JWL - Well, my current build (#3 for me) might be overkill for some, not enough for others. Try it on for size! Considerations:
1) We camp all over the west. Sometimes in big treed areas with lots of shade/rain, sometimes in the desert
2) We tend to drive to trail heads daily, usually about 30 -60 minutes a day. So one hour of charging from the truck
3) When parked at a trail head, we tend to park so the sun hits the solar panel
4) Solar & driving should be able to recharge a 50% battery state in a day in order to keep us going indefinetly
5) Most we stay in one spot with no charging is 2-3 days
6) We need to be able to monitor battery state so we don't get surprised and run out of juice
7) Match battery capacity to daily draw
8) Worst case, match battery draw to water draw. If we run out of water we have to drive to get more
9) Mountains/trees are worst for solar, as water is usually plentiful, sunshine isn't
10) Longest we've boondocked is 10 days in a row. More of that coming
11) We can get away with sponge baths. Typical water usage is a gallon each per day for water, washing, cooking, etc
12) Most battery draw used to be the fridge. Typically 20-40AH a day depending on outside temps
13) We are now adding an induction cooktop. That uses 160A when on high. Yikes. But, we will monitor typical usage this year (?) to see what that's like. We added another 100AH BattleBorn battery to run/cope with the high demand
14) I am limiting battery charging from my alternator using a DC-DC charger. Limit is 40A. This protects my alternator from burning out, since the dual BattleBorn batteries could stomach 200A of charging for far too long.
So with all that background, I can start to figure out what I need.
A) Item #4 tells me I can tolerate using half of my battery capacity in a day. That's 90AH in my case. 200AH of LiFePo4 that I am willing to take to 10% so 200 - (200*10) = 200 -20 = 180AH of capacity. 180* 50% = 90AH. If I go two days without charging, I am at my limit of 10% left.
We still need to monitor that so I can tell if this realistic and matches my projections, so #6 means I need a real battery monitor. Victron BMW 712 comes to mind. Cheap Chinese knockoff may work, as does the Trimetric. Volt/Amp meter is not enough.
C) To recharge 90AH in a day, I need about 2x as many Watts of solar as AH drawn. So, 180AH at least. That's in ideal conditions. Figure 60% of that as more realistic on most days. So, 180AH * 140% = 252AH. If using the 160AH panels that FWC is using these days, I would want two of them. I chose a great household panel (not fond of the flexibile panels designed for sailboat biminis, as these overheat and fail fast when glued down to a solid surface) that is rated at 330W. Literally the biggest I could find at the time that would fit on my roof. A little bit of overkill. Today I could get a 440W panel that would fit, and I would.
D) What if I can only charge by driving, because of shade/rain/snow? I limit my charging to 40A with my Renogy DC-DC charger. If I took that out, I could through 90A (most I have observed on my in-cab Blue Sea Ammeter) for a short while.... dunno how long it would take before smoke started coming out of my alternator. Not something I want to discover while 100 miles from nowhere. 90A/40 = 2 hours and 15 minutes of driving to recharge my 50% batteries. And that's a best case with LiFePo4 batteries. AGM and other lead acid batteries will resist charging as they fill up, so it will take way longer.
Driving while charging also means having big enough wires to carry the current your alternator can push out. Call it 50A. Using this table -
LINK - I would pick 4 AWG which is rated at 60 Amps. That is MUCH bigger than the stock wiring harness that FWC and other RV companies use... 14 AWG worst case for your typical 4 conductor trailer harness, 10AWG if you are lucky. 10 AWG is rated at 15A.
Driving while charging also means a DC-DC charger like the Renogy, RedArc or some other cheap voltage booster (rando linked to a good setup here).
If your alternator isn't "Smart" and your batteries are lead acid AGM or flooded, you can just use fat wires and a good battery separator like the Blue Sea 76xx series.
Situation #9 (and others) above mean I want a good solar controller that can make the best use of my solar panels. I may want to add portable panels to position them in the sun while the camper is in the shade. I like Victron MPPT controllers. I chose a 100/30 model for this setup as it give me some expansion room (up to 440W). The table towards the bottom of
this www page gives you sizing recommendations. With my setup, if I wanted to add portable, I could add about 160W and not typically exceed the limit of the charger... but could. I made the mistake of undersizing my controller on my Hawk build. If adding 100W or more of portable, I would add probably add another Victron controller to the mix.
Summary:
a) You need to monitor your draw = Victron or other BMV
b) You need to know how much you can recharge on a given day - that's solar and alternator capacity
c) You need enough battery to so that they don't get discharged too much between charges. AGM = 50%, LiFePo4 = 5-10% SOC
d) You will need enough solar to recharge with. Figure at least 2x the AH used. 160AH is a good size for the typical 75AH batteries installed in our campers from the factory
e) You will want a good solar controller that has expansion room, or get two
f) You may want a good ACR like the Blue Sea 7622 and/or a DC-DC charger or a combo unit (Victron makes one now)
The latest I hear is about more combo units. They are not the best in all conditions, but are super simple. Stuff like the CTEK, RedArc or Victron that combine several features.
I hope that helps.
