GoGreenSolar.com Toroid 4kW 120/240V Autotransformer. Dimensions (inches): 10 x 10 x 4 These GoGreenSolar.com AC step-up and step-down toroid transformers are greater than 98% efficient and cause less than 0.2% idle loss at no load. Nearly silent when operating. Use an autotransformer as a step-down to connect the 240V output of a generator to the 120V input on an inverter. This allows full output power of a 240V generator to be used for battery charging. Autotransformers can step-up voltage to operate 240V appliances and motors from the 120V output of an inverter. NEMA 3R enclosure with knockouts for conduit. 2-year warranty.