How to make a device which is "Reverse solenoid"

[Silent_88]

Hi Everyone,

This is Sentil from India. I'm a professional in the field of commerce. But i love science! then the obvious question "Why /How did you end up in Commerce". Thats really a long story.

But today I am here to get help on one of the side projects i am into to develop something like "solenoid in reverse". That is, i want to generate some power from the solenoid by mechanically moving the plunger of the solenoid.

I did some basic web research ( i still do ) and together with my lil elementary science knowledge, i understood how solenoid works and what is the principle and all the theory part. but i can't find anything on this " Solenoid in reverse" or "reverse solenoid" ( not sure if I am confusing you guys. this device is suppose to work just like "linear alternators") like no of turns of copper wire, how powerful should be the magnet, what should be the speed at which this magnet should move to and fro to cut the magnetic flux and generate output power.

It would be very help if somebody could help me with these doubts and help me build one.

Looking forward to hear from you all..!

Thanks
Sentil

P.S:- Do i need to post this somewhere else?

 

[Bystander]

http://www.ebay.com/itm/like/400948346212?ul_noapp=true&chn=ps&lpid=82

 

[Silent_88]

http://www.ebay.com/itm/like/400948346212?ul_noapp=true&chn=ps&lpid=82

Thank you "Bystander". Not sure this will answer by doubt but will definitely check the working principle of "Blasting Machine" !

 

[Jon B]

Hi Everyone,

This is Sentil from India. I'm a professional in the field of commerce. But i love science! then the obvious question "Why /How did you end up in Commerce". Thats really a long story.

But today I am here to get help on one of the side projects i am into to develop something like "solenoid in reverse". That is, i want to generate some power from the solenoid by mechanically moving the plunger of the solenoid.

I did some basic web research ( i still do ) and together with my lil elementary science knowledge, i understood how solenoid works and what is the principle and all the theory part. but i can't find anything on this " Solenoid in reverse" or "reverse solenoid" ( not sure if I am confusing you guys. this device is suppose to work just like "linear alternators") like no of turns of copper wire, how powerful should be the magnet, what should be the speed at which this magnet should move to and fro to cut the magnetic flux and generate output power.

It would be very help if somebody could help me with these doubts and help me build one.

Looking forward to hear from you all..!

Thanks
Sentil

P.S:- Do i need to post this somewhere else?

To generate some power from the solenoid by mechanically moving the plunger of the solenoid the solenoid has to be a magnet..

 

[Bystander]

but will definitely check the working principle of "Blasting Machine

From the pictures, the "antiques" are probably conventional rotary type dynamos with "slipping" linear actuators. I couldn't pass up Wiley Coyote and the Roadrunner, though.
More relevant to your inquiry, https://www.google.com/?gws_rd=ssl#q="faraday+flashlight" .

 

[Silent_88]

To generate some power from the solenoid by mechanically moving the plunger of the solenoid the solenoid has to be a magnet..

Yup...the configuration what I'm thinking of is like a copper coil and the plunger will be magnet!

This magnet I am intending to move it "to and fro "mechanically. Thats where the doubt listed below:-

1. No of turns of copper wire to get a specific power in Watts
2. How powerful the magnet should be?
3. What should be the speed at which this magnet should move "to and fro" to cut the magnetic flux and generate output power.?

Any equation available to get atleast some ball mark figure??

 

[Baluncore]

What you are doing is designing another of these shaker torches.
I do not recommend this product but show it as an example of the “see through technology”.
http://www.ebay.com.au/itm/No-Battery-Shaker-Style-flashlight-or-blinking-flasher-/371173532246?_trksid=p2141725.m3641.l6368

The magnet is on the RHS in the picture and slides along an internal guide through the solenoid coil. A rubber block at each end helps cushion the change in direction. You might think it is silly moving a heavy magnet backwards and forwards, but it is actually the torch that moves when you shake it, the battery remains in the same place. The best technique is wrist action that does not move the mass of your arm.

 

[Silent_88]

What you are doing is designing another of these shaker torches.
I do not recommend this product but show it as an example of the “see through technology”.
http://www.ebay.com.au/itm/No-Battery-Shaker-Style-flashlight-or-blinking-flasher-/371173532246?_trksid=p2141725.m3641.l6368

The magnet is on the RHS in the picture and slides along an internal guide through the solenoid coil. A rubber block at each end helps cushion the change in direction. You might think it is silly moving a heavy magnet backwards and forwards, but it is actually the torch that moves when you shake it, the battery remains in the same place. The best technique is wrist action that does not move the mass of your arm.

