I am trying to design a necklace with flapping Angels wings and a short burst of light for my wife. I am trying to power it off of her body heat or possibly small solar cells
The idea is to use a small peltier generator or several of them in parallel to charge a capacitor maybe to sporadically power a small DC motor and a small diode (light) for a short time. I am super new to this but I'm pretty good at figuring out stuff one way or the other any help would be much appreciated.

 

Welcome to AAC!

Your first task would be to conduct an energy analysis in order to determine if there will be sufficient energy from the source to power the load, given an assumed percentage efficiency.

In the end, you may discover that a better solution would be to use some coin batteries for your project.

 

Before you get into the design stage, you need to do a feasibility study. Find out how much power you can generate with peltier cells and solar cells that are the maximum acceptable size for this application and then check if that is enough to drive a small LED or motor for the length of time and interval needed.
My opinion is that you may find that driving a motor is probably out of the question, but you may be able to flash a LED occasionally.

 

It's Christmas. Here is a more feasible gift. Make a Christmas tree ornament that will flash an LED at about once every second, powered by a single button cell.

 

The power produced by a peltier junction depends on the temperature difference between the ends. The difference between body temperature and ambient temperature is maybe 30°F, a tiny difference for a peltier junction.

But it's even worse. The temperature of an object against skin is going to reach an equilibrium of a very small difference if the cold side isn't continuously cooled some way.

So starting from essentially zero output with a 30° difference to a way, way, way less oitput with a few degrees difference in temperature.

 

Thanks for all the input.
I should clarify that this device will be going off spontaneously. I may only generate enough power to have it go off five times a day the point is for it to be random.
Some rechargeable coin batteries sounds like a good option and it sounds like the peltier generator may not be a good option so maybe small solar cells would be the way to go.
I would just need a circuit that would let it go off sporadically. I've heard talk about 555 timer on other threads I wonder if this could help me in some way.

 

I'm currently sourcing some tiny DC motors so my power needs are not yet known but I am shooting for as little as possible also I do have a wicked multimeter from harbor freight to assist me in finding out my power needs. (That that last bit was meant as a joke don't crucify me lol)
In all seriousness though with nothing more than a multimeter I've been able to make and repair some electronics around the house.
Along with the help of some friendly folks from the internet of course.

 

Welcome to AAC.

I'm not sure the comments here have communicated the essential information they intended to.

What people are trying to tell you, gently, is that what you want to do is not feasible. The general category of your problem is called Energy Harvesting. It is an area under heavy research right now and if someone managed to do what you hope to, they would be in line for a Nobel Prize.

Here's the problem: the amount of energy available from your two proposed sources: your wife, and the ambient light falling on the surface area of reasonably sized necklace are simply not sufficient to cause motion in any mechanism that would also survive being worn.

As an example, you may have seen bobblehead type figurines that use a small solar cell and manage to cause the head of the figure to shake or rotate. This might suggest to you that your plan could work—but that's misleading.

The success of the design is based on two things:

• A relatively large PV (photovoltaic) "solar" cell.
• An exceedingly low friction mechanism.

The area of the PV is really quite large compared to something you could incorporate with any elegance into a necklace. The power from PV cell is all about surface area—something you don't have very much of.

The mechanism of the moving part depends of a very careful and static arrangement of a bearing—usually something like a needle point in a cup—and a very delicate spring. The entire device has to be level, because the bearing won't work in any position but the one it is designed for, within a very small tolerance.

So as promising as these devices my seem, they aren't applicable to your problem.

As @MrChips said right away, you have to do an energy analysis to work out what is possible. The Laws of Thermodynamics are very frequently the sticking point for "good", but naïve ideas. That's not intended as a slight—many ideas are very creative but conceived in a state of ignorance.

Sometimes this can lead to a breakthrough because those who aren't ignorant can be blinded to possibilities by their otherwise useful knowledge—but thermodynamics is basic: you either have the energy budget or you don't.

The analysis may seem daunting but you can do it pretty loosely. Usually an order of magnitude (tenfold) estimate will rule out things that simply aren't practical. But if you make a fast and loose estimate, and falls out in favor of the idea, you can look to refine it.

The basis for such an estimate is simple: you need to know how much work you need to do and how much capacity you have to do it. In electrical terms, this would be in Watts. Your problem to start is to work out how much work moving your mechanism will be.

You mentioned motors. This is probably not the most fruitful direction to explore. Instead, you might want to consider solenoids which are potentially more efficient for your application. In either case, you will be dealing with exceedingly small devices.

