Thursday, April 8, 2010

3G Microcell + PoE

I've blogged before about my attempts to get a PoE solution set up for the Microcell. The idea is that all of the network infrastructure in the garage is on a UPS, so it would be good to have the Microcell get its power that way as well. I tried making my own PoE breakout cable. It gave the appearance of working, but when the Microcell got to the point where it normally would start working, it just never came up all the way. There was no error indication on the front panel, it just wouldn't work. My guess is that somehow the transmitter caused enough voltage drop to screw it up. But I wasn't actually using the OEM power supply.

Well, long story short, I bought a passive PoE injector/splitter block off eBay, and it arrived today. Unlike my solution, it had the correct connector on it to use the OEM power supply out in the garage. I'm not sure if that made the difference, or maybe their wiring is somehow better, but it works perfectly. You can buy them here.

I didn't have much hope for the passive solution, so while I was at it, I bought a used DLink DWL-P200 PoE injector/splitter kit. Unlike the passive solution, this one is 802.3af compliant, which may give it more margin against voltage drop (since 802.3af uses a 48 volt supply voltage instead of just passing along the OEM supply's 12 volts).

UPDATE The DLink DWL-P200 arrived today, and it too works perfectly with the Microcell. My guess is that the DLink is the better solution, since it uses a higher voltage down the Ethernet wiring, with signaling between the two ends to enable the supply voltage, which offers some protection to all the devices involved. It also means that the supply voltage going to the device is better regulated than when the power supply was on the other end of 50 feet of twisted pair. The downside, of course, is that the DLink DWL-P200 is much more expensive than the passive solution. Though I was able to get a used set on eBay for cheap. Oh, and it turns out the DWL-P200 is not 802.3af compliant, since it actually pre-dates the 802.3af spec. Still, the higher voltage feeding into a low voltage regulator is likely to work better over long lines.


Andy said...

So is this using the AT&T Microcell? Are you using the AC adapter that came with the Microcell to connect to your UPS in the garage? Did you end up using the Dlink kit or does the passive (ebay link) work for you? How long is your ethernet cable carrying the power?

Nick said...

This is, indeed, the AT&T 3G Microcell. At the moment, I'm using the passive kit from eBay with its original AC adapter. That combination works. The DLink kit, I believe, should arrive today, so I'll update this post with those results. The Ethernet runs from the back of the garage to the distribution point near the front, then under the house to the kitchen. I'm going to guess that in total it's somewhere between 50 and 75 linear feet long.

Aron said...

Nick, I'm not sure that it would help in your setup, but it looks like the DWL-P50 is 802.3af compliant so it should play well with a PoE Ethernet switch.

I just got my MicroCell and need to move it to a more central location so I'm going to order the DWL-P50 and see what happens with it and my PoE switch.

Todd said...

So, does the microcell work with POE? I want to put mine somewhere that i dont have an outlet.

Nick said...

It's been a while since I had one, but I did use one with PoE for a while. The problem was that the Microcell didn't work very well in general, and trying to diagnose problematic hardware with unsupported power supplies isn't a great idea.

Of course, with the supplied power brick the problems remained, so that is suggestive that PoE was not causing any problems.

Just make sure your alternative power infrastructure can supply the correct voltage for the microcell and sufficient current.