Solar on a Skoolie - Design Help!

I am in the middle of designing a solar set up for a Skoolie I am converting and am running into trouble figuring things out and am starting to feel a bit overwhelmed by the possibilities.

Stuff that I have bought:

4x SW 270 - Mono
MSH 3012M - Inverter
ME BMK - Battery Monitor Kit
ME ARC50 - Remote
MidNite Solar 150
MNPV6 - Combiner Box

Stuff that I plan to buy:

4x - 6CRP525 - 395AH - Batteries

My plan is to mount the 4 panels in 2 strings of 2. I had initially wanted to do 4 strings of one (at least I think that's how I would say it? Parallel, basically) but when I checked the MidNite Size Tool it told me it wouldn't work. I'm also worried that by running the two panels in Parallel I may be creating to much voltage? I read, "Optimal input voltages for most MPPT controllers outputting to a 12-volt battery bank is in the 30-50 volt range." and if I run 2 strings of 2 my voltage would be at 60, Is that a concern even?

How do I tell what breakers to use to wire the panels into the MNPV6? I read that I should use the "Series Fuse Rating" and my panels are rated 16 Amps but I'm just not understanding how to turn that information into an answer. 

I'm trying to follow the classic wiring-flow diagram and don't know what exactly I need to use, and what I don't. Is there a book, webpage or an explanation I can read to try and understand this better? 

Even better, does anyone know if I could just buy a E-panel made by midnite solar instead? They don't make one for the MSH3012, but they make them for the MSH4012 which is like the sister model of the MSH3012. They are the same size and are almost the same. On their forum someone suggested it but said you may need a different size DC disconnect. Is that a possibility for me in this case?

For the Inverter to the battery bank I am planning to use a 4/0 awg cable (with the appropriate lugs crimped on) with a 400amp class T fuse, and a battery switch rated to 400amps (I believe I am understanding the Inverter manual correctly there). In the manual there are also shown to be 2 different Busbars between the inverter and the batteries but are listed as optional. Should I put those in?

If anyone has any questions, critiques, or advice I would love to hear them. If I didn't provide enough information please ask, I have a lot written down and even have some basic drawings started for of my diagrams. So uhh, help? 


  • PhotowhitPhotowhit Solar Expert Posts: 4,764 ✭✭✭✭
    Is the intent to be able to charge the batteries under power off the motor? If it is, I might be okay with it, but really, REALLY don't like that large of an inverter on 12 volt.

    Since 4 strings of 1 (all panels in parallel would work fine, I think you were running 1 string or all panels in series (each plugged into each other)

    For 2 strings of 2 you will not need a combiner box, just use a branch connector to combine the two strings. The combiner is incase a string or panel has a short the other strings can't over power it, so it's not needed since a single string would have the same fuse rating as the original and wouldn't over power it.

    Midnite E-Panels do make for a nice compact unit, with the inverter mounted on the front panel, but They usually have the breaker installed for the inverter, the largest breaker I'm aware of in an E-Panel is 250 amps. If Magnum makes a 4012 inverter I'm not aware of it, nor would I advise people to consider it.  Breakers don't instantly switch with minimal over loads, a 250 amp breaker would handle 3000 watts at 12 volts for most needs, 250 x 12 = 3000 amps x volts = watts.

    I would guess the 3012 would have the same foot print as the 2812 (I'm guessing it has replaced it...) The Magnum inverters have had the same foot print in the past. If you look through this spec sheet, you will see it fits most inverters, just the front panel is cut to mount a Magnum inverter.

    It will have spots to add breaks for incoming DC from solar and a place for a breaker between the Charge Controller and the battery so you can isolate the charge controller (CC) from the system. And I think, if you really want to or pick up another string be able to handle a few breakers for combining and just dump the single breaker for isolating the CC.

    Even with 4/0 cable you will want the inverter close to the battery bank!

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • lockeedlockeed Registered Users Posts: 2
    Hi! Thanks for taking your time to reply, I tremendously appreciate your help.
    The original intent for the large inverter was to be able to power a small window AC since my wife suffers easily from heat exhaustion. Looking back it was probably overkill. So now I'm trying to figure this system out. Now I hear you about not liking that big of an inverter on 12v, but I don't think I can change that part of the system. I could possibly sell the inverter for a slight loss and buy a different one but that is not a path I want to go on. Now, with that in mind, is there anything I can do to make the situation I am in better? Besides the parts I listed as bought, I'm still figuring out the system, and since it's a schoolie I can wire the AC section to fit the inverter, if that would help? I'm not sure.

    Do you have recommendation, running them all parallel vs 2 strings of 2? I'm guessing parallel, if my understanding is right the volts would mesh better with the battery panel.

    I looked at that link earlier and either I'm lost, or I the inverter I have isn't listed. 

    "Sinewave Inverters Modified Inverters MNE250STM MS2012, MS2812, MS4024 RD3924, RD4024E, MS4124E MNE250ALM MS2023, MS2812, MS4024"

    Are the ones listed there. But on the spec sheet for my inverter, it's listed with MS 4024: pdf folder/MSH4024M-Specifications.pdf

    And yes, the battery bank is going to be within 5 feet of the inverter. Since I am designing the entire floor plan, the solar requirements are getting priority.

    I have run into another part I would like to clarify. Since I'm designing the AC electrical system as well, I assume I should go with a 50 amp main breaker? Would anyone by chance know?
  • PhotowhitPhotowhit Solar Expert Posts: 4,764 ✭✭✭✭
    3000 watts is less than 30 amps AC. amps x volts = watts  so watts/volts= amps 3000/120=25amps. I would likely just run 2 15 amp breakers/strings. I don't remember what code is, someone else I hope will chime in, but since you won't be required to meet any code, I'd worry about safety. The wiring for AC is typically 14 gauge on 15 amp circuits.

    I suspect it replaced the 2812, if it has the same foot print as the 4024, then you are fine. A quick call to Magnum or Midnite should give you the answer. Magnum inverters, The first 2 numbers x 100 are the wattage and the last 2 are the DC voltage. Hence 3012 is a 3000 watt 12 volt DC inverter.

    Unless you purchased the inverter somewhere return friendly like Amazon, no I don't see an fix. Use what you have. FWIW-I've run a window unit off a 1400 watt inverter and have an 1800 watt inverter running my home, basically 1 - 15 amp circuit. It was planned for more, but I decided to switch from a 24 volt to a 48 volt home system and will wait until my battery dies to make the transition.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • littleharbor2littleharbor2 Solar Expert Posts: 1,094 ✭✭✭✭
    Have you got enough available headroom to heavily insulate the roof area? Preventing heat from radiating into the bus to begin with would ease the load on your AC. If feasible, a drop ceiling would allow you to run wiring, ducting and whatever else along with said insulation.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

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