DIY - Magnetic Linear Electricity Generator

There are on the market flashlights that work on this principle.

You could make something like this, but make it powered by compressed air...

https://www.freikolben.ch/en/linear-alternator

....or maybe steam or Stirling engine...

https://www.amazon.com/Jensen-Steam-Engine-75-America/dp/B00D0ULOTI

...or weight powered, or spring powered windup...

This is pretty cool...

https://www.amazon.com/Sunnytech-Stirling-Engine-Education-Electricity/dp/B01CE6Q71S/ref=pd_lpo_vtph_201_tr_t_2?_encoding=UTF8&psc=1&refRID=5A0F1024M57NTM12QP0H

Shake a flashlight (torch) and how they work

Have fun

Next time, I'll read all the posts before I run out to my shop and grab my shaker light.

This'd be great if you owned a paint shaker.

To the OP, sorry, you have picked a good project for a science fair.

The coil would be lighter and easier to move back and forth with the magnet stationary. Force equals mass x acceleration. (You would want to use flexible multistrand wire for connections to the coil.)

A loudspeaker used as a dynamic microphone works like that.

Just a thought...

This is really cool....and a little wet....

Correct me if I'm wrong, but OP wants to pulse the output of the linear generator so that it will power the solenoid to provide oscillatory motions to make the linear generator move so as to provide power to the solenoid so as to shake the linear generator, ad nauseam; aka a perpetual motion machine...

It won't work since unlike the hand-cranked flashlight, there is no external power applied. Sorry, but back to the drawing board (oops, CAD program).

No correction necessary.

After a while, that flashlight makes your wrist hurt.

Good point, ain't no free lunch. But maybe he is just animating it for his science fair display and isn't expecting more power back than he puts in.

I wouldn't use a copper tube, use plastic, like pvc....get the thinnest you can find....wrap the copper in separate coils and tie the outputs together to get a more constant voltage....What are you thinking about as the driving force? Manual by hand, crank, or some other force such as air or steam etc....This design would be similar to a wave powered generator....

http://systemdesign.illinois.edu/publications/Niu13a.pdf

I like this design as a single piston small engine with a spring that causes the piston to rebound after chamber ignition completing the cycle...

https://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjEl4msuvDcAhWCdt8KHQagD3oQjRx6BAgBEAQ&url=http%3A%2F%2Fwww.mdpi.com%2F1996-1073%2F11%2F1%2F135%2Fpdf&psig=AOvVaw0udeHES2zWEU-zbCXCDU-P&ust=1534470121385967

"...What are you thinking about as the driving force?..." The solenoid is pulsed to make the plunger move the magnets, and the output of the generator provides the power to move the plunger, etc., etc....a zero sum machine that has no usable output.

It would be interesting for Mr. Jawed to clarify his power source.

SolarEagle made me think of a variation on the fairground "ring the bell" machine...See how much electricity you can make...

Could put back-to-back LEDs on each winding to get a light display.

Winding coil round copper tube? The copper tube is a shorted turn on your winding - not good!

Hi Friends,

Thanks you all for your great comments and suggestions.

After reading your suggestions since last week, I have comes up with the desired hardware assembly as shown in the pictures attached.

It is just for the demonstration purpose to generate electricity not as a generic rotary type generator, but to show and discuss the possibility of generating electricity using linear motion.

Many of you thinks that it has to be powered by its own generated power, but this is not the case.

The task is to generate electricity using linear movement of the magnets inside of the Metal or PVC pipe tube with outer winding for electricity generation, which can be drive back and forth with ant linear movement machine as many of you shared videos as well.

But, my idea was to drive the linear movement using solenoid driving a non metallic /plastic shaft having linear motion when applied with 12V DC NE555 based standard 1 Hz to 10 Hz rate square wave Astable Multi-vibrator mode using N-ch FET for solenoid coil switching.

And the solenoid shaft moves the circular magnets attached to this non metallic /plastic shaft inside the PVC tube of the linear generator coils. The outer coils will generate electricity as proportional to the linear movement as well as magnet power of cutting magnetic flux in the outer coils.

Now see the pictures of my demo unit....

Instead of just using the same magnets as of the hand cranked LED lash light, I have used the circular ring magnets, as these are easy to fix with the solenoid shaft.

And after doing some experiments, I was able to produce some LED flashes making 500 turns of 28 AWG outer winding on the 20mm PVC tube with single 20mm circular magnets moving back and forth inside the PVC tube just under neath the coil.

But, as I need more power..e.g.. 20 watts ...12V with atleast 1.5A output current...I though that increasing the magnets will increase the output voltage and current...and perhaps,, makes one more coil with parallel to the next to get more electricity...

and places 2 groups of four circular magnets on the same shaft driven by the single solenoid plunger ..which is driven by the NE555 1Hz--10Hz Variable Pulse oscillator...making back and forth motion.

But... I rather confused that the output reduced while the single group of magnets with single winding was working somewhat sufficient ...producing 5v to 9v AC at 200mA to 300mA. Now, after this setup, the output reduced to almost 1V to 3V AC with very low current...I dont know why?

Please suggest the best configuration fr this setup, as I need to generate at least 12V with 1.5A current at output, no matter what power should I applied to the shaft driving solenoid.

Should I use the rectangular shape magnets or I have some other shaped magnets, but not easy to attach to the shaft for linear motion. The one as same as hand cranked LED flash light used is also generate very low output.

I hope taht many of you will now get the idea that what I am trying to do and share your best suggestions for this setup...

Have a nice day!

