Please help me fill up my diagram and power plan

minisolarminisolar Solar Expert Posts: 155 ✭✭
Hey Everyone,

I have been working on my cabin... Driving for 2 hours way and back (4 hours total) then working there for 6-7 hours... Fun! ;)

We decided to just finish up our little cabin. 

I would like to start planning exactly to the T how my system will be set up and wired and hoping I can get the help of the great people here. 

I am attaching the general components of my system and simple explanation. 

This is how am hoping to have my system run:

The generator will run from evening until morning (so 10-11 hours) at which time it will feed my indoor distribution box and charge the battery bank with IOTA - using the ATS so I can just plug generator and have it work it's magic. Then during the day the cabin will run off batteries and inverter. Then in the evening again I will charge until morning. 

The components will be installed on the wall in a "closet" outside my cabin where the batteries sit on a shelf and the components are above them on the wall. Generator will be about 50ft away (should I run a permanent underground cable to my generator?)

Then I will have a few 12v items indoors with more in the future (on diagram). 

I am attaching some of the items I bough or will buy to be part of my system:


Right now I have a female wall plug that I connect the extension cord from generator to it and it feeds my distribution box. Lucky for me it is located exactly where I want my entire system to be so I can  just use those wires in my system.

I am hoping I can get help here on all the connections - what wire to use, breakers, and so on. Even how to wire my batteries... 


  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    What sort of loads are you going to power with that huge inverter ?  Why not run them from the generator.

    Why are you intending to run a generator all night, and have quiet in the daytime ? What sort of loads will it be powering

    The Iota DLS is not a great daily battery charger, but it is a rock solid piece of gear.  A automotive 40A car charger may be better for short charging periods, and then use the Iota for finishing. 

    Insure the Iota voltages are compatible with your AGM Cycle Duty service requirements, which are different than flooded voltages
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • minisolarminisolar Solar Expert Posts: 155 ✭✭
    Ductless ac, converted freezer, microwave, and lights and so on. I will prefer it to be quiet during the day which is why I will use the battery bank during the day so I don't need to listen to the generator. 

    Running generator all night - support ac and freezer while charging my batteries when I can't hear the generator (honda gen + silence box + 50ft away from cabin + being inside cabin with ac running = can't hear the generator) 

    I got for the IOTA the specific AGM battery jack which is a smart controller that make the iiota charge in 4 stages to keep batteries healthy and safe. 

    • My near future 12v loads will be very light... phone and tablet charging. tiny wifi cam. pc fan... should I just hook all this to one circuit breaker? 
    • I was trying to read online about how to connect the iota to the batteries. IOTA gives some guides and they mention how important it is to connect it correctly to have a balanced charge. But none is showing when a bank is both parallel and in series. I am attaching a diagram of what I understand the batteries connections should be (please correct me if I have done something not right or efficient) and maybe you can add lines of how iota should be connected? 
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    The starting point is the Smart Gauge website:

    Don't get confused about only seeing "one battery" box per string... In reality, that box can be a single 12 volt battery, or multiple 2/4/6/12 volt batteries in series. The critical issue is where the parallel connections are made. You want the current bath to any one string of batteries to be the "same" (technically resistance, but using the same length of wires for each battery to battery series interconnect, and follow the parallel connection diagram is what you are after).

    The "optimum" connection point--There can be one or even two (i.e., kitty corner, A-C and B-D). Where to attach the loads and the charger(s) should be at the "optimum point(s)". you are looking to evenly (per string) charge and discharge your bank.

    For your 12 volt loads... I am a big believer in using several breakers... As an example, if your 12 volt plug for USB/Radio/etc. pops a breaker, it would be very nice to still have your 12 volt lights working--Rather than being plunged into darkness.

    Also, especially for 12 volt loads, you have to look at the current needed and length of wiring... For example, say you want to send 12 volts @ 10 amps 15 feet. A 14 AWG wire set and a 15 amp breaker would be good--From a current point of view. But look at the voltage drop:


    Voltage drop: 0.76
    Voltage drop percentage: 6.31%
    Voltage at the end: 11.24

    You are already dropping 0.76 volts... Run the battery to 11.5 volts under load/discharged, and you are in the 10.74 volt range--Pretty near the 10.5 volt cutoff for most any 12 volt device.

