Your classic farmer stealing power urban legend.

https://user.physics.unc.edu/~deardorf/phys25/rwp/exam1rwpsolution.html

8) Assuming a cost of $0.10/kW-h, what is the approximate value of the energy stolen by the farmer over the period of one year?

If we assume that the farmer used the equipment half of the time (an average power consumption of 36 W over the course of a day), then the total cost for one year would be: cost = (36 W)(24 h/day)(365 days/year)($0.10/kW-h) = $31.54/year. Even at the maximum power rate of 72 W, the value of the energy stolen would be only $63/year. This hardly seems worth the effort, risk, and cost (see below).

9) Estimate the cost to make the coil, assuming that the farmer used 12-Gauge copper wire at a cost of $0.15/ft. Evaluate the cost-effectiveness of the farmer's design and calculate the approximate pay-back period for his investment.

With 7140 loops of wire required and a length per loop of 20 m, the farmer would need 143 km of wire! At $0.15/ft = $0.50/m, this wire would cost $71,400! This means that even at the maximum energy consumption rate, the payback period would be at least 1000 years

11) What other insights can be learned from this problem?

Based on the calculations above, it seems that this method of stealing power is highly inefficient and impractical. I seriously doubt that any farmer has actually done this (perhaps this is a myth suitable for the Mythbusters to investigate!). This application of Faraday's law is essentially a power transformer with very low efficiency. There are many other applications of Faraday's law that pervade our modern lives; this is just one that is not advised

 

If we assume that the farmer used the equipment half of the time (an average power consumption of 36 W over the course of a day),

Except the urban legend, as I have heard it, says he ran his entire farm off it.

 

Except the urban legend, as I have heard it, says he ran his entire farm off it.

In a slightly more believable legend, the entire farm was run on methane.

How good is he? He can beat most men with his breath.

 

AFAIK, there is nothing wrong with that, but it is fairly well known that the efficiency of the process is really poor. So a whole lot of effort for a vanishinly small return. Sounds like the same business opportunity as selling shovels to miners on the way to the Klondike.

At least they made more than many of the miners.

 

Ok then it could be that the excitation currents are different for the LCR meters than in the actual circuit. You 'might' be able to apply a DC offset to the inductor to see if you can get the inductance to change.
The only thing that is hard to understand is what the core is doing for each type of test. It's such a huge inductance too. Cores that are not air have some unusual characteristics. The permeability could change quite a bit as you go from 1ma AC to 10 amps AC for example, and if you vary the DC offset it will change with that also.

Is there any easy way you could reduce the inductance in your inductor? You could try reducing it anyway. I assume you double checked the cap value also.

I reduced the inductance and it worked. I believe my core is saturated. I will reduce the number of turns and use a thick wire the next time. Thanks for your suggestions.

 

AFAIK, there is nothing wrong with that, but it is fairly well known that the efficiency of the process is really poor. So a whole lot of effort for a vanishinly small return. Sounds like the same business opportunity as selling shovels to miners on the way to the Klondike.

Actually, this sort of application is used to energize wireless sensor networks in remote areas. It won't be used to power up a house.

 

Your classic farmer stealing power urban legend.

https://user.physics.unc.edu/~deardorf/phys25/rwp/exam1rwpsolution.html

8) Assuming a cost of $0.10/kW-h, what is the approximate value of the energy stolen by the farmer over the period of one year?

If we assume that the farmer used the equipment half of the time (an average power consumption of 36 W over the course of a day), then the total cost for one year would be: cost = (36 W)(24 h/day)(365 days/year)($0.10/kW-h) = $31.54/year. Even at the maximum power rate of 72 W, the value of the energy stolen would be only $63/year. This hardly seems worth the effort, risk, and cost (see below).

9) Estimate the cost to make the coil, assuming that the farmer used 12-Gauge copper wire at a cost of $0.15/ft. Evaluate the cost-effectiveness of the farmer's design and calculate the approximate pay-back period for his investment.

With 7140 loops of wire required and a length per loop of 20 m, the farmer would need 143 km of wire! At $0.15/ft = $0.50/m, this wire would cost $71,400! This means that even at the maximum energy consumption rate, the payback period would be at least 1000 years

This application can be used to harvest energy for wireless sensor networks. This cannot be used to steal power for domestic use since the open coupling mechanism has a low efficiency.

 

This application can be used to harvest energy for wireless sensor networks. This cannot be used to steal power for domestic use since the open coupling mechanism has a low efficiency.

That's true for sure and why 500mW is a pipe dream in a practical (not on a power pole or near a MV power line) and legal 'free' power harvest system.