PoE recommendations for System Blue
#1
I've just received my System Blue kit which I'm in the process of assembling. I'm currently thinking to power it using PoE as I then only have to deal with running Ethernet cable to wherever I host the system. I'm therefore looking for a PoE injector/splitter pair, ideally 802.3af compliant.

I've seen there's a cheap TP-Link combo comprising a TL-POE150S & TL-POE10R however I've seen reports that this splitter is not galvanically isolated. Would this be a problem given it won't be connected to anything else to create a ground loop? (The problem I've commonly seen is powering a Raspberry Pi using this splitter and then connecting it via HDMI to a TV)

Has anyone else used PoE for powering their system and have any recommendations?
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#2
I am planning to use this passive PoE, works with 10/100 Mbps since there are only 2 pairs of wires for the data.

https://www.adafruit.com/product/435

I made a 2.1mm DC barrel plug to USB mini adapter to use with it.

I then got this power supply and bought the extra plugs to get the 2.1mm I needed.

http://www.powerstream.com/AC-1898.htm

That power supply is nice since you can increase the voltage in small steps, 5v, 6v, 6.5v, 7v, which will allow you to overcome the voltage drop caused by the Ethernet cable.

Currently the system is in my basement, I plan to run the Ethernet cable in the future and put the system in my garage.

I don't expect any issues.
Kevin McCormick KB0UOI
Macomb, IL USA
Stations: 1539
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#3
I'm using the TL-POE10R to power a TL-MR3020 and 4G dongle as a backup internet connection. Works fine but nothing is grounded at the far end. Reading around this forum it seems that providing a good ground to the main unit improves performance.

I've also heard about problems with the TL-POE10R and Raspberry Pi's connected to TVs but I'm not clear as to what the problem is. I just spent a merry 10 mins trying to find any DC paths between any wire and any other wire on my TL-POE10R and didn't find any. So there is no obvious "earth loop".

I don't use the TL-POE150S injector but a Phihong POE16R-1AFG (http://www.phihong.co.uk/product/poe16r-...t-phihong/). I like these units as they are a single box solution, not a two box (wall wart and injector) one. I suspect my Blue System will be placed in a remote location and using PoE makes doing that very simple.With the TL-POE10R available for GBP9.99 from Maplin (in the UK) not overly expensive.

Passive PoE, hum well, it works but it's horribly easy to accidentally plug something onto a "live" cable and damage that device. Cheap LED ethernet cable testers really don't like 12 V @ 1 A... B-)

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Cheers
Dave.
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#4
If you are worried about plugging stuff in accidentally, then use different colored cables, put heat shrink color, or colored electrical tape on cable that has passive POE.

In the case of the Adafruit passive PoE you have adapters at each end, so unless you unplug from the adapter and then plug the cable in to device can you cause damage.

In my case the far end will only have the Blitzortung detector, so not too worried about confusion.
Kevin McCormick KB0UOI
Macomb, IL USA
Stations: 1539
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#5
Different coloured cables are OK for a working system and no pressure changes. Not so good when you are chasing a fault and concentrating on that. It was fault finding on newly installed fixed cabling that led to my cheapy tester getting 12 V up it.

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Cheers
Dave.
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#6
(2016-09-04, 21:14)Allsorts Wrote: I don't use the TL-POE150S injector but a Phihong POE16R-1AFG (http://www.phihong.co.uk/product/poe16r-...t-phihong/). I like these units as they are a single box solution, not a two box (wall wart and injector) one. I suspect my Blue System will be placed in a remote location and using PoE makes doing that very simple.With the TL-POE10R available for GBP9.99 from Maplin (in the UK) not overly expensive.

Well my Blue system arrived a few days ago and is temporally setup. Been chasing a noise source that occurs every 25 kHz up the band on a HF communications receiver. Tracked down to a poor quality USB power supply, have selected the best I have but with the H-Field loops (38 cm 20 turn) connected the noise floor is around 50 mV mostly of this interference instead of the 20 mV or so of "just noise" with the antennae disconnected. Further work required probably involving a battery to confirm "silent" noise levels with antenna conecceted.

