RJ45 with integrated magnetics - different configurations

[T3sl4co1l]

Why they didn't also swap 3 and 6, who knows.

Tim

[peter-h]

More like somebody had 10 million PCBs made with the wrong pinout

[ajb]

That weirdo crossed over connector doesn't make sense for ethernet.  Any relatively modern PHY won't care about polarity within the pairs, and the 4/5 and 7/8 pairs aren't used in 10/100, so why bother crossing them at all?  Unless it's gigE, which certainly wouldn't care about pair polarity.  Maybe some sort of non-standard PoE, and it was easier to manufacturer the connector symmetrically and swap both outside pairs?

There are plenty of other uses for 8P8C connectors, like RS485, RS232, etc, so I would guess it's for something like that.  Maybe a console connection where someone forgot to swap the DTE/DCE ends between two designs?

[ajb]

For actual intended POE, the RJ45 is a different P/N anyway. It contains diodes and other stuff, IIRC.

The only necessary difference between a magjack that can be used for PoE and one that can't (aside from the termination difference that you've noted) is that for PoE you need access to the line-side center taps on the transformer (and the unused pairs if it's not a gigE part).  I suppose there's no fundamental reason you couldn't include the rectifiers in the magjack as well, but I don't recall ever seeing that.  Unless you mean TVS diodes, which, same situation--possible, but I don't think it's common.

If you had a product with both PoE and non-PoE variants, the easiest solution is probable to use the same PoE-compatible magjack on both and make all of the other parts DNI.  Or use a PoE module that plugs in to the standard board.

[Doctorandus_P]

The only necessary difference between a magjack that can be used for PoE and one that can't  is that for PoE you need access to the line-side center taps on the transformer.

Are you sure about that?
I have never used PoE myself, but I'd guess that the transformer windings must be able to handle the current, and do so without saturating the magnetics.
Core saturation is maybe not a problem, depending on how the transformer is wired, but it must be able to pass the current, so wires must be thick enough.

[peter-h]

Very true about saturation of the ferrite.

In most apps, the current won't be much because at 48V you can power quite a lot of stuff. A typical product might be a VOIP phone or a WIFI AP and they will be drawing a few W max i.e. below 100mA.

[westfw]

VOIP phone or a WIFI AP and they will be drawing a few W max i.e. below 100mA.

That’s very optimistic, since iirc, voip phones of increasing complexity were one of the things that kept the standard pushing up total power delivery up to 60W and more…
The “default” is 15w…

[peter-h]

That 15W has to be dissipated into heat however... I have a SNOM D375 on my desk (just an example; I would not recommend this POS to anybody) which can't be drawing more than a few watts. 60W would "melt" a VOIP phone

[Whales]

Now you have given me mental horrors about fan-forced VOIP phones.


"The outlet air grill has an aiming mechanism just like car AC.  You can point it away from you if it makes you uncomfortable"
"We keep trays under every phone in case the fans seize up and they melt again."
"Most of their processing power is used emulating java 7 inside an embedded web browser"
"No it still can't properly do early media, people have to say hello twice"

[spostma]

a bit late reply, but possibly useful.

As you cannot know in advance whether the uplink switch to be used with passive Poe is surge protected or not,
it could be useful to add a dc power ferrite choke in series with each DC power line insde the passive PoE injector.

After all, the PoE injector should be low-ohmic on DC signals, not on AC.

If you fear EM emission problemss, then a small 22R + 1nF snubber would be enough to suppress power supply emissions IMHO.

[hedley]

My company spent months trying to resolve the following issue - 10/100 ethernet worked fine on our new board . When we connected to POE or POE + ,  the link became unreliable after 50 meters of cat5e cable between edge device and POE switch . On board we have a WE 749012011 POE lan transformer . After 6 months of head scratching , pcb layout changes , specking to Wurth locally and in Germany ,  we had a response from an WE- FAE in Japan - " just flip the transformer so the common mode chokes are on the PHY side , and not the lan side,  as shown in many app notes and datasheets - Problem solved and we have 1000's of units in the field BUT I have no idea why it worked.

[peter-h]

You must have been using an RJ45 without integrated magnetics.

[Nominal Animal]

we had a response from an WE- FAE in Japan - " just flip the transformer so the common mode chokes are on the PHY side , and not the lan side,  as shown in many app notes and datasheets

Würth's own datasheet (from e.g. mouser.fi) does show the chokes on the PHY side, though.

You must have been using an RJ45 without integrated magnetics.

Sure, but it does illustrate why integrated magnetics are a good thing: one less thing to worry about.

