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linear generator - what am I doing wrong Awesome
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Posted by: Gabbo

09/19/2006, 19:02:34

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Ok, newbie here so please be gentle.
My problem is I am trying to make a linear generator, one that generates electricity from back and forth motion (as opposed to rotational). I am using a row of magnets on a shaft that passes back and forth through a series of magnet wire bobbins (two phased) then rectifying it.
Here's the thing, it doenst seem to be working. Can anybody out there who knows about such things throw me a bone?

so very much appreciated








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Re: linear generator - what am I doing wrong
: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: randykimball
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09/19/2006, 19:32:02

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Are you sure it isn't working.

Don't move the magnets inside the bobbins.... you want the magnets to pass magnetic flux through the wires on one side of the bobbins.

Here is a hoot of a way to prove if it is working.

Place a cheap compass (you know the ones about 1/2" in diameter that come in toys) over a thin wire that is connected to both extreme ends of your bobbins, and a good ways from the magnets.

As you move the bar the compass needle should be effected.

I would use neonib (slang for Neodymium) magnets and you need many-many turns of wire. Then you are only going to get a very small current. .... This is exactly how my seismic sensors work, I have a pair of 3/4" diameter neonibs facing each other in phase. I let the earth's motion (seismic vibration cycles) move the pair of neonibs adjcent to one side of the 16,000 turn bobbin which is suspended from a Lehman pendulum arm. Then the current is multiplied thousands of times and is recorded on my computer as a graph.

If you go to my web page you will see my home made Lehman seismic sensors using this method.
whazitfun.com
Click the Seismic stuff button. The whole concept is explained. There you can see how you need to place the bobbins in respect to the magnets in a picture on down the page.

Good luck..





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Tue, Sep 19, 2006, 20:02:25


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Re: Re: linear generator - what am I doing wrong
: Re: linear generator - what am I doing wrong -- randykimball Post Reply Top of thread Engineering Forum
Posted by: Gabbo

09/19/2006, 20:09:13

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Alright, your page was very informative and musical. I would assume then that your sensor is moving in a very minute manner to which the voltage is being seen via the computer interface.
I think that what I am getting is doing at least that (although I dont have a scope to prove this). In my application, the magnets on the shaft move up to 20 cm (there are 16 arranged with pole caps in an cNSNScSNSNcNSNSc and so on. The bobbins are wound 120 turns with 18 awg wire. There are 8 bobbins, 4 in one phase and 4 in the other.
I was hoping to see some measureable value (at least as much as the darn bike generator I am using for inspiration) but I seem to be getting nowhere.
The magnets by the way are neodymium and I must admit pack a big whollop to uncareful fingers.

The idea is to have something that looks like a shock absorber (but not work like one). The concept is used as a wave generator for bouys that bob up and down in the water. They apparently generate enough juice to keep onboard batteries topped up for running nav lights and or radio beacons.

any other clues?

John








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Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: randykimball
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09/19/2006, 20:21:00

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more clues....

More turns !!!!

Your bike gen set turns many RPMs so thus gets lots of magnetic flux lines crossing the wires in a hurry...
sooo.. you, to get similar results, need many more wires to make up for many RPMS.... The more wires the more flux lines cross-up in motion the more current.

Lots of neonibs (they have hords of mag-flux) and lots of turns of wire... no mystery.

Then store the current up in some caps... next project.

You've seen the flash lights that work this way? They do exactly what you are doing and store the energy into caps and light a bright LED... no batteries any where.





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Tue, Sep 19, 2006, 20:24:39


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Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: linear generator - what am I doing wrong -- randykimball Post Reply Top of thread Engineering Forum
Posted by: Gabbo

09/19/2006, 20:29:45

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Yes, caps to store the resultant energy after being rectified. I see where you are going on this (and my hand is cramping thinking of the winding of more wire).
The bike light uses steel fingers that wrap around the round magnet (which is magnatized (is that right?) in a n/s around the cylinder) It looks like it directs the flux to the bobbin which is sitting perpendicular to the spinning mag. A single spin of the shaft will light up a 3v jumbo LED. I was hoping to get something similar.

Yep, more loops I think is needed. And a scope to see if what I have now is doing anything (which might be enough for a concept model (smile).

Problem is this is the easy part of what I am trying to do.








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Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: randykimball
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09/19/2006, 21:05:30

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Doesn't take so much to light that LED.

Take the meter out of any old thing with a needle swinging meter in it. Remove any shunt wires or resistors... an amp meter won't do.

One out of an old stero or CB will do well...

These meters are very sensitive and cost MUCH less than a scope. Some Digital MultiMeters will catch a quick voltage spike... but an OLD Multimeter with the needle WILL catch your voltage spikes very well.... hunt one down! Set it on the lowest voltage.





