Has anyone done this on s19 models?
No and it won't be for a long while. Unless you want to have a "space heater" that even downclocked using 2000-2500W of 220V power that still requires a deafening fan from both the PSU and miner itself at your feet. This is for old gear that you aren't trying to get massive hashrates.
If we go by factory specs (3300W) a single hashboard would be about 1100W, so its not impossible. With decent firmware you can probably lower it a bit more. Of course those PSUs i don't think work at all with 120V so in American electric type countries you would need to plug to the a/c dryer range whatever circuit that brings 208V~240V (2 hots from 2 phases).
My guess is that two fans in a pusher config (like the S15) should do. How loud? needs to be tested...
The PSU will be underused, so maybe you can remove or disconnect two of the little noisy fans as well. Of course you could still remove all fans and do the larger and slower inline duct fan method.
I agree if you did go down to one single board I'm sure at some point there could be someone that could knock the power usage down. As far as taking the PSU off though I do not think it is possible with the way the S19 is but I could be wrong since it uses a bus bar for all of it's connections.
But his idea is to have a unit on a low power mode while hes at home and then just kick it to mine at it's rated capacity while hes not at home. Which would not be possible with out having to make hardware modifications if he were to setup the fans that way and remove the other two boards.
Now if he had an S19 with a broken hashboard it would make sense, but he wants to do this with buying an S19 new (or atleast in full working order to do so).
