Mini hand held generator creation help needed

Bernard

Joined Aug 7, 2008
5,788
Sounds something like a 4th of July toy from 1930s that spun a colored disc with a squeeze
handle. Power was applied only on squeeze with spring return. Disc had a flint to make sparks & a small gear. Handle operated a segment of a large gear which retracted on return stroke. It changed hands before I could take it apart.
 

Tonyr1084

Joined Sep 24, 2015
6,632
@Bernard I remember those things. The friction of squeezing the handle pushed the gear into place. With the weight spinning it pushed the gear away. When relaxing the grip the backward pressure kept the gear away from the spinning mechanism. There was a gravity fed flint riding on top of a rough wheel, which is where you got the sparks from.

Here's my concern with the thread starter's proposal: Push the plunger then pull it back. Try repeating that effort on a spring for five minutes, then see just how much your pectoral muscles hurt.

My solution to topping off a battery in a "No Charger" situation is to carry an auxiliary battery. Even a small one during a power outage after a tornado, took my phone from less than 30% to 85%. It was my computer that was struggling because I had no way to plug it in and charge the battery (laptop). My truck has a built in inverter. I just had to find an extension cord and run it in through the back window then plug my computer charger into that.

In all the years I've had these emergency batteries, I've only used the small one once. That was during a 20 hour power outage. Push - pull - push - pull - push - pull - ouch.
 

MisterBill2

Joined Jan 23, 2018
10,591
The charger will be far more effective with a rotary generation system, either spinning magnet or spinning coil. I have used both kinds. The most effective generator looks a lot like a permanent magnet synchronous motor, with a magnetic rotor . In fact, a small surplus stepper motor plus a rectifier would be a simple and easy ti build system, and no need to create gear teeth. The bobbing magnet in a tube with a coil is for toys and other silly devices.
 

Uilnaydar

Joined Jan 30, 2008
118
For reference, watch South Park - Big Jim episode. Disclaimer: Not safe for kids or work or polite society.... but if you want to build up the strength, this is what you want!
 
some thoughts. not gonna fly.
a pma/pmg will NOT COAST during the time when force is not being applied.
it a return spring is used, the operator would have to do TWICE as much work.
be sure to have insurance coverage, for the very rapid onset of carpal tunnel syndrome. cheers
 

djsfantasi

Joined Apr 11, 2010
8,085
Or as @LesJones said in post #9, use a rack and pinion to drive the generator with a full bridge rectifier. The rack will drive the gear clockwise and counterclockwise. The full bridge rectifier will convert the alternating voltage to straight DC.
 

MisterBill2

Joined Jan 23, 2018
10,591
For those folks who have forgotten it, a bridge rectifier always has two diode drops in series with the current. Not a big deal on a mains powered system, but on a human powered system that can be a fair amount of wasted power= wasted effort.
 

djsfantasi

Joined Apr 11, 2010
8,085
For those folks who have forgotten it, a bridge rectifier always has two diode drops in series with the current. Not a big deal on a mains powered system, but on a human powered system that can be a fair amount of wasted power= wasted effort.
Excellent point! Another design element to be considered. A standard bridge rectifier will drop 1.2-1.4V. Building your own Schottky bridge rectifier (or finding a part) reduces the voltage drop to 0.4-1.0V depending on the diode. This is possibly a significant improvement. You have to consider that the reciprocating drive adds mechanical resistance, also wasting a fair amount of wasted power. As someone said :rolleyes: “Wasted power = wasted effort”
 

Tonyr1084

Joined Sep 24, 2015
6,632
Here's a thought that just occurred to me - - - Peltier tiles mounted on an aluminum tube. The tube interior is exposed to ambient temperature air while the exterior is lined with Peltier's. The difference in temperature of a warm hand and a cool tube will generate some electrical charge and light a super bright LED. If you need brighter light, hold the tube between the thighs.
 

Thread Starter

Top-up

Joined Aug 17, 2019
15
@Bernard I remember those things. The friction of squeezing the handle pushed the gear into place. With the weight spinning it pushed the gear away. When relaxing the grip the backward pressure kept the gear away from the spinning mechanism. There was a gravity fed flint riding on top of a rough wheel, which is where you got the sparks from.

Yes this is what my idea was from

My solution to topping off a battery in a "No Charger" situation is to carry an auxiliary battery.

This is what i wanted to know as well if i added a little battery to the circuit would this help to stop the drop from the tiny delay?
.
 

WBahn

Joined Mar 31, 2012
26,398
Here's a thought that just occurred to me - - - Peltier tiles mounted on an aluminum tube. The tube interior is exposed to ambient temperature air while the exterior is lined with Peltier's. The difference in temperature of a warm hand and a cool tube will generate some electrical charge and light a super bright LED. If you need brighter light, hold the tube between the thighs.
Someone would have to run the numbers, but you are talking about a pretty small temperature difference and you need to move a lot of watts from the hot side to the cold side -- typical efficiencies are well below 10%. So most of the heat is going to go into the interior of the tube and raise the temperature there unless you have some means of moving that air out of the tube. Peltier modules typically have quite high output resistances in order to produce useful voltages. The thermal conductivities also tend to be pretty high so it is hard to move a lot of heat from hot to cold with only a small temperature difference.
 

