12V RV Solar Setup Advice

[distracto]

Hello everyone,

I am new to the forum as well as solar. I did a bit of research on the internet and finally installed solar on the roof of my RV. Some photos here https://photos.app.goo.gl/WFgvzziudcTLUvNGA (if this link doesn't work I will upload them elsewhere). If there is anything that doesn't make sense, please let me know!

I only use the solar to top up my battery bank and I use the inverter to charge my e-bike and laptop. I am not interested in running TVs, microwaves, A/C units or anything large for now.

My RV runs on 12V and I don't have the budget to upgrade the battery bank, nor am I comfortable in converting the whole thing to 24V or 48V even though I understand this is a more efficient method of solar collection.

(Battery bank looks like a mess, I have a shut off switch, quick connect for a NOCO trickle charger as well as the electric jack and house power all connected. I may need to clean this all up...)

System has:
2x 6V Rolls Battery 6 FS GC-HC https://www.rollsbattery.com/battery/6-fs-gc-hc/
2x 100W Renogy panels https://www.renogy.com/100-watt-12-v...gn-back-order/
300 watt inverter (i had this kicking around) with a power bar plugged in to power small 120V items
30A Renogy Wanderer PWM controller https://www.renogy.com/wanderer-li-3...ge-controller/
30A fuse between controller and battery
200A fuse at the battery before the inverter

My plan was to upgrade to a 40A MPPT Rover from Renogy and add two more 100 watt panels in parallel with the first two to have 400 watts of 12V solar.

A few questions.... If I apply the math of total panel wattage divided by battery voltage equals system amps times 1.25, then I am at 41.67A (400/12*1.25=41.67) - is this OK? Or should I go to a 60A controller? Or is this math completely wrong???
If I am only connecting straight to the battery and not connecting to the controller's load outputs, can I use a positive ground controller to save a few bucks or is this foolish?
Would it be smart to add two panels at the back of the roof in series/parallel? It is my understanding that this can maximise solar collection if the back is sunny and the front is shaded - I may be mistaken though.

I hope this is enough information to answer my questions!

Thanks for any input, much appreciated
James

[Mike90250]

If you are using 100w panels, they are likely in the 19V ballpark.

If you expect shade, you should run panels in parallel so if one is shaded, the others in the sun, will still work.

19V panels give very little headroom for charging a 12V battery via MPPT, you are better off sticking with a PWM charger.

Or you could use larger panels, that have higher voltage output ( something more than 25Vmp ) and put a +200w in front and a +200w in back, parallel them, and then a MPPT charger with 25V. would charge a 12v battery.