generating electricity using Earth's magnetic field?

[dude8604]

Someone was telling me that if you take a wire coil and move it, power will be generated because of the Earth's magnetic field (because of electromagnetic induction. Does this actually work and how can I test this? I'm having trouble finding info on this. Anyone have any ideas of where to look or what to search for?

I found out that there is a device called the Groves Earth Coil invented by an English scientist in 1900, but I can't find any more info on it.

 

[Akira13]

My physics prof (back my freshman year) demonstrated that principle to us. He took a large coil of wire (a bit larger than a dinner plate, coiled a few cm thick) and danced around the room with it. The ends of the coil were hooked up to a very sensitive ammeter. Great demo. I suppose you can just coil up a bunch of copper wire (insulated), hook the ends up to an ammeter ($15 at radioshack), and go at it.

 

[ReiAyanami]

if you take a wire coil and move it

input < output

 

[dude8604]

Originally posted by: ReiAyanami
if you take a wire coil and move it

input < output

what do you mean?

 

[syberscott]

Originally posted by: dude8604

Originally posted by: ReiAyanami
if you take a wire coil and move it

input < output

what do you mean?

Moving the coil uses more energy than you get out of it, it's not just "free" energy.

 

[ShawnD1]

Originally posted by: ReiAyanami
if you take a wire coil and move it

input < output

Do you mean input > output? What you said means the output is greater than the input (which is never true)


Trying to capture the earth's field is totaly pointless because it's much much weaker than magnets used at current power plants. If you hand crank a small coil inside large magnets like the ones used at power plants, you get a current which can be measured on an ameter and a voltage which can be measured on a voltmeter. If you have a big coil rotating in an open field and you're relying on the earth's field, only something really sensitive like a galvanometer will detect any sort of electricity being created.

 

[Fencer128]

NASA were going to trial this as a "tethered cord power source" on a satellite a few years back. It never happened then (might have done by now) due to the winch breaking as they tried to let the wire out.

I'm sure it works and it has/is considered for use in satellites (where gravity provides you with a "free" energy source to move the wire).

Cheers,

Andy

 

[uart]

Originally posted by: Fencer128
NASA were going to trial this as a "tethered cord power source" on a satellite a few years back. It never happened then (might have done by now) due to the winch breaking as they tried to let the wire out.

I'm sure it works and it has/is considered for use in satellites (where gravity provides you with a "free" energy source to move the wire).

Cheers,

Andy

A voltage (and current if the coil is loaded) is produced when either a fixed coil is placed in a time varying magnetic field, or alternatively, a coil is rotated (or otherwise moved so as to change the flux linkage) in a stationary magnetic field.

In order to extract electrical energy you must allow current to flow (ie have a non open circuit load), but the resulting current also interacts with the magnetic field to produce a retarding force. That is, the force always opposes the motion of the coil and hence extracts power/energy from whatever is moving it.

So I'm very dubious about any potential for "free" energy. Gravity does not provide free energy! It cost a lot of energy to get a satelite up there and if this retarding force is slowing it down and bringing it out of orbit premeturely then it is certainly NOT free. Perhaps if someone here can suggest a mechanism whereby the retarding force slows only the Earth (that is the energy is sourced from Earths rotational KE) then I might consider it "free" energy - well kind of.

 

[Fencer128]

Originally posted by: uart

Originally posted by: Fencer128
NASA were going to trial this as a "tethered cord power source" on a satellite a few years back. It never happened then (might have done by now) due to the winch breaking as they tried to let the wire out.

I'm sure it works and it has/is considered for use in satellites (where gravity provides you with a "free" energy source to move the wire).

Cheers,

Andy

A voltage (and current if the coil is loaded) is produced when either a fixed coil is placed in a time varying magnetic field, or alternatively, a coil is rotated (or otherwise moved so as to change the flux linkage) in a stationary magnetic field.

In order to extract electrical energy you must allow current to flow (ie have a non open circuit load), but the resulting current also interacts with the magnetic field to produce a retarding force. That is, the force always opposes the motion of the coil and hence extracts power/energy from whatever is moving it.

So I'm very dubious about any potential for "free" energy. Gravity does not provide free energy! It cost a lot of energy to get a satelite up there and if this retarding force is slowing it down and bringing it out of orbit premeturely then it is certainly NOT free. Perhaps if someone here can suggest a mechanism whereby the retarding force slows only the Earth (that is the energy is sourced from Earths rotational KE) then I might consider it "free" energy - well kind of.