Tonyr1084

Joined Sep 24, 2015
6,632
Not saying this is a wonderful solution, but it seemed to work for a 16 year old girl. She won a science fair with this flashlight.

 

djsfantasi

Joined Apr 11, 2010
8,085
°So thinking outside the initial problem, the latest problem you raised was the small heat differential.

How to maximize that differential? What about a cooling insert? Like a tube filled with some liquid that a) when frozen is less than 0°C (or optionally can be refilled with ice water), b) maximize heat sinking away from the Peltier module and c) maximize heat transfer to the Peltier modules.

With regard to (a), I belonged to a meal service. I saved all the cold packs. Whatever they are filled with is below 0°C and last significantly longer than ice.

Then how do we address (b)? I propose an aluminum tube inserted into an aluminum sleeve. The curved surface of the sleeve connects to a flat aluminum plate that the Peltier module is attached. If the LEDs are mounted at right angles to the body, then run aluminum fins vertically to fill the space between the curve and the Peltier pane. Convection will then add to the cooling.

I haven’t mentioned yet, but we need to maximize the heat from the operators hand to the Peltier module (c). If you hold your hand out and curl the fingers as if were holding the torch, you’ll notice a couple of things. The index finger is out a little further from your palm than the middle and ring fingers. And the pinky is closer yet to your palm.

This suggests a grip that is stepped so that each fingers contact is maximized with multiple Peltier modules.

So, multiple Peltier modules physically placed so as to maximize contact, a finned transition between modules and a cooling tube and a cooling tube that can be prepared in multiple ways (ice water/frozen solution)

Each of these concepts can be addressed in multiple ways. This one is just my brainstorming approach.
 

WBahn

Joined Mar 31, 2012
26,398
Not saying this is a wonderful solution, but it seemed to work for a 16 year old girl. She won a science fair with this flashlight.

Nice. Didn't look very bright (I wouldn't want to try to study by it), but it would be useful for some applications. Wonder how well it works under real conditions (such as warm temperatures and extended use).

Somehow I doubt her solution really qualifies as a solution for someone with no money (her stated objective) -- how much did those Peltier devices cost?

It would also have to compete with the low-cost handheld generators for most applications.

I wonder what the actual mW delivery is? Imagine charging your phone by just walking along holding something like this in your hand. Of course the coolest thing would be if you could build it into the phone so that the heat from your hand charged it while you were using it (though I imagine the energy use far exceeds the energy available plus you would have a harder time keeping the cool side cool).
 
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Tonyr1084

Joined Sep 24, 2015
6,632
@WBahn; I've wondered the same thing.

I worked for MacDonald Douglas back in the late 70's. I was inside a DC-10 fuel tank when someone outside decided they needed my extension cord more than I did. So they unplugged my light and left me in the absolute pitch blackness. Finding my way out was made possible by my watch light. Back in the 70's watches weren't as bright as they are now. The tiny rice lamp adjacent the LCD display barely cast a thin beam of light, like that of a putty knife, only wider. Scanning up and down with the light I could determine where the passages were that I needed to follow to get back to the access port. Never found the SOB who took my cord, but if not for my fancy and new technology watch, it would have been a very long time before I got out of there.

Was in a sub-basement - no windows at all. Someone turned out the lights and I was all the way across the room. Stocked with shelves and shelves of food stuffs. Being unfamiliar with my surroundings, ANY light at all would have been welcome. It's 100% disorienting when you have absolutely no point of reference; not even the sound of a motor to follow. Slowly I felt my way across the shelving until I got to the end. Then in a leap of faith I reached what seemed to be the far wall. I then followed that along until I found something steel, resembling a door. Sure enough, I found my way out. But that took me a good 30 minutes.

With super bright LED's today, a Peltier module might produce enough current to light the way out of such situations.

The thread starter wants to build a generator to light a light. In keeping with his request, they have shake lights that seem to work pretty well too.

 

MisterBill2

Joined Jan 23, 2018
10,591
For the hand driven generator, use a sector of a large gear with a light spring to return it to home position. That large sector, 2 to 3 inch pitch-line radius, drives a very small pinion that is coupled to a rotating magnet generator through an over-running clutch. So each squeeze spins the generator and it coats while the sector returns, only to be squeezed again. Only one diode is needed and no fancy gear teeth need to be made, just cut out a section of a large gear. And an over-running clutch is easy to get and not hard to make. And the gears stay properly meshed and so avoid excess wear. The peltier device would not make enough power to lite even a small LED with body heat as the power source.
 
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