Be careful about "getting on a role". One of the great things about a public discussion is that each of us brings our own knowledge and points of view....

I can be talking about 1/2 of the problem, and another person will talk about something equally important that I (or somebody else) skipped over.

In fact, I try to avoid any "one on one" off forum discussions for this reason. I am not perfect and really appreciate the other view points and when they catch me with typos and other errors.

We are using the forum for communications, and it is easy miss/mix up information between multiple posters/questions. I have made those mistakes more than once and why I use the equations and other sources for Q&A. And ask the reader/poster to validate everything I say (check my math, sources, and other posters' comments).

Take care,
-Bill "i really need new glasses" B.

Either 4s x 1p, or 2s x 2p is fine. 4s x 1p is higher voltage (Vmp-array) and less voltage drop/can uses smaller AWG cable. 2s x 2p is lower voltage, needs larger AWG cables to keep voltage drop "reasonable", and the lower voltage allows the MPPT controller to operate very slightly more efficiently. Other than cable sizing vs length (voltage drop calculator), there is no big reason to choose one or the other configuration. Having a relatively short 20 foot length and "free" 1/0 (or 1) AWG copper cable--Voltage drop should not be an issue.

As always, figure out your preferred solution (X/X copper cable on hand, or using smaller AWG like 8 or 10 AWG cable) and confirm the running calculator. You can run 4s x 1p on X/X cable too, even less voltage drop, but nothing that you would notice. More or less, just cost of cable vs using what is on hand.

Regarding the 20" between two battery banks on the bus... Just to confirm, is this 20 inches or 20 feet? 20" (inches) is not a big issue. 20' (feet) is probably a pain (want voltage drop between the two separate banks to be 0.05 or 0.10 (fix typo, not 0.01) volt maximum drop during charging (40 to 60 amps) from charge controller to "last battery in the string". Long distances, relatively high current, and 12 VDC requires heavy AWG cable(s) to keep voltage drop low (for faster/accurate battery bank charging).

Similar issue with discharging. Here we want a maximum of 0.5 volt drop from last battery in bank string to DC input of AC inverter (and other heavy loads). 

And what is the maximum wattage you plan to pull from the battery bank? 300 Watts, 1,500 Watts, 3,000 Watts or what?

-Bill

PS: If you ever try to add a panel and make a 5s * 1p array (slightly over panel), adding the extra panel to a 4s * 1p array is just unplugging, adding panel in series for 5s * 1p array. A bit more fiddling on converting a 2s * 2p array to a 5s * 1p array--But not a big issue.

Also need to know the cable lengths from Charger to Battery bank, and Battery bank to AC Inverter (and/or any other "heavy current" DC loads) to calculate voltage drop (voltage, current, allowed drop of 0.1 or 0.5, and cable run length).

-BB

You still have not given me a DC Discharge current...But to start with charging setup to show how it is done.

20' between batteries and (for sake of discussion) 5' between charge controller and "first battery bank". Total is 25 feet one way run (assumption of this calculator), 60 Amps max rate of charge, and 0.1 volt maximum drop (for accurate/fast charging--I.e., 14.75 - 0.1 volt drop = 14.65 at battery bank). Using 1/0 copper, 0.99 PF, plastic conduit (does not matter with DC). (be careful, the drop calculator now defaults to meters, NOT feet):
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=9&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=14.75&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=60&x=53&y=21&ctype=nec

Result

Voltage drop: 0.36
Voltage drop percentage: 2.42%
Voltage at the end: 14.39

Assume that you parallel the 1/0 cables--3 sets of 1/0:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=9&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=14.75&phase=dc&noofconductor=3&distance=25&distanceunit=feet&amperes=60&x=68&y=26&ctype=nec

Result

Voltage drop: 0.12
Voltage drop percentage: 0.81%n
Voltage at the end: 14.63

Even 3x parallel cables per + and - run (6 cables total)--Still not idea 0.05 to 0.10 volt drop.

Just for discussion, say you build that battery/solar power shed now. And you have 5 feet from charge controller to battery bank. Using 1/0 cables, 1 per "phase", 60 amps, 5 feet:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=9&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=14.75&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=60&x=38&y=24&ctype=nec

Result

Voltage drop: 0.071
Voltage drop percentage: 0.48%
Voltage at the end: 14.679

10 feet total 1/0 and you are in the zone. First configuration, 20'*6 cables=120 feet of 1/0 copper, and you are still not really ideal configuration for voltage drop, charging, at 14.75 volts (typical for FLA batteries).

Will the system still work/charge with 0.36 volt drop (1x cable set)--Yes, but it is a significant drop in charging voltage at the battery bank and will reduce current flow. You can jack up the charging voltage to 14.75+0.36 volts, then you run the issue of over charging the battery bank near the end of the charging cycle and the default float charge voltage is too high (gassing/over charging FLA batteries is hard on them, errodes plates, corrodes positive plate grid, and can overheat the batteries). You can monitor and play with the numbers (i.e., set near standard charging voltages when not using system, jack up charging voltage when using system heavily.

