Energy harvesting from the mains?

[cupoftea]

Hi,
In this video, at 1:30...

....it shows a device which has no batteries, but which gets all its operating power from the mains. It does this with a simple CT which clips round the mains line which enters the house. The same CT measures the mains current which leaves/enters the house.

What would you say is the best type of material for this CT? Surely it would best be iron? However, powdered-iron would be used as it would be cheaper to make “split ring”?

Also, I would have thought the having the current measurement function, and energy harvesting function, coming from the same CT, was somewhat of a compromise?

Would you agree it would be better if there were two secondaries, one for current measurement, and one for the harvesting? The harvesting one would pretty much be a full wave diode bridge into a big-gish capacitor? …and with a wee SMPS to give a known voltage output, and a clamping Zener in there for those occasions when the capacitor might otherwise get overvoltaged?

None of the web docs say much of the powdered iron material used....

https://www.diva-portal.org/smash/get/diva2:1651387/FULLTEXT01.pdf

 

[betwixt]

A single secondary should suffice as long as the circuitry is part of the burden that would normally be there.

Brian.

 

[wwfeldman]

somebody better educated, more experienced and smarter will have to explain the point of this gadget

unless you're stealing from your neighbor, getting power from the mains is a simple as plugging in your device

as for cupoftea's question:
if you use one secondary, then as betwixt said
if you use more secondaries, the current measuring function will be incorrect by the amount
of current used by the additional secondaries (or the current thereof reflected back to the mains)

 

[cupoftea]

Thanks, in order to harvest energy, the secondary will have to be a diode bridge into a storage capacitor.....AYK, this doesnt look electrically anything like the usual burden resistor.

 

[Easy peasy]

The series current pulled from the CT is the same regardless of whether there is a small transformer say in series with the main burden resistor "harvesting" energy, the sec CT current could indeed flow thru a bridge rectifier & cap & low voltage zener - or via a 50mW step up Tx to same to provide ~ 5V for the electronics - without distorting the sec CT at all ...

Design is all about imagination ...