I am kind of surprised it is this different. Did I miss something?
Only my actual objection, which was based on what you said you 'usually' use, 12v, not 24vac, as I stated:
As for efficiency, 48v-55v transmitted with less power loss than 12v...
(DC I assumed, since you specify 24vac later).
Anyway I'll admit that my comment was shortsighted and that you are correct that the DC stepdown must be accounted for in any real model. Even I know the awesome effeciency of the simple transformer at stepping up/down voltages AC voltages, one the holds no worthy counterpart in the DC world.
But I'm up for learning something regardless and I would like to understand your equations fully and see if I can witness that dramatic inefficiency 89% vs 22% that you are predicting, for 24vac.
I would like to ask you if you think that this simple test will be of any value:
i have a 5mp stardot camera which has poe, 24vac and 12vdc on the back. I don't have 100 M of zip handy, but I might have 20 for a first test.
I would just plugin either the 48, 24, or 12v adapters into a watt meter, power up the camera using a 48v passive adapter that will put the power on cat 5, verify that its working and record the kw/h usage of the whole system over 1 hr. Then do the same with 24ac and 12dc with zip cord... i will get you the exact specs of everything if you think its worth doing.
Will it show the difference?