Charge controller and battery bank size recommendations for 860w of PV on Sprinter

[WithAlligators]

Hey folks,
Sprinter build is getting started. I can source some 215w sunpower panels (but I'd totally go for some 345/360/370w if anyone has a source for Sunpower modules). With a custom racking system, I can squeeze 4 of them up there. Panels are a few years old, but specs are:

SPR-215-WHT-U
Peak Power 215W
Voltage 39.8V
5.4A current
Open Circuit Voltage 48.3V
Short Circuit Current 5.8A

My draws are as follows:
An ARB 47q running as a fridge
An Engel 84q running as a freezer as soon as the new models come out
A Maxair fan, and another as-of-yet-undetermined fan for air circulation
Occasional night time use of a 40" TV
Occasional night time use of a kinda thirsty (250-300w or so) gaming laptop
Onboard compressor
Device charging
interior lighting
microwave and possible AC use, but with a generator running.

So, My questions are as follows:

How big of an AGM bank can I get? Lithium still doesn't seem worth it right now. Especially after dropping so much dough on the sprinter.

What controller or controllers should I use? My last rig had a single 310w panel so that was easy. I would like a controller that is good and can do lithium chemistry in the future when I upgrade battery banks. I have a midnite solar classic kid and it's...weird. A controller that allows extra current to go to an accessory would be nice, but not necessary.

What's a good battery monitor? I've heard that Victron monitors are good. I still haven't got the whiz bang jr working for the Midnite Solar, and it's kind of annoying.

I'll probably use a Samlex ACR-160 between the bank and the starter, unless you guys think it's putting too much strain on my stock alternator. What would be a good alternative? A DC-DC charger? Open to any suggestions here.

Do you guys think it's overkill on the modules? I was shooting for a lot of input so I could potentially run AC during the day, but that seems kind of impossible, so minus that, do I need 860, would I be OK with 645? I had 310W on my old rig, and it couldn't keep up with my laptop and freezer running in the summer (though the freezer was a fairly inefficient Whynter 85qt) It also felt like my bank (2x 225AH Crown 6V batteries) dipped in voltage kinda quickly when the sun was down and I was running the laptop.

Cheers,
Alex

 

[Bear in NM]

Alex,

I may not be much help, and maybe this is just an OST for answers. But, I just purchased one (ACR-160), as I have a similar direction I am heading.

I have a new van that I will be mounting some permanent panels. My Van is a diesel with a marginal two battery charging system. I too am researching DC-DC options.

I read the manual on the 160, and for my application it looks like a great partial solution. Per the manual, it wants to be placed in line on the positive lines between the house and start batteries. And most significantly, it will work with alternator side of charging the start bat then flow to the house. But it will also work from the house side with the house side charging, then allowing the start to charge (per the manual). A two way switch. I am thinking of installing with a switch on the start side, so I can manually turn of the workings. I might want this if I find my alternator working too hard. With the panels permanently mounted (I also have a portable panel), I should be able to solar charge at camp, and and at home while parked with solar or a proper bat charger. This might solve my winter time process of keeping everything topped off.

Hoping you get some good suggestions from those who have done this. I have been looking at the Ctek and Redarc DC-DC offerings, and I keep defaulting to my fear of one device to do everything. I have built my trailer and portable system with components, so if bouncing around off-road breaks something, I am not dead in the water. But I do think that I too need a DC-DC solution.

Thanks for costing me 130 bucks....;^)

Craig

Edit; In my case, I am seeing my alternator only doing 13.5 to 14.1 which is too low for serious charging. I am running a Scangauge II on my van to accurately track charging voltage. If you have any way to minitor your stock charging system, and report this, it migt help with solutions.

 

[WithAlligators]

I have a Samlex in my current machine. It works well.

 

[Bear in NM]

Alex,

I hope the 160 works for me, thanks for the tip, and confirmation.

I was just pricing panels and goodies at my local solar shop. No way I can do the amount you are planning, but I should be able to double or triple what I have already proven to be able to live with.

Craig

 

[jeffjeeptj]

Look for handy bob solar. Strongly opinionated, but, seems to have background/experience to support his statements.
I have a Bogart battery monitor and love it. Have not tried other brands. Sure is nice to see percent charged and in/out flow info based on user input battery information.
My limited experience thinks if your panels are 39.8 volts open circuit and you want a 12 volt battery bank, then your controller choices will be focused on MPPT and may be somewhat limited. Use sufficiently large wires/cables and keep them short. 860 watts seems like enoigh for your stated loads.
Assure you have some type of on board charger. Remember, lead acid require a long duration charge to completely “fill up”. I have an Odyssey pc-2250 and use an Iota 55 amp charger when connected to 110 volt (shore power or generator).
I will likely get some flak for this, but, if you wire the batteries in series to get 24 volts (to widen the solar charge controller selection), you could tap 12 volts off one battery for the fridge, and 12 volts for the freezer. This does risk some unbalanced loads on the batts, somewhat mitigated by a longer charge cycle.

 

[WithAlligators]

I just saw this and was going to jump in to say: most fridges/freezers, the air compressor, and inverters (Though not my 400W Pure Sine, apparently) run off 24V. I don't believe the rest of my accessories would, though. Would it be wiser to run in 24V with a step down converter for fans/lights/USB charging ports/my 400W inverter?

 

[WithAlligators]

I already have a maxxair exhaust fan and a some 12V stuff I'd like to keep. How inefficient are converters?

Also, with 24V, how do I charge off the alternator and top off the starter with solar?

EDIT- research tells me they are really inefficient and mostly step down by dissipating V as heat. Sheesh.

EDIT again- I've found everything in 24V really, except an RV exhaust fan and decent interior lights, and smaller inverters. My little 400W PS Wagan is perfect for my laptop which pulls up to 330W. Are 24V inverters half as inefficient? So I could run an 800w inverter at 24V with the same ~40W loss as a 12V 400W inverter?

And some of these step down converters are in the neighborhood of 93% efficient. That's not too bad.

 

[Rando]

Look for handy bob solar. Strongly opinionated, but, seems to have background/experience to support his statements.
I have a Bogart battery monitor and love it. Have not tried other brands. Sure is nice to see percent charged and in/out flow info based on user input battery information.
My limited experience thinks if your panels are 39.8 volts open circuit and you want a 12 volt battery bank, then your controller choices will be focused on MPPT and may be somewhat limited. Use sufficiently large wires/cables and keep them short. 860 watts seems like enoigh for your stated loads.
Assure you have some type of on board charger. Remember, lead acid require a long duration charge to completely “fill up”. I have an Odyssey pc-2250 and use an Iota 55 amp charger when connected to 110 volt (shore power or generator).
I will likely get some flak for this, but, if you wire the batteries in series to get 24 volts (to widen the solar charge controller selection), you could tap 12 volts off one battery for the fridge, and 12 volts for the freezer. This does risk some unbalanced loads on the batts, somewhat mitigated by a longer charge cycle.

Besides being bloviated, 'Handy Bob' is also way out of date and just plain wrong on several counts. The Bogart stuff he recommends is circa 2003, and had been far surpassed by more modern equipment (Victron in particular). In this day and age there is absolutely no reason not to use MPPT, and in the case you would have to run MPPT to step the panel voltage down. There are several fine options for this, including Victron and Midnite, that would allow you to run a 12V battery bank, simplifying your life. The idea of splitting a 24V battery bank if also a terrible one - you would almost immediately unbalance the batteries, leading to overcharging of one, undercharging of the other and premature failure of both.