Neodymium magnets

[solis365]

I am currently in the planning stages of creating a small homemade generator, or at least the magnet/coils part of one. not sure yet what the mechanism will be to cause it to spin (wind? water? heat?)

anyway, my general idea is to have two rotating plates of magnets with a stationary plate of coils in between. i.e. magnets of alternating polarity arranged around the circumference of two discs. coils sandwiched in between. the magnets rotate, the alternating polarity of the magnet arrangement induces current... and so on to some 3-phase power generation.

this is not meant to be a huge generator, more of an experiment really, but i was wondering if anyone knew where to find the strengths of various-sized neodymium magnets, so I can figure out which ones to use to give me the kind of output to price ratio that I want. I also need to figure out what gauge of wire to use for the coils, but that depends on the magnet strength of course, so that can come later.

thanks in advance

 

[Pommie]

Why two sets of magnets? Just use one set that is double the strength or, better still, work out what power you have available and choose magnets and coils that will efficiently extract that amount of power. In other words, design the power plant first.

Mike.

 

[solis365]

the reason for two magnets, one on either side of the coil, is to control the shape of the field lines. Ideally, one would want a bar magnet with a coil wrapped around it. this is not feasible, as the wind power has to rotate either the coil or the magnet. so I will emulate a bar magnet by putting a magnet on either side of the coil.
........................... coil ...............................
.. .. ... .... ...| -----(-(-------> |
(magnet 1) S | -----(-(-------> | N (magnet 2)
.. .. ... .... ...| -----(-(-------> |


looks like that from the side. a single magnets field lines are thus:

......... _____ -->
. | ---
S|------------>
. | --- _____
.................. -->

(ignore the dots)
they curve outwards, meaning weaker field at the coil and in an undesirable shape.


i just wrote all that and realized a double strength magnet's field would be as straight as a dipole of each pole having half the strength, so never mind. (but i didnt want to delete my ascii art...) anyway, regardless, thats all besides the point. I'm just wondering if theres some way of finding out the strength of these magnets before ordering them.



also, dont know the amount of power first, since its likely to be a wind generator, though it could certainly be adapted to a waterwheel or a steam turbine. since its wind, theres way too many variables to build the "most efficient" magnet/coil setup... wind speed, turbine mass, blade drag, blade size...

once i decide on about how much voltage and current i want, then i can go about picking a number of loops for the coil and choosing a magnet strength, but i need to know where to find magnet strengths

 

[SMUGangsta]

Im not sure if this is any help, but it mentions magnet strengths on here supermagnete.de - FAQ - Frequently Asked Questions (and their answers!) - Questions About Neodymium-SuperMagnets

 

[RadioRon]

I bought magnets from these people. No problems:

K&J Magnetics - Strong Neodymium Rare Earth Magnet Products

Perhaps their component data can help.

 

[audioguru]

I have seen Instructables from kids who made their own generator from some coils and some neodymium magnets. When the generator was spun really fast then the generator lighted one LED dimly.

 

[Cotowar]

have you considered running a weak generator with a powerful step-up transformer? From my grasp of electronics and such, this is a very real possibility. You probably wouldn't be able to run your house off of it, but you might be able to get a heater or something going, or even goonier, the lights for the "lair" you do your projects in. You would be my hero if you powered your shop off a custom built generator.

Oh, and maybe look into powering the system off of a perpetual water source. What I mean by this is something similar in nature to a desktop waterfall, but read further to see what I'm talking about.

Maybe set up a system where you have a small water pump from a computer's water cooling system. Have this pump from a closed reservoir up through a tube to a second reservoir. Have the water flow through the bottom of the upper reservoir over a small water wheel (light plastic would work wonderfully) and into the lower reservoir. Have the water wheel spin your magnets for the low power generator, which in turn connects to a step up transformer that sends power to the water pump. Basically as long as your transformer outputs a higher voltage than the pump consumes, you are producing free electricity. You can also vary the pressure of the water as it flows over the wheel to get a faster spin.

