Give us the model number of your CONVERTER/CHARGER unit. Then we can look it up on the internet and see what the specs say... Also would like to get the model number of the Generator as well... when you say 900WATTS you don't get to use all that much... It probably tells on the front panel how many watts are usuable- I'm guessing around 800Watts is all that is usuable...
I Have a PD9260C 60AMP converter/charger and it takes a good 1000WATTs on the 120AC side to run it at full power...
Hopefully your converter/charger is much less then a 60AMP Converter/charger...
When you are doing this you will need to have everything else turned off when just using the generator to feed your converter/charger. My PD9260C unit uses a standard 120VAc Wall receptacle plug so it is easy for me to plug it into the generator 120VAc receptacle... My generator is 2KW model and has around 1850 Watts of usually wattage output...
Roy Ken