Carrier current communication on Low voltage/high current AC

Take a look at how X10 stuff works (at the AC voltage zero crossings). You might be able to adapt some existing chipsets and other hardware.

Just OTTOMH - brute-force baseband (9600 HZ Manchester, DTMF, ?) through a current transformer?

It's just I'm thinking "modulation", with a transmission line impedance of

Good Luck! Rich

Maybe pass the power wire through a low-mu core and inject the signal in series, rather than in parallel? Ditto receive end.

If there are any bridge rectifiers in the system, the line parallel impedance will be modulated by diode conduction!

John

Hello Spehro,

A resonant circuit would make for a smaller device to isolate the RF path. At 50A a choke can become rather bulky.

I would go much lower, below 150kHz, but avoid any Loran ranges. X10 operates on 120kHz and AFAIK they blast several volts onto the mains line.

Stay away from simple AM on-off protocols. That is one of the downsides of X10. It should at least be FM or something even more reliable. Your protocol may have to be fault tolerant against missed or misinterpreted bits. FEC and all that sort of things.

As to receiver filtering you can't use crystals at 9600bps. But LC is pretty stable below 150kHz. Another upside of staying under 150kHz is the abundance of ferrites that are suitable.

Using frequencies that others already have can yield FCC advantages similar to what FDA 510(k) does in medical: Prior art, less scrutiny. The downsides may be patent issues and the like.

Regards, Joerg

Hello Paul,

We have some X10 and I don't find this AM protocol all that reliable. It is also very slow.

Regards, Joerg

"Is also rejected"? Some sort of Royal decree?

John

Maybe think about transmitting the comms as a common-mode voltage. The 24Vac system can be connected to Ground at 60Hz (or have stray-C to ground), just devise something that makes that connection a high impedance at (and above) the comms carrier frequency.

That's one of three possibilities of selecting two of three terminals for the signal transmission , but for some reason it is forbidden for safety reasons. Also, the current carrier method of inducing a signal via transformer with secondary in series with line is also rejected- probably too much bulk required there.

I like it better than that execrable term "deemed".

Best regards, Spehro Pefhany

-- "it's the network..." "The Journey is the reward" snipped-for-privacy@interlog.com Info for manufacturers:

The one I hate is "good engineering practice" which usually means "I always do it that way but can't actually explain why."

John

I use the term "good engineering practice" to indicate to the client that, if they'd done it my way, they wouldn't be in ka-ka-land right now ;-)

...Jim Thompson

I should have added... I told a client more than two weeks ago, "your design failed because....".

They vehemently denied it could happen, that I was totally wrong, how could I be so wrong, all their simulations showed it was stable, etc.

Guess who's kissing my ass today ?:-)

...Jim Thompson

Or they just don't like the looks of something innovative, therefore it doesn't conform to "good engineering practice".

Best regards, Spehro Pefhany

The only problem is that you can't gloat and rub it in, it drives the clients away.

So all I can do is laugh with the wife over a glass of wine ;-)

...Jim Thompson

How about using the GND and Neutral? No series inductors needed, and no line voltage to worry about.

The GND and neutral are joined at the source, so the driver has to deliver current into a short circuit. A few dozen feet of wire will give enough impedance to develop a useful signal.

Hot +-------------------- Black ------------------+

Carrier current often uses wideband FM to reduce noise. The frequencies may be around 300KHz or so.

In fact, now that I think of it, I may have a use for this. Thanks!

Mike Monett

. * L1 50A,60Hz * L2 . +-----/////---+----+---->--------+--/////----+ . 60Hz supply ===== | '--||--, | ===== Load . +-----/////-------+-------+--+------/////----+ . * | | oops! | | * . C1=== | | ===C2 . | | | | . Tx Rx .

What about high-frequency capacitive loading by other stuff that's plugged into the AC mains? Another thing, L1 would have to be a big beast, handling the entire AC main branch.

Right. You can prove that you're smarter than them, or you can get repeat business, but not both.

John

Speff said it was 'low voltage' which doesn't sound 'utility' to me; I got the impression it might be some 'private' low-voltage system. And you can slip a split-core ferrite over even an insulated conductor.

A low-mu core with a high-ratio winding, resonated on the primary, clamped with a couple of zeners, won't have any spike problems. Making a voltage connection into a utility line takes about as many resonating and transient protection components.

Agree on that one. FSK or PSK makes more sense.

John

Except for needing four windings in series with the 50-amp circuit. Those will be huge transformers and nasty connections.

Why not

| tx | | rx | | | | | +---/////---+ +---/////---+

where the trannies are 1-turn primaries, just cores slipped over the insulated power conductors?

John

That should work nicely, of course one of the advantages of getting the frequency up is to use a smaller inductor. It's almost into reasonable air-core range, which could be helpful at one end.

I keep thinking I'm missing some obvious possibility with those chokes, but maybe not.

Best regards, Spehro Pefhany