60 watts of power to be fully compliant, but if you read the actually power for the unit, it about 30 watts, half of what is need.

Just keep in mind about power budgeting.