The MS 15L controller clips the amps to 15 even if it is getting more in. Now the 45 amp controller "limits" (clips) the amps to 45.
I am just still on about how the PWM 12v can get 15.1a Isc on 240w and so to meet the 20% overhead you need a 20a controller.
600w on PWM would do 38 amps at Isc. 20% headroom would mean you need a 45.6a controller
The MS45 says with 600w you max at 45a with no headroom and limits the amps to 45. So it sounds like they are saying the MPPT will do
45-38 = 7/38= 18% better
The thing is if the controller limits/clips the amps then you can max out the controller's amps rating because it won't go over that and overheat the controller or blow the fuse on the pos line to the battery
So you can load the clipping controller right up with panel wattage at 12v, but you have to get a higher amp controller for PWM, non-clipping type
The voltage input max rating is another thing. Not sure how they match up the v max and amps max for various voltages 12/24 etc.
They do warn to make sure you pick your max input voltage ( Voc --not the Vmp) ) at the coldest temp you will have the panels operating in and not at 25C.
