12 volt electric blanket

I bought a 110 volt AC double bed heat pad that uses a converter to produce 18 Volt DC. The pad uses very small wires, you do not feel it, and using DC current is supposed to be less danger than a 110 AC. I tought it would work directly plugged in 12 volt, while producing less heat, but it did not. The controler just tip off.

So I bought a converter to up the power from 12 volt DC to 18 Volt DC. It works, I think it uses less power to go from 12 DC to 18 DC. Otherwise, I have to use an inverter to produce 110, then plug in the converter provided that convert 110 to 18 volt DC.