We aim for "low maintenance" and "goof proof" systems (or at least as close as we can). The more interactions required on your part creates more chances for errors. Running system too low or too high of charging voltage can shorten battery bank life.

If you have 120 Feet or 140 Feet (4 pairs per phase)--It will work well. One of those design trade-offs. $$ for cables or $$ for a solar shed.

Three major locations/groups for circuit breakers.

First is the solar array. If you have 3 or more solar panels in parallel, then you need fuse/breaker per solar panel string (max series protection fuse/current rating from panel spec sheet).

An optional breaker at from Solar wiring to charge controller panel input--Handy to turn off solar array current if you need to service the solar charge controller--Purely your choice (breaker, heavy DC switch, etc.--Your choice).

The next to the battery bus.

Every + 12 VDC cable that leaves the battery bus needs a fuse/breaker per cable (branch circuit) that is rated for the max current of the cable (or less--Since many times with use much more copper for lower voltage drop). I.e., 14 AWG cable to LED lighting, 15 Amp fuse (using NEC tables wire ampacity tables).

Another question is the battery bank--A large battery bank can surge a lot of current (hundreds of amps or more) into a dead short. If you ave a short run from battery bank to battery bus (no chance of short circuit from failed insulation/tools dropped on batteries), most people don't worry about a breaker for Batt Bus to Batteries. If you have a lot of batteries in parallel--It is good to use a fuse per string so that one short in a battery/battery cross connect, does not feed current from the rest of the bank into the short. Again, not many people do this extra fusing, but for you, with a 20 foot run between two 1/2 battery banks--It is "asking" for a fuse/breaker near each battery bank to protect against a short/cut insulation/cable between the two banks.

Breakers/fuses are put near the source of high current (typically battery bank, battery bus). To protect down stream wiring.

Fuses can be cheaper (not always for high current fuses and fuse holders). Circuit breakers are nice. Protection+Handy on/off switch.

Fuses and breakers have "rated current" or trip point. And a working voltage (i.e., 48 VDC or 120/240 VAC, etc.--Note that DC fuses/breakers/switches are larger/heavier duty than AC versions--Check AC vs DC ratings). And there is the AIR (Amps interrupted rating). This is the the maximum short circuit interrupt rating. For example a 120/240 VAC home breaker is rated for 10,000 AIR (the max from a pole mounted transformer short).

https://www.solar-electric.com/residential/circuit-protection.html (wiring protection products from our Host NAWS).

There are details here (if you are interested--Or TMI--To much information):

http://forum.solar-electric.com/discussion/353232/oversized-wire-and-breaker

The minimum breakers... For each + cable that leaves the + Battery Bus. (for charge controller, for AC inverter, for any DC circuits such as LED lighting, Fans, 12 volt USB sockets, etc.).

None (at this point) need for solar array side (1 or 2 parallel connections). Battery to Battery Bus--If you are "sure" that no shorts can occur with wiring (no sharp sheet metal, no tools dropped on batteries, etc.), then no fuses/breakers.

There are lots of DC rated breakers. And some very nice high current/ignition protected fuses and holders. For battery fuse(s), Blue Sea makes some very nice compact fuse holders and fuses--Might be nice for present "distributed" bus battery bank:

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A (fuses sold separately)

Avoid "automotive" fuses... These are known for melting and melting holders running at even less than rated current:


-Bill

The "zone"--I was trying to say that, for example, if we use 0.05 to 0.10 max suggested wiring voltage drop from controller to 12 volt battery bank... If you have 0.12 volt drop--The system will still work OK. In solar (and many engineering problems) being close to the "correct/exact solution is not going to cause any surprises). That was what I was trying to say that this solution was "in the zone" we are aiming for and I would run it if I had no other reasonable options.

If you follow the Smartgauge battery wiring guide, it makes "all batteries" effectively 20' away from the battery bus (such as Method-2--That is the way it has to work so each battery "sees the resistance" from itself to the load (or charging source).

http://www.smartgauge.co.uk/batt_con.html

That is "worst case" voltage drop. If you don't have "enough copper" to keep the overall resistance low or make other changes (move the bus battery bank to a battery shed with charge controller+inverter+etc. or "buy more copper", effectively you are left with "laddering" Method-1 (batteries closest to the battery bus get cycled more. Or Method-2 where you have more resistance to each battery. Neither is an ideal solution.

The less than optimum solutions means the battery bank will supply much less current to the loads (with 0.5 volt max drop, less efficient charging with >0.1 volt drop). Or the batteries supply lots of current, and the batteries at the end of the ladder supply much less.

Sending 12 volt energy at "high current" over "long distances"--The only solution is either lots of copper, moving batteries to central location, or going to a higher battery bus voltage.

You have not told me how much current or Wattage (AC inverter output loading you plan to use). If you use 12 volt bus and 300 Watt load (~25 amps), that is much different vs 3,000 Watt load (~250 Amps) (even sending 25 amps 20 feet is not "cheap or easy" with low voltage drop.

