About Us Knowledge Base Community Forum Electronics Toolbox FAQ Shipping & Delivery

Community Forum

Share your projects and post your questions

Search
Register or Sign In
Forum

Very variable voltage with costant current

249 Views - Created 21/10/2018

21/10/2018

Posted by:
clauz

Users Avatar

Hi,

In tring to understand how to use the ADC for to monitor some lines of Ampere use of my office (PC, light etc)

I'm using 2 sensor, one SCT013 (max 30A) and one TA12L-100 (max 5A) and testing one PC that use 67W (read id with a socket multimeter). Avtually I'm using the ADCPi/demos/demo_readvoltage.py for tests.

The problem is that readed voltage it's very variable, from 0 to 0.012355 with many other (0.002471 0.009884 etc.)

Where i wrong ?

I tried to connect the 2 wire of sensors in some different input channels but nothing changes.

Thank you

Have a nice day

22/10/2018

Posted by:
andrew

Users Avatar

Location:
United Kingdom

Users Twitter  Users Website  

Hi

Are you reading the voltage directly from the current sensors or through an additional circuit?  The sensors will be outputting an AC signal at 50Hz or 60Hz depending on the frequency used in your area.  As the ADC Pi only has a maximum sample rate of 240SPS on one channel you will have difficulty capturing a full AC sinewave cycle to calculate the RMS voltage as the sample rate is too low.  If you just read one voltage sample then you have no way of knowing what point of the cycle the AC sinewave you have sampled so the voltage will be anywhere between 0V and the peak voltage. 

The easiest way to measure AC current is by using something like the i-Snail current sensors.  They contain all of the electronics needed to convert an AC current into a constant DC voltage between 0 and 5V which can be connected directly to the inputs on the ADC Pi.

AB Electronics UK Tech Support

23/10/2018

Posted by:
clauz

Users Avatar

Hi,

I tought that sensor will output an already usable level :|

I think that I'll use something else I seen online, because that sensor cost too much considering to use till 8 of them.

Thank you

Have a nice day

Note: documents in Portable Document Format (PDF) require Adobe Acrobat Reader 5.0 or higher to view, download Adobe Acrobat Reader or other PDF reading software for your computer or mobile device.