power line induction

[SkyLaneUSA]

I live in the country. I have a small sensor/microcontroller PCB that uses 1 to 5 mA. I can't use solar power, but the sensor is within 10 feet of 12K volt power lines. I have the sensor in a water proof container, and completely isolated from ground. I experimented with an antenna / diode bridge / and small 1uF cap to get DC power to the board. I get 1K+ volts AC at the bridge, but when I turn on the board it goes to almost zero. An electronics guy in class says it will never work. Any ideas or help would be greatly apprieciated. Lane

 

[gstormc]

You are getting 1kv at the bridge when it is switched off because it is unloaded, putting a load onto it will try and draw the current through the air but air being highly resistive the voltage drop is too great and therefore you get 0v at bridge.

If the unit only draws 1 to 5ma have you considered using a battery to power it? I am not sure as to what sort of voltage you need to run it but even a 1Ah battery would last 200 odd hours continuously, the bigger the battery the longer it will last.

Is there any reason you cant use solar power? Wind Power? Mains power?

 

[SkyLaneUSA]

Better Antenna

Thanks for the response! Weight is a problem, I can use a small button battery, but I want to keep the sensors going for along time. By mains power do you mean plugging it in to a wall socket? There is not any available, where these sensors are going. I am thinking about coiling a wire ( safety 1st ) around the power line to induce more current into the wire and board. These power lines go to pivot irrigation and wells that are not active for another month, so there is hardly any current running in the power lines now. Maybe thats the problem?

 

[Optikon]

I live in the country. I have a small sensor/microcontroller PCB that uses 1 to 5 mA. I can't use solar power, but the sensor is within 10 feet of 12K volt power lines. I have the sensor in a water proof container, and completely isolated from ground. I experimented with an antenna / diode bridge / and small 1uF cap to get DC power to the board. I get 1K+ volts AC at the bridge, but when I turn on the board it goes to almost zero. An electronics guy in class says it will never work. Any ideas or help would be greatly apprieciated. Lane

An antenna is not enough.. you need to make a transformer with many turns. An antenna probably is looking like < 1 turn. Wind a large loop of wire with many turns and see what you get.

BTW, this is theft.

 

[SkyLaneUSA]

I took a spool of transformer wire and connected it to the diode bridge. There was a static type of spark when I hooked it up. The tiny LED flickered when I turned on the board, but that's all that happened. I will try to find a charging circuit, and put a small battery on the board. Thanks for the help.

 

[Optikon]

I took a spool of transformer wire and connected it to the diode bridge. There was a static type of spark when I hooked it up. The tiny LED flickered when I turned on the board, but that's all that happened. I will try to find a charging circuit, and put a small battery on the board. Thanks for the help.

Put an ammeter in series with your coil effectively shorting the turn. This will let you measure short-circuit current. This arrangement lets you physically orient your loops differently to see the effects. You are making an air transformer that is coupled to the power line fields. Orientation and physical distance will each affect the amount of coupling. Find the arrangement that gives you the most short circuit current - this will be the best you will ever be able to do. If that amount in not large enough to power what you intend - trash the idea.

BTW, you shouldnt be doing this anyways because it is STEALING. You dont seem bothered by this. I understand that the amount of _power_ is quite low but if you stole a $0.10 piece of candy from a store, you can go to jail all the same. This is no different.

 

[SkyLaneUSA]

Thanks for your response and ideas. We belong to a rural electrification association. The farmers and ranchers in this area own all the power lines, transformers, etc. The REA buys power in large blocks and each farmer is charged a minimum + . Most months we don’t use the minimum amount. I am drafting a letter to the board and have a lineman over to inspect mainly my safety procedures on this tap to the grid.

The problem is that it doesn’t work. I will use the ammeter in series and try to make a better coil / antenna arraignment. But I am going to redesign the circuit and board someway to just try to charge a small battery or super cap when the voltage gets to low. Thanks again.

 

[mneary]

Your problem with induction is that the current in the line varies too much. You need a solution that doesn't depend on the current.

Your professional electrician/lineman may be able to purchase low wattage transformers to convert the 10KV to something that you can use safely; this would be your best option.

 

[kchriste]

BTW, you shouldnt be doing this anyways because it is STEALING.

