[AlmostHuman (OP)]

Hey!

Has anyone worked with power line communication? I need some guidelines on what to look for and what to expect of things available on market.

Lets say that I need to control about 100 different appliances connected over 1000 meters long powerline. Laying new wires is not an option. Preferred solution is power line communication.

Is this possible with x10 home automation devices?

Thank you!

[CliffordK]

Is that 1000 meters total?  Or 1000 meters between devices?

That seems awfully ambitious. 

Have you considered wireless?  If you have several "nodes" that are separated by a km or so, but have "line of sight", then you could set up wireless bridges.

Or, if it is all within a single building, wireless still might be an option.

[AlmostHuman (OP)]

1000 meters total. Wireless is pretty expensive, so I opted for power line comm.

To be exact, this is about street light control. So, about 30 to 50 lamps distributed over a 1000 meters. Every lamp has 2 modes, so it is about 60 to 100 outputs to be controlled. Wireless is nice, but I don't need that kind of comfort .


Thank you

[AlmostHuman (OP)]

Anyone?

[techmind]

I believe that the off-the-shelf powerline data-comms units designed for home-broadband distribution will have a range limted to 50 metres or so (although it will depend significantly on the wiring). But these are designed for high data rates (Mbps) whereas for controlling streetlights the data rate you need is miniscule. As a general rule, low data-rate comms can be carried over long distances (or with weaker signals) much more easily than high data-rate systems.

I suspect a proprietary powerline comms system (or some specialised off-the-shelf system designed for this type of application) could meet your requirements.


I presume you are hoping to use existing mains wiring. Can you be sure that a single cable joins all the lamps? If the lamps just get wired into the local mains-distribution (as I believe happens in the UK) then the signal paths and other appliances on the wire (potentially loading or interfering with the signal) could be a show-stopper.

[AlmostHuman (OP)]

Thank you techmind. Just a simple communication is needed, and the only showstopper left is... Well I can't find off-the-shelf simple comm device.

Everything I stumbled upon was for home use (1000 ft max), so I couldn't take it seriously.

Thank you, again!

PS If anyone have links to products I could consider, I'd be happy to have them . Development platforms are welcome as well. Thank you!

[Geezer]

You might take a look at this. These things use two-way communication, but I'm really not sure how they do it.

http://en.wikipedia.org/wiki/Smart_meter

I have a sneaky suspicion that an over-the-wire solution will end up looking very similar to a radio solution in terms of cost and complexity, but that's just my guess.

[AlmostHuman (OP)]

@Geezer

Your suspicion is a lot more than suspicion

[CliffordK]

A couple of weeks ago, someone from the power company came to my house to do an evaluation for meter upgrades.

I asked about smart meters, and they said that they were considering wireless networking rather than power line networking.  I would imagine that either way, they will end up with a lot of hubs and relays as "line of sight" gets broken up pretty badly.  But, it should save significantly on the meter reading, and give me a stimulus to recharge my EV at off-peak hours.

As far as smart street lights.  You might evaluate your goals.

Are they all wired in a string, or does each light connect independently to the main power?

If you have strings of lights, then you would likely turn them all on and off at the same time, and would treat several as a group.

If you want to know when a bulb goes out.  Then, measure the power consumption of the whole string.  If the string goes out of spec, then you have a problem, and need to check the lights.

You said 30 to 50 devices. 
What is your budget per device?
$100?  $500?

For wireless, Cisco is pretty expensive, but you might be able to find Linksys or similar wireless routers/bridges.  And, they should be able to act as signal relays or boosters.  You wouldn't need to go any faster than 802.11b (11 mbps).  For 10+ yr old technology, there should be quite a few available on E-Bay or at your local computer recycler.

Linksys might be interesting because the routers run on Linux.  I.E.  They might be able to be able to be manipulated as mini-computers, or perhaps you could select a small single board computer and add a wireless card to get full featured computing.

Your problem is...  if you had 1000 lights, you could afford to do customization.  But, your system is small enough that a lot of custom development would be prohibitive.  That is, unless you end up with a marketable product.

[Geezer]

Ahem!

We had an RF AMR (Automatic Meter Reading) module that used one entire transistor to transmit, and receive! The range was quite enough for "drive by" reading, although the "intelligence" was a bit limited.

Not only that, but the battery operated versions (for water and gas) had a demonstrated minimum life of ten years (no kidding).

[CliffordK]

Yeah,

The added all that automated stuff when I was in St. Louis. 

Then the Power company decided to shut off my power (despite the power bill being paid a couple of months in advance).  Then they started charging an estimated billing because I wasn't using enough power (after they had disconnected my power).

The Gas company also started charging estimated billing because I wasn't using enough gas.  Then, they sent a technician out to check the meter, check the seals, and run a sniffer around the pipes to verify that they hadn't been messed with.  Then, they didn't believe their own technician's reading, and refused to credit the amount overpaid, and continued to charge an estimated reading since the usage was low.

I believe that at least the gas company is setup so they don't have to do drivebys, but rather use wireless hubs controlled through the central office, so they get readings several times a day (which they refuse to trust).

-----------------

One other thought about the electric power networking.

Does the system go through different transformers.  I'm doubtful you would get a clean transmission through a transformer.  That would be a blessing and a curse.  It would naturally isolate different segments of your net.  It might allow you to decrease the range of individual components.  But, you would need to bridge between the transformers somehow.

