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[DaveC]

Hi,

In an attempt to tidy up my networking cupboard (and remove three wall-warts), I tried replacing the PSUs for my two HG612 modems and a Netgear 5-port managed switch that sits between them and my router (all require 12V and < 1A) with a 12V/2A barrel connector POE splitter and 3-way adapter cable. 

I have two VDSL lines, which both normally report around 83/23 (max attainable), giving me a line sync speed of the full 80/20.

However, when using this POE splitter - https://www.amazon.co.uk/gp/product/B07TML96C9 - both lines dropped to sync at around 65/16.

I left this installed for a couple  of weeks, wondering if it was just a temporary glitch, but no - it stayed the same speed, and I would get frequent (perhaps once or twice a day) reconnections.

Today I tried a different POE splitter - https://www.amazon.co.uk/gp/product/B08HS4NT13 - and the speeds returned to normal (80/20 line sync)

Putting the other splitter back, and immediately the line speeds dropped again.  New POE splitter: back to 80/20.

Reading the reviews of the first splitter, I came across this review from Germany:

"This PoE splitter should supply my Fritzbox 7490 with Ethernet and power, both are supplied by a Unifi switch. The product produces and transmits interference signals via the power grid, so that DSL connections are disrupted. My own DSL connection and that of a neighbor in the low frequency band were so severely disrupted that after several unsuccessful attempts by Deutsche Telekom, the Federal Network Agency was called on the scene and in the end I identified this device as the cause. Device decommissioned, interference eliminated. "


Anyone come across this type of problem before?

[burakkucat]

How odd. That's the first time I have read of such interference. I presume the injector contains switch-mode circuitry to drop a large input voltage range to a nominal 12V output and that switch-mode circuitry is defective.

If you were not going to send it back for a refund, stating "not fit for purpose", it would be interesting to see what's inside the block.

[DaveC]

Happy to oblige.  Hope these photos show what you're looking for.

[burakkucat]

Thank you. 

I'm quite surprised, as it was not what I was expecting to see! The soldering is clean, the components are clearly marked, the PCB itself tidy. The only deduction I can make is that a poor circuit design has been implemented. A rush to market without adequate testing, maybe?

[DaveC]

Yes, it appears well-made and the power side of it worked fine.  I have another one in my loft powering a 4G router, and am not noticing any problems with it in that scenario.

I'm just happy I have my full sync back now.

[burakkucat]

Just wondering . . .

You attached three devices to it, each device requiring 12V DC at < 1A. That PoE injector splitter is rated as being able to deliver 12V DC at 2A, maximum.

Now 0.75A is < 1A but if all three devices are drawing 0.75A then the total load on the injector splitter would be 2.25A. It might be that the injector splitter becomes noisy when pushed to its limit (or the limit is exceeded). 

[Edited to correct a consistent typo!]

[DaveC]

According to my notes (made from googling this info when considering this option), one HG612 draws "< 6W" and my switch's max consumption is 2.6W.  So if those figures are accurate, a total of < 14.6W, so still well within specs.

I didn't think to try it with a lighter load, but as I'm having success with a different splitter, I don't think I'll bother.

[burakkucat]

So the total load draws < 1.25A.

Understood. Thank you for explaining.

[Alex Atkin UK]

Its only going to be designed expecting a single load so there's no telling what might happen when using it for multiple.  Its not necessarily quite as a simple as "the total load meets spec".

I'd suspect the HG612 was causing noise on the 12V and with several they were all backfeeding noise to each other.  The replacement you are using perhaps is just that bit more stable with better filtering so is somehow overcoming it.

I'd be tempted to just stick a beefy capacitor on it and see if it helped, after checking if its fine with a single HG612 of course.