Long distance power transmission, use as high of voltage as you can. If you are using 4 panels @ Vmp=18 volts per panel or 4x in series = 72 Vmp-array, and Imp=9.73 amps.@ 80 feet on 1/0 copper cable:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=9&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=72&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=9.73&x=82&y=22&ctype=nec

Result 1/0 AWG

Voltage drop: 0.19
Voltage drop percentage: 0.26%
Voltage at the end: 71.81

Well under 1% drop ;(0.26 volt drop). Example of sending 10 amps 80 feet at 72 VDC. Very little power loss.

Regarding Voltage Drop Calculator--The Links to the VDC have all of the data field filled out. You should be able to press calculate and have it work.

You could use smaller AWG cable (instead of the 1/0) and aim for 1-3% voltage drop... For example use 10 AWG (and save the 1/0 for 12 VDC bus):
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=72&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=9.73&x=48&y=25&ctype=nec

Result 10 AWG

Voltage drop: 1.85
Voltage drop percentage: 2.57%
Voltage at the end: 70.15

You are losing 3% at full solar current--But that is still not too bad. Going below 1% drop is usually "overkill" -- I.e., spending lots of money on copper wire (perfectly OK to have lower than 1% voltage drop--System will work fine).

Have I taught classes--Nope. College and worked as a Systems Engineer/Designer (some electrical, mechanical, electronics). I really enjoy working integrating all this things together into a product. The teams I worked on--We shared experience and trained support staff to help us and to give them more skills and better wages/job opportunities. Also gave a few seminars on document services to engineers and support staff.

What do you think of me using the present #1 AWG cable that presently connects the two positive posts of the battery banks to become an additional - negative link between the negative battery posts, the motor home frame and the - negative bus posts strip, for the controller and inverter to connect to? 

I am not sure what you are asking... Is it to take the copper cables in the negative wiring and move it to parallel the existing positive cabling (lower resistance) and use the bus chassis as the ground/return?

If using chassis as return cable. Highly suggest you do not do this. Vehicle chassis and sheet metal do not make good heavy current conductors. Steel (and aluminum) have much higher resistance than copper, and more drop. Also each "transistion" (sheet metal to frame, frame to frame to negative bus, etc.) is another point of possible resistance/poor electrical contact (or fail over time water/weather/road salt/etc.).

Also you generally have rubber isolators between frame and body--Need copper straps to connect around isolators. Also if there is any moving parts (traditionally doors, and mechanical rods/cables for brakes, gas peddle, and even door hinges, etc... Any stray current through moving parts (bearings, bushings) can erode the bearings or even "spot weld" the bearings--Not good. For high power systems, stick with actual cables for +/- and Hot/Return electrical connections.
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=9&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=12&phase=dc&noofconductor=1&distance=21&distanceunit=feet&amperes=100&x=62&y=14&ctype=nec

Result = 21 feet to send 100a @ 12 volts @ 1/0 cable @ 0.5 volt max drop

Voltage drop: 0.50
Voltage drop percentage: 4.16%
Voltage at the end: 11.5

It is just the physics of the system. Want longer distance: More copper, or change specs (higher voltage/lower current).

Now do the same thing with 120 VAC, 10 amps (1,200 Watts), 12 AWG (heavy duty extension cord) with 3% max (NEC?) drop:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=1&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=120&phase=ac&noofconductor=1&distance=90&distanceunit=feet&amperes=10&x=56&y=15&ctype=nec

Result = 90 feet to send 10a # 120 volts @ 12 AWG cable @ 3% drop

Voltage drop: 3.60
Voltage drop percentage: 3.00%
Voltage at the end: 116.4

Send 1,200 Watts 4.3x farther on 1/16th the amount of copper (roughly 1/16 the price per ft) vs 1/0 copper cable @ 12 volts and 100 amps

Just the nature of the beast.

-Bill

You are very welcome Bill... Personally, I find that explaining/teaching reinforces my knowledge too (although age and such are taking some of that away too... Getting old is not for the young).


I guess that is from the home (on site) to the bus. Estimated available power @ 450 feet, 120 VAC, 10 AWG cable and 3% max drop. For discussion, lets go ahead and say 10 amps or (10a*120v= ) 1,200 Watts (Kill-a-Watt meter time)... Everything is trade-offs. In this case, we will see that the 3% drop requirement is ignored to get more power to the bus:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=pvc&necpf=0.85&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=120&phase=ac&noofconductor=1&distance=450&distanceunit=feet&amperes=5&x=0&y=0&ctype=nec

Result 450 feet, 120 VAC, 10 AWG cable and 10 Amps / 1,200 Watts

Voltage drop: 9.33
Voltage drop percentage: 7.78%
Voltage at the end: 110.67

Basically your 120 VAC loads are running at 110 VAC at 1,200 Watt loading. Your AC loads should be "happy" and not really have any issues at 110 VAC.

