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 Post subject: photovoltaic monitoring
PostPosted: Sun Feb 26, 2012 6:51 pm 
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Joined: Mon Feb 13, 2012 10:19 pm
Posts: 5
hi, any chance of changing the CT sensors to one way flow, when using current this could show the live usage and show a red LED on the energy monitor, when current flows the other way this would not be recorded so would register as 0 and show up as a green LED . . . so from a quick glance across the room if its red i know i am importing and green i am exporting

or if any one knows how to do this then post a comment


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PostPosted: Mon Feb 27, 2012 1:43 pm 
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Joined: Tue Jul 05, 2011 11:46 am
Posts: 35
[quote="emailfriendsuk"]hi, any chance of changing the CT sensors to one way flow, when using current this could show the live usage and show a red LED on the energy monitor, when current flows the other way this would not be recorded so would register as 0 and show up as a green LED . . . so from a quick glance across the room if its red i know i am importing and green i am exporting

No! Of course you _can_ get monitors that detect the direction of current flow, but the cc clamps are a relatively low cost, safe & non intrusive. They detect the magnitude of the current and can't tell its direction.

It is possible to use connect 2 clamps and 2 transmitters and a monitor and then use software to subtract the house power from the solar to get the 'direction' but this needs a bit of computing power. To see how do that I'm afraid you'll have to do what you should've done before posting & read the extensive discussion about this on this forum! ie rtff...


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PostPosted: Fri Apr 13, 2012 12:51 pm 
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Joined: Fri Apr 13, 2012 12:03 pm
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Why dont Current Cost make a device that can accurately calculate Household electrical consumption, subtracting

the generated exported solar power from the actual imported electricity?

Many people would buy it.


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PostPosted: Fri Apr 13, 2012 6:19 pm 
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Joined: Sat Apr 16, 2011 1:10 pm
Posts: 328
Location: East Sussex
Kefalonia wrote:
Why dont Current Cost make a device that can accurately calculate Household electrical consumption, subtracting

the generated exported solar power from the actual imported electricity?

Many people would buy it.


I have asked this.

I suspect the answer may be because it will have to be installed by a qualified electrician which of course cost money and thus would reduce sales.

Another brand has been working on a product to do this but they have failed to get the product to market. This product was targeted for homes with PV installs with two clamps and a cable wrapped around a feed to obtain the voltage.

Automan.


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PostPosted: Sat Apr 14, 2012 1:13 pm 
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Joined: Fri Jun 03, 2011 11:12 pm
Posts: 38
Location: UK
I'm going out on a limb here, so i may be wrong but.....

As far as i'm aware, current clamps (not neccesarily current cost clamps) would normally give out a positive or negative voltage depending on the direction of any current flow.

Therefore, using two clamps connected together in series, in opposite polarity you would get a differential reading. One clamp would subtract the value of the other, so to speak. You would of course, only be showing a difference between on grid and off grid, not the total houshold consumption.

I don't know if this is of any use to anyone or if it would work but maybe someone can do something with the idea?


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PostPosted: Sun Apr 15, 2012 3:32 am 
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Joined: Mon Apr 18, 2011 5:26 pm
Posts: 138
Location: Melbourne, Australia
Err... No! :roll: Sorry to rain on your parade!

:geek: Remember it's Alternating Current. Reverses itself 100 times a second.
Image

However, this is my contribution (pick holes in this)...
:ugeek: We could identify the direction of conventional current by seeing which direction the current flowed in the sensor during positive half cycles of the grid voltage.

With apologies to Julius Sumner Miller, Why is this so! Here goes...
Image
The above scratchings represent a clamp in minimalist terms .
  • The red line is the current carrying wire (mains cable);
  • the blue is a ferro-magnetic toroid to concentrate the magnetic field around the wire; and,
  • the black wire is a sensor wire in which is induced a current proportional to the current in the mains cable
.
The current in the sensor wire will of course lag the voltage as it is inductively coupled. I am assuming the phase angle is less than 180 degrees.
If during the positive half cycle flow is from Grid (bottom of picture) to house the current in the sensor wire will be in known direction, say, as shown in the picture.
If the inverter is at a higher voltage than the grid current will flow towards the grid during a positive half cycle and the current in the sensor wire will be reversed.
(Q.E.D).
Practicalities (before you kick me too hard)...
  • The clamp could be designed to sink a probe through the insulation to detect the voltage. Would also need to attach to the neutral wire. Probably breaks all kinds af safety rules - e.g. unfused supply
  • Alternative might be to put more logic at the transmitter, but would then need to plug into the mains. This may be a good thing could then sort out the power factor problem.
  • Existing clamps are unlikely to be as simple as my minimalist picture. Probably use split toroid with hall effect sensor Are they sending an alternating voltage back to the transmitter? Anyone care to pull one to pieces? or look at the output on a scope?

