OK so my plan is to install two 320w panels, feeding a 4s LFP bank.
Crude maths (640/12=53) leads me to spec a 60A MPPT.
Real life numbers are different, though. I've never seen more than about 80% of rated output from a panel (admittedly, this is in not-so-sunny Scotland); further, my bank will not be charging as low as 12v (I hope).
Using say 85% output from the panels, and a charge voltage in excess of 13v, drops my current to 42A. So I would spec a 40A MPPT instead, and just accept the lost 2A. It's a pretty big cost saving, depending on what brand you're looking at.
But am I being penny wise and pound foolish. Will the bigger MPPT run cooler and have a longer, happier life?
Crude maths (640/12=53) leads me to spec a 60A MPPT.
Real life numbers are different, though. I've never seen more than about 80% of rated output from a panel (admittedly, this is in not-so-sunny Scotland); further, my bank will not be charging as low as 12v (I hope).
Using say 85% output from the panels, and a charge voltage in excess of 13v, drops my current to 42A. So I would spec a 40A MPPT instead, and just accept the lost 2A. It's a pretty big cost saving, depending on what brand you're looking at.
But am I being penny wise and pound foolish. Will the bigger MPPT run cooler and have a longer, happier life?