Are all POE injectors the same?

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kenmasters

n3wb
Aug 31, 2016
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I know there are 802.3af standards, however, are there different POE injectors that have different power specs?

I bought a couple of Duhau IP POE bullet cameras (HFW4431M).. I had a POE injector from Ubiquity laying around. The POE injector says its DC48V 0.5A. The Duhau says it requires DC12V 1A. The injector won't power on the Camera. What could be wrong here? Wrong injector? The camera is brand new and will power on with a normal AC DC adaptor.

thanks
K
 
pschmehl said:
Read this: http://www.cam-it.org/index.php?topic=4261.0

Your camera specs will tell you what voltage it requires over PoE.
Click to expand...

The thread appears to have misinformation and nobody appears to be in consensus. As long as both cam and injector/switch is 802.3af compliant, it should work.. in theory. However, 802.3af is rated at VDC48V 320mA. Where as most cameras require lower voltage but higher power. One person believes that the switch will down convert as required... another person believes its the camera's responsibility to do this. In any case, no definitive answers.
 
if the injector/midspan/switch is 802.3af compliant, it will provide at LEAST 14W @ 48VDC.. which is ~0.30A or 300mA.. your Ubiquiti Injector complies with the power specifications and will adequately power any 802.3af complaint device such as your Camera.. it looks like its powerful enough to be 802.3at complaint as well as 0.5A @ 48V = 24W which is enough for PoE+

internally your camera is going to convert that 48vdc to 12vdc, if that conversion is 100% efficient (which its not, but lets assume it is) you'll get ~1.16A @ 12vdc (14W) after conversion which still meets your camera's published specs.. but really this is irrelevant as if your camera is advertised as 802.3af compliant then it will operate within that 14W envelope, or it is not complaint and should probably be advertised as an PoE+/802.3at device with a higher power envelope to operate within.

some poe injectors and midspans can quite happily provide more power than spec; for the supply side the spec defines minimum power requirements.. I have some PoE 802.3af injectors/midspans that will happily drive 18W, and 802.3at midpsans that will drive 36W, when spec requires only 24W.. but devices on the other end must operate within specified limits to meet compliance.. most cameras I have use 4-5W maximum... its only high powered PTZ's, High powered IR Lighting and WiFi access points that really consume PoE seriously.. even VoIP Phones use only a couple watts.

Remember, Watts/Volts = Amps..
 
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nayr said:
if the injector/midspan/switch is 802.3af compliant, it will provide at LEAST 14W @ 48VDC.. which is ~0.30A or 300mA.. your Ubiquiti Injector complies with the power specifications and will adequately power any 802.3af complaint device such as your Camera.. it looks like its powerful enough to be 802.3at complaint as well as 0.5A @ 48V = 24W which is enough for PoE+

internally your camera is going to convert that 48vdc to 12vdc, if that conversion is 100% efficient (which its not, but lets assume it is) you'll get ~1.16A @ 12vdc (14W) after conversion which still meets your camera's published specs.. but really this is irrelevant as if your camera is advertised as 802.3af compliant then it will operate within that 14W envelope, or it is not complaint and should probably be advertised as an PoE+/802.3at device with a higher power envelope to operate within.

some poe injectors and midspans can quite happily provide more power than spec; for the supply side the spec defines minimum power requirements.. I have some PoE 802.3af injectors/midspans that will happily drive 18W, and 802.3at midpsans that will drive 36W, when spec requires only 24W.. but devices on the other end must operate within specified limits to meet compliance.. most cameras I have use 4-5W maximum... its only high powered PTZ's, High powered IR Lighting and WiFi access points that really consume PoE seriously.. even VoIP Phones use only a couple watts.

Remember, Watts/Volts = Amps..
Click to expand...

All good in theory. But I wouldn't have asked if my Ubitquity injector worked. It doesn't.
 
POE works over the data cable to power your cam. Powering it via 12v works over the 12v connector. There's no need to do any conversions in your head between the two. The camera handles the voltage changes internally and it doesn't matter how the power arrives as long as either the POE specifications match or you're getting 12v to the 12v connector.

It's almost like being confused over how the 12v from your car's battery powers the 2v line out from the radio to your amplifier. Don't overthink it, just make sure that the POE injector matches the POE spec of the camera (802.3af) and everything's good. Even a POE+ injector (802.3at) will power things just fine because it's downwards compatible. Plug a 48v POE camera (802.3af or .3at) into a 24v Ubiquiti POE injector and things won't play nearly as nicely. Just plugging 12v DC into the 12v DC connector to power the cam does the same thing but is a different kettle of fish because the cam does the internal conversions after the power arrives.
 
