PoE Supply

[vidicam]

Good day all together,
A question about the power supply of a Reolink PoE camera.
You can power this camera with a DC voltage of 12 volts via the DC plug.
You can also power this camera via the LAN cable.
The specification indicates that the PoE standard is 48 volts with the mention "Active"
This voltage is applied across pins 4 and 5 and 7 and 8 return.
What does the statement “Active” mean?
Why is this voltage so high?
Have here an AC power supply from Reolink 100-240 Volt output voltage 56 volts.
Why is this power supply 56 volts?
And can I connect it to my camera without danger.
I find the whole thing very confusing

Regards, adri

 

[TonyR]

In devices that conform to 802.3af/at, "active" means the Powered Device (PD) negotiates with the Power Supply (PSE) to determine how much power it will receive from the PSE.

When a device is "passive", it will receive whatever power is applied to it. The wrong power applied can damage the device.

An 802.3af/at-compliant POE injector or POE switch with a 56 volt max output will not damage a 802.3af/at-compliant camera or device; the device will negotiate and receive the correct voltage which can be at the 56 volt upper level at origin (at the PSE) to help overcome voltage drop (at the PD) due to CAT cable distance and current drawn by the PD.

Lots of info here ==>> Power over Ethernet

 

[vidicam]

Thanks for your reply, it looks like a current source to me
where the current is stabilized and not the voltage
just like the power supply of LEDs

 

[TonyR]

Generally, a device that is passively-powered accepts a voltage range with a specified minimum available current and it draws what it needs, only regulating the incoming voltage to a level needed for its internal circuity. It may also have reverse polarity protection.

It's circuity is relatively simple, making it cheap and efficient......and easily damaged if the wrong passive power supply is connected. Usually, connecting a 24VDC passive POE injector to a passive device requiring 48 to 56VDC just won't work and no damage is incurred but the opposite is not true. Many Ubiquiti, TP-LINK, MicroTik and other devices are passively-powered by 24VDC and can be damaged with the wrong passive POE injector. Some earlier TP-LINK devices were 12VDC on pins 4/5 (+) and 7/8 (-).

Always best check and re-check the device to be powered and the device supplying the power.

 

[Starglow]

Thanks for your reply, it looks like a current source to me
where the current is stabilized and not the voltage
just like the power supply of LEDs

No. The connected device will draw whatever current it needs from the power supply and no more. As long as the current rating on the power supply is equal to or higher than what the device draws then you're good, but if the current rating of the power supply is less than what the device draws then it's going to overload the power supply. The voltage must be the exact same or within the specified voltage range that the connected device supports. So if your device needs 12 volts and you connect a 16 volt power supply then bad things are going to happen, but if the device is rated for an input voltage range of say 12-18 volts then the 16 volt supply will be fine. The supplied voltage and current capacity of a power supply must be properly matched to support the connected device voltage and current requirements.