Thank you for your kind offer, we do appreciate it.
We almost exclusively use the SCT-013-000 as it allows us the option to select the value and tolerance of the burden resistor to match the circuit being measured.
I use SCT-013-000V in the list above. I think I will contact linahaoming to how much is the value of TVS resistor & do I still have to use burden resistor if SCT-013-000V already comes with TVS resistor.
The SCT-013-000V has an internal burden resistor such that a voltage of 1 V appears for a primary current of 100 A. It therefore does not require the addition of a TVS diode, as the transformer will saturate long before a dangerous voltage can be generated.
I cropped the datasheet in the link above so that we can only focus on the schematic diagram only, which is shown in the photo below. For full datasheet, please refer to the link above.
As we can see from the schematic diagram above, there are 2 types of SCT-013, which is:
Current output type
Voltage output type
Both current output type and voltage output type do have TVS in the schematic diagram. However, based on the schematic diagram:
The TVS for the current output type in the diagram is a diode
The TVS for the voltage output type in the diagram is a resistor (I believe that is the symbol of a resistor)
Maybe I am wrong (or maybe the schematic should not use the resistor symbol for TVS for voltage output type), but this is the reason why I came out with the term TVS resistor. If the term TVS resistor really does not exist, then I think 1 of the following things should be done:
The resistor symbol for the voltage output type SCT 013 in the schematic diagram in the datasheet should be replaced with a proper TVS symbol.
If the TVS terminology used to label the resistor in voltage output type SCT 013 is really a resistor and not a TVS, then the term ‘TVS’ for the voltage output type in the schematic diagram should be revised to other proper term. For an example, the more accurate term for the resistor in the schematic diagram should be ‘Internal Burden Resistor’ or ‘Built-in Burden Resistor’ or ‘On-board Burden Resistor’ etc.
I’m sorry if the term TVS resistor that I use is not correct, but I came out with that term based on the resistor symbol that I see in the schematic diagram for Voltage output type labelled with ‘TVS’ in the datasheet.
One more thing, I contacted Yhdc via ‘linahaoming’ user ID in the first posting above to ask about the status of the burden resistor. Below is her reply:
Hello. The SCT-013-000V has an internal burden resistor such that a voltage of 1 V appears for a primary current of 100 A. It therefore does not require the addition of a TVS diode, as the transformer will saturate long before a dangerous voltage can be generated. This product do not have TVS diode, it has internal burden resistor, therefore output voltage is 1V. The value for the internal burden resistor is 18.6Ω
Based on this, in my opinion, the term TVS used to label the resistor in the schematic diagram for the voltage output type SCT-013 available in the datasheet should be replaced with other term such as ‘Internal Burden Resistor’ or ‘Built-in Burden Resistor’ or ‘On-board Burden Resistor’ etc. Otherwise there might be other people that will come out with the ‘TVS resistor’ term because the schematic diagram uses a resistor symbol labelled with the term "TVS’.
You are correct the “TVS” label on the voltage output type schematic is both incorrect and misleading, but there is little that we can do about the manufacturers datasheet, we can only advise you of the corrected terminology and the response from YHDC confirms what Robert and Bill have said, there is no “TVS” only a burden resistor in the voltage output versions.
Adding to what my learned colleagues have written, experience has taught me that, unfortunately, you cannot rely on data from Chinese manufacturers or distributors. When I joined this community, one distributor of the YHDC-SCT-000 (Seeed Studio) was publishing the wrong ratio for the current transformer. This is a relatively simple measurement that a first-year electrical engineering student should be capable of performing, yet a major distributor could not get it right. And quite often, important and necessary details are missing. This is why I measured and published a report on the two sensors that we commonly use.
I’m planning to purchase one, but at the same time I found a shop in my country selling a cheaper Chinese made AC-AC adapter (20% the price of the Macsot), but not sure about the reliability (in terms of output’ accuracy).
Should I stick with buying the Mascot adapter from RS website or try the cheap adapter in my country (or any other better alternative)?
If you buy an adapter other than those that I tested, you won’t know how it will perform until you get it. You will need to measure it to determine the calibration and how it distorts the waveform that you are trying to measure. Your hope is that it will not distort the wave at all, i.e. the shape of the secondary voltage wave is exactly the same as the mains wave, only reduced in amplitude. How far reality departs from that ideal will determine how accurate your measurement of the voltage and power is.
DO NOT be tempted to dispense with the transformer altogether, you will put yourself in serious danger should there be a fault in the mains supply.
At first, I would like to purchase the 1A Output current version. But then I think as a beginner, I should purchase the same model that has been tested and published in your report because the performance is already known.
So the turn ratio for the SCT013 100A is what ? I checked the manufacturer datasheet and the turn ratio there is 1:1800 (http://www.yhdc.us/ENpdf/SCT013-000-0-100A-0-50mA_en.pdf). What should i consider as correct, the 1:2000 or the 1:1800?
The turns ratio may well be trimmed by the manufacturer to obtain the required performance across the specified operating band. The current ratio, which is the value you need, is as specified - 100 A : 50 mA.
Or you can measure it yourself, or read the report in the Learn section.
But isn’t the turns ratio important to determine the burden resistor ? I am having some trouble with the measurments precision, precisely having readings when no current is flowing through the sensor. I’ll try to measure the turn ratio mysels aswell.
As @Robert says, The bottom line is you want the ratio of current in to current out, that may well match the ratio of turns, Or the manufacturers may have adjusted the number of turns to get the correct “current” ratio. eg perhaps it could take a ratio of 1003:1 physical turns to arrive at the “current” ratio of 1000:1.
Any calculations (incl the burden value) are all based on the ratio of the current measurement. The number of turns is only specific to achieving the target current ratio.
So from your information it would suggest the CT has 1800 physical turns to achieve an output equal to 1/2000th of the input. How they got there is not that important, what is important is the relationship the output has with the input, ie it is 1/2000th or put another way 2000:1.
Personally, I would doubt the number you quote for the turns ratio. It seems too far from the current ratio to be credible, and all the YHDC c.t’s that I’ve measured have been very close to the nominal 100 A : 50 mA ratio.
You cannot measure that. The only way to find it will be to unwind the secondary, counting as you go, which will destroy the c.t. You can measure the current ratio though. It should be nearly the same, but probably will not be exactly, as Paul says.
No, as I wrote and as Paul wrote, it is the current ratio that is important.
Your emonTx measures the voltage developed by the secondary current flowing in the burden resistor.
If you know the ratio of primary current to secondary current, and the burden resistor value, you can work out the voltage, given the primary current.
If you know the ratio of primary current to secondary current, and the primary current itself, and the burden resistor value, you can work out the voltage.
If you know the ratio of primary current to secondary current, and the primary current itself, and the voltage you want, you can work out the burden resistor value.
[Edit]
It would appear that there’s a problem with YHDC’s website and the Chinese authorities. It is down at this moment.
Here is a saved copy of the web page. Note that the turns ratio is not mentioned. SCT-013- family web page.pdf (435.2 KB)
