48v systems - sistemas de 48v

Hi, I’m using Starlink for backhaul on a solar powered node, and Starlink can use 48v passive PoE. So, in order to keep the node as simple as possible, I’d like to use a router that can also use 48v passive PoE or 48v DC barrel plug. Does anyone here have experience with a 48v system? Can you suggest hardware that can run Openwrt and uses 48v?

Saludos. Voy a usar Starlink para la conexión a internet en un nodo con energía solar, y eso funciona con 48v PoE pasivo. Entonces, para mantener el nodo lo más sencillo posible, quiero usar un router que corre Openwrt y que usa 48v. Alguien tiene experiencia pertinente, o puede sugerir hardware?

thanks, gracias,

Perhaps something like this from GL.iNet? GL-B1300 / Convexa-B - GL.iNet

@steve that router looks nice! The specs mentioned lead to another question that’s relevant to many routers: it says “supports 802.3af & 802.3at PoE standards”. I hoped to use passive PoE, which is non-standard. Below is what I’ve found about PoE so far, but I’m still not clear what I can actually do in practice with passive PoE (besides destroying routers by accident).

I intended to keep my node simple by taking wires from the charge controller 48v output (or optionally from the battery, but that would require using a low-power disconnect), wiring it to a barrel connector, and plugging that into a Mikrotik-style gigabit PoE injector.

In terms of power, the Starlink device in non-snow enviroments like mine (tropical rainforest) tends to consume about 50 W (1 A @ 48 V), or if the motors are removed consumes about 25 W (0.5 A @ 48 V). I’m not sure if I’ll remove the motors.

I have read the Wikipedia page about PoE, which explains that 802.3af and 803.2at involve power supply negotiation between the power sourcing equipment (PSE) and the powered device (PD), as described there in the “Stages of powering up a PoE link” table and the " Configuration via Ethernet layer 2 LLDP" section. It mentions that “To retain power, the PD must use at least 5–10 mA for at least 60 ms at a time. If the PD goes more than 400 ms without meeting this requirement, the PSE will consider the device disconnected and, for safety reasons, remove power.

Later, in the “non-standard implementaions” section, it mentions passive PoE, which is what I think I want to do. It says “In a passive PoE system, the injector does not communicate with the powered device to negotiate its voltage or wattage requirements, but merely supplies power at all times. […] Gigabit passive injectors use a transformer on the data pins to allow power and data to share the cable and are typically compatible with 802.3af Mode A.” The modes are explained in the “Powering devices” section. 802.3af gives up to 13 Watts and “in mode A, pins 1 and 2 (pair #2 in T568B wiring) form one side of the 48 V DC, and pins 3 and 6 (pair #3 in T568B) form the other side.

For that GL.iNet router, my challenges are:

  • importing it from another country, because I haven’t found a vendor here in Ecuador.
  • making sure the model I buy has the optional PoE module. (“With optional PoE module, Convexa-B can allow power supply over Ethernet with the existing data connection when you also have 48V PoE injector ready.”)

I found an OpenWRT page that lists all hardware with PoE capability that is also supported by OpenWRT. Perhaps there is a brand there that is available through local suppliers?

@steve yes, I’ve looked at that list too. It’s kind of useful, and also incomplete or inaccurate in some cases. What I’ll look for next is a list of routers that have PoE output of 48v 2A, and that doesn’t exist on the Openwrt ToH.

My core question is whether it makes sense to use passive PoE? Or, in what conditions is passive PoE more practical than standards-based active PoE 802.3af or at?

I was thinking that passive PoE would make the node simpler and save money, but in the end, maybe that’s not true. Maybe there’s a router out there that can receive 12v or 24v input from a charge controller, and output 48v 2A PoE? That could save money, because in general, 12v and 24v systems are much more common than 48v systems, and therefore parts are cheaper.

With a 12v or 24v system I could use a LibreRouter, since it uses 12-32v passive PoE input. It would not provide the PoE output for the Starlink.

If needed, another option is using a DC-DC step-up converter to go from 12-36v up to 48v – there are even guides on how to build such a converter. The important thing is to use good quality equipment that can withstand being in a box in the rainforest.

An example: Mikrotik hEX router limits PoE output at 48v to 450 mA, insufficient for Starlink. Plus it probably doesn’t change the voltage, so if it receives 12v or 24v in, it probably puts that out, but I’m not sure.

Another example: the TP-Link Gigabit passive PoE injector only supports up to 24 Watts, insufficient for Starlink.

I think spending more time looking online at various Starlink setups will probably generate some useful info.

1 Like

I have only ever used passive PoE on smaller devices so can’t offer much insight beyond that.

Have you thought of adding a step down dc-dc converter… they are pretty reliable, widely available, flexible and for the power requirements a router has, quite inexpensive.

I prefer to avoid using a converter, since it adds a new point of failure and makes installation just a little bit more complicated.

However, I’ve searched for converters, either to go from 12v/24v up to 48v, or from 48v down to 12v/24v. I have found only one model that can work for that (step up from 12v or 24v to 48v), and it is much higher capacity than I need (1200 W) so also higher price ($23) and would be less efficient in my case (drawing only 25 W at rest, 90 W at peak), and might even shut off due to low power draw. There are $100+ Victron converters available, but that’s too expensive for this situation. There are many smaller converters that cost between $1-$8, but they do not function in the 48v range.

My ideal is to use a solar charge controller with 48v load output of up to 3 A. This doesn’t exist in the entry-level Victron charge controllers. What they do have is a 12v/24v charge controller with 15 A continuous load. For the Starlink, I would have to couple that with the $23 converter, so not a great result. Victron has a 48v charge controller, but its continuous load output is limited to 1 A, i.e. 48 W, and that isn’t sufficient for peak moments of Starlink plus router.

Alternatively, I could look for a charge controller of a different brand, or some generic charge controller, that has 48v 3+ A continuous load output.

Here’s a table of the converters I found in Ecuador so far: