OT: Question about voltage drops using POE on DIY home routers

Just finished troubleshooting a diy outdoor wifi ap setup using home routers that are powered via diy poe.

12v is the stock adaptor.
Before i did the poe setup i tested the device (xiaomi router) using a 9v adaptor from a tplink router. it was stable for 1week. So i was confident the even with the voltage drop using poe the device would function fine at 9v.

But upon installion the device was not stable. sometimes its ok but most of the time its not.
Now i tested load voltage at the end of a long utp at it was just barely 9v (analog tester).
So using 12v adaptor as poe is still not stable.

Question is would it be safe to use a 24v adaptor?
15v adapter are kinda rare and a bit expensive (2x price of 24v).
I need to keep costs down as much as possible.


This depends heavily on the used voltage regulator inside your device.

What device do you have?
Do you know the used voltage regulator or do you have a hig res pic of the mainboard which shows the voltage regulator?


with step down module... more voltage... less loss

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Perhaps your 12v adapter does not have enough amperage for all those routers. What is the voltage at the output of the adapter when all the routers are connected?

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Would that would cost more?
I would need to buy a higher voltage adaptor and a step down circuit.

Its just 1 ap. Imo not using multiple device on a single adaptor.

= less cost

That looks like a Mi R4 Gb. The voltage regulators are the three tiny 6 pin chips next to the "4R7" inductors. I can't really see the numbers on mine.

If you're using more than 20 or 30 meters of cable I'd suggest going to a 48 volt system with a step-down converter at the router end. Or something that is purpose-built for PoE and outdoor use in the first place, such as the Nanostation AC loco.

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So its not safe to supply 24volts?
Even if voltage drops to 21v due to wire length?

Doing 48v with a converter at the end is costly i was figuring out a way to minimized additional expenses.

I think im gonna use this. Cost about 0.5 usd each.
With this i can still use the stock adaptor.
And in the future install only requires a short utp (with poe) this wont be needed as i have tested the device is stable on 9volts.
*Im setting up a mesh network. Some with outdoor ap (diy ap inside a waterproof box)

Ill just try to measure load voltage on the ends and just adjust the boost voltage.

What ia the voltage and Current ratings if your router and Power Supply. How long is your LAN cable.

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Stock adaptor of router is 12v 1a.
Cable length is around 35meters more or less.

You should try a 12V 2.5A power supply.

would that help?
using a watt meter i can wattage of device is around 3.8w idle
peaks at 5w max.

There could be transients that you can't detect with a meter.

5W at 9Volts is 0.5A approx and your cable is 15 Ohms so that's another 4 Watts for a total of 9Watts and your power supply is only good for 12Watts on paper.