Wiring diagram review

rw080761 Registered Users Posts: 2
This is my first project dealing with wiring so I was hoping to have people review my work and offer opinions on how to improve it.

*are the fuses sized correctly and in the proper place? 

* is it true you can run the grounding wires to negative side of the fuse block? 

Thank you for your time! 


  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    A few suggestions:
    I'd move the negative wire between lower battery and fuse block/buss to the upper battery to better balance current through the bank.

    150a fuse is too big IMHO for 4awg wire to inverter and interconnects.  Depending on wire insulation and length of run, something more like 1/0 or 2/0 should be used.  A 1000w inverter could draw ~90-100a continuous and surge to maybe 2x that.  With 75° insulation, NEC ampacity for 4awg is 85a.

    Likewise the fuse (or preferably a breaker, handier as a disconnect) between bank and buss should be sized to protect the wire used.

    The battery can be grounded, but check the inverter manual WRT neutral-ground bonding on the AC side.

    If this is short runs (eg boat/van) branch wire size is likely fine.  If longer runs (cabin/house), you may want to check voltage drop for expected load currents.  DC loads for mobile/marine use are usually ok with the voltage range (~10.5-16v) seen in battery charging cycles, but some designed for use in residential applications want stable DC output (~13v) from a power supply.

    10awg wire is probably ok for controller output, but I'd check the voltage at the output terminals vs battery bank terminals while charging to be sure voltage drop doesn't make the controller think it's supplying a high voltage than what's actually getting to the bank.  Personally, I'd use the biggest wire that fits on the controller terminals.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
    As far as I can tell, the fusing looks OK.

    For the battery bank, take a look at these diagrams for wiring your battery bank. Your drawing does not "balance current" flow between the two batteries as well as you would like (the battery next to the leads that go to the fuse block will cycle more current than the battery farther away):


    And a question about your overall design and expectations... You have a relatively large AC inverter, a smallish to medium size battery bank, and a single (?) smallish solar panel.

    I like to call the battery bank the "heart" of your system--And design everything around it (loads, charging). A 200 AH @ 12 volt battery bank should have 5% to 13%-20% rate of charge. 5% can work for weekend/sunny weather usage. 10%+ is better for full time off grid usage:
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 188 Watt array minimum
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 377 Watt array nominal
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 490 Watt array "typical cost effective" maximum
    And then there is sizing the array for your loads... Which is the rate of energy usage (Watt or AH @ 12 volts) times Hours of usage per day/night. For a battery bank, we generally assume 1-3 days of "no-sun" (cloudy weather) and 50% maximum discharge. For a cabin/home, typically 2 days and 50% discharge is optimum (all things considered). For an RV with minimum space and weight, assuming 1 day of storage and 50% maximum discharge is sometimes used (more genset usage, or simply cut back on energy usage during bad weather)... And knowing where/when you will be dry camping (US southwest in summer vs Canadian border in winter).

    Based on your battery capacity and a 1 day+50% capacity, the estimated daily energy usage (maximum suggested) would be around:
    • 200 AH * 12 volts * 0.85 AC inverter eff * 1/1 day storage * 0.50 max discharge = 1,020 Watt*Hours of daily usage
    • 200 AH * 1/1 day * 0.50 max discharge = 100 AH @ 12 volts (if you prefer to work in AH)
    Then the amount of sun. Let us guess that you camp around Pittsburgh PA, fixed array, mounted flat to your RV roof:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:


    Note, if winter camping, you really need to tilt the solar array to a 45 degree angle or more. Anyway, "hours of sun per day", if you are camping in "sunnier" weather/seasons, around April thru September or a minimum (long term 20 year average) of 4.12 Hours of sun per day. Your 100 Watt panel would supply, and a 377 Watt panel would supply:
    • 100 Watt * 0.52 off grid system eff * 4.12 hour of sun (ave September) = 214 WH per day (Sept)
    • 377 Watt array * 0.52 off grid system eff * 4.12 hours of sun (Sept) = 808 WH per day (Sept with 10% rate of charge array)
    AC inverters--Easy to buy a big one but difficult to supply a "worth while" amount of energy per day from a small solar system/battery bank.

    Your AC inverter running at 500 Watts would use 50% of your battery capacity in about 2 hours (500 Watts * 2 hours = 1,000 WH). And would take about 5 days to recharge with your present 100 Watt panel/solar array in September (214 WH * 5 days = 1,070 WH average harvest).

    Also, AC inverters take power "just turned on"... Smaller ones take around 6 Watts (tare energy usage) vs 20-40+ Watts for larger units (and inefficient units). With a small system, you have to take the AC inverter Tare losses into account (do you have a power switch somewhere to turn off the AC inverter when not needed?). For example, if your inverter took 10 Watts Tare and you left it on 24 hours per day:
    • 10 Watts * 24 hours = 240 WH per day
    Or more energy than your panel can harvest in September every day.

    Also, battery banks have a maximum output current that they can support. AGM batteries do have a higher output current capacity (in theory, your AGM batteries could support ~C/1 discharge rate--Or fully discharge 200 AH in 1 hour). However, you have to decide if that is the load profile you want/need... Do you want to run your AC inverter at 100% power for less than 1 hour and take 5-10 days to recharge... Or do you have something that draws a large amount of current for a short period of time (like a skill saw) and most of the time, the tool is turned off...