    Also, some items may be very sensitive to input voltage variations. I have seen lights that barely flicker when the voltage changes, and other that look like a real disco show... So having each load (or load type--I.e., all lights on one circuit, all fans/12 volt tools on another) back to the bus bar--Reduces the voltage variations too.

    Being able to turn some/all items off at a main panel is handy too--Lets you mange battery loads, and cut all loads when RV is not being used.

    Starting with a blank slate for wiring can be pretty intimidating... I like to at least start with the "black box" approach. Take a section and work that one first.

    For example, 1,500 Watt AC inverter with 12 volt input... That means a design current (my suggestion) of:
    • 1,500 Watts * 1/0.85 AC inverter eff * 1/10.5 volts cutoff = 168 maximum expected load
    • and 2x that current for short surge current (starting motors, etc.).
    • 1.25 NEC derating for continuous current (and breaker derate to prevent false trips) * 168 = ~210 Amp minimum breaker and wiring from battery to bus bar.
    You have three parallel strings of batteries... I would suggest that each string be designed for, at least, 1/2 of the needed current (if one string fails, etc.) -- So that would be 210a/2=105 Amp per series battery connection.

    Not everyone (anyone?) does it, but using a fuse/breaker per series string is good for safety... The Blue Sea fuse holders are very nice and small (not cheap, with fuses):

    But there is also the idea that using circuit breakers are nice too for many locations (such as loads leaving your 12 volt bus bar, AC panels). Breakers, besides adding safety and no fuses to replace if popped, they are also handy on/off switches (debugging, turning off loads, etc.) and you do not have to add separate on/off switches.

    Especially with 12 volt wiring--The voltage drop is critical. I suggest that you aim for a maximum of 0.5 volts from the battery bus bar to your loads/AC inverter DC input etc. That means short/heavy cables. You can use the voltage drop calculator above to play with cable AWG and length.

    Another black box you have is the automatic AC transfer switch. Assuming you don't get an AC inverter with internal transfer switch... Just look at your needs. Two power inputs. One from AC inverter, the other from Genset/RV exterior plug. Connect Genset to the input that has the "sense" input (basically relay power to switch to Genset input when available, one genset "goes away", revert to AC inverter power).

    Another option... Look at getting a "small" AC inverter (300 Watts or so) like the MorningStar. It has a "search mode" and uses less power on standby/operation than the larger AC inverter. You could wire this directly to your smaller loads (120 VAC LED lighting, radio, computer charger, etc.). You may not need it in this case (large enough battery bank, plan on running genset overnight)...

    And look at the "logic" of your system design. For example, the Iota would be connected directly to the genset/AC external input. There would never be any need for it to be downstream of the automatic transfer switch. You would not expect the batteries to power the AC inverter to power the Iota Battery charger to recharge the battery bank you are discharging with the AC inverter....

    At this point, you are looking at several fuse/breaker panels... You need one at the AC input to your RV (genset/AC power in, output to Iota Charger, AC transfer switch, and possibly other genset/mains power loads like A/C, fridge/freezer, power tools, exterior outlets for genset loads). A second one for the output of your Transfer switch (internal lighting, fans, microwave, etc.). 

    And a third "panel" at/around your DC bus. Obviously, very heavy connections to battery bank (each battery string fused 150 Amps) and a ~210+ Amp breaker to your DC inverter input. And probably a handful of other breakers to 12 volt lights, usb chargers, 12 volt RV water pump, etc.... 

    Things like a ceiling fan... There are (as I recall) both DC and AC versions available--You just have to look at your energy budget, price, etc. to see what works best at the time for you.

    Battery Monitor--There are several types of those. Ones that are "voltage only" reading. You connect the monitor to the battery bus and it attempts to estimate the battery state of charge based on battery type, and the voltage "history" (charging/discharging/etc.):

    And there are those that use a "shunt" or high current rating precision power resistor that connect between the battery Negative connections and the 12 volt negative bus (so that all battery current flows through the shunt). And you have a sophisticated meter that measures the voltage drop across the shunt (current), and battery bus voltage--To better estimate state of charge and give you more data on the battery bank (charging, discharging Amps, Amp*Hours, etc.): (shunts may need to be ordered separately) (Victron, Xantres, others)
    Or your Amazon link...