Even if you have very little surplus power, could you not run it in parallel with the pump to an additional step up transformer that powers whatever else you need? I honestly don't know about this part, and I came up with this solution in about 30 seconds, so give me a slight break if it won't work. The only thing you'll have to watch is the evaporation rate of the water, but honestly, if you completely seal off the tank, won't the water stay in there forever (assuming the system does not degrade over time). IDK, and I really don't think it would be a big deal to dump a measuring cup or two full of water into a tank every couple of months. You might also look into fluids that have a lower viscosity than water as they will flow faster over the water wheel (i think).

I hope that gives you some ideas, and let me know what you come up with. I'd be interested in building something similar.

 

[solis365]

you can step up the voltage, sure, but unless its an ideal transformer (nothing is) then you lose some power there, and, even if the VOLTAGE is higher, the current will be lower. Power = V*I = R*I^2 = (V^2)/R

since you have loss in the nonideal transformer, you lose power with this.

basically what you have described is a perpetual motion machine; getting energy for free, which cant ever happen. even if we could design things like lossless transformers or frictionless ball bearings to create a perpetual motion machine, we could never extract any energy from it because that would introduce loss and make it, well, not a perpetual motion machine any more.

also having a non-sealed system in a PC water cooling system will let algae grow which is a terrible thing. less viscous liquids likely have a much lower specific heat than water, meaning they wont conduct and carry away heat as well. im sure some exist, but they would probably be very expensive.


oh and audioguru, got any links? im sure its easy to try at this and fail, especially if you dont rectify right... basically im going to have it generate 3 phase power and rectify that... 9 coils, 2 magnets per coil, 3 sets of 3 coils in series. i can at least look at their designs and see what NOT to do, and look for common flaws. besides if you dont figure the magnet strength, wire gauge, and # of coils right it wont be efficient at all.

its worth a shot, even if i fail i've got some NdFeB magnets to play with at the end

 

[audioguru]

A reasonable size generator (a dinner plate size) might be able to light a single LED dimly when it is spinning very fast. It will need a lot of work to keep it spinning fast. The coils have resistance so they lose power by making heat.

 

[Roff]

Cotowar, do you realize that if what you think were actually possible, no one would be buying electricity, gasoline, batteries, or any other kind of energy?

 

[solis365]

A reasonable size generator (a dinner plate size) might be able to light a single LED dimly when it is spinning very fast. It will need a lot of work to keep it spinning fast. The coils have resistance so they lose power by making heat.

this is the website, im basically stealing his generator design but scaling it down (the huge magnets he's got are like $20 each, plus i have nowhere to put 1000W of power, nor do i need it. this is just an experiment)

with the proper wire gauge, resistance should be a very minimal issue

 

[blueroomelectronics]

Which website?

 

[Leftyretro]

Cotowar:

To make it in simpler terms, your idea seems to hang on the idea that a step up transformer increases power, it does not, it just changes the voltage but the total power transferred is always less then unity.

Lefty

 

[solis365]

forgot to actually hit ctrl+v, heh

Low RPM Disk Alternator

that but perhaps smaller

 

[jbeng]

Here's another place you can get NdFeB magnets:

**broken link removed**

Of course, like so many people, you haven't filled in your location, so we have no idea where you are, or if they will ship products to you there.

Jeff

 

[Cotowar]

Cotowar:

To make it in simpler terms, your idea seems to hang on the idea that a step up transformer increases power, it does not, it just changes the voltage but the total power transferred is always less then unity.

Lefty

Yea, very true. Could you use it to charge a big ass capacitor and discharge the capacitor quickly for high current devices? I'm asking because I honestly don't know.

Also, just as a side note, and not to argue, but say you were to use a super small gauge wire on the lower side of the transformer, such as 36 AWG. Then on the high side, could you use like 0 AWG to get lower resistance and thus a higher current while maintaining the same voltage? Bigger gauge has lower resistance and since V = I * R, if the R value goes down, I has to go up if V is to go up. I don't know exactly how much this increase is in reality, so if someone could clarify that I'd really appreciate it.