    For FLA (flooded cell lead acid deep cycle storage batteries) and not a bad idea for a "balanced" AGM design... For a 12 volt system suggest around 125 to 250 Watts AC inverter per 100 AH of 12 volt battery capacity:
    • 200 AH (at 12 volts) * 125 Watts / 100 AH = 250 Watt AC inverter maximum "nominal" recommendation
    • 200 AH (at 12 volts) * 250 Watts / 100 AH = 500 Watt AC inverter maximum "maximum" suggested
    Since you have AGM batteries, you could support your 1,000 Watt AC inverter--But you can drain your battery bank very quickly.

    I will stop here. I have made lots of guesses as to your location and energy needs and camping habits. I could easily be more wrong than right--But the math and background information is there for you to see how the calculations are made and what assumptions we need to design a "balanced" off grid solar system.

    Questions, corrections?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
    And, your negative wiring question... Yes, most quality off grid 12 VDC loads for battery systems have both a + and - wire... And the minus wire should be run to a negative battery bus bar/connection.

    And run one 6 AWG or larger cable from the negative bus bar to the RV Frame (negative bus bar ground bonding). Both for safety and if you have (for example) a 12 volt car radio that uses frame grounding for the negative lead.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rw080761
    rw080761 Registered Users Posts: 2

    this is the sheet that came with the inverter... im not seeing a consumption rating but i thought if i provided it to seasoned eyes maybe this would have more specific info for my set up.

    im only thinking about running a freezer-converted-fridge off the inverter which will require a 12v thermostat which i cannot seem to find any specifications as to watts/hr drawn... i thought this would have been a cheaper way to have a giant fridge space and not pay 1200$ for the ones like dometic which seem overly fancy and not much actually storage space. the estimate for the  freezer-converted-fridge consumption was around 150-180watts per day.

    I updated the diagram and threw in another solar panel which i then will have to upgrade my MPPT from a 20a to 30a.
    Also as was mentioned before the inverted only calls for 4AWG but at the recommended fuse of 30Ax4 which is 120A which is more than the wiring is recommended for (100A) so im not sure whats going on in this instance!

    This is a setup for my converted Sprinter van. I bought a tilt rack for the solar panels and am currently in Pittsburgh PA but will be just north east of Toronto Canada for the month of August then spending the month of October north of Grand Fork ,North Dakota working a seasonal harvest gig then west to California for the winter...

    Thank you so much for all of your responses so far! Any revised suggestions would be super appreciated!!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
    I probably would suggest you start with ~250 WH per day for the freezer/fridge conversion. And that you only plan on using 50% of the predicted output of your solar power system (to rid through cloudy weather/account for placing warm food in fridge and cooling down, hot van interior, etc.).

    A 1,000 Watt AC inverter is typically on the "small side" for running a standard compressor based refrigerator/freezer... They have pretty harsh starting current requirements. Typically, suggest around 1,200 to 1,500 Watt AC inverter minimum... But if your inverter may be enough (especially if you run no other AC loads).

    A 12 volt thermostat probably will not draw significant loads (electronic?). What will help you conserve a lot of energy is figuring out how to power cycle your AC inverter (only turn on the inverter when the refrigerator is running). Even at 10 Watt Tare loss, 24 hours per day = 240 WH per day--Pretty much the energy requirement of your refrigerator.

    Trying to hack a thermal controlled on/off switch for your AC inverter--And have it be reliable (switching >10 amps @ 12 VDC is not "easy", finding a 12 volt AC inverter with remote on/off is not easy either). Your inverter has an optional remote--Perhaps that has a remote on/off function you can use.

    Otherwise, I would be looking at a DC unit instead (yes, I am not a big fan of the price either):


    And you have the choice of running just from >75 Watts of solar panel (no battery bank--cool during day, coast at night) or running from your  solar + 12 volt bank, no AC inverter issues, and run the 12 volts for some LED lighting, cell phone charging, and a radio...

    The other suggestion--Some folks have found perfectly workable propane powered (or DC compressor powered) refrigerators from RV wreckers...

    And just run the AC inverter when needed (power tools, possibly running a laptop computer, etc.).

    Regarding the AC wiring and fusing (or circuit breakers)--I like to suggest that you take your power needs and multiply them by 1.25 for off grid solar wiring... Even though NEC is pretty conservative, off grid is a harsh environment (higher temperatures, can have many hours of continuous current) and the x1.25 helps keep wiring cool, loses lower, and avoids false trips of fuses/circuit breakers.
    • 1,000 Watts * 1/0.85 AC inverter eff * 1/10.5 volts battery cutoff * 1.25 NEC derating = 140 Amp "rated" branch circuit and fuse/breaker capacity
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    North of Grand Forks ND in October can be chilly and somewhat gloomy, with short days, low sun angle, and a tendency to be overcast for long stretches.  It can also be very nice, but best prepare for the worst.

    If no shore power is available, you may want to consider a small inverter type generator. 

    You may also want a way to heat the van.  Snow is quite possible.  I'm in the same general area, and had to shovel nearly a foot of snow off the dock and boat when closing up in mid-Oct last year.  Some years can be shorts and t-shirts though.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter