Designing a new 48v system - few questions

[Montana Minimalist]

First time post!
I'm building a 48v system for my off-grid house. I live there full time and currently have a very small 12v system running my lights, water pump and small refrigerator. I'm not using a inverter with this setup. I use a Honda 2000i for my larger loads like my PC, fan, microwave and guitar amp! I want to get a few more things like a freezer and maybe an AC. My goal is to only use the Honda for back up and charge the batteries when needed. 
I just picked up 12 - 245 watt panels (VOC 37.5)  and I'm not sure what Classic CC will be best for my system. I used the Classic sizing tool with a 3S 4P  PV array and then a 4S 3P array, the results were obviously different.
My first question is what Classic (150, 200 or 250) would get me the most out of my system?
My second question would be what would be the best way to wire the PV array 3S 4P or 4S 3P ?

Also, I'm looking at inverters and upgrading my 12v 800ah GEL battery bank to lifePO4.
Any help would be great!

[mike90045]

What is your record cold temperature in the area ?  That's going to be important to find the limit of panels in series.

How far will the array be from the CC ?  20'  80' ?  That distance figures into the losses and expense of the cable. 
Also, the higher the array voltage, the hotter the CC runs down-converting it to battery voltage.  Too high and you waste power as heat.

[Montana Minimalist]

Thanks for your reply mike900045
The coldest record is -40 and the normal lowest is 15 degrees. It gets below 0 here every winter.  My panels will be no more than 20 feet from CC.

[ClassicCrazy]

You will get more capacity from a Classic 150 compared to the others . As Mike said keeping the PV voltage closer to the battery voltage is best so the Classic runs cooler and more efficient.

Larry

[Montana Minimalist]

Thanks Larry, the Classic 150 may be the way to go.

[Vic]

Yep,   Classic 150 and strings of three PVs  would be the most efficient,   practical for input voltage to the Classic.

IMO,   Vic

[mike90045]

You don't have really long cable runs from PV to controller - line losses will be low, so if after running the Midnight String Check Tool
http://www.midnitesolar.com/sizingTool/index.php
enter your module info, and your local cold temps, and make sure the VOC stays below 150V when cold.
  When the controller sees more than 150V , it goes to idle mode, until the panels warm and get below 150V, then it starts charging the batteries. 
(I'm pretty sure, when in hyperVOC mode, it's not able to charge batteries, but if it can please correct me)

[Montana Minimalist]

You don't have really long cable runs from PV to controller - line losses will be low, so if after running the Midnight String Check Tool
http://www.midnitesolar.com/sizingTool/index.php
enter your module info, and your local cold temps, and make sure the VOC stays below 150V when cold.
  When the controller sees more than 150V , it goes to idle mode, until the panels warm and get below 150V, then it starts charging the batteries. 
(I'm pretty sure, when in hyperVOC mode, it's not able to charge batteries, but if it can please correct me)
Excellent info thank you so much I really appreciate it!

Yep,   Classic 150 and strings of three PVs  would be the most efficient,   practical for input voltage to the Classic.

IMO,   Vic

Cool thanks Vic!

Do you guys have any  recommendations for wire sizing from the PV to the Classic and from the Classic to the 48v battery bank?

[Vic]

You don't have really long cable runs from PV to controller - line losses will be low, so if after running the Midnight String Check Tool
http://www.midnitesolar.com/sizingTool/index.php
enter your module info, and your local cold temps, and make sure the VOC stays below 150V when cold.
  When the controller sees more than 150V , it goes to idle mode, until the panels warm and get below 150V, then it starts charging the batteries. 
(I'm pretty sure, when in hyperVOC mode, it's not able to charge batteries, but if it can please correct me)

Yes,   with strings of three 60-cell PVs,   it is essentially impossible,   on this planet for a Classic 150,   to enter Hyper Voc  --  should not need to worry about that.

MidNite Classics,   and the KID,   will suspend operation while the Vin is above the max operational input voltage  --  150 VDC,   in the case of the Classic 150 (etc).

The cable sizing for the Classic 150 in this system would primarily depend on the Imp,   and actual distance between the Combiner box and the Classic.  With strings of three PVs there is a reasonable margin in voltage drop from the Combiner and the Classic.   Would guess that number 10AWG  would be fine for the cable run from the Combiner and the input to the Classic,   given the short distance twix the Combiner and the CC.

IMO,   Vic

[mike90045]

Thanks Larry, the Classic 150 may be the way to go.

What's the Vmp & the Imp for your panels.
I'm running a "seat of the pants"guess on the Vmp is 30.5V, which makes the amps about 8.
The issue I see, is 10ga is rated for 30A, and with the numbers I invented for your PV , 32A is running thru the wires
Same with controller output, likely should be #6, to carry the amps without heating up.  Runs are short enough, resistance is not causing much voltage drop.

[Montana Minimalist]

Here’s the specs on the panels. I couldn’t find the IMP.

Rated Power: 245W
Open circuit voltage (VOC): 37.5 V
Max power voltage (VMP): 30.2 V
Short circuit current (ISC): 8.68 A
Max power current:  8.13 A
Power Tolerance 0/+3%
Maximum system voltage: 600V (UL)
Fuse Rating: 15 A
IP65 Junction Box w/MC4 Compatible Connectors

[ClassicCrazy]

The IMP ( current maximum power )  is the Max Power Current

Larry

[Montana Minimalist]

Thanks Larry, the Classic 150 may be the way to go.

What's the Vmp & the Imp for your panels.
I'm running a "seat of the pants"guess on the Vmp is 30.5V, which makes the amps about 8.
The issue I see, is 10ga is rated for 30A, and with the numbers I invented for your PV , 32A is running thru the wires
Same with controller output, likely should be #6, to carry the amps without heating up.  Runs are short enough, resistance is not causing much voltage drop.

It looks like my VMP is 30.2v and the IMP is 8.13a

The IMP ( current maximum power )  is the Max Power Current

Larry

Thanks Larry

[harryn]

AFAIK, MC-4 connectors are rated for 20 amps, so that factors in as well.

Depending on where you live, the actual panel current might not ever reach more than 75% of the Imp, so assuming 8 amp rated panels, 3 parallel is the max in one PV wire.

4 S for those panels when it is cold and clear will push very close to the limit.

Perhaps consider to run 2 PV wire pairs, each supporting 3S 2P?