This is probably why the power company doesn't like networking their meters over the power lines.

If everything is on the same side of a single transformer, you might just try it out.  The ranges listed might be a little conservative...  you said 1000 feet, and you need about 3000 feet.

Can you set up multiple subnets?

Say from A-->B-->C
Then from C-->D-->E

Using C as a bridge.

[Geezer]

Yeah,

The added all that automated stuff when I was in St. Louis. 

Then the Power company decided to shut off my power (despite the power bill being paid a couple of months in advance).  Then they started charging an estimated billing because I wasn't using enough power (after they had disconnected my power).

The Gas company also started charging estimated billing because I wasn't using enough gas.  Then, they sent a technician out to check the meter, check the seals, and run a sniffer around the pipes to verify that they hadn't been messed with.  Then, they didn't believe their own technician's reading, and refused to credit the amount overpaid, and continued to charge an estimated reading since the usage was low.

I believe that at least the gas company is setup so they don't have to do drivebys, but rather use wireless hubs controlled through the central office, so they get readings several times a day (which they refuse to trust).

Oh dear! I can assure you I had nothing to do with that, although I was involved in certain goings-on in Pittsburgh, but it's probably best if we don't go into that [].

We've had a driveby electric meter here for at least ten years, and it seems to do work just fine. (The propane comes in a tanker truck, and the water isn't metered (yet).)

[SeanB]

Here labour is still cheaper than automation, and meters are expensive. The regular reading also detects tampering.

As to street lighting, there are various options.

You can use a series setup where you pass a constant current though a wire and each lamp is designed to use a specific current, normally 6.6A. The lights have a failure mechanism that shorts the bulb, keeping the circuit intact. You do need a constant current transformer, and the voltage applied can be over 10kV at the supply end. Not used as new any more, but a lot of them are around. Control is from either a single photocell or a time switch next to the regulator

Otherwise you have a parallel system, where each individual lamp is run on either 120, 230, 277 or 400V, depending on the country and method of supply. You can have a dedicated wire for lamps, with a photocell or time switch acting as a group control, or each fixture will have it's own photocell, and be connected to the regular mains supply cabling.

Mains signalling is easy, if you want to do a simple system you just have to send audio tones ( normally around 10W via an isolating transformer and a pair of low value capacitors to both provide isolation and make a high pass filter) onto the mains, and at each point you recover the audio frequency and detect it to operate a switch. This is what X10 is, at least from the power line interface side. You could use X10 modules ( cheap and already type approved) and a few X10 range extenders if you go too far. Allows simple signalling, and does not generate too much interference. If you have a 3 phase or split phase supply there are X10 bridges to repeat the signal across the phases, and these can be very useful.

[Geezer]

That sounds like a pretty good solution Sean. What sort of distance can you get by injecting a 10W audio tone?

[syhprum]

We had this audio on power line system in Maidstone when I was a boy but I think it has long since gone, I think the power required would be quite high as the amplitude of the super imposed tone was about ten percent of the regular supply voltage.

[CliffordK]

Good point that you only need a very crude signal.  So, no need to fully support networking, if the signal required is just a few commands.

Lamp On Dim
Lamp On High
Lamp Off
(and perhaps an Error response).

A little more complex if individual lamps are treated independently.

"Tones" are regularly used as test equipment, and I believe are generally low power.  I have ones that can plug into either phone lines, or even one to plug into 110V power lines, but unfortunately no digital detector or frequency detector. 

It might be a problem if there was bleed-over into residential systems.

Transformers on the grid will likely isolate the signals and limit their scope.

[Geezer]

Of course, if the distribution for the lighting system was independent of everything else, you could transmit the power as high frequency "squarish" waves and PWM them to send the control signals.

That's how this works http://en.wikipedia.org/wiki/Digital_Command_Control

[CliffordK]

Geezer,

Are you sure you don't work in Military Procurement?

AlmostHuman is looking for ways to save power and money.  And, you come up with rebuilding the entire electrical grid.

How many devices are line frequency dependent?  Older mechanical clocks?  Analog TVs?  I presume most of the new digital equipment run independent of the line frequency.

[Geezer]

Are you sure you don't work in Military Procurement?

Oh no, I'm really only interested in World domination.

Mind you, it does bring up an interesting question. What would happen if we actually did transmit power with higher frequency squarish waves? DC would probably be best for the long haul stuff, but there might actually be some advantages for local distribution. I should probably start another thread!

[SeanB]

Geezer, depends on where the first transformer is, as this will pretty much stop it going further upstream. It was used years ago to control street lights from a central control, bu injecting the tone into the high voltage system ( although at a much higher power as you were injecting into 33kV or more) and providing some oil filled capacitors at the substations to pass the tone through to the detector, before the transformer.

In a long line you would simply place a choke in the supply side ( if you want, as the supply transformer will do the same) and inject. The tone will be detectable to the end of the line, at least a kilometer or two if you use a tone of around 1kHz or so.

Injecting a 1kHz tone onto an active phone line is detectable for kilometers without doing anything more than coming close to the line with the detector. Works on any POTS line, though you do have issues with data lines that might take exception to the source and not work properly for data, though the tone is there if somewhat noisy.