Can I build a demonstration electric generator like this? (With a tube)

[Deeg]

I'd like to build a simple generator to demonstrate it to some kids. I was thinking about winding magnet wire around an acrylic tube, inserting a rare-earth round magnet, and sealing both ends. Then the kids would then shake the tube so the magnet bounces back and forth, sort of like shaking a spray-paint can. Would this generate any noticeable electricity?

 

[Roff]

Have you seen shaker flashlights?

 

[Deeg]

Yeah, I was vaguely trying to replicate something like that. Like a dope I didn't think to look at a break down of a flashlight. Thanks for the link Roff. I'm surprised how short the coil is.

 

[Nigel Goodwin]

Yeah, I was vaguely trying to replicate something like that. Like a dope I didn't think to look at a break down of a flashlight. Thanks for the link Roff. I'm surprised how short the coil is.

Bear in mind many of the Chinese made shaker lights are no such thing, they just have a battery feeding the LED, and shaking does nothing.

 

[MrAl]

Hi,

Just a couple tips...

1. It would probably work best to use a cylindrical magnet that could slide up and down in the tube, although it may be hard to find one that fits really good.
2. A thinner wall tube is better as there is tighter coupling between magnet and coil, although the magnet has to fit the tube good also.
3. The more turns of wire the better, but the gauge has to allow the required current flow without too much loss.
4. You probably have to use a bridge rectifier to rectify the AC output of the coil into DC for use as lighting an LED.
5. It would probably help to have a capacitor to store some of the energy generated.
6. Some bumper padding at the ends to reduce the collision force at the ends, but even better some medium strength springs which would store some of the mechanical energy and help get the magnet moving back in the other direction. This means much less effort on the part of the human for generating a given amount of energy and could make a big difference if the springs are chosen carefully.

Perhaps others here can come up with some more ideas too.

 

[Deeg]

Thanks for the suggestions MrAl. What size cap should I look for? Can I use a couple of caps in parallel?

 

[BrownOut]

When the magnet strikes the ends of the tube, things will began to pulverize. Springs would be good, or else some heavy duty streachable rubber bands to keep the magnet away from the ends.

 

[Roff]

Google "shake generator".

 

[MrAl]

Thanks for the suggestions MrAl. What size cap should I look for? Can I use a couple of caps in parallel?

Hi there,


It depends on what you intend to drive with it really and it depends also on how your final coil and magnet work out in generating current and voltage. Start with maybe 10uf and see how that goes. The cap is good if you want to shake up the tube a lot before turning on the LED (or other device). I could also see using a rechargeable battery if the coil and magnet can generate enough energy.

Also, if you can get the mechanics set up right dont forget the springs at each end as they also store energy that would otherwise be wasted. If you are after super simple then you may want to do it without springs, but that's up to you.

That shaker link is interesting but i think they forgot about the LED reverse voltage specification. At least one Schottky rectifier might be a good idea unless there is little reverse emf from the coil. A good coil/magnet setup will definitely generate reverse voltage too however, so a bridge rectifier made from Schottky's would be nice.

Of course the better idea is to use a regular small DC motor and some gears and a hand crank. That will generate much more energy than a tube with less cost too. It's a little harder to get the gears right though, where the crank has to be geared up for speed so the motor turns fast. That means tough gears and a sturdy hand crank as well as the right gear ratio.