How much power can be drawn from a CT Clamp?

Question

If I have an AC line powering some device, I can put a CT clamp around either the hot or neutral wire, and measure some low ac voltage and current. I understand this is because the AC line creates a magnetic field due to the right hand rule, and I am essentially harvesting the power with a transformer. I have two questions:

1. Does a CT clamp add more load to the AC line, or is it that the AC line would create that magnetic field no matter what, and I am just harvesting it?

2. How can I get more total power out of a CT clamp? I am not able to loop the input around multiple times, but would like more power. Will more secondary windings do this? widen the ferrite core? I'm not sure.

Any help appreciated.

Answer 1

Question 1 has answers in my question Primary voltage drop in current transformer on this site.

Question 2: CTs have a VA rating just as VTs do. You calculate the maximum burden (resistance) using the VA rating and the rated current. For example, a 5 A, 3.75 VA CT can have a maximum output voltage of 3.75 / 5 = 0.75 V. That means that the maximum output burden (at the rated primary current) will be R = V / I = 0.75 / 5 = 0.15 Ω. Remember that the voltage will fall with falling primary current.

Tip:

• Voltage transformers like open circuits (no load) and don't like short-circuits (overload).
• Current transformers like short circuits (no load) and don't like open circuits.

Answer 2

A CT might be able to draw 100 mW of linear power from a few kW power source drawing 10A so it's not efficient nor free energy unless tapped into someone else's line.

A novel method I read about storing extra energy is using a nano crystalline CT with very high mu that would normally saturated 3/4 of the time is counteracted with a control coil to prevent saturation but still stored more energy than put back might boost up to 46%. Their CT with a lot of effort (!) was able to store almost 1/2 W. But the impedance must be matched to get MPT (max power transfer with 50% thru)

The limitation is the thermal resistance of thousands of windings to create 1/2 W with matched impedance from N^2 and the voltage available into a linear load, not LEDs. Plus the ability to added a second winding to counteract the saturation effects that kill the inductance and ability to store energy. But the linear load gets an irregular pulse response and not a sine wave. That's the challenge.