On Saturday, October 20, 2018 at 3:15:28 PM UTC-7, Jeff Liebermann wrote:
On Sat, 20 Oct 2018 13:39:27 -0700 (PDT), wrote:

Running on body heat would give you sort of unlimited run time.

There are problems trying to utilize body heat. The worst is the lack
of an easy cold junction. In order to produce electricity, one needs
a temperature DIFFERENCE. If the body is the warm junction, where's
the cold junction? Simply heating something will work if you use a
thermocouple, but the efficiency is very low and little power will be
produced. For example, using the ambient air as a cold junction will
produce a fabulous 0.3 microwatts with this contrivance:
https://www.dailymail.co.uk/sciencetech/article-4368596/Incredible-powercell-converts-BODY-HEAT-electricity.html

There are other ways that seem to be better:
https://en.wikipedia.org/wiki/Energy_harvesting


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Remember that you can use either junction as the cold one. You don't care in what direction the current flows. All you need is a differential. Using germanium you can get away with really low voltages.