Need Help with Passive PoE Splitter

I have bought something similiar to these from eBay Passive PoE Cable Set - CAB-10759 - SparkFun Electronics, can't post the actual eBay link as the listing is no longer on eBay. I am planning to use this with a non-PoE gigabit switch. On the other end, it will be powering a non-PoE IP Camera. However, I am feeling apprehensive and I am not sure if there is something wrong with the set I have.

As we can see the splitter has one 2.1mm DC socket, and 1 rj45 connector. I have tested positive for continuity on the rj45 connector pins 4/5, with the +V on the 2.1mm DC socket. Which means if I applied say 5v on the DC on the 2.1mm socket, wouldn't the voltage enter the port of the router/switch from the rj45 connector, and thus damaging it?

Wouldn't it damage the device at the other end as well, as the voltage is also entering the rj45 port of the device?

I also understand that 100mbps network uses only 2 pairs of wires, and gigabit all 4 pairs of the cat5e cable. So I'm not sure if the set I have was made to use only for 10/100 devices, and that plugging it into a gigabit switch would actually damage it.

Any advice appreciated

OK, this is a "passive splitter".

You must use the same splitter on each end of the Cat 5 cable (that's why they are always sold as a pair). It will intercept the centre pair, so you cannot use it on a Gigabit network. (It will of course, simply default to 100.)

And you will have the full resistance of the Cat 5 cable in series with your 5V supply, which means you will not get 5 V coming out the other end. This sort of arrangement should be used by feeding at least 12 V down the cable and putting a switchmode 5V regulator at the other to get your 5 V and the ground will not match if there is an alternate ground path. These considerations are where "active" PoE comes in.

Byork:
I have tested positive for continuity on the rj45 connector pins 4/5, with the +V on the 2.1mm DC socket. Which means if I applied say 5v on the DC on the 2.1mm socket, wouldn't the voltage enter the port of the router/switch from the rj45 connector, and thus damaging it?

Which RJ45 connector? Pins 4 and 5 on the "RJ-45" plug - the one that connects to your router - certainly should not connect to anything. If they do, the adapter is faulty.

Here's my take on the matter.

Remember this thing comes in a pair, the injector end and the splitter end.

For the INJECTOR end, pairs 4 and 5 which plugs into the switch, are not connected to the barrel connector. The other end for the data cable which runs between the switch and device would have them connected in order to send the power down the connected cable.

On the SPLITTER end it would make sense that they are connected to the end to be plugged into the device in order to power a PoE compliant device. Also, I suppose that there may also be another barrel connector to break out the power should the device be non PoE compliant.

Regarding, GB Ethernet, there are some standards which use all 4 pairs, and another standard where they just use 2 pairs as with 10/100 mbs. I can't remember the names of them, but you should be good with the latter (2 pairs). I would also have a concern with the standard which uses the 4 pairs.

In any case, there may be voltage drops in the cable, depending on the length and current drawn, which is why true PoE devices will work over a wide range of voltages.

Hope this makes sense.

Paul__B:
Which RJ45 connector? Pins 4 and 5 on the "RJ-45" plug - the one that connects to your router - certainly should not connect to anything. If they do, the adapter is faulty.

Paul, that was exactly it, the RJ45 pins 4 and 5 on each end of the splitter itself(not the cat5e cable); the end going into the router, and the end going into the device, are both connected to the external DC input voltage. That's why I was reluctant to use it, esp on a gigabit switch, until I could make very sure.

donovanpl123:
For the INJECTOR end, pairs 4 and 5 which plugs into the switch, are not connected to the barrel connector. The other end for the data cable which runs between the switch and device would have them connected in order to send the power down the connected cable.

On the SPLITTER end it would make sense that they are connected to the end to be plugged into the device in order to power a PoE compliant device. Also, I suppose that there may also be another barrel connector to break out the power should the device be non PoE compliant.

I agree with you that's how the injector part should work, but mine works otherwise as explained above to Paul, which I why I think it's not properly made, or made exclusively for 10/100Mbps networks.

For the "Splitter" end you mentioned, I would think it should not be connected to the external DC power as well, as external power barrel is there to serve its purpose of powering the device.

