Thunderchild said:
as I recall it was a copper and nikel plate joined together that when heated by a flame would generate power. is this practical and with what other metals can I do it. I presume that they can be connected in series so enven if one volt is generated I can make 12/13 volts by putting then in series.
What you describe is a "thermoelectric generator". It is based on the Seebeck effect, which is the same as Peltier effect but used in reverse. In fact, Peltier cooling modules are effective thermoelectric generators in themselves.
A Peltier module is capable of far, far more power than many copper/nickle junctions. Thermocouple wire has a much more powerful Seebeck coefficient than copper/nickle and can sustain higher temps. But the Peltier modules are still far more powerful and practical.
Of course "powerful" is a relative thing. The power output depends on the difference between hot and cold sides. The maximum temp the module can sustain on the hot side is the biggest limiting factor. The cold side must have a GREAT heatsink to keep the cold side as close to ambient temp as possible or the power output goes to hell. Works far better in arctic conditions.
Great practical reference:
https://www.ferrotec.com/usa/thermoelectric/ref/3ref13.htm
A device capable of a few watts of power requires a significant heat source and very large heatsink. Fan-cooled sink would be great, but it's easy to spend the device's entire power output just running the fan.
Our deep space probes, which are too far from the sun to effectively utilize solar cells, are powered by thermoelectric generators. The heat source is plutonium. They don't use the radiation in any special way, it's so radiactive it heats the hot side up. A very elaborate candle.
Russia made a bunch of nuclear cesium isotope thermoelectric generators, but for terrestrial use, generally to power navigational beacons in very remote unmanned locations that could not be powered any other way. Scary truth is many of them were never accounted for, nor is there even an accurate estimate of the number produced. Some have been "stubled" across acually melting the snow with just the heat of the radiation. So don't build one of those!