How to power a Raspberry Pi 3/4 over an Ethernet cable (up to 100 m) using passive PoE — with off-the-shelf parts costing under ~$2.
Complete setup — Raspberry Pi powered over Ethernet via passive PoE.
Warning: This uses passive PoE with T568B wiring:
- Blue / Blue-White → + (positive) terminal of DC supply
- Brown-White / Brown → − (negative) terminal of DC supply
If you don't know what passive PoE is, do not proceed — buy a proper PoE HAT instead.
Parts needed
1. PoE injector cable (~$0.80)
PoE injector cable — splits power and data onto the Ethernet cable.
Connector detail of the PoE injector cable.
Wiring detail of the PoE injector cable.
2. DC-DC buck converter (~$0.50) — look for Hesai brand on AliExpress, 12–24 V input, 5 V / 3 A output.
DC-DC buck converter — 12–24 V input to 5 V / 3 A output.
Assembly
3. Solder jumper wires — Cut female-to-female jumper wire into 4 pieces and solder to the buck converter as shown:
Jumper wires soldered to the DC-DC buck converter.
Wiring diagram — connecting the buck converter to the PoE splitter.
4. Heatshrink and connect — Cover the DC-DC converter in a heatshrink sleeve and connect to the Raspberry Pi:
DC-DC converter in heatshrink sleeve, connected to the Raspberry Pi.
5. Final setup — Feed 12 V DC and network into the PoE injector, then run a CAT-5 cable (up to 100 m) between the injector and the Raspberry Pi:
Complete setup — 12 V DC + network through PoE injector to Raspberry Pi over CAT-5.
