A simple solution for HomePlug problems
Posted on 10 Dec 2012 at 09:18
Paul Ockenden helps a reader suffering from interference on his powerline networking kit
Many of the things I write about in this column are inspired by emails that I receive from readers, messages you send me via the various social media networks or the comment threads and forums on this website. It’s a formula that’s always served me well, but this column was decidedly less electronically inspired – what follows is the result of being accosted while queuing for what passes as a latte in a well-known American coffee chain.
There I was, minding my own business and awaiting my pint of four-shot, low-fat brown liquid when suddenly an irate man came up and started berating me, accusing me of writing rubbish in this column. There was no "Excuse me, are you the chap who writes for PC Pro?"; no "I wonder if you could help me with something that you wrote about?". He went straight into a mega-rant about how I’d recommended powerline networking as a good alternative to Wi-Fi, and how he’d gone out and bought the kit on my recommendation, yet it hadn’t worked.
As soon as some of the heavy plant fired up, the HomePlugs lost their signal
I’ll have to admit that my first instinct was "this bloke’s a nutter". But it turns out my ranty man wasn’t like that at all. Beneath the red face and close-to-exploding neck veins, he was actually quite rational – and genuinely quite upset.
It turns out he runs a small factory-cum-workshop housed in an ancient building, and over the years he’s struggled with data networking. Since he only leases the property he isn’t allowed to drill holes in the walls and ceilings to install a wired network, and since these walls are really thick, Wi-Fi reception is fairly flaky. He’d read my advice about using HomePlug kit in such situations and then spent several days tearing his hair out being unable to make it work.
At this point I did what any self-respecting coward would do – rather than stand up to his insults and defend my advice, I offered to pay for his coffee, sat down and chatted through his problems. (I almost ordered him a decaf; I was worried that a couple of shots of espresso might set him off again – luckily, he remained calm.) He explained how he is sporadically upgrading the various moulding and milling machines in his factory, and that the newer models almost always need some form of data network connection, without which he has to run around the factory plugging a laptop into each machine in turn to download designs – hardly a productive way to work.
After a few minutes chatting to him, his problem became obvious – or rather, I thought it did. His factory was fed by a three-phase supply and so if different bits of kit were plugged in on different floors of the building, they’d probably turn out to be on different phases. Just in case you don’t know, the 240V mains electricity supply to your home is probably 120 degrees (one-third of a cycle) out of phase with your neighbour’s supply, and a further 120 degrees from the house next door to them. There are numerous generation and transmission benefits to running a three-phase system in this way. But although domestic properties and small offices will be fed by a single one of these phases, larger offices and factories typically take a feed from all three of the phases – in fact, much factory machinery (and on the IT side, many big UPS units) require three-phase current.
HomePlug in the office
Since HomePlug was primarily designed to be used in the home (it says so on the tin), there isn’t usually anything in the manual to warn you that the system won’t work in a building with more than one mains phase. The problem is that the three phases are usually quite separate, with no physical connection between them within the building, so if you impose a HomePlug signal onto one of the phases, it can’t be heard on either of the other two. I explained all of this patiently to my now-calmer companion, and he went away to experiment with plugging his HomePlug units into different sockets. Phew, another happy reader!
Well, actually, no – because this story has a part two. I bumped into the same chap a couple of days later and he said he was still having problems: all of his powerline networking adapters were now on the same phase, and when the factory shut down he could communicate between his CAD suite and the workshop machine controllers. But as soon as some of the heavy plant fired up, the HomePlugs lost their signal. It was immediately obvious to us both that the problem was mains-borne noise, and that perhaps HomePlug units weren’t the right solution for him.
By pure luck, though, that very morning – honestly, I’m not making this up – a parcel had arrived from the nice people at Solwise, containing a sample pair of its new SmartLink-based powerline networking adapters, which are designed specifically for noisy environments such as his. The NET-PL-500AV-SMT adapters, to give them their full name, use a relatively new chipset from Atheros that’s designed to combat noisy mains.
Where a normal HomePlug unit transmits signals via the live and neutral wires within the mains cable, these new SmartLink adapters can switch to employ live and earth instead. The live wire (or "line" for our international readers) is always going to be noisy in a factory environment, but the earth wire will often be a little quieter than neutral. The switching is done automatically – there’s no need to configure anything.
To be honest, I was a little sceptical – surely the things are still connected to the live wire, and that’s still going to be crackling with noise – but my new-found friend and his factory would give me the opportunity to do a proper real-world test on these units. And you know what? Much to my surprise, they did make a difference. It isn’t a complete solution – throughput still dropped whenever the machines started up – but the SmartLink units at least kept the connections alive rather than dropping them.
We discovered that, although these units can talk to other HomePlug AV adapters, to use their Smart Link feature you need all the adapters in the network to support it: as soon as you introduce one non-SmartLink device it seems to lock all of the adapters into using live and neutral. This wasn’t exactly clear from the documentation, but knowing how the units work it’s hardly a surprise.
