Cheap Chinese inverters. All I can say about them is don't bother.
We installed ours on saturday and within seconds of turning it on were deafened by the fan noise, scared to use it and quite frankly very unimpressed.
So we swiftly unwired it and filed it under B for bin. Lesson learned. When we get back from our next break I will order a decent one and install that in its place. One that wont set the boat alight!!