What made it more confusing was I have been reading reviews, Q&A on Amazon on similar products, and many people were saying they have used it on non-poe gigabit switches and they work, despite the listing description stating for 10/100Mbps networks.

Byork,

I think you are using this one incorrectly. I may be that it is made to be used in a structured cabling system, where you would have female RJ45 ends on both ends of the permanent cabling. On the injector end, you plug the male RJ45 end into the permanent cabling system. Then plug a patch cable into the female end of the injector, which then goes to the switch. To confirm check if there are any connections from the barrel connector to pairs 4 and 5 in the female end. There should be no connections; in that way no power would be sent to the switch.

On the splitter end, you plug the male end into the permanent cabling system, and then plug a patch cable into the female end, which in turn, goes to the device.

Paul is right, with no connections to pairs 4 and 5 on the switch or the device, GB switch will fall back to 10/100 mbs.

Somewhat like this.

donovanpl123:
Somewhat like this.

I don't think the product was intended to be used the way you described, or at least not the one that I purchased according to the original listing. These products usually come in pairs, with one end of the splitter coming with male 2.1mm DC connector, and the other end with a female 2.1mm DC connector.

According to your image both 2.1mms are female, and the splitters are shown intended to be used on PoE enabled devices.

As I mentioned before on both ends of the RJ45 connectors, regardless of the end with the male or female DC connector, their pins 4 & 5 are connected to the DC power. This could have seriously damaged my non-PoE switch and camera. I am most certain now the seller has sent me the incorrect or faulty item from what I intended to purchase according to his listing.

Normally ethernet jacks are isolated, incorporating pulse-transformers to pass the signals
through - its worth checking this of course.

MarkT:
Normally ethernet jacks are isolated, incorporating pulse-transformers to pass the signals
through

Which means you will be connecting the pulse transformer directly across the DC supply.

Note that a "proper" PoE injector uses balanced pulse transformers with the centre tap connected to one of the DC lines so that positive is on one pair and negative on another. And it will ipso facto, work perfectly on Gigabit. :grinning:

Byork:
According to your image both 2.1mms are female, and the splitters are shown intended to be used on PoE enabled devices.

As I mentioned before on both ends of the RJ45 connectors, regardless of the end with the male or female DC connector, their pins 4 & 5 are connected to the DC power.

Byork, the image was created by me by copying the product image from your link just to illustrate the connections. I copied the picture a second time and flipped it to represent the other end (splitter/injector). Hope that's clear. If, indeed, both switch and device were 10/100 mbs, then you could connect as you were going to.

However, because they are GB, then consider implementing the following:

Barrel Connectors
I understand that one has a male and the other a female 2.1mms. The female end would mate with your male power adapter. The male end would plug into your device if you choose.

RJ45 Connectors
Is there a RJ45 plug (male) and a RJ45 jack (female) on the injector and separately on the splitter? If so, then I think I am correct. If so, proceed to check if the pairs 4 and 5 in the RJ45 socket (female) are NOT connected to the barrel connector. If they are not, then I am correct.

Explation
There would be no power connections on the female RJ45 ends. Therefore, connecting patch cables into these and then connecting to your switch/camera would not cause any problems since pairs 4 and 5 are unconnected. On the male RJ45 ends, where the power is connected from the respective barrel connectors to pairs 4 and 5, power would be injected your PERMANENT cable to the other end. I assume that your camera has a DC jack where you would plug the barrel connector on the splitter.

Thanks Mark, Paul.

Donovan thanks, I appreciate you trying to help. I have attached a picture to make things clearer.

If so, proceed to check if the pairs 4 and 5 in the RJ45 socket (female) are NOT connected to the barrel connector. If they are not, then I am correct.

Yes they are connected.

I have triple tested continuity for the connections as drawn in the picture. I believe you will find it fishy too.

Well, if that's so, then it is only meant to work on 10/100 mbs devices.

One wonders though, how PoE is implemented on a GB network.

donovanpl123:
One wonders though, how PoE is implemented on a GB network.

Perfectly easily as I explained in reply #8. Look it up on Google if you choose not to believe me.