The 22 watt rating for the appliance is the main determinate and as it is less than the inverter and the 12V supply there should be no problem.
The only gotcha would be If the leg massage machine has motors. The start current of a motor may exceed the ratings.
Wayne o wrote:On my new motorhome, I have a plug in power outlet rated at 120w (12v).
I also have an inverter (12v to 240v) to plug into this power outlet and this is rated to 150watts.
Wayne, to answer you directly as you requested - the answer is yes.
I suspect you have been thinking that the output capacity of the inverter is larger than the rating of your power outlet so the inverter may overload the outlet? If that is your problem, then cease looking at the maximum capacities of the components. Instead, look at the actual current/power being drawn whilst the system is operating. You indicate that the steady power draw of your machine is 22 W. The 12 V current to drive this via your inverter is 22 divided by 10 (and not 12.) This takes into account the power lost in the inverter to run the inverter. That means that the inverter will draw 2.2 A from your power outlet. This is within the capability of your power outlet as it is capable of delivering 10 A. (However, if the efficiency of your inverter is not particularly good, then allow up to 3 A to drive your inverter.)
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.