I do have one suggestion I expect could be a better route considering how fraught the mechanical motion path appears: created the illusion of motion using light. LEDs can be very efficient, and a series of them, along with some sort of reflective material light the holographic stickers that can be found from many sources, might be able to create a convincing display of motion.

Your idea of accumulating power over time and then using it at a threshold is promising, but a Lithium coin cell, or a stack of button batteries, seems more likely to be successful than any energy harvesting you could reasonably do in this context.

Whatever you choose, good luck and I hope she loves what you make.

 

Couple things from the peanut gallery:

Some rechargeable coin batteries sounds like a good option

About a decade ago I had some old used up coin cell batteries. I have the habit of tossing them into a jar and accumulating them until I have enough to bother with recycling them. Turned out there were 3 or 4 of them that I wanted to toss into the jar but they still have a very little bit of energy remaining in them. Tossing them into a jar is not a good idea because they could short themselves out one to another and potentially cause a fire. So I became of the habit of taking a clothes pin with some aluminum foil and wrap the battery and clip it in order to drain off the charge. One particular day I was playing with some LED's and discovered that the coin cell still could light the LED's. These LED's were Super Bright LED's. I clipped them to the coin cells with clothes pins and let them light up. They were lit continuously for over two weeks. So MrChips' suggestion of using coin cells is highly practical.

I may only generate enough power to have it go off five times a day the point is for it to be random.

The second thing is this: Five times per day - that's a long period of time on average between flashes. That's once every 4 hours, 48 minutes. If no one is watching at the moment of flash - it's going to go unnoticed. Plus, the idea of having to wear some jewelry 24 hours just to get a single flash every almost 5 hours seems like a task better suited as a torture device than a beloved ornament.

Now: To go the coin cell route you're going to need other electronics as well. Small as they can be - it's going to be hard to find circuitry that can work as you hope for. Not impossible, I certainly am unfamiliar with micro-miniature electronics, but I'm sure they do exist.

And like others have said, "Welcome to AAC."

 

Sitting here thinking about your proposal, I've held in my hand some very small lithium batteries. They're rechargeable. With the proper charging device the necklace can be charged overnight then worn as desired once a day, for an evening or for any other reason. The likelihood that the battery could deliver enough power for a few hours is easily conceivable. I'm not talking about those big 18650 cells, those would be gaudy and difficult to conceal. Just doing a quick search on Amazon I found this:
https://www.amazon.com/YDL-battery-Rechargeable-Lithium-Connector/dp/B07BTV46XB/ref=sr_1_50
It's just under an inch long, little wider than a half inch and just under a quarter inch thick. It also has its own built in BMS (Battery Management System). With Lithium batteries you want to be careful about how you charge them and how much you discharge them. I don't know how good this battery is, it only has a 3.8 star rating and only 645 reviews. But the cost is low.

Now, the cost of designing or finding a tiny package of electronics to do the things you wish it to - that's going to take some research. Simply flashing an LED once every 5 seconds isn't going to be hard. Finding tiny circuitry for your wife to hang around her neck with very little weight to it - that's going to be the challenge. Would she wear a bowling ball around her neck? I doubt it. OK, way over exaggerated, but it conveys the idea.

[edit] forgot to mention the charger. And the cost goes up. However, when it comes to a gift - money is not the main concern. [end edit]

 

Thanks again for the responses fellas even though I may not get to the end I desired this has been enlightening.
I guess a little more clarification would help as always.
The necklace my wife is wearing is already Guady. As far as building the mechanical side of it that will be extremely simple with a little bit of spring steel and some plastic and wire. I'm a 20 plus year Machinist and fabricator so making it move will be no challenge it's just the electrical side that I am not versed in.
I should clarify how many times a day it would go off and the duration.
Maybe once an hour and just for a few seconds long enough for the light to shine a little bit and the wings to kind of flutter. The DC motor will turn and just flick the wings a little bit couldn't be any simpler (famous last words for any project I've ever started). There won't be an on/off button it will just run as it finds the power it needs.I say again as far as my building skills I have literally seen a product on television or thought of one and using old appliances and electronics laying around the house made the product that night.
I have a few items that I'm going to source and try to throw something together. Small solar cell, small DC motor and some rechargeable button cells. I have a few diodes laying about but I'll look around to see what else is out there. I may not get the end result I want but I'll have fun trying to get there. Thanks again

 

 

Here's some earrings I was thinking of incorporating

 

There may be other voltaic devices that could deliver more energy based on ambient illumination, than what is available from heat and a Peltier device. So that might be an alternative choice. Certainly simpler to apply. There might even be IR devices that capture heat energy but do not require heat flow. (a logical guess, not a verified fact).

