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The c.t. measures current - it has not the faintest clue whether the load is inductive, capacitive or what. All it sees is current. My initial reaction would be that the current drawn by the fan was so small that you could not measure it with your multimeter.

thanks for the reply,

fan is rated 60W @ 230V, so the device should be drawing 0.26A.(P=VI)

my current sensor specification mentions 100A/5V so for 0.26A i should be getting 13mV ((5*0.26)/100)

multi meter's smallest scale mili volt  so i think i should be able to get a reading.

so is there any problem with the lower limit of ct sensor? and should i get more sensitive sensor?

thank you

Maybe you could try with a 60W bulb, which should draw the same amount of current as your fan.

You could also try wrapping one core of your cable several times around the CT.  That should increase its reading. 

The technique is shown here near the end of this page

According to the specification that I've found (3rd party, possibly not reliable; the YHDC website seems to have gone) is your c.t. is 120 A : 40 mA so you should be seeing 83 µA for 250 mA primary current. I don't know where you get the 5 V from as it does not.have an internal burden.

There is no inherent lower limit for a c.t., though errors increase markedly at low currents.

To :calypso_rae :    I'll try and give you the feedback.... thanks you

To: Robert Wall : yes, I think it does have an internal burden resistor to give voltage output. Sensor  has no physical difference with the one you are saying which gives current output, but 100A/5V is printed on it other than 120A:40mA

Again if my sensors output is current I shouldn't be getting any voltage reading for kettle(850W) or table lamp(100W). Thank you for the reply. 

"Again if my sensors output is current I shouldn't be getting any voltage reading for kettle(850W) or table lamp(100W). Thank you for the reply."

I don't understand what you're getting at there - if your c.t. doesn't have an internal burden (you need to check - the type number you gave does not mention one and does say "current output") then the output voltage will be as high as necessary to drive the current it sources into the load, or until it is limited by saturation.

a

above is what written on my sensor, and I tried measuring the current output but I couldn't get a reading at all (with 100W table lamp) and the resistance between terminals are 4.55k  Ohms. Thanks .

If you have an Arduino, or similar, you could build a simple circuit so that your CT can be tested.  By running the first sketch on my Summary Page , you will then be able to see the values that your ADC is generating when different amounts of current are flowing. 

I think you will find that the Atmega processor is a much better way of detecting the CT's output than a multi-meter.

Ok, I'll try with an Arduino and get back with the results, thank you.

That picture certainly doesn't show the c.t. that the data sheet that I found relates to (with the same type number!).

It also reads 100 A / 5 V D.C.

That solves the mystery. There is a rectifier in there. The diodes in the rectifier only turn on at around 0.6 V, so - depending on the configuration of rectifier and burden inside the c.t. assembly, there may well be not enough current to generate enough voltage to overcome that forward voltage drop, hence you read nothing.

The bad news is, that is unsuitable for the emonTx. The emonTx expects a bare c.t. and an exact replica of the current waveform to do its calculations on direction of power flow, real and apparent power etc. That c.t. cannot give you the information necessary for that, it is lost in the conversion from a.c. to d.c.

The emonTx expects a bare c.t.

Good point, Robert.  Maybe the rectifier components could be removed?

I agree and  thank you Robert, since the sensor is sealed I don't think taking it apart wont be a good idea other than buying a new bare C.T sensor widely used in open energy monitor, Also I couldn't even find a datasheet for my particular sensor.

But what I don't understand is getting voltages such as 6.8mV (0.0068V) (with100W table lamp plugged)from multi meter because if there is an rectifier diode there shouldn't be a reading at all, could you let me know why is this kind of thing happening ?

appliance                        sensor op voltage

table lamp 100W ----------------->   6.8mV

kettle 850W  ---------------------- >166.2mV

Thank you for both Mr Robert & Mr Calypso_rae

Remember a c.t. is a current source, so - subject to its limitations due to its VA rating and running into saturation - it will generate whatever voltage is necessary, but remember of course it does not have an infinite impedance so it's not perfect.

I'm guessing what's inside: I suspect there's a bridge rectifier with the burden resistor on the d.c. side. Provided you have enough flux in the core, the diodes will conduct and pass current into the burden, and the flux balance in the c.t. will be restored. If there isn't enough primary current to generate that flux, too much (proportionately) will go into feeding the losses and magnetising the core and  there won't be enough left for the burden. [That's about the simplest I can put it.]

What you're looking at with those very low currents is a serious non-linearity as the rectifier turns on.

Your guess should be correct.If I couldn't return the sensor to shop for another I'll dismantle it and include the pictures here, now I know I should be getting sensors with current output. Good day & thank you for the help ! 

You seem to have bought an unknown quantity and paid the price. Regrettable, but I consider "Current Transformer" is not an accurate trade description of the device that you have. True, it contains a c.t. but it is not just that. The additional components prevent its use where a true current transformer - such as the one sold in the shop - would be appropriate.

True... so I updated the forum topic, so anybody else bought same type of sensors can easily identify what post to check. Luckily I just bought one of them.  

Thank you.

This thread may be outdated but finally I managed to get the data sheet of the sensors I have https://drive.google.com/file/d/0B1C7UMFACOZEdGVPRnZNMEp0bW8/edit?usp=sharing

Yeah, well...  

I can't help saying "I told you so!"  Inside, it is pretty well much as I envisaged.

This sensor is no good at all for use with any OEM kits or products. The software we use replicates the function of the bridge rectifier in even the simplest cases, and if you use the "_voltage" sketches, it also adds information about the direction of power flow that this sensor inherently removes.

Thanks for tracking down the data sheet. That's final proof of what had to be the case all along.

Hi,

By mistake my provider I received three of these. As my knowledge is scarce not sure whether I can use with my emonTXv2 ... or throw it away?

thanks

Read the post above. If you want to use it for something else, do that. Otherwise it is useless.

ok, thanks. That's what I thought ... but my English is not very good. :)

But your English is very much better than my Spanish!