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What kind of short circuit problem do you mean? If the insulation of the wire failed while having contact to the aluminum at the same time, something really went wrong, because the wire should never get so hot that the insulation fails at all.Maybe try a different wire type.
It may scale up. You should use several heating fields under the platform and supply them in parallel (the aluminum spreads the heat very evenly). Of course you need a sufficient power supply for that, or several supplies in parallel and, more important, you should use several switches (e.g. SevenSwitch) in parallel, because their abilities are limited too. But if you scale up everything in parallel it should work like charme.
Off-the-Grid Lighting Solution (LED Moser Light Evolution)
Stop using Ferric Chloride etchant! (A better etching solution.)