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I want to light up a led with my hand heat by using a peltier cooler. how can I light up a led with 30 millivolt-0.1 volt with a joule thief? Should I connect more transistor in parallel or give more turns on toroid? I have made a joule thief which can light up a led with 0.7 volt.

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how can I light up a led with 30 millivolt-0.1 volt with a joule thief?

A joule thief will not work below 0.6V to 0.7V. If you want to light an LED with 30mV you will need a supplementary battery/power source. There are energy harvesting chips that "say" they can energy harvest at 20 mV but they use a supplementary supply to get the process started then move their power control circuits to the "harvested" larger voltage.

Linear technology and Texas Instruments both have parts that will do this.

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  • \$\begingroup\$ Parts as the LTC3105 claim to have as low startup voltages as 250mV, so that is at least quite a step more than 600mV \$\endgroup\$ – PlasmaHH Dec 14 '15 at 11:14
  • \$\begingroup\$ @PlasmaHH It's a good part but it still doesn't get you operation below 100mV. \$\endgroup\$ – Andy aka Dec 14 '15 at 11:45
  • \$\begingroup\$ But I have a seen a video where he is glowing led with oly 0.136 volt using a BC108 transistor. youtube.com/watch?v=Gjx-V_cCl7A \$\endgroup\$ – Abtahee Salekeen Jan 5 '16 at 10:46
  • \$\begingroup\$ @AbtaheeSalekeen the problem I think here is that the initial impulse on connecting the battery (at 1.5 volts) is enough to turn the transistor on and start the process. Once started the average battery voltage may well be 0.1 volts (as seen on a DVM) but the duty cycle maybe 1:10 i.e. the transistor is on for 90% of the time and off for 10% of the time. Due to the internal resistance of the battery (maybe 1 ohm to 10 ohm on a badly discharged battery), shorting it out produces 0V and opening the short produces maybe 1V but the average looks like 0.1 volts on a meter. Don't be fooled. \$\endgroup\$ – Andy aka Jan 5 '16 at 11:02
  • \$\begingroup\$ but he can light up a led by using a peltier cooler too in this video which produces only 0.1 volts.youtube.com/watch?v=B_w5z8WY1pQ \$\endgroup\$ – Abtahee Salekeen Jan 5 '16 at 16:41

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