I am doing a research about Residual Current Device at the moment.
One of the processes is rectifying the output of toroid core wich is an AC voltage and I use a full bridge rectifier to convert it to DC voltage.
Vrms from the rectifier is around 80mV, then I added a capacitor to stabilize the wave but the Vrms output is very big (around 17Volt).
Does the capacitor value give a huge effect on the output?
Because from what I read before, as the capacitor value increase, the more stable wave we get.
Thank you

 

Edit: I misunderstood the question.

It is unlikely that the output of the rectifier was 80 mv RMS if adding capacitance gets you 17V RMS (or about 17V DC).

The output of the transformer is a probably a little more than 12V RMS. After coming out of the rectifier it should still be 12 V RMS.

Can you give the details of your measurement including the meter used and the meter's settings? Maybe we can figure out where things went wrong.

 

And the frequency.

 

Did you measure the transformer output on DC volts range? It should be ACV.
That may account for your very low reading.
Current transformers usually run into a termination resistor as well so it may be worth adding one to get a more stable reading.

 

check again with and without the capacitor again and tell us the readings.

 

The relationship between the rms AC and the capacitor smoothed rectifier output will also depend on the waveform - sine or spiky.

 

The relationship between the rms AC and the capacitor smoothed rectifier output will also depend on the waveform - sine or spiky.

Yup, applying a small load - more than just the DMM impedance could help eliminate artifacts.

 

Edit: I misunderstood the question.

It is unlikely that the output of the rectifier was 80 mv RMS if adding capacitance gets you 17V RMS (or about 17V DC).

The output of the transformer is a probably a little more than 12V RMS. After coming out of the rectifier it should still be 12 V RMS.

Can you give the details of your measurement including the meter used and the meter's settings? Maybe we can figure out where things went wrong.

Actually, I'm using a toroidal current transformer. The RMS output was 725mV directly measured from toroid core output, then it was rectified using a bridge diode, the rms output measured was 71mV. Then I added a capacitor in order to remove the ripple, but the RMS measured is too big as I've mentioned before.

 

Did you measure the transformer output on DC volts range? It should be ACV.
That may account for your very low reading.
Current transformers usually run into a termination resistor as well so it may be worth adding one to get a more stable reading.

actually it was measured in ACV

 

Actually, I'm using a toroidal current transformer. The RMS output was 725mV directly measured from toroid core output, then it was rectified using a bridge diode, the rms output measured was 71mV. Then I added a capacitor in order to remove the ripple, but the RMS measured is too big as I've mentioned before.

Do you know anything about the waveform of the current?

 

It does sound like it is a spiky waveform as mentioned above. The RSM relationship that most multimeters are calibrated to only applies to sine waves.

Have a look at..
http://www.electronics-tutorials.ws/transformer/current-transformer.html
About a third of the way down it explains why you should never leave them unterminated. The result is very high output volts.
For proper calibration, the current transformer has a design termination resistance, usually fairly low if memory serves me well.

 

Do you have a shunt resistor on the output of your transformer?

It would help if you could describe your setuup and measurements in some detail.

 

Do you know anything about the waveform of the current?

I don't know about the current waveform, haven't tried to observe it before. but I'll try to do it asap. thank you for your suggestion.

 

Do you have a shunt resistor on the output of your transformer?

It would help if you could describe your setup and measurements in some detail.

no, I don't put any resistor on the output.
I use an oscilloscope. I set 1Volt/div 10ms/div and connect the CT to AC power source

 

If your current transformer does not have an internal shunt resistor you will need to add an external shunt, otherwise what comes out of the current transformer won't look very much like the current waveform, and things like added capacitance can tune the secondary and make the response "peaky".

Can you tell us anything about your current transformer -make, model, even a photograph?