Probably wanting to use PoE I also tried the above combination of splitter and injector. It powered up and worked, with no measurable voltage between the chassis/ground of the controller board and the house supply earth. I suspect that issue of the spliter not being isolated only rears it's head when the power source feeding it is grounded. The Phihong injector is not grounded, so the supply is floating with respect to ground.

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.
Cheers
Dave.

Stations: 1627
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#7
(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
Cheers
Dave.

Stations: 1627
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#8
Back again...

Bought another TL-POE10R and capacitors (2 x 0.1 uF 50 V ceramic, 1 x 100uF 25 V electrolytic) from Maplin, the caps take the purchase into the free P&P range. Chokes from Amazon but an add on item that has gone up 50p each since I bought mine, 220 uH, 4A and made made up a small PCB(*) to mount them on. Works a dream. Smile

'Scope images, input has  just over 100 mV of noise as before, output less than 10 mV of ripple. Both images taken with the 'scope set at 20 mV/div and 2 ms/div. Controller is now reporting a much healthier 4.9 Volts input and is quite happy. No noticeable noise being received either. There are still some quite large spikes/dips that follow the GPS LED and RJ45 data LED flashes but nothing seems to be objecting. I did try adding another 100 uF of capacitance on the filter output, made no real difference. Circuit is chokes in series with each power line, 0.1 uF across the input and output sides of the chokes and the 100 uF across the output side.

Checked for voltages between house supply earth and the 0 V rail, 38 V 50 Hz. Very variable and joining the two together through an ammeter gave a whole 20 uA of current flow and the volts disappeared, not going to worry about that. Worth bearing in mind and checking out if the PoE injector used is earthed (mine isn't). Adding the ground connection didn't make any difference to received noise levels, whether it improves signals is for later.

(*) I actually made two boards. It was going to be four as that is how many fit across the bottom of a sheet of "press 'n peel" but the guillotine found it harder to cut than I expected... A PDF of the layout is attached. The board is symmetrical, there is provision for 2 components across each side of the chokes. When fitting the chokes try and work out which wire is the "start" and put that in the same shaped pad for each choke. In theory any stray magnetic fields from the chokes cancel rather than couple.

The second board is drilled but not cleaned and up for grabs.


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.pdf   PSU_Filter_PCB.pdf (Size: 11.97 KB / Downloads: 11)
Cheers
Dave.

Stations: 1627
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#9
"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."

:-)  The reason for this resistor is to give the switch-mode power supply a resistive load.
In a switch-mode powersupply there are a resonant circuit. If this is loaded by an inductor with a high Q, it can interfere with the circuit and change the frequency so that considerable circuit becomes inefficient and generates a lot of noise.
I have seen noise signals from the power cable due to standing waves in the cable.
One can also say that the resistance terminating the cable.

I always have an oscilloscope turned on when I testing electronics.
When the oscilloscope is not used, the probes just lying loose in the vicinity, and there I discover if there suddenly is a radiation - have seen it many times (of cource, I have worked with high frequency in more than 50 years)

/Richo

P.S. By the way - it's a good solution you made
Stations: 584, 585, 1570
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#10
(2016-10-08, 15:56)RichoAnd Wrote: In a switch-mode powersupply there are a resonant circuit. If this is loaded by an inductor with a high Q, it can interfere with the circuit and change the frequency so that considerable circuit becomes inefficient and generates a lot of noise.

This PoE splitter doesn't need any help to make noise. Here is its output when loaded only by a 100R resistor. Slightly lower in level but it's only got a 50 mA load, the other image was taken with the 350 mA or so of a Blue controller as load.

(2016-10-08, 15:56)RichoAnd Wrote: P.S. By the way - it's a good solution you made

Thank you. I could have used a bit of strip board but wanted to play with the press 'n peel. Only the second time I've used it, came out much better. Dust between the board and film when doing the transfer is not good. As to the board, the thermals around the pads etc are too narrow at 0.01" and right on the edge of the press 'n peel resolution. Learning all the time. Smile


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Dave.

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