HOWEVER, you may notice some 120 VAC lighting (if you have any in the bus) dims/blinks as heavy loads cycle (such as the refrigerator--In my cases, it was because decades of a few drops of rain water got into the connections in my main home breaker panel and made for poor electrical connects over time). Some Lights are very "blinky" (I had twisty fluorescent bulbs that like to blink with voltage surges) and others may not. Changing brands of lights can help you find "better bulbs" for unstable 120 VAC voltage (buy one bulb and see if better than what you have, etc.).

And, details matter. You have not said what the total loads you want to use are (peak continuous Watts). And I do not know what refrigertor type that you are/want to run (is it a 120 VAC home/apparent fridge, a 2 or 3 way RV fridge that you run from propane or 120 VAC. Is it a 12/24 volt compressor based RV fridge, or what)..

Adding a refrigerator to a solar power system makes for much larger off grid power system (i.e., 500-1,000 WH per day vs 3,300+ WH per day as an example). The electric water heater (a couple gallons of water at 600 Watts for 20 minutes per day?). Details.

At this point, I would be suggesting a 1,500 Watt max 120 VAC load (1.5 kWatt AC inverter) would meet your present power usage. Refrigerator type/brand/model/Kill-a-Watt meter 24 hour per day measurement and Electric Water heater expectations (or convert to LP gas RV water heater--Find a used one from an RV wrecker?).

If you think that I can run our solar array with 10AWG copper electrical wire 80+ feet,  I will have enough 1/0 wire to temporarily double or triple the run between battery banks.and make the solar wiring from controller to solar array run much simpler.

Yes--I double checked my previous post and you would have 2.57% voltage drop (and harvest loss)... Still works, and you would not really notice the loss in "real life". You could even add a 5th series panel (175 Watts, same specs) if you feel "adventurous" and want to over panel the MPPT controller a little bit (I believe it would be fine, but it is your system, your choice, your money). As always, make sure good ventilation/air circulation for MPPT controller, AC inverter and such. Heat and thermal cycling are killers for electronics:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=72&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=9.73&x=48&y=25&ctype=nec

Result 10 AWG 4 series panels array 80 feet cable run 

Voltage drop: 1.85
Voltage drop percentage: 2.57%
Voltage at the end: 70.15

Running triple 1/0 cable between batteries will be a task, and will require the cable to be run separately in two lengths of conduit.
stedddd
I would not.

Having a solar power shed next to the bus. And 2 series * 3 parallel Golf Cart Batteries (6x batteries total at 6 volts @ 200 AH batteries for a 12 volt @ 600 AH battery bank and call it good--Or even 2s * 2p for a 400 AH battery bank if you don't run "large" Refrigerator and electric water heater (whatever those power draws are).

The bus/motor home presently has the battery's negative posts connected to the frame. The engine, accessories and 120 volt system expect the frame and body to be 12 volt and 120 volt to be negative. I expect that the negative connections throughout the frame and body to be less that electrically solid.  My question was, should I duplicate the negative circuit for solar use by running a heavy copper cable from the two batteries negative posts to the negative bus supplying negative for the controller and inverter.?s

For long term reliability of "high DC current" power systems (typical for Off Grid Solar), yes, Positive and Negative DC power should each have their own Copper DC Cables. Do not run "high current" through the bus chassis and frame. In "normal" power systems design, there is only One Battery Negative to Earth/chassis/Frame ground connection (single point grounding) for this reason--To avoid high AC or DC current running "in parallel" through chassis and frame (or copper plumbing, LP metal gas lines, green wire safety grounds, etc.). Single point ground ensures that you do not have all of the problems of parallel current flow (noisy electrial power interfering with radios/TV, burning out a small ground wire with heave DC current, etc.).

If your present system has been working reliably for you--I am not going to "cancel" your successful results. If it works, it works.

We keep "dancing" around what your loads are... 300 Watt loads are nothing compared to the 3,000 Watts you want to future proof/plan for. 300 Watts is "rounding error" for a 3 kWatt system. This is the issue of trying to design for the future loads with present available hardware.

I am thinking of mounting the solar array on a boat trailer.  It would allow me to put the solar array into the barn when we are away for long lengths of time  I would love to make it so that the solar array can automatically turn during the day to directly face the sun.

It can be done... Big issue with solar panel mounting is the structure needed to withstand strong winds. Depends on what your "stormy weather" winds are... I am in a sheltered area so not a big issue. In Florida with hurricane winds, Middle USA with tornadoes--Big issue. Damage from different causes. Hail, direct wind, derbies blown into array, etc. And to add damage to power systems from direct/nearby lightning strikes.

https://duckduckgo.com/?q=+solar+farm+storm+and+wind+damage&iar=images&iax=images&ia=images

Most(?) people these days are building fixed arrays (maybe some you can change tilt 4x per year) with one array facing south east, the other array facing south west... "Virtual tracking". Solar panels are "cheaper", building tracking arrays (structure, motor(s), controller, etc.) all add complexity. But a good tracking array--Typically just need a couple shots of grease once a year in linear actuator and on on pivot points. One of those paper design thought experiments. See what works better for you (somewhat larger array of cheaper panels and racking vs fewer panels and more complex/costly racking/structure.