There are, in fact, RJ45 female connectors with integrated magnetics and POE taps, for example Abracon ARJM11xx-114 for 100Base-T and POE+.  Mouser has these in stock for under 3.5€ apiece, and they cost less than the Würth transformer above (at Mouser at least); both having similar current capability (600-720 mA).  I have no idea about the quality or reliability, though, just pointing them out.

[peter-h]

Wurth stuff (German i.e. chinese) is extremely expensive. I doubt anybody uses it in production. Chinese e.g. Hanrun are 1/4 of the price, and then you get counterfeit Hanrun which are half the Hanrun price (but work just fine).

The Abracon ARJM11A1-009-NN-EW2 (£1.61 at Mouser, 1k+) is about 2x the price of a Hanrun HR911105 one which has an identical circuit; that's perhaps the most common non-POE layout around.

These will get blown up by a cheap chinese POE power injector.

The Abracon ARJM11D7-114-AB-EW2 (£1.74 at Mouser, 1k+) should not get blown up.

Personally I would not use Wurth or Abracon due to the price. Both are chinese and rebadged while lifting the buy price about 4x

[Ice-Tea]

Wuerth is expensive but especially so if odering through Farnell or other distris. If you have a decent project and contact them they discount deeply. Obviously not as deep as the chinese but, well, you get what you pay for.

[peter-h]

you get what you pay for.

What would be the benefit of a Wurth versus Hanrun?

I mean, nobody in Germany will be making these. Wurth must be badged chinese product. The only Q is whether it is Hanrun or one of the lesser known ones e.g. Hulyn which are half of the Hanrun price.

I have built boards with Hanrun and Hulyn and all seem to work exactly the same.

[nctnico]

My experience with ethernet connectors is that they may develop contact problems over time. So I like to use connectors from a good brand with a decent layer of gold plating. 99% of problems in a network are due to contact issues.

And for sure Wurth stuff is made in China like anything else but I'd assume there is at least some quality control. In my designs I use a mix of various brands (typically TE, Molex or Wurth). Depending on what is available and pricing.

[Ice-Tea]

you get what you pay for.

What would be the benefit of a Wurth versus Hanrun?

*shrugs*

Consistency of quality? Hi-pot testing that was actually done *and* checked? Gold plating that's actually as thick as what it says on the datasheet? Plastic that's not faul yellow after a year? Local stock? Support? A correct invoice? Someone that understands your language?

All of the above?

The candy the reps something bring you? 

[nctnico]

Haribo macht Vati froh 

[Nominal Animal]

Personally I would not use Wurth or Abracon due to the price.

Me hobbyist caveman.

The Abracon was the cheapest RJ45 with both magnetics and POE+ support that Mouser sells.  I can't see any way to find them at e.g. LCSC, other than checking each of the 2500 or so connectors they have, or by first looking up a manufacturer and part, and then checking if LCSC sells them.  Looking at the 40 or so HanRun RJ45 they do have in stock, HY931147C seems to be the only POE compatible one.  It even includes the full bridge rectifier diodes, although it is probably limited to max. 350 mA (IEEE802.3af).

[JPortici]

you get what you pay for.

What would be the benefit of a Wurth versus Hanrun?

*shrugs*

Consistency of quality? Hi-pot testing that was actually done *and* checked? Gold plating that's actually as thick as what it says on the datasheet? Plastic that's not faul yellow after a year? Local stock? Support? A correct invoice? Someone that understands your language?

All of the above?

The candy the reps something bring you? 

keg of beer! speck!
Though that's the mechanics' Rep.
Our Rep brings us nothing but nagging

[peter-h]

Of course; for low volume I use the usual people like Mouser. But for production they cost too much.

[Siwastaja]

Wurth stuff (German i.e. chinese) is extremely expensive. I doubt anybody uses it in production.

I have used WE stuff small scale because the distributor markup for their parts is generally 3x but WE is willing to sell small quantities directly unlike most other manufacturers, so you easily get the price down by 50-70% by just asking a quote.

For example, power inductors I look at Mouser or Digikey, a Coilcraft part costs 3€ and WE part 6€ @ 1000pcs, but when I do a few clicks on WE website, I get free samples delivered plus a quote for 2.50€ @ 1000pcs, and can also buy just 100.

So clearly the stuff is not expensive, it's just more expensive at distributors.

[Siwastaja]

The candy the reps something bring you? 

This, whenever the rep calls me about the new catalogs, I make sure to remind about the most important thing, because one time he forgot the gummy bears. Next time I was compensated by maybe 20-30 of those small bags.

Unironically, this candy thing alone is a decent reason to design in a WE part. We do design choices for much more arbitrary and meaningless reasons after all.

[langwadt]

Very true about saturation of the ferrite.

afaict the current should mostly cancel except for any difference in resistance of the wires in a pair