All commercial POE products I have seen feature DC current to power endpoint devices. What are the reason(s) why AC is not used for POE products?
Electrical – Power over Ethernet: AC
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All commercial POE products I have seen feature DC current to power endpoint devices. What are the reason(s) why AC is not used for POE products?
Best Answer
AC is only 70.7% as efficient as DC at transferring power at a given peak Voltage. That is, to provide the same power as 48V DC, you would need 48/.707=68 V peak-to-peak.
Sure, you could increase the voltage, but the PoE voltage is specified at 48V to avoid electrical shock, as dry human skin begins to break down and conduct at about 48V. This is why the plain old telephone system (POTS) over Copper wire was 48V as well.
Another reason is that you don't want AC to couple into your receiver and negatively impact the ability to receive data. Usually DC blocking caps are used to block the DC before the transformer.