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kenmasters said:
I know there are 802.3af standards, however, are there different POE injectors that have different power specs?

I bought a couple of Duhau IP POE bullet cameras (HFW4431M).. I had a POE injector from Ubiquity laying around. The POE injector says its DC48V 0.5A. The Duhau says it requires DC12V 1A. The injector won't power on the Camera. What could be wrong here? Wrong injector? The camera is brand new and will power on with a normal AC DC adaptor.

thanks
K
Click to expand...

Which Ubiquity injector is it? The ones I have are all passive POE. If the camera is expecting 802.3af/at, this could be your problem. Do we know if the Dahua IP cameras support passive POE? Active POE devices negotiate which pairs to use for power as well as power requirements. Passive POE is either mode A or mode B, and that refers to the pairs the injectors use for power. I believe passive Ubiquity injectors are mode B. If the cameras are looking for active POE (802.3af/at), the passive injectors will not work.
 
rotorwash said:
Which Ubiquity injector is it? The ones I have are all passive POE. If the camera is expecting 802.3af/at, this could be your problem. Do we know if the Dahua IP cameras support passive POE? Active POE devices negotiate which pairs to use for power as well as power requirements. Passive POE is either mode A or mode B, and that refers to the pairs the injectors use for power. I believe passive Ubiquity injectors are mode B. If the cameras are looking for active POE (802.3af/at), the passive injectors will not work.
Click to expand...

PoE mandates the device work with A or B. It is the switch/midspan that can choose which implementation it uses. There is a basic level of negotiation that happens with a fully compliant PoE setup that you don't get with a passive injector. Some cameras can't cope with that. An example would be newer Axis cameras. They boot up and then look at the PoE hardware to see what power level has been negotiated. If no negotiation has occurred (passive injector) they just shut back down again. That becomes a problem when you want to test them on an old Cisco 3550 series switch, because while it supplies power it's pre-standard and doesn't negotiate.

I ran some March Networks, Bosch & Hik cameras on a completely passive setup (2 power supplies wired in series to give ~48V) and they ran just fine. I borrowed some Ubiquity cameras from a mate to test and they wouldn't work with anything but their own proprietary injector, and that injector wouldn't run anything else (it was some bastardized 24V setup). At least your injector is 48V, but it's likely it has the polarity wrong or something non-standards compliant.

It's all fun until it doesn't work :)
 
rotorwash said:
Which Ubiquity injector is it? The ones I have are all passive POE. If the camera is expecting 802.3af/at, this could be your problem. Do we know if the Dahua IP cameras support passive POE? Active POE devices negotiate which pairs to use for power as well as power requirements. Passive POE is either mode A or mode B, and that refers to the pairs the injectors use for power. I believe passive Ubiquity injectors are mode B. If the cameras are looking for active POE (802.3af/at), the passive injectors will not work.
Click to expand...


I am not sure if this is a passive or active injector. It says "switching mode power supply" at the back. Model # GP-A240-050. Output 24V 0.5A +4,5pins -78pins.

It would make sense that there are two types of injectors.
 
if its outputting 24v its not 802.3af, its a pripotary Ubiquiti Passive PoE module.. its only going to work on Ubiquiti gear and should never be used for anything else or you risk damage.

there's many types of PoE implementations, stick with 802.3af/at devices only and you'll avoid much headache and heartbreak... PoE is a generic term and does not signify anything really other than power is somehow provided in parallel with data.. so always verify the PoE implementation before plugging devices together, or the magic smoke may be released.
 
kenmasters said:
I am not sure if this is a passive or active injector. It says "switching mode power supply" at the back. Model # GP-A240-050. Output 24V 0.5A +4,5pins -78pins.
Click to expand...

I think we've found the problem...

edit: where did the 48v come from that was mentioned in the first post??
 
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Kawboy12R said:
I think we've found the problem...

edit: where did the 48v come from that was mentioned in the first post??
Click to expand...


Thats my bad. For some reason I thought it was 48V. I guess that's the magic number. I waiting on a few more injectors to arrive to try again.
 
Let us know if the camera and injector both still work. I've heard cautions about mixing them but never known a first hand story.
 
Ive got a couple dead Ubiquiti access point here that somehow got 48v off a power device it shouldn't have.. but thats double its rated voltage and sure to puff, undervolting it if it's using the same polarity should not really damage anything.. hopefully.

supposedly if I crack these open and replace burnt out diode the'll work again.. just havent had the time to try.
 
The camera didn't go up in smoke when using a 24V ubiquity injector. But not sure if the same would happen if you use 48V injector on an Ubiquity device.
 
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