Off Grid Home Forums Technical Discussion Will my house burn down if…

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    I actually posted the following but put it somewhere unlike (here).

    Ideas please.

    Here’s the skinny on something that I would rather someone else tell me to do before I just jump in and try it (thereby potentially signing off the planet):

    I have a box (for all intensive purposes and for the context within this post we’ll call it a house).

    There’s a mppt 6oa using a 48v array but charging down to a 12v battery bank (comprised at present of 18 6v 210ah batteries connected in series and parallel).

    My problem is that since I moved the bank to the other end of the house, my existing wiring scheme has me lacking at the other end of the house (my primary need area).

    That’s a problem now my question is this:

    Will I ruin some serious equipment here if my present lead of 12v power were to leave and return to the battery bank or will that just blow a few thousand dollars?

    And further, if looping back (so the whole system loops around back of the home and continues around the front of the home supplying all 12v devices along the way….only to return back to the battery bank….sheesh why does that sound like a bad idea?)

    If the aforementioned is indeed a bad idea, this next one ought to throw a monkey wrench of ideas up for grab: I have another 60amp mppt charge controller, a smaller battery bank of 7 12v batteries w/approx 125ah each, and even another dozen or so extras panels that I could hook up back where I started in the first place but would I really screw up if I were to have the incoming 12v battery bank in the same power grid created by the first battery bank?

    The latter idea sounds like it will work, but my concern is that the 60a mppt charge controllers will use the supply/access grid to charge long distance to the other battery bank (wouldn’t that heat up things?).

    Sigh….I’m just too flippin’ old to move the whole system back where I started and I really don’t want to rewire the whole place, nor do I want to create two separate non-linked service lines in.

    I really hope these are questions that are deemed good questions (man, I’m wracked over this dilemna~)

    Thanks for any ideas/constructive criticisms you might have.


    That is more power requirement than I have, but I would not have batteries in the same structure as the living structure, unless you have active ventilation of a battery room. Even so, it isn’t healthy.

    Everyone I know that have a 48V system stepped down have a separate “power house” even if it is only a small shed near the house.

    If you have a wind generator, locate the wind generator further away from their dwelling, only bringing the 48V to get to their “power house” shed, and then, 12 VDC or 110 VAC into their home to avoid the noise of the wind generator and/or invertor.

    I have 12 VDC because it is silent.


    @ kennyhendrick if you have quantity 18 6V 210 Amp hour rated batteries and use a 12V system I calculate you have 1890 A-H capacity which is about the size of the systems I often design for. You did not say how far you moved the batteries and what size cables you used. It is possible to calculate the corect size wires for the distances involved. The description you gave makes me think you are attempting to build a ring main system such as is often used in military craft or by power utilities.

    Yes there is the potential for problems especially if you do not follow good practices for over current protection. However even if you do use adequate protective fusing I can see potential problems with charging this system that will result in the system suffering premature battery failure. You obviously have a substantial investment in batteries alone so I am wondering why you did not get the system professionally designed in the first place.

    @ conieD what makes you say only 12V DC is silent. None of my systems are noisy.

    although the comment about batteries should be located in a seperate building most of my designs are for boats wher ther is no option for a separate building. Ther are simple engineered solutions to build a safe battery system inside the living accomodations area.

    You can contact me at 2elnav(at) netbistro (dot) com for further details. This forum text window is too limiting for a complete technical answer. I could provide you with calculations for correct wire sizes.


    I have an excellent system. It does everything I designed it for, and more.

    I once saw an interesting name for a power system: “Ample Power System”.

    I am not selling anything. Obviously, you are. It is more than annoying!

    I was only offering “my experience” living with solar power off-grid: the OP asked for.

    I only mentioned my 12VDC system is “quiet” because there is no “sizzle” like one has standing near every brand inverter I have been near.

    It is also electronically quiet for my amateur radio “building” projects.

    I suppose one could make a case about EMF, and other such things, but I won’t.

    The batteries are “sealed” from Wagstaff’s, Portland, OR. Nevertheless, I have active ventilation to the outdoors in my closed compartment, where the batteries are.

    I understand this is good practice.

    I can not think it is “healthy” for the OP to reside in the same space, without at the minimum having a separate place for his batteries, and, active ventilation.

    I would not be surprised, if what he proposes violates building codes and fire codes that are “good laws” for a private residence.

    I am no “Philadelphia lawyer”. In fact, my family has no lawyers. But we do have several competant and famous engineers.


    If promoting a concept is selling something then I guess I am guilty. I have been installing inverter systems since 1995 and have learened a few things along the way. Boats are by their nature self contained and thus off-grid. Construction codes are for the most part as stringent as building codes on land. For the rest they are tougher.

    what the OP was apparently asking about was if he was likely to burn something down by constructing a ring main. What he never said was what size wire he was using,nor how much load current he was expecting. Land wiring simply looks at load current and specify the wire gauge accordingly. Boat wiring code looks at how much load current is involved as well. this usually means calling up a ;arger wire than what the land code calls for. Quite often when dealing with low voltage like 12V we end up having to upsize in order to reduce the voltage drop to amounts specified by the marine code. For example for critical motor and control circuits we are not allowed more than 3% drop but lighting is allowed 10% voltage drop.

    When dealing with 12V a 10% drop is 1.2V

    For a 120V AC 1.2V is only a 1% drop.

    I never said ventilation was not provided for the battery bank on a boat. What I did say; on a boat the battery is still stored on board where people also reside. You never see a boat towing a raft for a battery building.

    The marine construction code stipulates how a battery compartment must be built

    in a safe manner.

    The cost of installing large enough wire to be safe is much greater in 12V systems than in 120V systems. Sine wave inverters are not noisy. MSW inverters are. This is something ham operators have learned from way back.

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