That 75 amper is the "LK" model, which is both a fixed voltage 4-stager and an adjustable voltage. The two holes in the side are for operating that choice. A small screwdriver is required.
The left hole has a switch behind it that snaps back and forth sideways. To the left, you get a normal four stage operation, that is automatic so you don't have to do anything, same as any converter. To the right it becomes an adjustable voltage single stage, which you then turn the pot behind the right hand hole.
If you want 14.8 for your Trojans or whatever, just set that and do the recharge, and when they are full, dial it back to 13.6 and leave it there. If it is 35F out, 14.8 is now 15.2 so set that. (the 14.8 is for 77F)
You should not twiddle the pot on the right when you have chosen normal four stage operation or it will skew all the set stage voltages. But you can put it back where it belongs if you mess up.
You have to set the pot to 13.6 before you switch back to normal four stage.
You need a voltmeter where you can see it when adjusting the voltage, and the converter should be disconnected from the battery bank when you do that. Once the battery is connected, the voltage you see will be somewhere between what the battery was and what the converter is set at. As the battery recharges the voltage you see comes up to eventually be what you set the charger at.
The PowerMax ads say that their 75 ampers are power factor corrected, but they are not, so ignore that. Their 100 ampers are PF corrected.
Your PD 9280 is not PF corrected (PF is 0.7) so expect that 75 to draw almost as much VA from a generator --but the 75 does not require a 20 amp (120v)circuit-- it runs on 15a ok.
The LK has an internal fan so it doesn't have the usual fan sticking out, but you need to mount it where you can get at those two holes in the side.
