Help with MPPT sizing for RV

[Onixid]

Hi, I will soon get a new RV on which I will need to install solar panels, MPPT charger and 2 x 100Ah Lead Acid batteries (12v).
I have 4 solar panels with the following specs:

Pmax: 100W
Ipmax: 5.6A
Vpmax: 18V
Isc: 6.2A
Voc: 20V

My idea is to create a parallel + series setup (so a parallel between 2 couples of panels in serie).
I've been trying to figure out the math to come up with the proper sizing for the MPPT charger, but I'm not sure it is correct, so any help would be greately appreciated.

If I got it right, the Voltage calculation for the solar panels is based on Voc and the Amps calculation is based on Isc, so:

4 x 100W = 400W
20V x 2 (serie) = 40V
6.2A x 2 (parallel) = 12.4A

12.4A x 1.25 = 15.5A

So I would need a 20A MPPT charger which supports an input of 400W at 40V.
Is that correct?

I tried to run the numbers in the Victron Energy calculator (image attached) but the suggested charger doesn't match at all with my calculations.
Can someone explain why?

 

[DThames]

An MPPT charger amp rating is on the battery side. So 400W/12V would be more like 33A on the charger battery side. So I would think 30A or 40A charger. 30A would be pretty good if you know you will never add more panels. You will only see a full 400W from the panels under perfect conditions which might happen for an hour or two per day, on a clear cool day, with a non tracking mount.

 

[Onixid]

Thank you DThames, I clearly missed such important piece of the puzzle...
So, MPPT excluded, my calculations were actually correct?
Also, when calculating the length/size of the wiring from the solar panels to the charger should I take into account Voc or Vpmax and Isc or Ipmax?

 

[kernel]

Use imp and vmp. On the battery load/charger connections use lowest battery voltage before low voltage disconnect and max power current demanded/ available respectively.