But how is "linear alternators" different from shaky flashlights? Do they work on the same principle or some other laws of physics?

 

[Silent_88]

From the pictures, the "antiques" are probably conventional rotary type dynamos with "slipping" linear actuators. I couldn't pass up Wiley Coyote and the Roadrunner, though.
More relevant to your inquiry, https://www.google.com/?gws_rd=ssl#q="faraday+flashlight" .

Thank you so much for that link. I did some research on farady's law and figure out the relation between current and number of turns of copper coil. Now, that i understood farady's law and the current is depended on the "rate of change of magnetic flux", how do i increase this variable in a practical situation? Is it like i just have to increase the magnet's strength? if yes, could you suggest some ways to do it? or is there any other way?

 

[leright]

Thank you so much for that link. I did some research on farady's law and figure out the relation between current and number of turns of copper coil. Now, that i understood farady's law and the current is depended on the "rate of change of magnetic flux", how do i increase this variable in a practical situation? Is it like i just have to increase the magnet's strength? if yes, could you suggest some ways to do it? or is there any other way?

An increase in the rate of change of the flux, thus producing an increase in the solenoid voltage, can be achieved simply by moving the magnet (or "plunger mechanism") more rapidly, since a faster moving magnet will cause the flux through the coil to change more rapidly.

 

[Silent_88]

An increase in the rate of change of the flux, thus producing an increase in the solenoid voltage, can be achieved simply by moving the magnet more rapidly, since a faster moving magnet will cause the flux through the coil to change more rapidly.

Yup...Just as i tot..! but in my project the speed of the moving magnet has a upper limit, beyond which i may not be able to increase the rapidity. In that case what should i do?? increase the number of turns of the coil?

 

[leright]

Also increasing the number of turns obviiously increaese the rate at which the flux changes, since if you double the flux you will also double the rate at which the flux changes through the coil. Same with increasing the strength of the magnet.

 

[leright]

Remember that the total effective flux through the coil is the flux through one turn times the number of turns.

Let's illustrate this with an example. Say the magnetic field is uniform across the cross section of the solenoid but it changes as B*sin(wt), where f = w/(2*pi). Therefore the flux is B*N*A*sin(wt), where N is the number of turns of the soilenoid and A is the area of the solenoid turn. If you take the derivative of the flux to get the "rate" at which it is changing you get B*N*A*w*cos(wt). So B (which is related to the "strength" of the magnet), N (turns), A (diameter of the coil), and w (how fast the magnet moves) arep retty much the parameters you can control. Lowering the resistance of the wire by using a low resistivity material and heavy gauge wire will also perhaps be beneficial

 

[Silent_88]

Also increasing the number of turns obviiously increaese the rate at which the flux changes, since if you double the flux you will also double the rate at which the flux changes through the coil. Same with increasing the strength of the magnet.

Thanks leright.

Hey tell me something, the copper coil through I am moving the magnet, does it has to be of particular area ,that is, the pie*r^2 of the coil should be larger to get a high rate of change in magnetic flux?

 

[leright]

If you have to compromise between gauge of wire and number of turns I would choose mrore turns. I don't know what types of constraints you are dealing with.

 

[Silent_88]

Remember that the total effective flux through the coil is the flux through one turn times the number of turns.

Let's illustrate this with an example. Say the magnetic field is uniform across the cross section of the solenoid but it changes as B*sin(wt), where f = w/(2*pi). Therefore the flux is B*N*A*sin(wt), where N is the number of turns of the soilenoid and A is the area of the solenoid turn. If you take the derivative of the flux to get the "rate" at which it is changing you get B*N*A*w*cos(wt). So B (which is related to the "strength" of the magnet), N (turns), A (diameter of the coil), and w (how fast the magnet moves) arep retty much the parameters you can control. Lowering the resistance of the wire by using a low resistivity material and heavy gauge wire will also perhaps be beneficial

Thanks leright. With that para, you just answered almost all of my doubts except one. And that is about of the strength of permanent magnets! Earlier i was searching the net for powerful magnet and one of the site said N35 is the strongest and can operate in high temperature like 150 degree celius. Could you help me understand that's true?

 

[leright]

Thanks leright. With that para, you just answered almost all of my doubts except one. And that is about of the strength of permanent magnets! Earlier i was searching the net for powerful magnet and one of the site said N35 is the strongest and can operate in high temperature like 150 degree celius. Could you help me understand that's true?

Yes, I believe N35 is the strongest room temperature permanent magnet.

 

[Silent_88]

Yes, I believe N35 is the strongest room temperature permanent magnet.

