power for the CVR/FDR 1 and 2 comes from the primary busses under normal circimstances, and will run when powered by the APU. the CVR/FDR 1 is also connected to the battery bus. an imersion senson or G sensor will shut it off to prevent data loss in an accident, cant remenber the figures though, something like 18G Horizontal and 20G vertical. dont quote me on the figures though, i dont have my books open at the page right now to confirm that!