Well, that's why I put "free" in inverted commas. The key to making this viable is to make the acceleration due to magnetic braking negligable over the life of the satellite, or, as I believe was more the point of the NASA mission, to use the generation of a voltage in the wire as a secondary source of power alongside solar. This would potentially allow for the replacement of heavy, expensive panels with a cheaper wire. Any change of orbit bought about by the wire interacting with the magnetic field could be compensated by say, an ion drive.

Cheers,

Andy

 

[Matthias99]

But the point is that you'll never get more net energy out of the system than you put in (and you're putting in zero, other than the gravitational potential of the satellite, which has to remain constant to maintain its orbit). What's going to power the ion drive?

AFAIK, there's no way to slow down the earth (and thereby increase the satellite's speed -- think conservation of momentum here) without applying a force to it, which requires an energy expenditure. This would require increasing the KE of the satellite (and thereby its gravitational potential), and that energy has to come from somewhere. You're still not going to make a net energy gain.

You could potentially use a lightsail (see thread on light having mass/momentum ) to compensate for it for "free" -- that is, while requiring no expenditure of power on your part. But that may not be feasable, depending on your orbit and power requirements. It's also more complicated, and just as easily damaged, as solar panels. Maybe if you had a lightsail and you shot a laser at it from a ground installation... it's not "free" power (except from the satellite's perspective), but it would be a way to "beam" power up to the satellite. I'm not sure efficency would be good, though.

 

[f95toli]

The thing is you ARE putting energy into the system. The satellite has a lof of kinetic energy and that energy comes from the chemical rockets used to put it into orbit in the first place. The wire WILL slow the satellite down and eventually it will crash but if the process is slow enough that is not much of a problem.

The main problem that this invention is trying to solve is that it is difficult to store ELECTRICAL energy, batteries are too heavy and uses a lot of space. NASA is also experimenting with things like flywheels (start spinning the wheel before launch and extract energy by breaking) for the same reason. The whole point is to save money by reducing weight.

 

[Matthias99]

My comments were based on the assumption that you *didn't* want the satellite's orbit to decay, and so extracting power directly from its KE/gravitational potential was not an option unless it was being replenished somehow. Satellites are expensive.

I realize the problem -- however, I'm not sure that a sizable enough coil to generate a decent amount of power would be more efficent space/weight-wise than batteries and/or solar panels.

Somebody with a physics/engineering degree (not me) needs to run the numbers.

 

[Geniere]

The ?tethered cord power source? experiment was attempted in two shuttle missions. The experiment had two purposes, I believe.

Determine the feasibility of generating power from induction in the ionosphere.
Determine if use of super-long radio wave and transmission reception was possible.

The experiment used an Italian designed satellite and tether. The tether was about 14 miles long, with one end connected to the satellite, and the other end connected to a crane and hoist in one of the NASA?s space shuttles.

The first mission failed due to the hoist becoming jammed. The second failed due to the tether breaking just short of full deployment.

Voltage is generated when a conductor is moving relative to charged particles such as found in the Ionosphere. The conductor does not have to be wound like a coil. The return path for the current flow would simply be the Ionosphere itself. This process is similar to the method used by power companies on Earth; the return conductor is the Earth. The experiment was based on sound physics.

In the second mission, data collection began immediately from the tethered satellite and after the tether broke, continued for a day or so until the satellite burned up.

I recall seen the incident on a TV news show. When the tether broke, a brilliant flash of lightning occurred between the severed ends. The breakage occurred in or near the hoist.

Apparently enough data was obtained so as not to require further experiments.

 

[PowerEngineer]

Originally posted by: Geniere
This process is similar to the method used by power companies on Earth; the return conductor is the Earth.

The world-wide standard for electrical power is three "phases" of voltage/current, each of which is (ideally) 120 degrees ahead of one other phase and 120 degress behind the other. If the loads on a three-phase system like this are equal, then the sum of the currents at the neutral point comes out to zero. You can think of this as the return current for one phase flowing back through the other two phases. Power companies do try to limit the amount of so-called ground current for a number of reasons, not the least of which is that ground current tends to drive corrosion of underground pipes, etc. One way to do this is to keep the loads on each phase as "balanced" as possible; this can become tricky since feeders into neighborhoods are generally single phases.

In fact, detection of ground current in even small amounts (through a connection between a three-phase neutral and "ground") is often taken as a sign of an electrical fault and triggers the deenergization of the equipment. (The so-called solar storms of charged particles induce DC currents in power systems that can show up as ground current and cause unnecessary equipment tripping, which is one way these storms can disrupt power systems.)