I think I'll patent this idea! Oh wait, one can't patent ideas and I've just put it in the public domain, curses!

_________________
Seeker
"The Truth is out there!"


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PostPosted: Mon Apr 16, 2012 5:20 am 
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Joined: Fri Jun 03, 2011 11:12 pm
Posts: 38
Location: UK
SeekerAfterTruth wrote:
Err... No! :roll: Sorry to rain on your parade!

:geek: Remember it's Alternating Current. Reverses itself 100 times a second.


That's ok.

The reason i said what i did was because i remember a few years back working with some current clamps for a job i was doing, but they solely had a DC output. I can't remember the full details, they may have only been capable of measuring a DC current and not AC and therefore that's why a pos/neg output for current direction but i seem to have this vague recolection they would also measure AC and yet still give a directional current flow in relation to source versus load. Bizzare i know and i most likely am wrong.

I agree that i must have been in cloud cookoo land when i think about it because AC should give a +/- swing.

I also had a vague recolection that it wasn't just a simple ferrite ring and coil arrangement, and this thing had "something" else in there such as a hall sensor maybe and some averaging circuitry or something along those lines. It was quite some time ago and my brain aint getting any younger!

I'll have to try and dig out the datasheet if i can even find them again and then offer my thousand appologies for being away with the fairies the other day.

It will still be possible to do a differential approach obviously, just maybe not as simple as wiring out of phase, like i first dreampt up.

I guess you can tell i'm much more used to working with DC these days and mostly low voltage/low power etc.


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PostPosted: Thu Apr 19, 2012 8:36 pm 
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Joined: Fri Jun 03, 2011 11:12 pm
Posts: 38
Location: UK
SeekerAfterTruth wrote:
Are they sending an alternating voltage back to the transmitter? Anyone care to pull one to pieces? or look at the output on a scope?


I decided to do just that with a CC clamp i wasn't using after you suggested it...

Yes, they do output AC.

I connected one up to a Scope, clamp placed around the live wire to a 60W 240V lamp and i got a reading of about 80-100mV Peak to Peak. The scope was very old and highly likely to be out of calibration so no guarantees on the voltage reading. With the lamp out of circuit, but the power still connected through the cable i pretty much got a flat line. I did this to rule out any mains hum to ensure i was getting a proper reading. The scope was set to the 5mV range but it was through a 10x probe, so works out at 50mV per division. Obviously, i had just under 2 divisions peak to peak.

I also pulled it to pieces. OK, peeled off the "E-on" label on one side and removed the two screws! Inside there is just a single coil, wound on a plastic bobbin and placed on the "C" half of the ferrite. The other half of the ferrite, on the hinged part completes the loop. This was one of the older style "D" shaped clamps is the best way i can describe it.

Nothing fancy at all and essentially just as you pictured above.

I also tracked down the current transducer i used a few years back. I didn't get the full data sheet at the time as i was just browsing through the Farnell catalogue (i still need to do that) but it was a hall effect current transducer manufactured by "LEM" and costs about £17 + VAT It was rated at 800 Amp and has it's center point set at 2.5V and gives a DC output swing +/- depending on current direction.

Admittedly when i think back to the job, we were using it to measure very high DC currents only and you were very right to correct me on my error as i had completely failed to take into account that it is AC and not DC. Duh! :oops:


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PostPosted: Sat Oct 20, 2012 11:12 am 
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Joined: Sat Oct 20, 2012 11:06 am
Posts: 1
Monitoring and control of photovoltaic systems is essential for reliable functioning and maximum yield of any solar electric system.


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