monitoring on the other hand is pretty neat.
I still want to finish designing my whole-house mains power monitoring system. there are some existing projects that do this but I looked at the schematics and they do a bunch of things wrong, especially around the CT sensing.
@gsuberland Please do share if you get something nice working. I've got some old SEL gear hooked up, but would like a bit higher bandwidth system to see when fun things happen.
@AMS I do actually have a mostly-completed design but it's from way back, when I wasn't as clued up.
the general topology is one mainboard that's fully low voltage, then pluggable fontend modules for doing the mains measurement.
the modules have a pair of ADuM3473s or similar providing two isolated inputs and six isolated outputs in total, plus isolated bipolar power (with LDOs afterward) referenced to mains neutral. then I use direct resistive division and shunt current measurement.
@AMS the isolated inputs are two clocks used to drive the voltage and current ADCs. the isolated outputs pull the serial data back from the ADCs. so each module can do three power feeds.
the idea behind doing direct in-path resistive shunt measurement is that with CTs you get phase error, which is a bit of a blocker for trying to measure power factor or fast current transients.
and the frontends are modular for easy replacement but also because many ADC ICs go out of prod/stock real quick
@AMS it isn't a cheap design (those isolation ICs are like £10 each) but it's still a lot cheaper than buying a commercial one with half as many features.
@gsuberland My thought was resistive voltage and nice closed loop LEMs (or fluxgate LEMs if I find some cheap) for current.
@AMS yeah that's another way to go with it
thing is, I'm gonna be measuring voltage on each line anyway since I want to be able to see if breakers do anything wonky, for example, so since I already have to have some sort of isolated voltage measurement I might as well do the current measurement while I'm at it
@vxo @AMS they end up being a bit more expensive in total, last I checked. with something like AMC3330 + AMC3302 it's about £10 per voltage + current channel (assuming I use the MCU's ADC to measure the amplified output, and I don't need any more opamps for biasing and such), whereas with the ADuM3473 option I can use commodity ADCs and get three voltage + current channels for about £22.
@gsuberland @vxo Yeah, they're like $4 in ones I guess (I'm used to the 100k+/yr pricing at work). 8mm isolated though and nice >80dB noise floor which makes things nice and easy from an isolation standpoint. Being cheap means I'd probably go non-isolated neutral-referenced power and voltag and isolate the current sense. Wifi makes for cheap and cheerful isolation to get the data out.
