Question 1 - Two 12V 11Ah batteries in series = 24V @ 11Ah or 24V @ 22Ah?
In series it would be 24V @ 11Ah, and in parallel it would be 12V @ 22Ah, either way you can only get out 264W for one hour.
Question 2 - I would like to establish the efficiency of the inverter. I am not looking for an nth degree calculation here but ± 5%. I was thinking of connecting a load, measuring the voltage and current on the LV and HV sides then calculating the power. The difference between the power in and power out I was thinking would be what is being consumed internally and therefore the inefficiency?
most inverters your lucky to see 75% efficiency from what i hear, but i dont get what your saying about using an old PSU as an inverter.
Question 3 - I do not think that I will connect 220V to the PSU input when power is available. The batteries I plan using are going to be of sufficiently larger capacity and therefore may not charge correctly. Will need to measure the charge current before a final decision is made. If I do not connect the 220V supply this should not cause any damage?
huh?
Question 4 - When 220V power is not available at the input to the PSU, the PSU has a standard feature which is a buzzer that sounds at a too regular frequency. I have not located this yet but would think that it could be desoldered from the board without any negative effects?
Should be easy enough to desolder it, and there wouldnt be any negative effects unless the buzzer is hooked up in series with some other safety sensor built into the PSU, but probably not.