Self Powered Current Measurement

[wigman27]

Hey all,

I am working on designing a power meter. I know you may say there are hundreds out there however, I would like mine to be a little different (from any I have seen anyway). I am planning on having a base unit (Beaglebone or similar) inside with remote current measurement in the main switchboard or somewhere else. These current measurement devices would be interrogated at a certain interval and logged online directly.

My main question is, is there a way to successfully power the current measurement unit (CT or hall effect) using induction? would I be able to power the device using the output of the CT? Even if I have a small lithium battery built in that charges itself when the unit is not being interrogated for data to smooth and regulate the supply.

I am guessing its not, but I just wanted to put it out there and see what you thoughts where.

Also, side note.
Is there such a thing as a compact 3 phase plug in Australia? about the size of a standard power point?

Lee

[wigman27]

I obviously forgot to mention that I need to power the CT as well as associated control gear and transmitter

[HackedFridgeMagnet]

Is there such a thing as a compact 3 phase plug in Australia? about the size of a standard power point?

No it is a fair bit bigger http://www.fastlec.com.au/p/Industrial/IP66-Switchgear/10A-5-Pin-Straight-IP66-3-Phase-Plug/IP-PLS3PH510?gclid=CJKVhoaJxL0CFRRxvAodrDEApg

My main question is, is there a way to successfully power the current measurement unit (CT or hall effect) using induction?

You could do it theoretically, but you wouldn't be allowed to in Australia and it would be an unnecessary hassle as you would need probably more than one turn of an individual conductor, not the whole sheathed cable.

The easy way is just use the mains and get the volts. You already have accessible terminations in a switchboard.

I obviously forgot to mention that I need to power the CT as well as associated control gear and transmitter

Actually the CT is the only thing you dont need to power.

[David Hess]

I am working on designing a power meter. I know you may say there are hundreds out there however, I would like mine to be a little different (from any I have seen anyway). I am planning on having a base unit (Beaglebone or similar) inside with remote current measurement in the main switchboard or somewhere else. These current measurement devices would be interrogated at a certain interval and logged online directly.

My main question is, is there a way to successfully power the current measurement unit (CT or hall effect) using induction? would I be able to power the device using the output of the CT? Even if I have a small lithium battery built in that charges itself when the unit is not being interrogated for data to smooth and regulate the supply.

This is certainly possible to do.  The switching power supplies in the old Tektronix 7000 series oscilloscopes power the primary side switching regulator control circuits, which are galvanically isolated from the line input, completely from the primary side current sense transformer.

The big problem I see though is that 50/60 Hz current transformers are intended to operate below a specific burden voltage.  At higher voltages, the transformer will saturate.  You can see this effect in current probes where using a low impedance load, often provided by a virtual ground, allows lower frequency operation.  To get around this either the transformer will have to be a custom model intended to operate with a higher burden voltage or another transformer could be added to step up the low voltage output.

Available output power will depend of course on the minimum primary current.