Measuring 230V AC current (contact-less) with 5V AVR

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Hello,

 

i need to measure current(power) on a 230V AC power line, without soldering anything onto the line itself. The power draw is from 10 to 100W so lets say max 0,6A Ipeak. And i wish to have 5W or better resolution(20mA or better). So far i have tested several contact-less solution like ATO-63-B225-D10 and HO 50-SP30, they work great above 100W or 200W and are cheap, but the problem is that they are designed for higher currents/power so at my low ones, they have to bad sensitivity. Something like HO 8-NSM/SP33-1000 would be perfect (80mV/A output), but for this i need to solder it on the power line, which would void certification on the final product.

 

I am asking if anyone knows of a solution for my problem.

 

Thanks in advance.

This topic has a solution.

Last Edited: Fri. Mar 13, 2020 - 09:45 AM
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There are plenty of small clip-on current transformers available; eg,

 

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/introduction?redirected=true

 

https://www.sparkfun.com/products/11005

 

I just googled, "small clip-on current transformers"

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Both are not sensitive enough, they are both for higher currents. The ATO-63-B225-D10  is also a current transformer, but the current are so low that i need to put 10k Ohm on the load side, to have just few mV of output to measure with my mc. And at that point, the transformer is too weak and just collapses and output 0 uA. Without load it outputs 7.8uA when measuring 23W load.

Last Edited: Thu. Mar 12, 2020 - 11:48 AM
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They were just a couple found in a minute's googling - I'm sure there must be others ...

 

Refine your search terms for the sensitivity you require

 

can you loop the current-carrying wire through a few times?

 

otherwise, just amplify the CT output ?

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Last Edited: Thu. Mar 12, 2020 - 11:55 AM
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Or simply wind your own CT. Since you only want to measure small currents, then there will only be a few turns at most. Choose your core carefully. Another idea is to use a hall effect device like a ACS712 and carefully position the current carrying wire. For a 5A device, you should be able to achieve your 20mA resolution - just be sure to factor in the noise of the device. I was able to detect a relay operating from a distance of 20mm - this wasn’t intended.

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awneil wrote:

can you loop the current-carrying wire through a few times?

 

^^^That

 

Wrap the cable 10 times through a 10A sensor and you have a 1A sensor.

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So if i understand correctly, i should loop the wire that carry 230VAC throught CT couple of times? Will try it.

If that fails then i will do what "awneil" suggested; add a simple BJT current amplifier on the output of current CT i ahve.

 

Thanks for sugestions all, will post results.

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wire that carry 230VAC

Just to make it clear it's any ONE of the wires. (if over both you better get 0, if not you have a ground fault :) )  

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Yes ,of course, over only one of the wires :P 

Update: i made 10 loops of 230VAC wire on the CT and now i get around 3mA current, which combined wiht a 1k resisotr gives 0-3V reading which is perfect for my application. Thanks again for this tip and i am kinda embarrassed i didnt think of it :P

Last Edited: Fri. Mar 13, 2020 - 09:07 AM
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If that's resolved the issue, see Tip #5 (in my signature)

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I did :D

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i need to measure current(power) on a 230V AC power line

 

By the way, remember current is not the only consideration to measure AC power.

 

A high quality inductor or capacitor can draw lots of amps, but draw almost zero real power.

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Fri. Mar 13, 2020 - 04:17 PM
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Thanks for this tip, but this measurement is more like for "average" information to the consumer and is not used to do any billing calculation or something like that. And i know what will be plugged on the 230VAC socket (ebike charger) and i tested and compare my solution measurement to a industrial power consumption meter and it was around 4% difference, which is good enough for my application. 

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how about this 5amp  (max ) job...should work nicely

 

https://media.digikey.com/pdf/Data%20Sheets/AlfaMag%20Elect%20PDFs/CT_Series_Br.pdf

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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looks interesting but i need one with wires on, not pcb version. I got the CT from my first reply working with multi loops solutions.

Thanks anyway.

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 but i need one with wires on, not pcb version

Did you even mention that? 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!