Passive POE options

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Joined: 27 Jan 2016
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PostPosted: Wed Jan 27, 2016 13:01    Post subject: Passive POE options Reply with quote
I thought I'll share my experience with Passive-POE (feeding power remotely to the device on the unused pairs of the ethernet wire, typically with a little adapter) with several TP-Link products (WA5210, WA7210, WA7510, WA701 and even SC3230 webcams)

This is what I've seen so far:

1. Some products come Passive-POE ready and typically include a separate litte POE injector box or connections on the power brick (like on some Ubiquiti units) while others supposely do not support POE at all. If the LAN port has all the 8 pins, then POE should be possible.

2. Voltage needs vary wildly between devices: 5V, 9V, 12V, 15V, 24V etc., with varying currents 500mA, 750mA, 1A, 2A, etc.

3. All ethernet wires have electrical resistance... some more others less depending on the quality of the copper. On longer cable runs (typically 50+ feet), some devices will not get the full voltage and will typically boot... some LEDS light up... and as soon as the radio turns on drawing extra power... voltage falls and the unit resets... over and over again. From the original 12V I've seen the TP-Link TL-WA5210G fall to 8~9V which causes constant rebooting.

This is what I had to do:

1. Decide on a standard voltage for everything: 24V. The higher voltage, the better. Active or "real" POE is 48V.

2. Get just one 90-250VAC-24VDC adaptor to feed all your devices together. You'll have to add all the currents (say 500mA + 750mA + 1A + 1A + 250mA = 3.5A) and just get a 5Amp supply to have room to grow. I have even used laptop's power bricks which are typically 19.5V and several Amps. Think about plugging this 24V supply into an UPS.

3. Inject 24V to all your POE devices either using the included adapters (like TP-Link has) or making your own with RJ45 jacks or a dedicated 1U 24 x RJ45 rack patch panel. You'll have to know which pairs have TX and RX signals and which to + and - of the 24V supply. In Amazon search for "passive 24v POE injector" for already-made units.

4. Install DC-DC regulators in ALL units that require less than 24V. Some Ubiquiti units do not need any changes. All TP-Links I have are 5V, 9V or 12V and thus require DC-DC stepdown regulation.
- The regulators could be the cheap analog LM78xx series 3-pin chips (replace the xx with the voltage... 05, 09, 12, 15, etc.) for US$1 + a heat disipator and a few capacitors or a more expensive but efficient DC-DC switching regulator for US$5-10 with + a tiny heat disipator and a few capacitors.
- They can be installed inside the unit (obviously taking the cover apart and soldering some wires on the PCB) or outside with couple ethernet jacks or even a special ethernet adapter cable with the regulator mounted inside a tiny project box. Look for "passive poe injector splitter" in Amazon... you'll only need to cut the power supply wire and just solder the inline regulator on these.
- None of my units have any warranty left so I do not care about opening up the units and hacking the PCB inside and thus not needing external special splitters and such.

5. If things are done correctly, the original power jacks on the units do not get disabled at all so you can ALWAYS use the unit with the included factory 5, 9 or 12V power brick.

6. On external/outdoor and specially on roof/tower-mounted units, ALWAYS connect the grounding terminal either through a separate wire or using the drain wire on a shielded ethernet cable. On TP-Link units, grounding provides 4 kV lighting and/or 10 kV static (ESD) protection.

I've been running several TP-Link TL-WA5210 and TL-SC3230 IP cameras with integrated 12V regulators for almost 3 years without ANY problems at all. Those cheap LM7812 12V regulators can regulate from 14V up to +35V and always give exactly 12V +/- 0.1V to the unit. Some of these units are at the end of 210+ ft (70+ m) of wire where the original 24V drops to ~18V (with +25% voltage loss) and the regulator still mantains exactly 12V inside the unit. My grounding wires ARE ALL connected and the units survive frequent semi-tropical storms. Of course, a direct lightning hit will melt your antenna, roof supports, grounding wires and your precious Point-to-point CPE.

If anyone is interested, I can draw up some diagrams but everything is online. You can even buy adapters for "real" 48V POE to passive POE... nothing new or exotic.
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