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Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- randykimball Post Reply Top of thread Engineering Forum
Posted by: Gabbo

09/19/2006, 21:11:32

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You remind me of a friend of mine who owns a large cattle farm outside of the city. He thinks like you in that its better to reuse old stuff that makes sense than new stuff that requires a manual. Excellent idea and I think I have an old meter that would do just fine.

I have been away from formal school for almost 30 years and your suggestion started to take me back! Thanks for that. Dont tell the folks I work for now, it would set a precident (I work for Nortel).

Let me see what I can dig up.

thanks again








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Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: randykimball
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09/19/2006, 21:55:43

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Before you get away there is something I want you to do.

Find a piece of aluminum plate, bar, extrusion, angle... something at least a couple of feet long. One that a round cylinder (like a neonib) won't fall off of when it rolls on it.

Lean the aluminum down at about 45. Place a cylinder shaped neonib at the top and try to roll it down the aluminum surface.

What... ?? What the heck just happened?

Well, the magnetic flux produces so much current in the alumium around the area the moving magnet is in that the induced flux from that current tries to pull the magnet back up... the results is the magnet rolls down in slow motion... you just 'got'ta do this.. It will feed your brain towards the concept you are working on. ... you'll get it. Do this and then go think about it. (yep, aluminum wire helps, and so does size and number of turns)

Got ya hooked?

Ain't physics a thrill?





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.


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Posted by: Gabbo

09/19/2006, 22:12:32

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thats an old trick. I was telling my son about the use of the copper tube with holes in it. Dropping the magnet down the tube you can hear it huff past the holes as it stops goes up a bit and then down then up and so on. Pretty spiffy when seen for the first time.

Yah, I'm hooked. Just now I got to figure out how to put it all together. Actually thats one of the ways I was thinking it wasnt working, since I wasnt getting any reluctance when passing the bobbins over the magnets (or vice versa), it wasnt pulling back (or if it is just not very much).

nifty idea though.








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Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: randykimball
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09/19/2006, 22:23:16

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If you are using 18 gauge wire and have it wired right and you shunt the ends together without any serious resistance... it should "reluct" just fine... as long as you are cutting the wire coils with plenty of flux. Remember flux is current, not voltage... low voltage means you can't have much resistance....
..run the resistance up there and you'll get some voltage... just not much current.... depends on what you need.... it is the power that is kinda weak! .... low power in = lower power out. You aren't going to get lots of energy out without putting lots of energy in. Things like this work well when you have lots of time... as in the bouy. .. or need to keep a small current drain supplied.




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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- randykimball Post Reply Top of thread Engineering Forum
Posted by: Gabbo

09/19/2006, 23:14:18

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yes, exactly. What needs to be done is to determine what the output needs are required. Little power in is little power out - conservation of energy.
I need to step back and re-think. Time is the key, you hit it right on the tip.

Let me see what I can put together (and find than old analog meter)








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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: zekeman

09/20/2006, 09:39:16

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Just how fast and what stroke are you moving that magnet array? Also, I dont quite understand your 2 phase rectification. I would first get the results of one bobbin output before even thinking about rectification. It also seems to me that if you have these bobbins, you hook them up in parallel and you should have AC out of the output and then rectify, unless that's what you are already doing. And how are you oscillating the array?







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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
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Posted by: Gabbo

09/20/2006, 15:49:37

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the stroke is about 16 inches from end to end through the bobbin array. I agree that I should have done one and tested it before I did the others (darn level of excitment). The two phase was just to try to increase efficiency, but I guess at this stage a single phase would be just as effective. I am not rectifying it at this point (that I havent built yet). I have tried to put an LED on the output leads to see if there is enough forward bias to turn it on or not - no luck.
Oscillating the array right now is manual done, so I can vary the speed as long as the arm doesnt give out.

Is there a math equation that would eliminate the guesswork? I seem to remember something in my school daze that there is but for the life of me it comes out as a blank.








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Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong
: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: linear generator - what am I doing wrong -- Gabbo Post Reply Top of thread Engineering Forum
Posted by: zekeman

09/20/2006, 23:58:36

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Just to step back a moment, I ham having trouble confirming that you are inducing voltage in the wire loops. A better description or a sketch would do wonders.
You must remember, you can only induce voltage by the change in flux penetrating the plane area of the loop. From your first post, I'm not sure I get it.







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Posted by: Salman

01/01/2010, 18:13:03

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hi,

I am thinking to work on using linear generator (dimensions: 120mm*80mm*25mm) in shoe to power up electronic devices used by any person in motion. What challenges should i keep in mind to implement this?








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