Power Over Ethernet for ECI modem

I have an old Openreach ECI modem, can I power it via PoE? Its power supply output says 12V 1A. I'm inspired by this post so I can position my router near the master socket but away from my UPS. (The PoE injector would be on a UPS protected supply.)

Can be done?

I know nothing of PoE, I assume the injector fits between my router and the splitter and only sends power 'one-way' downstream, cos powering an ordinary Ethernet port would fry it, right?

So I just need an injector and that splitter kjwkjw uses? The specs seem to say it does 12V 1A power out.

OTOH I have read people having trouble making a FritzBox router work via PoE as it seems to demand more power than usual during startup. But maybe that's just a Fritz issue and its a full router, not just a modem.

i have never tried it, you would require a POE infector and POE Splitter

the POE splitter will convert the 48v to 12v

have a look at this https://community.fs.com/blog/what-is-poe-splitter-a...

Easy, have been running modem over POE for years. Can either use a kit (https://www.tp-link.com/uk/business-networking/accessory/tl-poe200/#overview) or POE splitter linked to a POE switch. Just need the right size DC plug to fit the modem.

I’ve used the TPLink TP-POE10R splitters to power a variety of things using network PoE over the years. One recent example below.

Just be mindful that these particular splitters from TPLink are not isolated. So it’s possible / probable that the 5V/9V/12vDC selectable output could float above ground. TPLink themselves obscurely warn about it in their docs. See ”warning” from TPLink. I’ve checked the voltage between the negative side of the barrel connector on the setup below and a grounded power socket, and it’s not showing any residual voltage, for what it’s worth.

The gear that I’ve used to power in this way has either been standalone or otherwise isolated and not connected to another power or ground source. Just be mindful with the ECI modem, although in itself it should be isolated from the line side with an isolation transformer in the modem circuitry.

Here’s test bed setup I’ve been using for the past few months that’s powering both a network connected GNSS/GPS base receiver and a fibre to coax converter (the receiving GPS antenna is quite remote - too far for coax due to signal loss - instead its connected at the other end via a matching coax to fibre converter). For ease of connection on the mock-up, the 12VDC power out from the splitter is connected to the power input of both devices via the good old wago terminals on top of the TPLink splitter. Apologies for the slightly untidy wiring, but it is a ‘prototype’ 😎

GNSS Base Receiver test mock-up

Showing reverse side of splitter (this is their latest v5 iteration, for what it’s worth)

In reply to a post by NGDragon:

Easy, have been running modem over POE for years. Can either use a kit (https://www.tp-link.com/uk/business-networking/accessory/tl-poe200/#overview) or POE splitter linked to a POE switch. Just need the right size DC plug to fit the modem.

For a PoE switch, I'm looking at getting a Ubiquity EdgeRouter X. But that's passive so not so good. Its also 24V, these proper injectors are 48V - I think. Anyway there seems to be a question as to how powerful an EdgeRouter is as far as PoE is concerned. I think a proper set may be the better, safer, option.

So why am I reading that a FritzBox router won't startup using PoE? That would be a bit of a better option than using the old modem. Naturally, I can't find the forum posting again. I think it was Italian so may have lost something in Google Translation. But the jist seems to be that the FritzBox was demanding more power on startup than expected, not getting it on PoE and going into an endless startup loop. Does that make sense? I suppose I could try and see - probably with a spare router first though!

Lastly, where do you get the correct DC adaptor and how do you know which one you need? It seems to me every mains adaptor I have is different in some way. I'm always nervous of using the wrong power source on the wrong device. And despite that, I recently killed a radio....

You can’t mix “passive” PoE with “active” 802.3 af / at / bt based kit. They are completely different beasts.

Either find an 802.3 compatible switch or injector to use. I’ve not seen any passive PoE splitters with selectable output DC voltage like the TPLink splitter above.

The Fritz is probably drawing too much power on startup (not out of ordinary) that either the splitter or switch/injector are unable to supply. See power classes of 802.3 PoE below for info:

Summary of PoE Markings

In reply to a post by Pheasant:

Showing reverse side of splitter (this is their latest v5 iteration, for what it’s worth)

Reading the output on that picture and the penny drops. The FritzBox power supply says its output is 12v 2000mA. So the TPLink wouldn't be able to power it, would it? And if so, are there other brands of PoE that could output 12v 2A? Or am I just going to have to use the ECI modem?

Yes the power budget of the TPLink is 12 watts @ 12vdc. Not massive but enough for many applications.

I don’t know of other splitters with higher power outputs off the top of my head. You’ll need to do a bit of research on that.

Also see my note above about the PoE device “classes” (particularly the switch or injector) that is actually supplying the power. It has to be of an equivalent or higher class rating of the splitter to be able to supply enough juice that the splitter is demanding. No point putting an 802.3at or 802.3bt splitter on a lower power output rated 802.3af injector or switch.

Edited by Pheasant (Thu 08-Jul-21 10:13:22)

Rather than mess about with PoE splitters and injectors why not jut use another cable in parallel. You could use Cat5e/6 (2 pair) and push the power down that.

As teh modem will only deliver 80Mbps then it only reuires 2 pairs in a normal Cat5e cable - rewire your link to just use those four and repurpose the other two pairs for power. And using two pairs would mean a lower voltage drop.

Edited by MHC (Thu 08-Jul-21 10:25:48)

If doing that then I wouldn't mess about with twisted pair cabling, but put in a proper multicore power cable. Less chance of nuking stuff too, if someone thinks it's 'just' a data cable.