HI guys, hope you are well.
Apologies for novice questions, I am new to this.
I would like to use my arduino uno to make a type of circuit breaker for 230V loads. I have got an emontx shield and some CTs and am in the process of creating the test rig.
Where can I find some code to take the current I am measuring with the CTs and set a limit, that when passed sends a signal to a digitl i/o and then to a relay to turn off the supply?
Any other help is most appreciated.
Thanks
Re: Using arduino as circuit breaker
If there is the slightest possibility of the safety of any person or property being put at risk should your project fail to operate as intended, DON'T DO IT.
In any case, you must have a proper protection, a circuit breaker or fuse, in place. You also probably need to make your device 'fail-safe' - in other words, you have to evaluate whether failing to turn off the supply is better or worse that turning it off, insofar as you can predict the failure mode of your device.
Having written all that, a demo sketch on Github for the Shield is your starting point. You need to add a relay board driven by one of the I/O ports, and you need (presumably) a pushbutton to turn on the output and the relay, and you need to detect that the rms (or the peak - remember polarity) is greater than some limit and use that to turn the output off. You might well want to start with one of Robin's (calypso_rae) 'continuous' sketches so that your sketch can react immediately (meaning after only 1 cycle). Or you might decide that it's possible to accept a short-term overload (mimicking a standard circuit breaker), in which case you'll need to accumulate the 'overcurrent' value and only trip the output when a predetermined value of that is exceeded.
Re: Using arduino as circuit breaker
Brill, thank you very much.
I must stress this is only experimental and will not be controlling genuine circuits, it's just a thought I had. The test rig is set to run at approx 2A with a 3A fuse and RCD back up with all cables and connections adequately protected and covered, I was an electrician many years ago so the safety aspect is something I take seriously. The arduino will be set to operate at 1A, when the load bank exceeds that I hope to isolate supply.
Cheers, this gives me a good starting point.
Re: Using arduino as circuit breaker
"I was an electrician many years ago so the safety aspect is something I take seriously."
I had no means of knowing that, and let's just say that some individuals can have a cavalier attitude to safety, so I was urging caution for reasons obvious to you, but possibly not to others.
There's an interesting bit of software coming if you want "thermal" trips. And make sure you have a fairly low ratio CT if you want 2 or 3 A max scale - the split-core YHDC-013-000 with the standard burden is barely reliable at 1 A.
Re: Using arduino as circuit breaker
Or since the fault current is limited upstream, pass the load wire n times through the core to get a scaling factor of ~n.
Re: Using arduino as circuit breaker
Thanks for the feedback, the YHDC CT is a starting point but is not too effective at low amps, unfortunately that is what I am starting with so will have to see where I get! Have already thought of looping the wire to scale up the current, which seems a simple way to improve accuracy.
The 'thermal' software sounds interesting, would be good to see.
Found interesting using the openenergy.org method in different way
http://www.homautomation.org/2013/09/17/current-monitoring-with-non-inva...