PERMANENT MAGNETS VS BATTERIES

It seems to me that the simple problem is that which you have already tried to prohibit in this discussion. Getting power out of a magnet is a very difficult and complex proposition. So, if the mechanisms of so doing are so heavy and complex that they outweigh the advantages? Seems to me that batteries will be the method of choice until that little problem is solved.

You cannot get the energy back from a magnet ecept, perhaps, for a small amount (I would estimate perhaps 3-4%). It is simply unobtainable. It's not a matter of finding the right technology or discovering a more efficient method. It's just not there.

Magnet battery

Regards JD.

Dear all,

Magnet flux has no energy. So, simply you can not draw power from it.

To have energy, both magnet flux and electric flux are necessary at the same time.

Can I ask where 400kJ / m^3 came from?

Regards

Thanks for that lead to magnet Battery.

My friend from Indonesia- kindly note Kilojoules/meter^3 is published spec for a permanent magnet. It differs from one to other depending material used to make magnets.

"You say I started out with practically nothing, but that isn't correct. We all start with all there is. It's how we use it that makes things possible." -- Henry Ford

"Kilojoules/meter^3 is published spec for a permanent magnet"

Which spec? Sounds like the energy required to magnetize the magnet. To get energy out requires that something moves. What is it that moves here?

Okay, take a really big magnet of 1 m³ = 400 kJ = 400 kW-seconds ≈ 0.11 kWh. This is probably not very efficient as an energy storage method.... As the OP's example also showed, this is less than one percent as effective as a car battery.

Drawing out this puny amount of energy will only deplete the magnet, which will then need to be remagnetized.

In general, the energy from devices involving a magnetic field does not come from the magnetic field. Instead, it comes the energy of whatever pushes a coil through the field--falling water, combustion engines, wind, whatever.

deep discharge battery about the size of a common car battery:

768 [inches^3]
1.26E-02 [m^3]
12 [volts]
50 [Amp-hours]
2160000 [Joules] or
2.16 [Mega-Joules]

super magnet about the size of a common car battery:
400000 [Joules/m^3]
1.26E-02 [m^3]
5034 [Joules]

simple capacitor about the same size as a car battery:
(I have one of these under my workbench;)
100E-06 [Farads]
10000 [Volts]
5000 [Joules]

The energy stored in one of those (fun) super magnets is tiny compared to a similar sized common battery. The energy stored in this particular magnetic field is in fact about the same as the energy stored in the electric field inside a similar sized high voltage capacitor. Storing energy in magnetic or electric fields is common. It is done everyday, everywhere a switching power supply is used. Getting the energy back out of a permanent magnet is just a lot more difficult than the more common capacitors and inductors that are commonly used for this task. There is no magic here. Permanent magnets just make really poor batteries.

Ok guys -- Take a fairly decent sized neodymium-iron magnets, maybe a kilo in weight and larger block of steel. Lay them on a flat smooth level wood tabletop with a pole of the magnet facing the steel block. Place them just far apart enough so the friction of the table top is enough to keep them apart without your help.

Now, place some soft elongated part of your body (perhaps a pinky finger; perhaps another part to make it a good story for someone to tell later) on the table between the magnet and the steel block.

Repeat after me: "Magnets in free space have no potential energy" Now call the someone else in your life into the room and ask them to pick up the phone and be ready to dial. Don't ask why. You just said "Magnets in free space have no potential energy" didn't you?

Now, firm in your beliefs start pushing the magnet slowly toward the steel block; but do not move that soft body part out of the middle. Keep moving the magnet. Let's see just how strong your belief in the absence of magnet potential energy really is.........

Seriously here....... if we can solve one of the serious hardware problems associated with creating strong enough magnetic fields to contain the plasma of a nuclear fusion reaction we may gain a byproduct of a magnetic field with serious energy storage capacity.

Ed Weldon

Great word picture, I'm sure everyone knew exactly what you were describing.

Lifting the same magnet 1 meter above your head and releasing it will give a similar result. However, despite the pain it's still not a very efficient storage mechanism.

No one is saying magnetic system can't store potential energy, but rather that it's not very cost effective to do it that way.

Dadburn it! That's not magnetic potential energy. That's mechanical potential energy from whatever pulled the magnets apart to start with.

I'm not quite sure about the very first time they are brought together, but after that first time, you are absolutely right!

I liked the last comment by Mr Ed Weldon. Magnets are extremely powerful. BUT---

Comments by mjb and Tornado cannot be over looked from technical angle. Magnets seem to have limited applications. I was trying to imagine using it to replace batteries and it seems- is NOT possible.

To dkwarner - my only suggestion is do download specs for a permanent magnet and you will find kilojoules/m^3. Is it energy stored or energy which could be extracted etc- is not my point of discussion. Assuming 100% eff (not possible in real life) - I also assume that it is energy that can be extracted- by mechanical movement or without mecahnical movement (that is ingenuity and even this is available on web site. Pl see motionless electromagnetic generator) etc etc.

So may be we could now shift focus to target applications where powerful magnets can really be used (noty as replacement for batteries)

Higher energy density magnets have already been extensively used to make more compact and typically more efficient motors, generators, alternators, etc. This trend can continue within the limits of the materials involved. The stronger permanent magnets in these devices only affect the simple equation governing energy conversion if they improve efficiency (0 <= eff <= 1.0).

energy_in * eff = energy_out

Please, let's not go into the discussion of eff>1.0 on an Engineering Forum

What about Hall effect?

Isn't this related to static magnetic fields?

EEStor

...soon Igor....soon

Sorry, but capacitance cannot be measured in gigawatts. Wrong units. Good joke, though!

Earlier I had asked a question- why J Naudin lab, a french lab is not responding, though they have made lot of interesting experienments and put lot of details on the web site. A 20 W CFL is shown to be working brightly using Neodymium magnet, without any motion - only solid state switching.

May be the lamp can operate only for a few minutes (that is not mentioned on their site!!) - which means very little practical application!!

So however powerful the magnets may be, its applications are quite limited !! Definitely not as energy storage devices.

"Determine that the thing can and shall be done, and then we shall find the way." -- Abraham Lincoln

Yes Blink. The conclusion is permanent magnet is just an aid /accessory / catalyst- not a source of power by itself. You are right that even batteries are not efficient when it comes to electric vehicles. So we continue our exciting search for a high density kilojoules / meter cube source (maybe comparable to fossil fuel), but with less carbon emission!!!

I had seen advantage of magnetising permanent magnets in a short time as compared to batteries - and went on wrong track. Well the journey to final conclusion that magnets are not worth pursuing - was exciting.

I am not so sure we are at the end of this thread.

The article linked here describes "have been able to prove the existence of a "spin battery," a battery that is "charged" by applying a large magnetic field to nano-magnets in a device called a magnetic tunnel junction (MTJ)"

They are not talking about any potential created by magnets drawing together, instead they are charging the magnets with energy.

As far as I have been told the forces involved with magnets have not been defined so perhaps there is room for discovery in manipulating those forces. Re-read the article and tell me what you think.

Drew

I read an article on that just a day or two ago, and as I recall, as yet they haven't done a lot with those. Small matter of scale, as in too small. However, given time, it might actually be a viable form of energy storage. Stand by for further developments.

Nobody can say what lies down the road, but for now MTJs are not energy storage devices. They are memory storage devices, not that different, except in size and cost, from the old ferrite beads.