There seem to be jumpers to connect POE into the RaspberryPi. I have a case with two little fans which are meant to connect to the GPIO. I think they could be connected to the pins of the POE but I would like to know if this is likely to cause problems. I don't want to use POE.
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If you want to "close" this Question, please read this. If an answer isn't "selected", your Q will stay in the Zombie Box & come back to haunt us for years. – Seamus Jun 14 '20 at 20:16
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POE voltage range is 37 to 57 V. Unless your fans support such high voltages, there's no point in connecting them there.
If you don't connect your Pi to a POE source, then there will be no substantial voltage on the POE header, and the fans will also not work.
Dmitry Grigoryev
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The PoE "implementation" on RPi (3B+ & 4B) is a bit of a sham IMHO. I say this because the necessary hardware is not included.
As a practical matter, wrt powering your fans you would need to do a fair amount of work to use the power. POE is governed by a rather complex group of standards and specifications. Delivery of power to the RPi's terminals would need to be negotiated with the upstream POE provider. Strictly as a personal viewpoint, requiring a "HAT" to use POE on a Raspberry Pi strikes me as some type of a joke - but personal viewpoints aside, in your case I'd opine there are better and easier (certainly less expensive) methods to power a fan.
If you want a more practical way to power your fan, this question has been asked and answered here, and in a variety of blog posts - for example.
If this doesn't fully address your question, please let us know.
Seamus
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I wasn't clear. There are four jumpers associated with POE. I wondered if two of them had 5 Volts on them that I could tap onto to power my fans. My case is a bit of a tight fit and I can't put a meter on them. – Mjp Jun 10 '20 at 22:39
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@Mjp: I would guess No, but that would only be a guess. I'd suggest you read this answer, and make a comment to the author (Peter Green) - he seems to know something about this! – Seamus Jun 10 '20 at 23:19
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