peltier Small voltage storage

yuvish

     You can store energy in a capacitor, but only a small amount. See http://johnhearfield.com/Physics/Capacitor_energy.htm

for an explanation. Look at supercapacitors for larger amounts. Also a good article is http://electronics.howstuffworks.com/capacitor.htm.

Clem

Capacitors are not good at storing big energy values. But we can do the math...

If we assume that led to use 20mA, you'll need during one hour.  If we assume that the capacitor is charged to 5.5V at the beginning and may discharge to 4.5V, we can calculate: I = C dV / dt -> C = I dt / dV = 20mA * 3600 / 1 = 72F. That's quite a large supercapacitor.

I have a green led that is quite bright. At 1mA it shines sufficiently. Then you'd only need 3.6F. Use four of these: EECHZ0E475 - PANASONIC ELECTRONIC COMPONENTS - CAP, DOUBLE, 4.7F, 2.5V, RAD | Farnell element14 (two series two parallel) and you're in business!  (Not quite as impossible as I thought at first!).

Next, if you put your peltiers in series, you'd have 1.8V. A circuit like joule thief might be able to use such a voltage to charge the capacitor. Or you could look into a step up converter that has a very low start-voltage.

Hey Roger,
Thanks for your help.
You're really good.
If i go for your circuit, will I be able to mimic the brightness of a torch?
also, can 1.8V power supply charge a 4.5V capacitor?
I mean, can't only a 4.5V or more power supply charge a 4.5V capacitor?

yuvish

also note that you need to cool down the other side of the peltier, otherwise it will quickly get the same temperature as the coper plate, resulting in no voltage output whatsoever. The peltier generates power over a temperatuur difference!

Gerrit.

Voltages can be transformed up or down. The thing is, some of the losses occur at "fixed voltage". so if you transform down from 12V to 0.9V (in your computer for the CPU), having a 0.6V diode drop in the output circuit means you're throwing away 40% efficiency.

In your case the "input voltage" is the one that's low, so it is difficult to keep the efficiency high.

You are obviously working on a "project for school". I don't think you learn as much as you should if I do all your homework.

You are leaving out relevant information. So when I suggest that it might become possible to do with capacitors I've had to reduce the intensity of the led quite a lot.

Other info you're leaving out is how powerful the peltiers are. What is their current rating?

I suspect that they are capable of 1 or 3A, which means that the standard "joule thief" at 60mW is not loading the peltiers optimally to extract the maximum amount of energy. If you measured the voltage at 0.6V, the peltiers should be capable of 600 to 2000mW, ten to thirty  times more!

So in that case you should be looking at a configurable step-up converter that works with low voltages.

(and note that the amount of heat you need to transfer away goes up when you start electrically loading the peltiers.).

yes I added a heat sink on the other side.
I bought this.
Will this work? http://www.ebay.com/itm/141289152186

How she came to this?  https://www.youtube.com/watch?v=yrnNmzSSn0w

A point of clarification

The Seebeck effect is the is the conversion of temperature differences directly into electricity and is named after the Baltic German physicist Thomas Johann Seebeck.

The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors and is named after French physicist Jean Charles Athanase Peltier,

This question is actually about the SEEBECK effect.

When using the tiles as a Peltier devce, it takes quite a but of current to create the termperature gradients (Amps)

when using the device in its Seebeck mode, the thermal differences DONOT create AMPS until you have a very large temperature differential, and is very dependent on the materials used to make the tile, see here https://en.wikipedia.org/wiki/Seebeck_coefficient.

a 50$ tile could produce 20Watts ish of power if it has a 275degC temp differential, thats about 4Amps at 5V see a typical PDF here http://www.customthermoelectric.com/powergen/pdf/1261G-7L31-24CX1_20140328_spec_sht.pdf. thats enough heat to melt solder

you will not get even close to this with a hand or just sitting it in the SUN even if the other side is on an ICE block, it would give out perhaps 1 or 2 watts at about a volt.

the boost convertor you have chosen should work ok for your needs, the storage meduim from what I have seen about the output of these devices may be better connected to the output of the boost convertor and could be a LIPO or something, this way your not limiting yourelf to only a few volts which over a day would fully charge a cap/supacap/other device and the rest could be wasted. by converting imediatly to a higher voltage you can store more energy possibly and then use this directly to drive the LEDS / LOAD when needed

Hello Peter,
Yes that what I was thinking the battery should be connected to the output of the voltage booster.

I think you have solved my circuit problem.
Thank you very much for your help.
If you think I have missed something, please do inform.

re. the flashlight girl - I didn't spend long but I couldn't find a schematic or ANY technical discussion on the web. There is some mention of voltage conversion circuits.  Judging by the video there isn't much power going into the LEDs. You can't extract much thermal power from your hand without damage (to you) no matter how you do it.

Don't expect useable torches made like this anytime soon -  and the energy to manufacture the peltier devices probably far exceeds the likely lifetime output in this application.

Your ebay gizmo looks like the so called 'joule thief' on a nice little board. A chip for LTC would work better but cost more.

MK

Ya I searched, the girl used the LTC 3108 for linear Tech.
https://www.google.mu/search?q=lipo+battery&rlz=1C1TGIB_enMU523MU523&es_sm=93&biw=1242&bih=585&source=lnms&tbm=isch&sa=X&ei=2vmfVayPMoG0UevksZAN&ved=0CAYQ_AUoAQ#tbm=isch&q=LTC+3108&imgrc=_

But thats expensive.
Could not find this on ebay also