[lstodd]

It doesn't measure voltage and thus can't measure true energy consumption = power, only currents. It then must estimate power based on some preset voltage. Not to mention those clamps can't have precision or time resolution for truly interesting stuff.

A toy, in other words. It might be good enough to get a rough idea what eats more or less and when, but it'll never match the utility power meter which is what you're paying by.

cdrc: I rewire my houses myself, because those licensed loons can't be trusted with a 12V light bulb. At least that way _I_ am sure it won't blow up or burn or whatever.

[generallee5686]

The IoTaWatt does measure voltage. You plug in a calibrated AC wall wort as well as the DC USB power supply.

[lstodd]

Well, sorry, then. Missed that bit on their site.

Still, inductive current measurement with the sizes of the clamps they show and typical currents they're measuring isn't accurate at all. Not even considering that voltage measuremens via a wall wart would depend on what load is currently sharing the same wiring.

This might be my bias since I design similar stuff for solar offgrid, where a percent or ten off are that much in capex divided by battery lifetime, then multiplied by battery cost. It bites.

I don't trust inductive clamps at low currents. I would never trust measuring voltage on the same line as a load.

Hall sensors or current shunts; voltage dividers - all driving MCU ADC channels via optoisolated opamps. Everything measured as near to the source as possible. Otherwise you're getting nearly worthless data.

[Gibbon1]

> Not to mention those clamps can't have precision or time resolution for truly interesting stuff.

That's actually not correct. Clamps / current transformers are totally fine.

[lstodd]

Then you haven't taken into account noise building up in every half inch of a cable that leads from the clamp to the instr-amp. Or do you advocate clamps with built-in ADCs? No objection then, as long as the wires carry digital signal but for the fact that this would cost so much it isn't funny. One might as well stick to off-the-shelf PLC-style rail-mounted IO modules and shunts/transformers then.