A question about monitoring mains power consumption

[aferenbach]

Hi there

Sorry if this is a very basic question. I am looking to add something between the wall socket and my kettle which keeps an eye on when the kettle stops using power. When that happens it supplies 5v to an external device which will make a custom sound so I know my kettle is boiled. I just wanted to know if there is a simple circuit that I could put together that could do this. Ideally I would like to branch out and have one wired to my toaster so I know when my toast has popped and so on.

Can anyone point me in the right direction as my efforts at googling have got me nowhere

Thanks in advance

Andrew

 

[Karthik rajagopal]

You can use an AC current sensor module with a microcontroller to do the sensing and alerting. You can get one of the micro current transformer based boards easily on market.

 

[aferenbach]

You can use an AC current sensor module with a microcontroller to do the sensing and alerting. You can get one of the micro current transformer based boards easily on market.

Thanks so much for your quick reply. Can you include a link or two to the items I should be looking for. I see a bunch of things that connect over the mains cable but I don't know what sort of output they give.

 

[Karthik rajagopal]

https://www.arduino-tech.com/dc-5v-...dule-35a-precise-with-overcurrent-protection/

Use the product shown in the above mentioned link. It also has an op-amp to detect over current. So, you can set the over current limit using the potentiometer and can directly drive a buzzer with it without any microcontroller.

 

[shumifan50]

Measuring AC means the output from the suggested board will also be following the waveform of the AC source, so the interface to the MC must take this into consideration. I use an ACS712 current sensor. Coding is quite tricky as you need to get the peak readings and then calculate the RMS value. Someone on here might be able to suggest a good (much better than my oversampling) to make the peak readings.

 

[Bluejets]

I am looking to add something between the wall socket and my kettle which keeps an eye on when the kettle stops using power

I can hear mine boiling click off from my office and the kitchen is 8 metres away.
I'm surprised you don't want it to send you an email........

 

[hevans1944]

@aferenbach: Andrew, this is an interesting app! The Allegro series of Hall-Effect current sensors seems to be the best solution. Since this is an on/off application, there is no need for a microprocessor, or a need to digitize the actual AC current. Just sensing the presence or absence of an AC current is all you need to do, and this can be accomplished with an analog comparator, whose output can operate a relay to turn on a light, sound a buzzer or bell, or instruct a computer to send you an e-mail. You will need a toggle switch to arm and disable the alarm however.

OTOH, if you are comfortable (or want to get comfortable) working with Microchip PIC microprocessors, that could be the cheapest and easiest way to interface to the Allegro ACS712.

You will need to provide low-voltage (5V) DC power for the Allegro chip and the comparator (or PIC microprocessor), but this can be provided by a small DC "wall wart" power supply. If you want to place the circuit in its own case, with an outlet receptacle on one side and a receptacle plug on the opposite side, that would be feasible. It would also allow you to use a so-called "capacitor divider" power supply to rectify and reduce AC mains power to 5V DC power. Capacitor dividers are normally not recommended in this forum, but if the circuitry is entirely enclosed in a molded aluminum box it should be okay.

If a PIC is programmed for the task, it can sound an alarm for a fixed interval of time and then shut the alarm off until the Allegro senses that the electric kettle is turned on again. Same-o, same-o with an electric toaster. Please let us know what your capabilities are with regard to building circuit boards and mounting them a suitable metal enclosure.

If you have zero experience with PICs, we can help you choose one and also help program it. The Allegro is available in several different current sensitivities, so it helps to know what amperage your electric kettle and your electric toaster uses, The Allegro is very tolerant of currents higher than its rated "linear output" current, so choosing a model that covers the ten to twenty ampere range is probably good enough for your application.

Please let us know how you want to proceed with construction. Be aware that, if successful, the design will be copied by Asian manufacturers and sold on eBay for less than the cost (to you) for the parts required to make it. Or just wait until someone living in a Pacific Rim country reads this thread and offers a product for sale next week or sooner... I say these things not to deter you. It is a worthwhile project, and you will learn a lot by completing it. Just don't expect to retire early on the profits you make from selling it. This, after all, is a hobby forum. We do electronics here because we love to do electronics.

 

[shumifan50]

As an extension to the project you could use one of the ESP32-S2 micro-controller, as they are cheaper and easier to program (using Arduino IDE) and give you WiFi (libraries available plus lots of examples on web) and you could then use a TRIAC to switch the kettle/Appliance on/off from a tablet or mobile phone (be aware that the kettle might run dry if no water in it). The ACS712 comes in a variety of current sensing ranges. The kettle would be 1KW or 2KW meaning a current of approx 5-10 amp(220/230V), so the middle range ACS712 will do the job or the high end one which will leave some headroom. When switching the Triac it is advisable to opto-isolate it from the 230V and for this the MOC30xx is perfect as it does zero crossover switching, saving the element of the appliance as it does not suddenly apply 230V, it switches at zero volts and then follows the normal AC curve to 230V, reducing the mechanical shock on the element. This will be a good project for learning electronics and programming.
As a side note: the interface to the tablet/phone could be a web page as there is a standard sketch available for implementing a webserver on the ESP series of MCs.

 

[Minder]

Bit of a misleading title, "monitoring Mains Power consumption" when really asked is the presence or absence of current.
Mains Power would be Wattage metering.