SCT-013 current sensor

[robert-hh]

@Stefano-Floriani In that case the signal at P14 is way too small. For 230 V you should get a reading in the range of about 150 for a 9 bit ADC setting (see the chart and table in my previous post).
You can either reduce the value of the 390k resistor R6, or increase the value of the 10k resistor R7. You may also try to remove C4, because that one also reduces sensitivity. When the setting is right, you should measure with an multimeter an AC voltage of about 0.7 V~.
The transfer ratio of optocouplors vary a lot.

[Stefano Floriani]

@robert-hh

I'm so sorry, I thought you did the tests with the resistances, I don't have the equipment or material to try.

Thanks you

[robert-hh]

@Stefano-Floriani I tested with the values in the schematics. But the optocouplers vary a lot between individual items and families. So the resistor values have to be determined for each and every item.
Thats one of the reasons I suggested using a small transformer. The variation in the transfer ratio of small transformers at their nominal load is way lower, only like 10%.

[Stefano Floriani]

@robert-hh
this is the result running your script:
run()
(0.07947586, 5.907588, -0.961557) 0.5722438
(0.0303492, 5.957881, -1.419681) 0.1505412
(0.05318971, 5.931093, 0.2570791) 0.9671368
(0.08792933, 6.089819, -0.7879818) 0.7052775
(0.07133265, 5.925827, -0.5397768) 0.8578235
(0.1326455, 5.954846, -0.7830648) 0.7087548
(0.1046322, 5.97505, -0.6961006) 0.7673484
(0.09087696, 5.942791, -0.4167922) 0.9143923
(0.02481544, 5.990963, 2.182606) -0.57435
(0.08708447, 6.019161, 0.1956226) 0.9809269
average: 0.07623314 SDev: 0.03126099
I have used two resistor 390k ,10k at one watt .

[robert-hh]

@Stefano-Floriani Obviously you are running without load. Then the phase is not stable. But the value for voltage is still too low to be of use. What type of optocoupler are you using? I used a 4N27 type.
This kind of circuitry is hard to set up without any kind of measuring tool.

[Stefano Floriani]

@robert-hh

[robert-hh]

@Stefano-Floriani Looks like a Motorola device. Comparing the data sheets, they look similar. The device I used seems to have a higher CTR, but not by a factor of 40 different.
Ar you sure that you assembled the diode D1 in the right direction? If not, the LED current will be way lower.

P.S.: The PCB design is dangerous! There is not a sufficient distance between the high voltage and low voltage side! Traces from the HV side MUST NOT lead to the LV side. And in a safe design there would also be a cut in the PCB below the chip between the HV and LV side.

[robert-hh]

@Stefano-Floriani You could try to use other optocouplers, like 4N37, which has a higher current transfer ration (CTR). But again, this circuitry is using a chip designed for digital mode in an analog mode. That makes finding the right values difficult.

Edit: Other devices with higher CTR: CNY17-4

[Stefano Floriani]

@robert-hh

I have assembled the diode D1 the right directiont?

THanks a lot

[Stefano Floriani]

@robert-hh

Please, How many volts should there be at the output of the 390k resistor?

[robert-hh]

@Stefano-Floriani At the output of the 390k resistor (input of the Photocoupler) there should be the diodes voltage, which is about 1 Volt AC. Over the 390k resistor you should have 230V.

At the 10k resistor a good voltage is 2 V peak-peak or ~0.7 V AC.

[Stefano Floriani]

@robert-hh

I've remove C4 (470p) now is value[1] it's 50.99931,

Bye

[robert-hh]

@Stefano-Floriani That's better. The capacitor worked here as a means to suppress noise. You can also increase the value of R7 to 27k. Then the value should be at about 150.