
PoE for Raspberry Pi for under $2 - albert007_d
http://albert-david.blogspot.com/2019/09/poor-mans-poe-for-raspberry-pi-3-under-2.html
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linker3000
Using a 1N4148 diode for reverse polarity protection might be a bit under-
specced: the Pi-3 + peripherals can draw something near 800mA under heavy load
and the 1N4148 is rated at 300mA max continuous current, 500mA max repetitive
peak. Something like a 1N5817/1N5819 schottky diode would be better - and
maybe a 3A 1N5822 if there's any power-hungry USB peripherals. That buck
converter claims to be good up to 3A.

Ref:
[https://raspberrypi.stackexchange.com/questions/43285/raspbe...](https://raspberrypi.stackexchange.com/questions/43285/raspberry-
pi-3-vs-pi-2-power-consumption-and-heat-dissipation)

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squarefoot
True, and a clear sigh that it was chosen by misinterpreting the data sheet
[1].

The way the author trims the output voltage is also wrong: these small modules
come by default with the trimmer feature enabled, that is, if you need a
voltage different from those written near the pads just leave the pads alone
and use the trimmer. But if you need one of the fixed voltages available, then
before soldering the corresponding pads, the re's a thin track that needs to
be cut in order to disable the trimmer so that a vibration or touching it by
mistake won't affect the output (small trimmers like that one are the weakest
point in every cheapo module). The thin track is just left of the "ADJ" pad;
if you look closely it closes the trimmer pad to make the board adjustable by
default so it has to be cut to use fixed voltages.

Also, the chip used in the regulator module is a MP2315 whose safe input
voltage can be between 4.5 and 24V, which is ok for a 12V input like in the
photos, just to add some data since it wasn't specified.

[1] Never, ever, ever, ever base any project on the absolute maximum ratings
of any part. Especially when they're completely misleading as in this case:
the 2A which the 1n4148 should sustain (it can't) are related to a peak surge
of 1 microsecond, and not even close to the continuous current which is a
fraction of what a Raspberry PI can draw.

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jononor
Has anyone found proper PoE injector/extractors modules that do negotiation
(not passive) at a decent price?

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philcrump
The "DSLRKIT" splitters that are around on Amazon are reasonable in my
experience, although the nominal output voltage varies by upto 10% between
units.

The 802.3at-specced ones are a little more efficient than the af for the same
power draw, I'm using them at home in a couple of applications where I'm
feeding 802.3af but the power budget is cut a little close.

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pwinwood
I would put a suitable USB plug on it rather than wiring to the GPIO pins as I
am certain in a rush I would plug it in wrongly damaging the Pi!

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albert007_d
Thats the reason why diode is used for protecting the non-PoE switch's Port
when raspi is accidentally powered through micro-usb port(or usb-c for pi-4)

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funvill
be careful POE can be anything up to 48 volts. Unless you control the input
voltage. I suggest using a DC-DC converter with a larger input voltage.

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tjoff
It is passive POE, you _need_ to supply your own input as it won't work with a
POE switch or anything like that.

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aaronax
There are some switches that supply passive PoE, such as many of Ubiquiti's
products.

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tjoff
Sure, but you have to explicitly enable it. When would you not have control
over the input?