Some folks with manual tilt racking, after a few years they don't bother with the effort. Pick one angle (winter, summer, or "best year round" angle and leave it be).

If you want a more complex/complete solar harvest website calculator, this one is good. It is setup for Grid Tied power systems, so I play with some of the options to get "off grid equivalent answers (plus it has a 1,000 Watt minimum array size).

https://duckduckgo.com/?q=portable+solar+power+trailer&ia=web

Whatever project you wish to tackle. If you trailer mount your array, you may want to add the charge controller, battery bank, and Inverter there too. And now you have a portable solar power system.

Or you get a nice Honda euX000 (or equivalent inverter-generator) and have 2-4 5 gallon gas cans with fuel preservative (recycle once per year) or pick an Propane genset and a couple 100 lb LP tanks for a week or two of emergency power (LP gas can supply cook stove/hot water/etc. too).

Dual fuel genset (gasoline/propane) not to big genset (large gensets consume lots of fuel which is wasted on smaller loads (say 1x frdige, some lights, RV Water pump, etc.). This model (or similar) goes on sale at Costco for several hundred dollars off at times:

Firman 3200W Running / 4000W Peak Dual Fuel Inverter Generator

https://www.costco.com/firman-3200w-running--4000w-peak-dual-fuel-inverter-generator.product.100843922.html

Lots of possible projects and so little time & money.

-Bill

My wife and I have been talking about camping trips together (or camping in an RV--She was never that hot on sleeping on the ground or in a tent)--But so far, family obligations have been demanding a lot of our time in the last few years.

Yes, you can use 10 AWG on the solar array (4 or 5 panels in series) and use 10 AWG (or heavier) cable without any issues (just the voltage drop depending on AWG and current).

Placing 3 cables together for positive battery busing, and 3 for negative busing--Yes it can be done and from the math it sort of works OK...

There are people that can stuff a 440 Hemi in the back of a boat and make it look like a piece of artwork. And there are people like me--"Artwork" does not describe what mine would look like.

The issue is the bus was originally designed with two banks. The Vehicle SLI bank for the motor/running gear, and it sounds like a second "house bank" that ran interior lights, ventilation fans, possibly lift gate, whatever else and the two banks were isolated except for (probably) a bank connection relay/etc. to charge the house bank when the motor was running. As designed, the bus was never intended to have both banks connected in parallel for increased total capacity. The idea was somebody could run the house bank dead, and the driver could still start/drive the bus.

If you want to try and splice the two banks together with 3x 1/0 Cable--Sure, try it and see how well it works or not.

I am a little confused--Are you trying to "update" the RV bus for more road trips? Or is the chassis pretty much on blocks as a cabin/bunk room when needed?

There are better solutions (higher battery bus voltage, using Lithium Ion batteries, etc.) that can make for a killer RV Power system. But, as you know, this is not going to be inexpensive or easy.

If the RV ends up being a cabin on blocks, then a separate solar shed is a good solution (controller, battery bank, AC inverter in the shed--No existing bus/RV limitations).

If you are looking to update the RV for the road--The Bus interior may need a make over. Design a space for 4-6 Golf Cart battery bank+charge controller+AC inverter inside the van. And don't try to use the "house bank" location unless you can fit 4-6 golf cart batteries in a revamped house battery box/area. Leave the SLI vehicle battery alone--Except to wire up with an isolation switch to use the vehicle alternator to charge the house bank when driving.

And still need to put some hard/fixed numbers on your power expectations (Watts, Watt*Hours, etc.) from your loads and harvest expectations from solar. What is that refrigerator (300/600+ Watts, 60 Watts, still looking for 3 kWatt AC inverter usable output in the "future", etc.)?

-Bill

Thank you for the kind offer Bill... Will see what happens.

Regarding parts, our local Ventures/Scout leader had to retier their old 15 passenger van because the new rules required active suspension for a safer vehicle...

And I have friend that is a (mostly) retired machinist who has been making parts to support old trucks and machines that no longer have support/replacement parts available.

A major issue with solar power as emergency backup is the battery bank. Batteries age from the moment they are assembled. You can get dry charged Lead Acid (flooded cell) batteries and they will last roughly 18 months before you need to add the acid/electrolyte... Not really a 'useful' storage life extension. "GC" batteries may last 5 years on float charge (keep batteries cold, they age much slower. For every 18F below 77F, they age 1/2 as fast or last 2 longer).

And there are Lithium Ion (typically LiFePO4 or lithium iron phosphate)--They have very low self discharge and can last 10+ years "in storage". Plus in active use, they have greater cycle life, less internal resistance, and accept higher charging current and supply higher discharge current vs Lead Acid. But lithium are expensive.

