25mV Joule Thief powered by peltier merely using our body heat -Free energy 24/7

[magpwr]

Hi acmefixer,

It's been some time since you provided suggestion on ZTX transistors in youtube.I did purchased ZTX1048A and ZTX pnp version.
"I will be revealing a "one button" programmable code lock using pic12f629 and  using ZTX transistors in H-bridge configuration using one 1 AA battery to power gear motor. in youtube"
Once 70rpm motor arrives.The standby power is <15uA.It's a unique  circuit using only 1xAA battery to operate microprocessor and power the latch or lock example lock for drawer.


I did waste money purchasing  just 2x J105 while waiting for (10 x 2SK170)for 2USD to be delivered since the spec for JFET although it looks like it was the best N-channel JFET with lower turn on resistance.

As usual i start test using ultra cap 50 Farad charged to around 100mv using 1AA battery for 1 to 3 seconds.

I placed the JFET into same toroid with 4:100 but oscillation did not happen <100mV.

From the link you provided it looks it will work around 300mv maybe.

The circuit does needs alot of components which may increase current draw.

[acmefixer]

@magpwr  I needed a low voltage source, so I started experimenting with a thermocouple.  I got this from an old water heater or furnace, so long ago I can't remember which.  I put it in the flame of the burner on my stove and it measured 42 millivolts.  I connected a 1 ohm resistor across it, and the DMM dropped 2 mV to 40 millivolts.  So it is capable of driving a very low resistance load.

The Joule Thief takes about 130 milliwatts and 88 milliamps at the normal 1.5V, and much more current at lower voltage if you want the LED to be lit to its full brightness of 20 milliamps.  So getting a Joule Thief to run at less than 1/2 volt is a very difficult and challenging project.  I think that it would be much, much better to put several peltiers or thermocouples in series to get at least a few hundred millivolts, so that the Joule Thief doesn't have to use power MOSFETs in parallel to get the power the LED needs.  I also think that working at 40 millivolts from the thermocouple is just a really big problem, since even the shortest leads of the components can have tens of millivolts drop at high currents.

You're going to have to find out this for yourself.  I know from my experiments at a half volt from a single solar cell.  Best of success, and good luck.

[gyulasun]

Hi Folks,

I found a Lin Tech "energy harvesting" product line for solar, Peltier/Thermoelectric  and Piezo electric voltage sources and they work as DC-DC converters.
Here is the full family:  http://parametric.linear.com/Energy_Harvesting   and this is an IC able to start and operate from already 20mV DC difference:  http://www.linear.com/product/LTC3108   it produces 4 different DC outputs between 2.35V to 5V.

Its working principle is that the minimum 20mV DC input feeds a step up transformer and an inner switch chops up the DC input via the primary of the transformer and the up-transformed pulses at the secondary of the transformer is tuned to resonance by outside capacitors and this AC is rectified and taken care of by the built-in circuits.  An interesting solution.  Digikey, Farnell or others have it.

rgds, Gyula

[magpwr]

Hi  gyulasun,

I'm did research on LTC3108 previously.

But the key component looks like too tiny for me to work on.Besides it needs more discrete component eg:capacitor.

But price of component for my 25mV joule Thief likely below < 8USD and the efficiency could be comparable with LTC3108.

The efficiency is not tested yet.Base on input voltage x current and output voltage x current.

[conradelektro]

@gyulasun: Very interesting, thank you for drawing our attention to the LTC3108 and its family of DC-DC converters.

This shows what can be done professionally with a low Voltage source like a Peltier Element. The price for a stable output Voltage and the other niceties (PGOOD)  is of course a few mA used up by the many electronic components.

The high price of about Euro 10.--  probably means that the market demand is low.

In the data sheet one reads: "The LTC3108 can also be used to trickle charge a standard capacitor, supercapacitor or rechargeable battery, using
energy harvested from a Peltier or photovoltaic cell."

But exactly for this application magpwr's very simple circuit might be better, because one does not need all the high end features (PGOOD, noise reduction with various capacitors, three different stable output Voltages).

Once more I am thinking about building a very simple device with two Peltier elements that charges a small 1.2 V rechargeable battery whenever I light the ceramic stove in my living room. See the attached drawing, the "device" is intended to lean against the ceramic stove.

Greetings, Conrad