O2 Concentrator instead of O2 tank

There have been tests of portable units and the major issue with
them going up in altitude is not that they don't work, but they
get a lot because the compressor works harder.

That is really an interesting point. Prior to this thread--I had never
given any thought to the possibility of anyone using a portable concentrator
in the cabin of an aircraft, as my interest had been to eliminate the use of
refillable bottles for normal use. I had simply presumed that the
compressor(s) would be driven directly by the engine(s) and that any
necessary intercooling would be provided prior to the concentrator unit; or
alternatively that a purpose build self contained unit would be installed.
Therefore, this thread has been something of a revelation.

Peter