One option is to build out the solar system using GC batteries and get it functioning to meet your needs (and you learn its capabilities).

After those batteries "age out"... Just mothball the system and when you think things are getting iffy, the buy the battery bank and recommission the sysnktem.

This does not help you when you get walloped by an ice storm that takes out the utility power... No time to buy batteries, and once the short term emergency is over (utility repairs)--You have the relatively expensive battery bank with another 3-5 years of "useful" life/emergency life.

It is difficult to justify anything other than a small(ish) off grid solar power system for emergency backup because of (in my humble opinion) that Off Grid solar needs batteries (lots of them for larger systems) and the batteries age out over time.... And a fuel based genset (propane is close to ideal) for the random short term outages. Genset "pickled", propane does not "go bad". Only fuel costs are when running the genset.

There are Off Grid inverters that will run without batteries and use the solar panels for all power... More or less, the solar array has to be something like (at least) 2x larger than your AC loads (i.e., a 1,000 Watt array will run a ~500 Watt AC load during sunny weather, middle of the day). At least you save the costs of batteries (new and replacement every X years).

Your power needs could probably be meet with a 1,000 WH per day off grid system and a 300 Watt AC inverter... Except for the refrigerator--And the options are:

• Standard Energy Star Fridge that runs on 1,000-1,500 WH per day (check energy star guide). Need a full size battery battery bank and ~1,200-1,500 Watt inverter minimum
• Chest Freezer Conversion--Basically a chest freezer with an add-on refrigerator thermostat (and I have seen a few new chest freezers that can keep refrigerator temperatures without a new thermostat). Around 250 WH per day.  Still need ~1,200 Watt AC inverter minimum, but a much smaller solar array to keep cool
• DC fridge from battery--Smaller fridge, compressor based, run from 12 or 24 VDC battery bank. Somewhere around 350-750 WH per day
• DC fridge from solar panels--There are some DC refrigerators that run directly from solar panels (i.e., run during sunny weather and  rely on the insulation to keep cold at night. 

Example of DC refrigerators (Lowe's and NAWS):

https://www.lowes.com/search?searchTerm=dc+refrigerator
https://www.solar-electric.com/residential/solar-refrigerators-freezers.html

Old magazine article about various fridge options (overview is still valid):

https://www.backwoodshome.com/solar-powered-refrigerators/

DC refrigerators tend to be very costly... And the direct from solar panel DC fridges tend to be smaller and marketed for vaccine & medical storage, etc.

 I ordered another 1250 watt solar panel, so I'll have a 4 panel series array.

I guess you intended to type you ordered a 4th 175 solar panel for a 700 Watt array? Panels in series or in parallel do need to match specifications.

The inverter asks for a 350 amp fuse/circuit breaker but I think I'll install a lower amp breaker to give more protection to the system. I'll also have a system monitor so I can watch it.  How low should I go ? If I trip the circuit breaker I'll disconnect or turn off something.

Circuit breakers are there to protect wiring. Not devices or loads (at least not directly). I don't suggest using a circuit breaker (especially on the DC input to AC inverters and other DC electronics) as "throttle". Killing DC power to heavy loads like AC inverters can cause an inductive kick (voltage spike) to the DC input and cause the AC inverter to fail (or not last as long as it should). Breakers should only be used as emergency shutdown devices (or powering down when the AC inverter is unloaded).

If you are planning on using a standard (and basic model) of Energy Star Refrigerator (compressor type), you should plan on something like 1,500 to 1,800 Watts of "available" power for reliably starting of the fridge. A suggestion:

• 1,800 Watts * 1/0.85 inverter eff * 1/10.5 VDC battery cutoff = 202  = ~200 amp minimum DC breaker for inverter to avoid false trips.

The fridge itself will probably use around 120 Watts running and around 600 Watts defrosting (turn off door anti-sweat heaters if it has them). So, you could run down to:

• 600 Watts  * 1/0.85 inverter eff * 1/10.5 VDC battery cutoff = 67 amps @ 12 VDC and run just the fridge

Your choice... These are rough guesses--Depends on what you use for fridge (i.e, a chest freezer/converted to fridge would run around 120 Watts or so--Not Frost Free model).

For breakers, DIN Rail breakers are handy:

https://www.solar-electric.com/search/?q=Din+rail+breaker+box

Square D QO "standard home breakers" are also DC rated (you need DC rated breakers/fuses for DC power circuits):

https://mariaelectricals.com/square-d-qo-breaker/

The Qwik-Open “QO”and Qwik-Open-Bolted “QOB” breakers are rated for the following systems:

Good for your lower current circuits...

Lots of other breakers out there--Just watch the voltage rating (AC vs DC):

https://www.solar-electric.com/residential/circuit-protection/circuit-breakers.html

-Bill

Sounds beautiful...

Wife would like a Sprinter or maybe a Ford Transit. Not too big to park, tall enough to walk upright in.

If the battery bank currently meets your needs--Sounds good.

