To determine the size of the inverter required to run an air conditioner rated at 18000 BTU with a rated input of 2700W, you need to consider the starting (surge) power and the continuous (running) power of the air conditioner. The inverter's capacity should be able to handle both the starting power and the continuous power without any issues.
Starting Power (Surge Power): Air conditioners often require a higher initial power surge to start the compressor and other components. This surge power can be significantly higher than the continuous power rating. As a general rule of thumb, the starting power can be around 2 to 3 times the continuous power.
Continuous Power (Running Power): The continuous power is the power consumption of the air conditioner during its normal operation once it has started and stabilized.
Given that the air conditioner has a rated input of 2700W (continuous power), the estimated starting power could be around 2 to 3 times that value, which is 5400W to 8100W.
Therefore, you would need an inverter with a capacity of at least 8100W (or higher) to handle the starting power of the 18000 BTU air conditioner. Make sure to choose an inverter that is rated for both the starting power and the continuous power to ensure smooth and efficient operation of your air conditioner.
Keep in mind that it's always a good idea to provide some extra headroom when selecting an inverter. Inverters are typically available in various sizes, so you may consider choosing one with a slightly higher capacity to accommodate any other electrical devices you might want to power simultaneously or to ensure better performance and efficiency of the air conditioning system.