In other words, does a 1000-watt inverter, draw the same as a 500-watt inverter if they are charging only a laptop? The laptop will draw the same amount and the inverter capacity is really just that, capacity?
i.e. 1000-watt inverter CAN draw UP TO 1000-watts, and the same for 500-watt inverter.
My issue is that I plug in a 1000-watt inverter to a battery, and voltage is dropping to 12.2v. I was informed that I should keep my battery voltage, above 12.4v to keep it healthy and I worry that 12.2v constant (during full solar input) and 11.8v (at night when there is no sun) is killing my battery.
I am currently using a 1000-watt inverter, and now I'm wondering if it is overkill and need to downgrade to a 500-watt inverter to charge a laptop/run cable modem/router (~100-watts/per hour).
Best Answer
If two 100% efficient inverters, one 500W max throughput, one 1000W, are used to drive the same load, they will pull the same power from the battery.
Of course neither will have 100% efficiency. Even at no output load, they will draw some power. The chances are high that the 1000W inverter would draw more idle power than the 500W, but it's not a foregone conclusion. A well designed 1000W inverter could be more frugal at no and low loads than a badly designed 500W.
For your application, rather than suffer the inefficiencies of two stages of conversion, it will be more efficient overall to use a single 12v input DC to DC laptop SMPS, and one to your router/modem, unless they are 12v input (mine are) in which case run them straight form the battery.