The converted freezers have been around for a long time. Chest freezers are nice because they don't let the cold out. Uprights, easier to get at the food (not a bunch at the bottom and having to move the top/trays around for access.

Brain works faster than the fingers... Especially as we get older (and neither working as well as they used to).

You size the wiring to meet two requirements. Large enough to carry the maximum sustained loads--And for solar/off grid, espeially for lower voltage DC wiring--Use heavier wiring to keep voltage drops low/reasonable. You can size the breaker for your actual loads, or even larger rated breaker because of the heavier cable for lower voltage drop (i.e., 12 amps @ 14 AWG cable but use @ 10 AWG to reduce voltage drop. A 15 amp works fine (loads) and you could use a 30 amp because that is the rating for a 10 AWG cable.

Note with most North American fuses and breakers. Generally they are rated to trip at 100% of rated load (a 15 amp breaker will trip at 15 amp). This may take minutes or hours (or even longer at 100%). And not trip at 80% of rated load (15a*0.8=12amps "never trip").

If your loads are on/off (fridge, hot plate, etc.), you can run your loads up to (near) 100% and not really have any issues. If your loads are constant (say charging a battery bank @ rated current for 5+ hours--Then you might think of over sizing by 1/0.80 or 1.25x. For example you have a 40 amp charger charging the 12 VDC battery bank, then the branch circuit (wire and breaker) rating would be:

• 40 amps / 0.80 NEC constant current derate = 50 amp minimum rated wiring/breaker/fuse

This derating is to prevent "nuisance trips" and avoid "heat buildup in wiring, etc."...

The rule of thumb for breaker/fuse placement (marine?) is 18 inches maximum from "bus bar" to breaker/fuse. Nothing magic, just the idea that the run of "unprotected" wiring is kept short (i.e., not much chance of short circuit to ground in that 18" segment before the breaker).

With power systems (be it battery bank or 120/240 VAC), the Return bonded to "ground" and green wire safety ground system (typically -12 volt bus and Neutral/White wire in AC power systems), this ensures that the Return (Neutral) is never above zero volts--So there is no need to have a fuse/breaker in the return wire.

For "floating power systems" (DC battery bus is not tied to chassis/earth/plumbing ground), then need breaker/fuse on both the + outgoing cable and the - return cable... This is to ensure that "weird" short circuits and field wiring that the neutral cannot get overloaded.

And a ground rod in earth is there (pretty much) for lightning diversion. 12 volts to "dirt" or 120 volts to dirt does not do much. I.e., dirt is a poor conductor and 12 vdc or 120 vac to 25 Ohm resistance (max "acceptable" NEC ground rod to dirt resistance) is only:

• for 12 volt bus to ground: I=V/R= 12 volts / 25 Ohms = 0.48 amps
• for 120 volt bus to ground: I= 120 volts / 25 Ohms = 4.8 amps

So a "short to  ground rod" is not going to trip a 15 am breaker....

Once you have spec'ed the Load Current, the AWG wiring to use, and the working voltage (12 VDC or 120 VAC), then picking the fuses and breakers is just looking up the specs.

And you have to decide if you want the space that a "breaker panel" and Square D Q0 or DIN rail breakers take up, or use something smaller--Your choice. Breakers nice on/off switch. You can get some pretty small/nice fuse and fuse holder too.

For the solar array to MPPT Charge controller circuit. In your case, you presently will have 4 or 5 solar panels in series, running on some heavier gauge cable (to keep voltage drop low). Around 9.73 Amps Imp and ~12 Amps Isc (short circuit current from array). The 10 AWG cable is good for 30 amps.. So no breaker or fuses needed (larger controller, and larger solar array with 3 or more parallel solar panel strings--Then we are talking about a "combiner box"--Basically a fuse/breaker panel--And other post).

Many people will put a switch or a DC rated breaker (15 amps or more for this system), near the Vpanel input for the solar charger (and the second breaker between controller and battery bus--Near battery bus). This two breaker (or DC rated switch on the Vpanel input) makes it easy to cut power and reset the charge controller, or remove the controller for service without having to do it at nigh or throw blankets on the panels (depends if you are OK working on "hot circuits or not". Breaker or switch on Vpanel input and breaker on Vbatt output for controller is very nice for maintenance.

The controller Vbatt output... If you had 5 solar panels the controller would output near 60 amps into a discharged battery bank under full mid-date sun. So, here I would use the 80% rule:

• 60 amps (charging 12 volt battery bank) * 1/0.80 NEC derating = 75 Amps or round up to 80 Amp rated branch circuit wiring and breaker...

Portable array--Idle hands are the devil's workshop.

-Bill

Just an FYI--I cannot tell, but if your cable/bus connections are aluminum blocks (vs stainless or some other "bright" metal)--Be aware that aluminium (depending on alloy) can start to from an insulating surface corrosion within just a few seconds of exposure to oxygen/moisture in the air.

Using an antioxidant approved for aluminum grease is required by code.

https://mikefullerelectric.com/antioxidant-paste-for-aluminum-wiring/

Also, you can check the aluminum blocks and wiring for signs of overheating (possible poor connections).

