Hi peoples, I have searched but not found …
Does Core sell a module for measuring mains (240V A/C) electricity - current / power / voltage ? Core have plenty for measuring <24V DC or low voltage AC; and relays for switching 240V AC … so i guess I’m using the wrong search terms and/or didn’t recognise it.
We can buy smart power plugs with energy monitoring for $15, so I assume there must be a chip to do the measuring, and at a reasonable price.
I don’t think Core will have anything that requires fiddling with mains wiring. I have a device (which I have not used for some time) that plugs into a power outlet then the appliance is plugged into that. Measures lots of things. Volts, current, power, power factor and accumulated power (kWh) over time. . Display is a bit small and is sometimes a bit hard to read. Useful device from Jaycar designated MS6115. I don’t Jaycar stock them any more but seem to be still available. i think I paid something less than $20 at the time
Cheers Bob
And yet … they have so many 250V A/C relays from as little as $4.20 which, if I understand correctly, allow us to directly connect (is that “fiddling with” ?) mains power. WisBlock Relay Module RAK13007 is just one example. Some even handle 40A, though I understand 10A (or preferably 16A) is appropriate for appliances.
We have lots of options to switch appliances on and off - but not to detect whether they are operating. Something a $15 smart power plug will do for about 12 months until the warranty runs out. Or a Shelly 2PM - but it seems gross waste to have a microcontroller and Wi-fi in each power plug device just to communicate over wi-fi to a microcontroller sitting 20cm away.
As for your Jaycar power monitor, I’m assuming it has no digital interface ?
And yes, I am well aware that mains power is not just dangerous, but can be lethal.
Yes, that is correct. You have to look at the screen.
Cheers Bob
And yes the Relay itself is mains rated but as pointed out recently the modules they are mounted into are NOT.
Hi Donald
I just checked the link you provided. I had not come across that one before.
They get away with that rating by having cut outs in the actual board to provide air gap isolation but I don’t consider that makes this item less dangerous.
I agree there seem to be some double standards here but I suppose that if Core provide adequate warning they will have fulfilled their obligation. The Vendor cannot be really held responsible for what the end user does with their product if as I say adequate warnings are provided.
Having said that I just rechecked and could not find any warnings relating to this product. I think Core do issue a general warning re mains wiring on their documentation which may be adequate. I reckon the end user in this market has to be considered aware of the real dangers and have enough sense to be very careful and use qualified people for this task
There is a small warning notice printed on the board itself re high voltage.
Cheers Bob
FYI, my use case is that I have Ethernet-over-power to the laundry downstairs, where I have a chest freezer, washing machine and dryer plugged into a power board.
I currently have 3 smart power plugs with power monitoring, and a Wifi access point to connect to them. I have replaced the power plugs from time to time, requiring adjustments to my Home Assistant system and automations.
I have noticed that power boards either:
I am thinking that my ideal solution would be:
Of course there is still a lot of research for me to do. I half expect that there will be a good reason why there is not already a real smart power board on the market … but surely the cost should be less than 4 x $15.
Hi Donald
I have what you might call a half smart power board. There is one socket powered at all times. Then there is a “control” socket that is powered all the time but when a plugged in appliance is switched on (say a TV) the remaining sockets are powered. That enables the de powering of auxiliary devices by switching off the “main” or “control” device.
I think you want to do the opposite of this.
The freezer would the appliance to leave running at all times but a good idea to monitor temperature..
As your washing machine starts up where it left off when power restored this would be the logical “slave” device to switch off when the dryer is started. In other words a priority switching system. That is what you appear to have now.
If the power board breaker pops when everything is on that indicates the max 10A has been exceeded. That could suggest you could use another circuit from your power board to the laundry maybe. Power circuits are 16A with a 20A circuit breaker so maybe another power point on the same circuit might be enough. I can see why you want to measure power now. Volts and current will only tell part of the story without knowing the power factor BUT will be absolute worst case and leave plenty of head room.
Cheers Bob
I remember those, and when I finally decided I had a use for one … they had disappeared off the market. Actually there seem to be quite a lot of things taken off the market just after I find out about them 
Like Feijoa cordial.
The freezer doesn’t really want a relay, but I would like to continue monitoring its power usage. As you can see I’m not too fussed about how accurate the readings are - basically whether they are drawing power or not.
I have become very wary of appliances with electronic controls because they need someone to press the ON button after power is turned on … it’s getting quite hard to find the old-style appliances that use manual switches and dials. So I was amazed to find out that the Electrolux washing machine would resume where it was up to when powered back on. And that means it is fairly easy with an automation to stay under the 10A where it’s relatively safe.
Hi Donald
We have a new Beko front loader with fancy electronic controls (even with your phone I think if you are so inclined). I am pretty sure it resumes after a power failure. Must try it some time when I get a chance.
Cheers Bob
Gentlemen hello,
Can I suggest the following construction that would leave a minimum of risk to exposure to coming in contact with 230V live connections.
230V Power Monitor_0001.pdf (735.3 KB)
Referring to the attached diagram, take a 1 or 2 single phase extension core and remove the outer sheath 2 expose the 3 conductors without damage to the individual core insulation and with a suitable PVC enclosure mount the cord through slots cut into the 2 ends. Place a suitable 20A to 1V split (hinged) current transformer over the active conductor (red or brown) bring the secondary signal cable out through a suitable hole. Secure everything and attach the screwed lid. To be safe have your work verified by someone qualified if possible. Once done there is no need to open the lid again.
For the voltage signal use a suitable single phase plus back transformer 230V AC to 5 or 10V AC.
Now connect the current signal and volt signal to some suitable electronics and provide suitable signals to drive 2 ADC’s on the RPi Pico and and discrete inputs, for example with some zero crossing checking you could calculate the phase angle (hence power factor - kVA)between volts and amps, use interrupts for this. To be successful you will need to know the polarity of both volt and current signals, although this could be checked by trial and error. From here all you need to do is code to your hearts content and provide an output, possibly with an OLED.
With the extension core and plug back plugged into the same outlet plug your intended load into the cord socket and happy measuring any load single phase up to 10A.
To verify your accuracy use an initial load that you have data for. I would start with a resistive load, pf of 1.0 initially with only watts involved.
Keep in mind power measurement in the real world to achieved using both current and voltage instrument transformer and not primary connected. The plugins we buy are meant to be used as supplied and not played with internally.
Have fun.
Bryan
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