The split-core current transformer shown in the photo is available at a low price on many auction portals and online stores. The transformer has the parameters of 100A / 50mA. So when 100A alternating current flows through the cable through the transformer, the AC milliammeter at the transformer output will show 50mA. The current ratio of the transformer is 2000. The output signal is led out on a mini jack connector. The transformer casing enables the core to be opened and the conductor to be measured is enclosed.
By checking the measurement results at several points, you can see the linear characteristics of the transformer:
For the measurement of smaller currents, it is worth using a transformer with a smaller measuring range. For the test, we put 5 turns on the transformer core, which changes the ratio and output currents,
Another type of transformers are those with the output voltage depending on the current flowing in the tested line. An example of a 30A / 1V transformer. A separate description of the transformer here SCT013 30A / 1V . The input current in A divided by 30 should produce the corresponding output voltage in V.
Alternating current of 0.66A causes the appearance of a voltage of 21.32mV at the output.
By recording the output voltage of the transformer, we can, for example, examine the current consumption in the home electrical installation.
What applications do you see for cheap transformers with limited measuring accuracy?
The transformer can be transformed into a primitive oscilloscope probe for observing the waveform of current changes. Below is the shape of the current consumed from the network by a 100W bulb and a 13W LED:
Inrush currents of, for example, different types of light sources can be observed:
The cheapest transformer is a ferrite core with a wound winding and terminated with an appropriate resistor value. The fact that the disadvantage of such a solution is the lack of a constant component, but the price varies between PLN 5-10 in the retail.
If there is interest, I can compare such a rather primitive solution with the I-prober 520 probe.
I am thinking about the construction of a measuring device which could measure the current consumed by a typical electric motor simultaneously on all phases, e.g. in order to detect e.g. a weaker current path in a contactor. It doesn't have to be super precise, my motors are from 4 to 55kW. For this 3 simple voltmeters and I would have a set. Of course, there are devices for this purpose, I even have such a recorder in my company, but there are 12 service technicians and one recorder.
As you can see from the diagram, the CS1050L transformer has a rectified signal, I had such a circuit at hand, so I used it.
And now the meat, i.e. the measurement results:
inverter supply voltage 10V I run a series of 8 periods for an RLC chip with a frequency of 80kHz
legend: yellow - CS1050L blue - I-prober 520
calibration: I-prober - 520 1v / A = Imax = 1.86A CS1050L - 300mV / A = Imax = 2.10A
inverter voltage 20V, the rest unchanged
Results: I-prober 520 1v / A = Imax = 3.48A CS1050L - 300mV / A = Imax = 3.93A
measurement error = around 12%
Such a large error could result from incorrect calibration of the current probe, unfortunately this is a new purchase and I have not read the manual well and suspect that I set the offset incorrectly. All anomalies result from the lack of any filter on the measuring resistor, and the I-prober 520 probe has only a 5Mhz band, so it is possible that it cuts out all disturbances.
Sorry to be so quick and a bit careless, but sometimes better than not.
Of course it is possible to implement the arrangement you see in the results above.
I have been working on the construction of an electricity meter (3 phases) for a long time. I have already purchased most of the elements on the occasion of another order, unfortunately the lack of time prevents the design and construction of such a device. I haven't bought transformers yet and I was wondering about these. The absolute error is around 1% so it's not too bad. The price is also affordable because on Chinese portals with the shipment it is about PLN 25 per item. Where did you find such transformers for PLN 10-12 in retail?
Unfortunately, I am describing here transformers to be used up to 10A, in your case you need much larger transformers and thus more expensive. However, LEM transformers may still be an alternative to classic transformers for you.
What I tested was a typical pulse waveform with quite a lot of harmonics because the RLC circuit operated in the capacitive range. The CS1050L documentation says that it is designed to work above 20kHz and that was my purpose.