-Bill

I think you mixed up (my suggested) antioxidant (conductive) vs (your search for) dielectric greases...

I have used dielectric grease around marine wiring to keep out the salt air/water.

One thing to watch out for... If you have relays/switch contacts and use silicone grease--That stuff can be death for open contacts.

The issue is that the silicone grease out gasses and gets into switch contacts. When the switches "arc", the heat turns the silicon to a glassy/insulating material and ruins the contacts.

Anyways... My suggestion was for antioxidant grease for aluminium electrical connections.

-Bill

4. Generally, you want the switch to be on the positive bus, if your negative bus is chassis grounded. In general, you never want to switch off the ground lead. Ground is always assumed to be at zero volts... When you disconnect the negative bus from ground--Then that assumption is no longer true. It may not hurt anything electrical--But if somebody starts wrenching somewhere on the negative bus (battery terminals, bus connections, etc.), you now have the chance of a wrench from negative to ground creating sparks. Nothing may happen, just just depends on the rest of the current paths (other batteries, other equipment, etc.).

Fuses/breakers, just like switches, should be installed on the "hot side of the battery bank" (typically positive with negative chassis ground). Fuses/breakers are there to prevent excessive current flow in the wiring from starting a fire. Some of this depends on your design... For example, if you put 4/0 cable on a motorcycle battery, then the cable will short the battery without overheating. If you put a 6 AWG cable on a 200+ AH battery bank, there is a good chance of the cable starting a fire if shorted (for example, very roughly, a 6 AWG cable has a 600+ Amp fusing current) vs around 55 to 75 amps (NEC ratings).

https://www.powerstream.com/wire-fusing-currents.htm
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Fuses and breakers should be rated for at least 1.25x the maximum continuous current to prevent false blow/trip of the over current protective device... If you have high surge current that goes on for more than a few seconds, you may want a larger fuse/breaker.

Fuses are there to protect against over current and short circuits. Many people don't put fuses/switches between parallel battery banks. And some people do.... If you parallel battery strings, a fuse/breaker per string can be nice (drop wrench in on string, and other parallel strings feed paralleled current from the other strings... If is always nice to limit "damage" and "potential damage" to wiring and reduce the chance of fire by "partitioning" where failures can occur.

Others use the "switch per string" so they can diagnose issues, charge a weak string, "cut" a bad parallel string out of the bank until it can be repaired.

Breakers are nice because they are also useful as switches when needed. Breakers can be switched under load... Most other simple knife and marine A+B switches should not be switched under load except in an emergency (back to DC Arcs and switch design to break/quench arcs).

And a good AC+DC current clamp dmm so you can measure (for example) current in parallel battery banks (look for weak batteries, poor connections, etc.).

https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE (cheap and good enough for smaller systems)
https://www.amazon.com/Auto-Ranging-Resistance-Klein-Tools-CL800/dp/B019CY4FB4 (mid priced with other features)

5. Generally, a common mistake is a (too) large AC inverter and too small of battery bank. For off grid use, if you run for 5 hours per night for 2 nights on a FLA battery bank sized to 50% planned max discharges--That is a 20 hour discharge rate (most AC inverters can surge 2x rated power for a few seconds to a few minutes). Having an inverter that can suck your battery bank from 100% to 0% in one to two hours--Just not very useful for a typical off grid home (maybe starting a well pump, running an arc welder for short periods, etc. might justify a larger inverter).

For a full time off grid system, generally 10% to 25% rate of charge works well (5% for a "standby/emergency system" can work too).

Batteries are expensive and solar panels are "cheap"... Spending money for "more panels" (15-20% Rate of Charge)--And your battery bank may last 1.5x longer (less cycling stress on battery bank)....

In any case--Always suggest starting with loads. Then define battery bank to support the daily loads. Then AC inverter, solar array, and charge controllers can be chosen to "fit" the needs to keep the battery bank "happy" (i.e., a balanced system design).

6. Mixing battery types is always a questionable choice. As long as you "respect" the max charging voltage (around 14.4 for AGM, and from 14.75 to 15.5 volts for FLA charging/EQ charging). I guess you could use your bank disconnect to EQ the FLA batteries once a month. Then reconnect the AGM for the rest of the month...

Mixing batteries (type, age, etc.) is always a bit of a roll of the dice. You will have to monitor electrolyte levels (water/SG), individual battery voltages, how well they share current, etc...

Similar issue with buying older batteries... Mixing and matching can cause headaches as one (after another) fails, is debugged, replaced.

I always come down to the "risk vs reward" questions... If the value of using a mixed battery bank exceeds the risk--Why not try it.

In general, you want "matched battery capacity/abilities" in a series string (the weakest battery in a string, limits that strings AH capacity)... And "matched overall voltage" in parallel connections (weak cell voltage will not supply much current to load, a shorted cell can cause rest of string/batteries to overcharge, and such).

-Bill