What is turns ratio of transformer used to couple energy from the mains live wire?

[treez]

Hello,
The Onzo "smart energy kit" uses a clamp-on ferrite to couple energy out of the 230VAC mains in order to power an energy meter. It also uses this to sample the electricity usage.
What is likely to be the turns ratio of this transformer? (obviously its a single turn primary)
Do you agree that its more likely to be a resonant inductive coupler than a transformer?

You can see the clamp here...

**broken link removed**

 

[FvM]

Do you agree that its more likely to be a resonant inductive coupler than a transformer?

Not necessarily. Resonace would require a tightly tolerated transformer inductance. Using a high permeable core as any usual current clamp does might be more suitable.

I didn't find a required minimal load current for maintaining device operation mentioned in the information.

 

[treez]

apparently when current flows, it couples some to its secondary and charges a battery........ive heard its a 600:1 transformer, but surely that cant be right?

 

[FvM]

ive heard its a 600:1 transformer, but surely that cant be right?

The order of magnitude sounds reasonable. Would transform 10 mA..16 A into 16 µA..26 mA. But transformer inductance would be critical at lower currents, so maybe we need the suggested resonant circuit...

 

[Dan Mills]

It will be a current transformer, and yea 600:1 sounds reasonable.

The transformer secondary will be loaded with a low impedance so as to keep the core flux minimal (This might actually be a constant power input switcher of some sort as the core flux then falls with increasing line current).

Google "Current transformer" for some discussion of the operating mode of these parts.

Regards, Dan.

 

[betwixt]

I'm not sure it charges a battery from the current clamp. I use something similar here and the display is powered from a small battery. Essentially it is just a voltage measurer, using the voltage induced in the secondary winding (which is probably 600:1) to measure the current in the wire it is clamped to. With it's LCD display and an ADC which I would guess is powered up to take a measurement about once every 2 seconds, the battery lasts longer than a year. The settings and totals are stored in NVRAM so they survive through a battery change.

Brian.

 

[FvM]

The term "energy harvesting clamp" in the advertizing suggests that the unit is powered from the current transformer, without a disposable battery.