Thanks again..! cheers

 

[leright]

Good luck with your project. Let us know how it turns out.

 

[Silent_88]

Good luck with your project. Let us know how it turns out.

Definitely! Will post a picture as well..!

But just to understand, how much power do you think i can generate if the turns are like 1600 with N35?

 

[leright]

Definitely! Will post a picture as well..!

But just to understand, how much power do you think i can generate if the turns are like 1600 with N35?

Definitely! Will post a picture as well..!

But just to understand, how much power do you think i can generate if the turns are like 1600 with N35?

One tip, instead of moving the magnet into a stationary coil it might be best to use a configuration like a generator, which rotates a coil with a crank in a magnetic field produced by a stationary magnet. Of course, the amount of power is limited to the amount of mechanical power you put in, but there will be of course some losses.

You might want to read up more on Faraday's Law and electric generators to get some ideas.

You'd be surprised how much work it takes to light up even a very small light bulb with a hand crank generator. :)

 

[leright]

So if you want to light a 20 Watt light bulb you will need to give at least 20 Watts of mechanical power. You burn about 300 kcalories per hour walking briskly (I think), or about 1.2*10^6 Joules/hour, or 333 Watts of power.

 

[Baluncore]

But how is "linear alternators" different from shaky flashlights? Do they work on the same principle or some other laws of physics?

They are the same.

 

[Nidum]

Do some experimental engineering . Design and make something starting from best guess at configuration and with available materials .

 

[Merlin3189]

One way of improving electrical machines, that rarely seems to get mentioned (except by Eric Laithwaite), is improving the magnetic circuit.
Air is thousands of times less permeable than iron (I leave that vague, because there is a lot of variation between different alloys), so the length of air gap the flux has to pass through is often the limiting factor.

For rotary machines this idea is well understood and applied (except by inventors of free or cheap energy generators!) but I'm not sure how it will work here.
Perhaps instead of one large sliding magnet in one long coil, it would be better to have a series of short magnets sliding between a toothed stator and a series of coils?

 

[Nidum]

One of the main problems with linear generators is that for a large part of the forward and reverse stroke very little power is generated . Generation is velocity dependent and with SHM only middle third or so of each stroke is likely to do anything useful .

In the early days of the power industry there were a few 'beam engine' generators . Steam cylinder one end and big coil with plunger magnet the other end . Some early electric motors worked this way as well - big coil and magnet plunger at one end and crankshaft at the other end .

There have been many proposed uses for linear generators over the years most of which have disappeared . The only application I know of which seems to have been reasonably successful is in tethered bobbing buoy wave power generators .

 

[Merlin3189]

One of the main problems with linear generators is that for a large part of the forward and reverse stroke very little power is generated . Generation is velocity dependent and with SHM only middle third or so of each stroke is likely to do anything useful .

I wonder if this was also true of a simple single (or bi-) phase rotary generator? Only two peaks per revolution.
By adding more poles you got more peaks per revolution, but still peaks and nulls . By going to 3 phase those peaks overlap.

And does this matter?
For the torch, I assume, the AC is rectified and smoothed by a capacitor or battery/cell and used to power a DC driver for a LED. It may actually be better to have peaks of high voltage rather than a continuous low voltage, as these can be more efficiently rectified.

How efficiently input energy is converted to electrical energy, what average power can be achieved, how well the generator fits the source of energy and costs are all important considerations.
Your wave generator may suit this type of generator because linear oscillating motion may be easier to derive from waves, than rotary motion.
The linear generator torch may be less efficient than a rotary generator turned by a handle, but it can be operated by one hand and maybe it will charge without any special attention from the natural motion of walking.

I carry no torch for linear generators, but they may well have niche applications. So the interesting engineering questions arise about how to make them as good as we can.

 

[Baluncore]

Perhaps instead of one large sliding magnet in one long coil, it would be better to have a series of short magnets sliding between a toothed stator and a series of coils?

That is how it is done in free piston alternators. A stack of magnets moves with the piston in a ceramic cylinder. Many coils, (with 1/3 the pitch of the magnets), are wound around the cylinder and connected as three phase power for rectification and battery charging.

I remember an interview with Eric Laithwaite in the 1970s. He said human powered flight was impossible.

 

[Baluncore]

One of the main problems with linear generators is that for a large part of the forward and reverse stroke very little power is generated . Generation is velocity dependent and with SHM only middle third or so of each stroke is likely to do anything useful .

But with a linear generator the coil is inductive, so the current is no longer SHM. The rectified current flows for longer at the battery voltage.