Actually, it's not. He would actually be reducing the losses in the power lines by tapping the magnetic flux. By drawing current off the "secondary" coil via his makeshift transformer he is reducing the voltage drop on the primary and helping reduce power transmission losses. On another note; this reminds me of the fluorescent tubes "planted" under some power lines in England:
https://news.bbc.co.uk/1/hi/england/bristol/3509651.stm

 

[TheVictim]

I've thought about building a tank circuit with a 10uF nonpolarized electrolytic cap (speaker crossover) and a .7H inductor which should be resonant at 60hz to power a small transmitter, but then again a .7H inductor isn't exactly small.

This would just be for ambient 60hz, I'm sure if I got anywhere near a large power transmission line it would self destruct.

 

[Optikon]

Actually, it's not. He would actually be reducing the losses in the power lines by tapping the magnetic flux. By drawing current off the "secondary" coil via his makeshift transformer he is reducing the voltage drop on the primary and helping reduce power transmission losses. On another note; this reminds me of the fluorescent tubes "planted" under some power lines in England:
https://news.bbc.co.uk/1/hi/england/bristol/3509651.stm

According to US law it is. There are people from the south sitting in jail right now. Home-made donut transformers on power lines has been tried before and deemed illegal.

 

[Hero999]

Actually, it's not. He would actually be reducing the losses in the power lines by tapping the magnetic flux. By drawing current off the "secondary" coil via his makeshift transformer he is reducing the voltage drop on the primary and helping reduce power transmission losses.

I don't believe that. For a start the electricity company already uses inductors to ballance the line capacitance and because your transformer is fully loaded it will appear resistive rather than inductive, only unloaded transformers are mostly inductive.

 

[SkyLaneUSA]

Filling the tank

The tank circuit sounds interesting. I will try to find a formula so I can adjust the size of the components. Will the tank circuit oscillate on its own, so you can draw some power off of it?? Thanks

 

[TheVictim]

A tank circuit appears like a short circuit to its resonant frequency, so it should oscillate from ambient 60hz. You'll get something out of it without even having an antenna. 10uF and .7H are resonant at 60hz. I picked the 10uF because it was the largest non-polarized electrolytic I have lying around. I'm sure a better Q can be obtained using a larger cap and smaller inductor.

Methinks a resistor should be added to keep from loading the tank circuit down too much with a bridge rectifier. The bridge rectifier should probably be made from germanium diodes.

I really do think this circuit would die if it was placed in too close a proximity to transmission lines.

 

[SkyLaneUSA]

I don’t have any nonpolarized electrolytic caps, so it will be awhile till I can experiment and test it. Are nonpolarized caps expensive? I think I have silicon diodes, I will try to find germanium. When you say the circuit will die, do you mean it will burn out the components. This will be fun to experiment with, Thanks.

 

[TheVictim]

If the current through the inductor or the voltage through the capacitor greatly exceed their maximums then yes, they would fry.

On the flip side I don't want the diodes dropping a bunch of the voltage across them with weak 60hz ambient around, hence a preference for germanium diodes.

 

[SkyLaneUSA]

My meter is pegged @ 1000 VAC and screeches real loud before I turn on the board. So I might need a very high rated cap. I might experiment with some polarized caps first.

I talk to a physics teacher and he says it won’t work for the same reason birds can sit on power lines. He said the only reason I get the high voltage readings is because the e – field can sense ground. (Although thru very high resistance). Someone else told me the lines I am under are 3 phase and you can, get power thru the air by some way having separate circuits for each phase. I am going to try the tank circuit and if that doesn’t work, I may have to give up.

 

[kchriste]

I don’t have any nonpolarized electrolytic caps, so it will be awhile till I can experiment and test it. Are nonpolarized caps expensive?

You can put two polarized electrolytic caps in series/back-to-back configuration (connect the two + terminals together and the remaining - terminals will act as a nonpolarized electrolytic cap at 1/2 the capacitance) in place of a nonpolarized electrolytic cap.

For a start the electricity company already uses inductors to ballance the line capacitance and because your transformer is fully loaded it will appear resistive rather than inductive, only unloaded transformers are mostly inductive.

Oopps you're right. I was only thinking from the point of view of the load and not the supply.