An alternative could also be hearing-aid batteries, which come in both disposable and rechargeable versions, although the cost will be (negative expletive here).

 

The DC motor will turn and just flick the wings a little bit couldn't be any simpler (famous last words

The smaller the motor the more likely it will spin crazy fast. Flicking a wing to make it flutter will be a challenge. At least for me it would be. You'd need some kind of gear reduction to achieve what I'm envisioning.

 

Of course, a wing with a tiny magnet on it near a coil of wire. Briefly energize the coil and the wing will either be attracted to or repelled from the coil. Polarity of the coil or orientation of the magnet will be needed to have the wings jump up. No motors, no gears, just the electronics and a magnet per wing.

 

The smaller the motor the more likely it will spin crazy fast. Flicking a wing to make it flutter will be a challenge. At least for me it would be. You'd need some kind of gear reduction to achieve what I'm envisioning.

 

And just like that my simple design now has a planetary gear system lol.
I had thought of that and I do like the idea of it. I've done a bit of hobbing and gear shaping it's a fun area.

 

I like the magnet idea.

 

Welcome to AAC.

I'm not sure the comments here have communicated the essential information they intended to.

What people are trying to tell you, gently, is that what you want to do is not feasible. The general category of your problem is called Energy Harvesting. It is an area under heavy research right now and if someone managed to do what you hope to, they would be in line for a Nobel Prize.

Here's the problem: the amount of energy available from your two proposed sources: your wife, and the ambient light falling on the surface area of reasonably sized necklace are simply not sufficient to cause motion in any mechanism that would also survive being worn.

As an example, you may have seen bobblehead type figurines that use a small solar cell and manage to cause the head of the figure to shake or rotate. This might suggest to you that your plan could work—but that's misleading.

The success of the design is based on two things:

• A relatively large PV (photovoltaic) "solar" cells.
• An exceedingly low friction mechanism.

The area of the PV is really quite large compared to something you could incorporate with any elegance into a necklace. The power from PV cell is all about surface area—something you don't have very much of.

The mechanism of the moving part depends of a very careful and static arrangement of a bearing—usually something like a needle point in a cup—and a very delicate spring. The entire device has to be level, because the bearing won't work in any position but the one it is designed for, within a very small tolerance.

So as promising as these devices my seem, they aren't applicable to your problem.

As @MrChips said right away, you have to do an energy analysis to work out what is possible. The Laws of Thermodynamics are very frequently the sticking point for "good", but naïve ideas. That's not intended as a slight—many ideas are very creative but conceived in a state of ignorance.

Sometimes this can lead to a breakthrough because those who aren't ignorant can be blinded to possibilities by their otherwise useful knowledge—but thermodynamics is basic: you either have the energy budget or you don't.

The analysis may seem daunting but you can do it pretty loosely. Usually an order of magnitude (tenfold) estimate will rule out things that simply aren't practical. But if you make a fast and loose estimate, and falls out in favor of the idea, you can look to refine it.

The basis for such an estimate is simple: you need to know how much work you need to do and how much capacity you have to do it. In electrical terms, this would be in Watts. Your problem to start is to work out how much work moving your mechanism will be.

You mentioned motors. This is probably not the most fruitful direction to explore. Instead, you might want to consider solenoids which are potentially more efficient for your application. In either case, you will be dealing with exceedingly small devices.

I do have one suggestion I expect could be a better route considering how fraught the mechanical motion path appears: created the illusion of motion using light. LEDs can be very efficient, and a series of them, along with some sort of reflective material light the holographic stickers that can be found from many sources, might be able to create a convincing display of motion.

Your idea of accumulating power over time and then using it at a threshold is promising, but a Lithium coin cell, or a stack of button batteries, seems more likely to be successful than any energy harvesting you could reasonably do in this context.

Whatever you choose, good luck and I hope she loves what you make.

So you say I'm on the verge of making a Nobel prize winning discovery ehh?
This day keeps getting better and better.
I'm familiar with the perpetual motion machine concept. Energy harvesting is something I'll have to read up on.
I do appreciate you guys being gentle but "can't" is a dirty word in my house.
We all know there are no free lunches in nature and that the price will have to be paid somewhere, so I'm thinking the rechargeable button battery may be the one to pay.