Thanks for the feedback! As you have discovered, 20 Watts is a decent amount of power for a handheld device. One thing that you should keep in mind is that in order to produce 20 watts of output power, you will need at least 20% more input power (24 Watts) to drive your generator as well as overcoming all the friction and resistance losses inherent in all real-life devices. Good luck in your search.

I think you did well getting 1.8 watts on your first attempt.

A/ There is a limit to how much power you can get out of the solenoid/plunger...

1. Electrically, if coil has resistance R and you apply V volts, you could put in V²/R =W watts. But that would all go to heat the coil.
2. For a linear electrical system source with voltage V and Resistance R, you get maximum power if load R_L = R - but half the power disappears in source resistance, the coil resistance R here, & that max power is (V/2)²R = W/4. This is not a linear system, but the best you can do is maybe W/2.
3. If you energise the coil after the plunger has compressed the spring & make it hit the end stop you will waste energy, maybe it will be an elastic collision & you get the energy kinetic energy at moment of collision on rebound - but Murphy's Law... so you do not want to energise solenoid with too long a pulse.

B/ Mechanically, I guess the solenoid gives power on one stroke & returns with the spring (which has some of the energy put in on power stroke).

1. The energy put out on power stroke is force x distance. In your solenoid force & distance are pretty much fixed, although you could increase force a bit with more current (more volts - which will also get max current (force) quicker & operate over more distance. Saturation will limit how much force you can get above nominal & heating of coil may damage it - as a rough guide a 35% increase of resistance "hot" above room temp cold value for a copper coil indicates continuous max.
2. The energy in 1. is pretty much fixed, you can only get more energy per second by energising solenoid more times per second.
3. The return stroke takes time, depending on spring & mass of plunger & magnet, which takes time out of your second for putting energy in! There might be an optimum where plunger oscillates with less than full travel. The electrical power taken out will slow the return stroke - not clear if your generator coils have diodes to remove power on both strokes.

Electrically, the volts produced is proportional to velocity - it seems doubling magnet mass has halved velocity and reduced your output.

Lighter magnets & experimenting with on & off times of 555 may give improvement, but have a look at A1. & A2. to see if possible power exceeds your required 18W by a good margin.

I guess you start by increasing solenoid energise time from less than data sheet "energise time" to find point of diminishing return & then reduce "off" time till it is no more than mechanical spring return time.

No doubt for each on/off time set there will be an optimum electrical load resistance, but you need to get the strokes per second up to maximum possible.

You do not have any "iron" or ferrite to improve the magnetic coupling - winding coils on "pot" cores with pipe through middle would increase flux. Or maybe iron "I" laminations assembled into "U", so magnet crosses top of U, with its N & S poles on top ends of U (or maybe C assembly with magnets crosswise to tube, alternating N-S in stack)

67model

I just noticed your solenoid is marked 24V 68 ohm in photo - 0.353 amps x 24V = 8.5 watts. That is much short of 18 watts. If you blasted it with 48V, that would be 2 x 17W, the problem is to get output as electricity, not heat.

Getting 1.8 watts out looks pretty good - but you did not write if that was peak or rms.

67model

Hi 67 model,

Thanks for the detailed feedback on my crude design.

As you mentioned "Electrically, the volts produced is proportional to velocity - it seems doubling magnet mass has halved velocity and reduced your output.

Lighter magnets & experimenting with on & off times of 555 may give improvement, but have a look at A1. & A2. to see if possible power exceeds your required 18W by a good margin."

After this, I start thinking to give it a try with a twist....

I got some spare high wattage Car amplifier sound system Loud Speakers with the range of ohms / 40 Watts and 100 Watts...

Is it possible to have these speakers to be used as linear electric generators by vibration the voice coils of the loud speakers via any linear motion attachments?

The vibrating frequency will be controlled from 1Hz to 100Hz, as does the power amplifiers vibrate these voice coils to generate sound waves of the same power.

I think that by reversing this analogy, I may get what I want to produce...e.g. 10W to 20 Watts of AC voltages at variable frequency!

The loud speakers structures are easy to handle and the paper cone can be uninstall to make it easy to attach the linear moving attachments...

Let me know what you guys suggest?

The modifications just need the linear attachment.... ;)

Thanks again.

Yes, loudspeaker arrangement is an effective linear driver and generator.

Many vibration test tables are driven by loudspeaker-like drivers, even kW level. I have used loudspeakers with the cone taken off & attached threads to the circle inside the spider to vibrate PCBs or various vibration transducers.

There is a version of a Stirling Engine with oscillating parts held by diaphragms which drives a "loudspeaker type" generator. It does not need any bearings or cranks.

But I like your solenoid drive set-up, since it makes it very clear it has linear motion while movement of L.S. is more of a fuzzy fringe - anything over 25/second, like cine projector or TV scanning, merges into a steady image or blur. Maybe you could get the pulse output to drive an electro-mechanical digital counter - like those that were used for operation counters before electronics.

I guess you could have both, as an example of moving from the basic idea, Faraday's pushing a magnet into a coil, to using a shaped magnetic "circuit" to get a strong field around the coil and more power. It also uses an item familiar in the home, maybe not understood.

Higher resistance L.S., like 15 ohm must produce more volts as generator than the 3, 4, 8 ohm versions which helps with the range of loads possible - a 20W amp for 15 ohm gives about 50V peak-peak on sine test.

I saw the information about this electricity generator before. It is excellent.

There is also a simple gen which use only wire...The two wires are connected end to end, and the voltage and current are not only the coils, but many factors are the most direct.