Oh, and you don't need heat dissipation in the liquid really. as long as you have adequate airflow, the pump will cool itself, and the water isn't actually touching the generator at all. All it's doing is spinning a fly wheel.

Oh, and a good example of what I'm trying to do is a water wheel outside an old mill. The way those work is by spinning slowly, and through gearing they got machines running quite quickly. The water supply is endless, and thus the power generated was endless as well, even though it was a small amount.

Forgive me if my idea is retarded, its just me thinking wishfully to distract myself from the horrendously redneck town I live in.

 

[audioguru]

Your home-made generator will have low output power. Low voltage and low current. Its AC can feed a transformer and the transformer will stepup the voltage but the current will be reduced by the same amount so that the power remains almost the same.

It can be rectified and used to charge a capacitor. It might take a week. Then the capacitor can give a single momentary pulse of power to something and the capacitor will need to be charged for a week again.

Some electric motors make good generators. A powerful generator is described on the internet and uses a motor from a furnace fan. It doesn't have magnets but uses the residual magnetism produced from the last time it was used as a motor and the magnetism becomes very strong each time it is used as a generator.

The manufactured motors and generators use laminated iron cores, not just air.

 

[solis365]

I don't know; there seems to be a fairly large community of people building these things, especially in DIY wind generators. ive been doing some more searching and have found more people documenting the same or similar design, with claimed power outputs of 300 to 1000 watts. (one is Low RPM Disk Alternator but there are others if you dig around a bit. Hugh Piggot is a good name to search)

if the power output is so very, very low, then how do you explain the operation of hand-held "shakeable" LED flashlights? all that's doing is shaking a (small) magnet through a coil (not particularly fast either, human shaking speed), and a few seconds of shaking will light several LEDs quite brightly for a considerable amount of time. furthermore, the magnet inside them is strong, but not so strong as to stick you to a car or a fridge or something if the thing is in your pocket, which is certainly possible with the size of the magnets i'm looking at. (a 2"x1"x1/2" NdFeB can have upwards of 200lbs of pull if its a good quality one).

i don't know if you've had any experience building anything like this, if perhaps you even work in commercial generator design, i don't know, but so far you havent given any reasons why it should fail, other than "the coils make heat." everything ive read shows that this is not a significant problem. otherwise you have simply said that "it won't work."

 

[audioguru]

I don't know; there seems to be a fairly large community of people building these things, especially in DIY wind generators.

Bryan on this forum made his wind gererator from the motor of a washing machine. It works very well.
A do-it-yourself generator cannot compete with a manufactured one.

The article you posted uses an 8-foot diameter windmill to power the generator. You have a small amount of water to slowly spin a little one.

if the power output is so very, very low, then how do you explain the operation of hand-held "shakeable" LED flashlights? all that's doing is shaking a (small) magnet through a coil (not particularly fast either, human shaking speed), and a few seconds of shaking will light several LEDs quite brightly for a considerable amount of time.

Many "shake-lights" cheat and hide a little battery inside. It lights a few LEDs dimmly. I have never seen a bright shake-light and the light doesn't last long.

EDIT:
On the internet is a do-it-yourself generator powered by a hampster. It charges a battery then lights an LED dimmly for a couple of hours like a solar garden light.

 

[solis365]

oh, hah, this whole exchange was for nothing, i wasnt the guy who posted about the water wheel thing (it really wouldnt be particularly useful...). no, i actually am considering hooking this up to a windmill, and i do plan on making it a fairly hefty generator. just, instead of 300-1000W i'd be happy with 30-100, so I can scale back the magnets a little bit. this isnt a desk-sized thing

i said i was considering water power as well, but certainly not a fish tank pump, i mean like constructing a small dam in a brook near my house...

back to my original question, how do I find out the actual field strength of magnets? can't seem to find it anywhere... perhaps I would have to buy a meter and try it out on various ones