Paul @BG455322435 goodto know! just getting in to hand engraving and will need to keep my tools sharp. I think I'd try flattening the stones on my surface plate by hand, however.

Paul you Can, but why would you? considering the power requirements of a cellphone (5v @1amp hour) the cost of components if pretty high. You'd be more economical to use wind or make a steam turbine to produce electricity. efficiency for those systems is on the order of 25-30% compared to 5-8% supplied by TEG modules. think of cost per sq. meter or cost per watt. if only size is your consideration, a pocket sized Peltier system for USB charging would cost more than 20 Euros/ $35 USD

Paul I can SEE 2 contacts, however I do not see an O-ring, tho others have shown it. what ohms is the resistor?