Southern Electric "Cost Monitor" RF clamp meter

[Tim S]

Anyone got one?

I just dumped EDF and switched to SE. Nice little surprise waiting for me when I got down to the bungalow:

little clamp meter to whack on the meter tail, and a batter powered RF transmitter (433MHz). Base unit sits in the house and tells you wn=hat you're using.

I know it's hardly a unique concept, but it was free :) Brought it back and hooked it up in Pembury.

There's a little RJ45 underneath, which upon some searching turned up the above web site which suggests it's a TTL level serial link that spits out readings in XML every 6 seconds at 2400 baud.

Need to go and see if I have a MAX232 somewhere and hook it up to the PC :)

Only deficiency is the base unit doesn't have a Rugby Clock receiver for time, otherwise it would be nearly perfect...

Cheers

Tim

[Pete Verdon]

Yep - I'm one of those "folk at Hursley Park" mentioned in the link. Must admit I was never one of the more active ones though.

I did that with mine, but by now they have actually produced the promised cable and are selling them (including USB versions) via an eBay shop. Might save you a bit of faffing putting one together.

Pete

[gazz]

current cost sell the usb lead and have some software on their site to download, so you can get the data from it,

depending which model of the meter you have, it may store the data for 45 days or more... i bought a current cost one and it stores 90 days of data i believe... whcih is going to be very handy when i the managment company finaly replace our boiler, as they are going to be getting a bill for the extra electric from having to heat the house with lecky heaters.... they think i can't prove it's costing almost 100 quid a month extra, but i have the graphs in both monetry units and killowatt hours... up from an average of 3kw a day before the boiler died, to over 14 kw a day after.

[ARWadsworth]

The time signal is now transmitted from Cumbria

[Bob Minchin]

I can't see the value for logging the data from Current Cost units apart from the initial technical challenge. With so many domestic loads being non resistive, and these units not taking a phase reference, they are bound to be inaccurate. Yes they will give a relative indication to help track down wasted power but that is about all they are good for. It would be so easy to have a smarter clamp head that also plugged in to a mains socket and have the pic calculate true RMS power. Does anyone know of a unit that does this properly?

Bob

[Dave Liquorice]

USB only available now, I asked about RS232 a while back and they said "until stocks exhausted".

[Tim S]

ARWadsworth coughed up some electrons that declared:

Yep - I know :)

I still call it "rugby" though - bit like buying a "biro", everyone knows what you mean :->>>

Now, a real man would throw the base unit away and hack the RF...

Cheers

Tim

PS

Have a couple of MAX232 RS232 converters, so I'll see what it does later. The real fun will be to see if it accepts commands...

[Tim S]

Bob Minchin coughed up some electrons that declared:

This is true - but don't most PSUs at least try to have a power factor of 1?

That leaves motors and old style tube lights.

I expect the problem was that many people don't have a 13A socket next to the meter.

However, seeing as the base unit plugs in, if they used an unregulated AC wallwart, perhaps with some extreme cleverness, they could achieve high accuracy time synchronisation between the clamp unit and the base unit, then the clamp could send a current sample set with timestamps and the base could take a high resolution sample of the voltage profile.

It would be an interesting exercise...

Cheers

Tim

[Andy Burns]

The CC128 specifically says "this version does not listen for incoming data" whether that means the Classic model does, I don't know.

[Tim S]

Andy Burns coughed up some electrons that declared:

They missed a trick - it should be possible to at least program the time and unit cost into the device.

I think the clamp TX is the most interesting bit. The base unit could be far smarter. Also I notice, it's not very flexible in terms of funky unit cost profiles.

[Bob Eager]

Well, if you have the right sort of meter, theer's always this:

[Dave Liquorice]

I don't think any of them accept commands, they spew out the data on a regular basis.

Average Joe Blogs won't be interested in plugging it into their PC or doing fancy cost unit profiles (it does E7). Those that do want that will have the skills to manipulate the raw data provided.

[Andrew Gabriel]

I made one about 25 years ago, but it only generates a power (Watts) output, and not any long-term integration (total energy use).

Might be able to modify one of the plug-in ones to use the sense coil/clamp. I did try opening one of my plug-in ones to see how it did the sensing, but even with the case screws removed and the two pieces of the case slightly separated, something was still holding it together which seemed like it needed enough force it would break, to I chickened out of opening it at that point, not wanting to break it.

I don't think the consumer quality ones do, but I haven't bought one recently. Industrial rack-mount ones do (at least, quality ones), as it's rather important if you have 1000 of them in a data centre.

and CFLs, and wall-warts.

It would be needed at the sensor end.

[Tim S]

Andrew Gabriel coughed up some electrons that declared:

Not necessarily. If the base unit could synchronise time (delta time, not absolute) with the sensor over the 433 link, at least to the millisecond level, the sensor could send a batch of current readings with timestamps to the base.

The base being driven from an unregulated AC wallwart would take a series of hi res voltage readings with timestamps and, having found the intersection of current readings and voltage readings, could in a leisurely manner do the maths.

It assumes:

1) You can achieve the timing accuracy with a weedy microcontroller - I think you could manage mS without any problem.

2) You can time lock over a 433MHz link to the same resolution - not sure.

3) You assume that your wallwart transformer is maintaining a stable ratio bewtween mains voltage and output voltage and the waveform comes through largely uncorrupted.

Note - I didn't say it would work, just that it would be an interesting exercise :)

Cheers

Tim

[Bob Minchin]

Much easier to do the measurements at one point and there is mains power for the processor. many samples of the both waveforms are necessary as the voltage 'flat tops' regularly - or at least it does here. Just have a look with a 'scope (and suitable probe!!) sometime. So many domestic devices with SMPSUs these days to blame.

Bob

[Tim S]

Bob Minchin coughed up some electrons that declared:

I agree - *if* you have a socket near the meter...

I do here (Pembury) but in Robertsbridge the meter is outside, which is common with many properties. I suspect the designers conceeded that a large portion of th users wouldn't be able to source a direct connection, short of a pin in the cable.

Although having said that, I wonder how well a capacitative pickup would work - with a sticky electrode on the sheath of each meter tail?...