PoE recommendations for System Blue
(2016-09-25, 18:23)allsorts Wrote: Unfortunately even though it powered up it's not a workable PoE solution. The noise was horrendous, one channel was permanently over the 120 mV trigger level! I also think that the system crashed when I tried to change from manual to automatic.

Not being one to give up easily and having solved or come to conclusions on the action required for the noise problems decided to revisit the TL-POE10R PoE splitter. Prised the case apart (four broad clips about 1/8" from the ends on the long sides). The pass through ethernet (all four pairs) is galvanicly isolated with a HST-24001SCR 1:1 isolator. Couldn't quite work out what was going on on the DC side. I don't think it is truly isolated but there is some separation. Pretty sure the output ground is not directly connected to the DC-DC convertor ground. The output has a 470 uF electrolytic capaciitor across it.

Anyway used the TL-POE10R to power the system and it was just as bad as before. 'Scope showed strange wave form of about 100 mV p-p and a frequency of about 40 kHz on the power supply rails. During my research into noise I'd come across RichoAnd's power supply filter (https://forum.blitzortung.org/showthread.php?tid=1802).

Having a couple of unknown ferrite toroids(*) and small reel of enameled copper wire wound 60 turns around each one (40 mm dia 5x5 mm cross section approx). Popped those in series with each power leg and most of the horrible noise had gone. The system wasn't happy though, roughly every second it would register a "strike" and there would be a simultaneous burst of noise on the power supply rails. Adding a 0.1 uF capacitor across the output side of the two toroids, cleaned things up even further and the rogue "strikes" disappeared.

System still not happy though but then it was only getting 4.2 to 4.3 V. The wire I used for the toroid windings was not very thick and there was a drop of about 0.5 V across each one. I didn't find the load resistor did anything useful other than get warm and ensure that the PoE splitter started up if the system board was disconnected.

So I reckon that the TL-POE10R with addition of a less lashed up filter can be used to power a System Blue from proper PoE. This is very much a "works for me" using the non grounded Phihong PoE injector. If anyone else has a play I think it would be wise to check that there are no out of spec voltages or voltages between parts that shouldn't have voltages.

(*) Yeah, I know I said I didn't have any toroids in my "Aerials and Chasing Noise" post. I only have 2 not 3 and I like the KISS approach of a plain multi-turn loops. Smile

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RE: PoE recommendations for System Blue - by allsorts - 2016-09-29, 23:08

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