Is it safe to use a 40v 20w PoE injector to power a 12v 5w camera ?

A

Albert Muda

n3wb
Mar 7, 2017
10
0
Well, the title says it all: Is it safe to use a 40v 20w PoE injector to power a 12v 5w camera ?

Something in me tells me a power source that emits 40v could break a device that wants only 12v.

On the other hand, something tells me the power source could maybe adjust to deliver just what's needed.

Can you help with that ?
 
Albert Muda said:
Well, the title says it all: Is it safe to use a 40v 20w PoE injector to power a 12v 5w camera ?

Something in me tells me a power source that emits 40v could break a device that wants only 12v.

On the other hand, something tells me the power source could maybe adjust to deliver just what's needed.

Can you help with that ?
Click to expand...
post a link to the injector you are referencing.
 
Albert Muda said:
Well, the title says it all: Is it safe to use a 40v 20w PoE injector to power a 12v 5w camera ?

Something in me tells me a power source that emits 40v could break a device that wants only 12v.

On the other hand, something tells me the power source could maybe adjust to deliver just what's needed.

Can you help with that ?
Click to expand...
PoE will not deliver any voltage if no PoE negociation is done so using a PoE splitter only on your camera's side will not bring any power to it.

"Real" PoE is very specific and need both Switch AND Camera to be able to handle it and "talk" PoE to each other (well in fact it's only the camera that talk to PoE switch to tell which power/voltage it requires).
 
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Albert Muda said:
For example, this: Avaya 1151D1 Specs

It's normally used to power a phone.
Click to expand...

You have to know a few thing about the whole "PoE" thing because you have :

  1. Real both-end PoE with PoE switch and PoE camera and as @fenderman said it is managed thru 802.3 or 802.3af protocol (rememeber I told you the camera need to "talk" to the PoE source before it deliver any power)
  2. Active PoE Injector in Ethernet cable if you have a normal switch (not PoE) but you want to "inject" true PoE to your device connected at the end of Ethernet cable and may be it is what your Avaya 1151D1 do but I am not 100% sure as it's tech spec do no mention anything about 802.3 so it may be a pure 40V injector (and anyway 40V is not not 48V so it is definitely not a 802.3 compliant power injector) and whenever it may not power up your 12V camera that is not 802.3 PoE so the pair of wire inside Ethernet cable that transport the power are certainely not wired inside the camera so it may just be uneffective.
  3. "Passive" power injector (and I said "power" not "PoE") that is done using an Ethernet cablr splitter both sides or an Ethernet connector "bridge" box thet you connect Ethernet cable coming from you normal non-PoE swicth that inject for example 12V and then you connect an other Ethernet cable to this brodge and at the end you use an Ethernet splitter that will separate into Ethernet plug and Jack 5.5 connector that will go into you 12V non-PoE camera.

Here is a small picture of those different "PoE" approach we start with the Passive basic power injection inside the Ethernet cabel, the most used solution to power most 12V Cameras

upload_2017-3-20_21-50-51.png
Here we have a mixed solution that can convert 48V from a real PoE switch to provide 12/9/5V to non PoE device using standard 5.5 Jack Power plug :

upload_2017-3-20_21-52-32.png
This is a real PoE injector that will proide 802.3 complaint PoE :
375-75W-Gigabit-PoE-Injector-right.png


Those are only a few examples
 
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Albert Muda said:
OK, much clearer. Thx.

So, it seems this piece is not PoE. This article reads "commonly used to power IP phones where PoE is not available": What is Power over Ethernet (PoE)?.
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That's it ! so you may simply use the 12V power supply of your camera and a pair PoE splitters to inject the 12V on one side near the switch and extract it on the other side into the 5.5 jack power plug of the camera.
 
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Dodutils said:
Here is a small picture of those different "PoE" approach we start with the Passive basic power injection inside the Ethernet cabel, the most used solution to power most 12V Cameras
Click to expand...
I'd strongly suggest that you don't promote 'passive PoE' as being able to operate over 130 feet - that's very optimistic - especially with no specs on wire gauge in the cable or power load of the camera and its IR. People have seen problems with lengths of a few 10s of feet.
And what makes you believe it's "the most used solution to power most 12V Cameras" ?
 
alastairstevenson said:
I'd strongly suggest that you don't promote 'passive PoE' as being able to operate over 130 feet - that's very optimistic - especially with no specs on wire gauge in the cable or power load of the camera and its IR. People have seen problems with lengths of a few 10s of feet.
And what makes you believe it's "the most used solution to power most 12V Cameras" ?
Click to expand...
I do not promote anything I only show examples of different existing methods to make him understand difference between all those PoE and so-called PoE.

But talking about it passive injection is no problem as you can use higher voltage power for example 24V and use a DC Buck provide only 12V to the camera, that's what I do for example to provide power to RasPi across passive PoE injection thru 150ft cable except that I use a 12V power suppply and then use a DC Buck (based on LM2596 or XL4005 for example) to lower voltage down to 5V so whenever only 9V reach the end of the cable it is still enought to provide 5V.

Also some cameras can work with lower than 12V so the PoE injection loss may not be a problem but there is also the Amps question especially if the camera uses IR LED.

The "cleanest" solution (with no "surprise") if you do not have 802.3 PoE camera complant is a 802.3 PoE transformer you connect at the end of the cable that can provide 12V from the 48V PoE as showed in my second example but it requires a PoE switch.
 
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