I normally like to give products and services a real-world workout, but this turned out to be a bit more real-world than normal, all thanks to an encounter with a red-faced man in a coffee shop. Finally, just so that you don’t think I’m being mean, I should end by telling you that I’ve shown him this part of the column and he laughed, saying he’s more than happy for me to print the story exactly as written, so long as I don’t mention him by name. What a great sport!
How does HomePlug work exactly?
I tried HomePlug in my not-so-big apartment (80 m2) and even there it was absolute rubbish. It worked OK-ish within the living room but of course wifi works great there as well! I then tried connecting the bedroom but signal quality was non existent. I was then told (by our IT manager) that HomePlug doesn't work between "breakers" (not sure about the English term here). Where I live (the Netherlands) eletricity is set up in a lot of different "breaker groups" - 1 for the living room, 1 for the bedroom, 1 for the bathroom, etc - and since these "breaker groups" are not electrically connected here is no way for HomePlug to work across them.
I then Googled some and even found a HomePlug device which should be integrated between the "breaker system" and your mains access. Apparently it then manages communication between HomePlug devices in various "breaker groups" within your property. However, with some fiddling I was actually able to get a connection from bed to living rooms, but signal strength seemed exceptionally low (and the rooms are within 10m of eachother) and it was unusable.
Mr. Ockenden, do you know anything about the electrical side of this networking system? Seems there are all sorts of stories going around, but that nobody has the full knowledge to definitively say when HomePlug will work and when it won't.
By TheoB on 10 Dec 2012
Homeplug devices work best if on the same circuit, but they should also work OK on different circuits (or 'breakers' to use your terminology) within the same house or appartment. At least, the's the case with UK wiring - I can't believe things are that much different in NL?
It's not an exact science though - it'll always depend to a large degree on the quality of the wiring within your home. If there are breaks in one of the rings, for example, it can have a big impact on homeplug performance.
By PaulOckenden on 10 Dec 2012
Thanks for the fast reply :) Would hope that wiring is the same everywhere but since they can't even agree on socket lay-outs...I have no idea to be honest.
Anyway, I live in an 8-year old apartment so wiring quality should be decent. I did actually hear that lower quality would make HomePlug work better since there is more "leakage" between circuits? But I guess that would mainly cause interference?
I think it's important to note that the "stated speeds" are only attainable in perfect conditions. If you are working across circuits could it help to use higher rated plugs? Or will the maximum attainable speed be the same no matter the plug, due to physical constraints of the electrical system?
By TheoB on 10 Dec 2012
I would employ an electrician to carry out a earth loop impedance test to check that the earthing is up to scratch as if the earthing is poor that maybe of issue.
What may help is to employ Screened shielded twisted pair patch cables from the home plug to the kit, this may improve the data rates.
By Chrisfjr1300 on 10 Dec 2012
The 'stated speed' is pure marketing BS. Just like the stated speed with Wi-Fi, ADSL, etc. etc.
And faster on the box doesn't always mean faster in the real world. For example, 500Mbps homeplugs will very often be faster than 1Gbps units.
But with homeplug especially, the topology of your home wiring will have a big impact on the maximum throughput.
By PaulOckenden on 10 Dec 2012
@Chris, for normal homeplug units the Earth quality won't (or rather shouldn't) make any difference, as the signal is across the L+N lines. It's only with these newer SmartLink devices that the devices can (optionally) use Earth rather than Neutral.
By PaulOckenden on 10 Dec 2012
Thanks, Paul :) I actually tried the 300Mbps version since "that should be plenty" (my wife bought them and listened to the sales rep...).
Does seem that for streaming video etc good old fashioned ethernet is still required! Now if I could only get my wife to not mind the cables ran through the hallway ;)
By TheoB on 10 Dec 2012
Sorry Paul I did not make myself clear, there maybe a earthing issue "at factory-cum-workshop housed in an ancient building"
As this type of homeplug uses the earth instead to reduce noise, IMHO the earthing may need attention.
By Chrisfjr1300 on 10 Dec 2012
I have it working in Germany (Netgear AV 300mbps) and the signal is good enough at the moment.
I was getting around 12kbps (yes kbps, not mbps) from my 802.11n wifi between the router and my office (around 5M). Putting in the Netgear mains networking means that I get "more than" 3mbps (my DSL speed).
I'll be upgrading to 35mbps fibre in January, so I'll see whether the HomePlug gets good throughput or not, or whether I will have to start running CAT5e cable around the house (my fiance is moaning that syncing her laptop with the NAS takes forever (around 12 days for our 40GB photo collection), she can't actually open files on the NAS. When she wants something, I have to take the laptop down to the router and connect it by cable.
If the HomePlug is good enough for the new broadband, then I'll get another one for upstairs.
By big_D on 10 Dec 2012
@TheoB; If the circuit breakers include RCD protection, that might explain the problem. RCDs have a sensing coil that measures the difference between the current flow in the Live and Return wires, and if there is more than 30mA difference,the breaker trips. This coil is essentially an inductor, whose impedance (i.e. resistance to alternating current) will increase with signal frequency. The effect of this tiny inductor will be minimal at 50 Hz, but might be huge at Ethernet frequencies.
By ewenflint1 on 2 Jan 2013
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