    The above links are just suggested starting points for searches... I am not off grid, so I have not used any of the above.

    Anything that generates heat (Iota charger, AC inverter, solar charge controller--if added later, etc.)... All needs good air circulation. Do not install in the top self of an insulated closet/service hatch.

    Batteries... FLA and AGM batteries. Hot batteries shorten service life (75F is nominal. 93F is 1/2 aging life. 57F is 2x service life--Different from cycling life/or if you "kill" your batteries through over discharge, under charging, poor servicing).

    FLA batteries like to be >~40-50F for best power output. But can easily go well below freezing if kept charged. Li Ion batteries generally operating below freezing is not good.

    AGM batteries do not vent during normal operation. However if they are over charged and/or are getting old, they do vent--So both FLA and AGM Battery banks should be vented to the outside (prevent hydrogen build up during charging, and sulfur/rotten egg smell from electrolyte "mist").

    You probably know much/all of the above, but that is where I would start. When you start connecting the "black boxes" together, review how the work as a "system" and that you do not get any unintended operations/current flow (i.e., battery bank running AC inverter running DC battery charger to charge the battery bank). Also, avoid other installation mistakes (such as you want all battery current running through the negative current shunt to main DC bus bar--Anything connected to the "battery side" of the shunt will be "invisible" to the battery monitor).

    Make sure no sharp edges that can cut cables. etc...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • minisolarminisolar Solar Expert Posts: 155 ✭✭
    Thank you so much Bill. 

    I will start adding connection and wiring to my diagram and then ask more specific questions.

    Btw, we haven't bought an RV. We decided to finish up our tiny cabin and later on expand it... I have a standard distribution box there which is fed by a female wall inlet that I plug my generator to. When I hook up the battery bank, ats, and so on - I will use that connection to feed my distribution box from my ATS via inverter/gen 
  • Wheelman55Wheelman55 Registered Users Posts: 174 ✭✭✭
    How are you connecting gen set to district box?  Are you using a cable with male plugs on each end?
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 3 - Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
  • minisolarminisolar Solar Expert Posts: 155 ✭✭
    Wheelman - I have this:

    And that feeds my dist box and a regular extension cord runs between gen and this adapter. I will now use the wires that run from this adapter to the dist box to connect my ATS to my dist box so it will alternate gen and inverter as the main feed. 

  • Wheelman55Wheelman55 Registered Users Posts: 174 ✭✭✭
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 3 - Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
  • minisolarminisolar Solar Expert Posts: 155 ✭✭
    I am considering burying pvc conduit the 50ft between my silence box location and power system... Especially since I need to splice the power from the gen to feed both ATS and IOTA. 

    the IOTA has a regular outlet plug on it for the gen feed so the feed to it from the generator will have to be via outlet. I can either put a regular heavy duty 20am outlet or should I go with a self testing gfci 20 amp outlet?

    I don't want to over do it and cause issues later on with the gfci interfering with things. 
  • minisolarminisolar Solar Expert Posts: 155 ✭✭
    I finally finished setting up my Cabin for my family to stay there (no RV!!! yeah!) and I am now ready to tackle the power system. Currently my cabin runs off my honda generator but I will need to have my battery bank and inverter set up asap. 

    General plan is to build a wooden "closet" that will mount on the outside of my cabin and will house the battery bank, inverter, ats, iota, and so on. Then I will use the generator at night to power my cabin and charge batteries at the same time. Then during the day I will use the battery bank and inverter for power. 

     I think Bill's approach to break it down works well. 

    Then let's start from generator to inverter and IOTA. 

    I will bury some 10/2 direct burial wire and run it to my generator. I will use a waterproof junction box to connect a male plug to the 10/2 so I can plug and unplug generator. 

    From there the 10/2 will run to my power system "closet". It will run into an electrical box that will feed a GFCI - that the IOTA will plug into and also run to the ATS. I think between iota and generator and between generator and ATS a 10/2 is more than enough. total run is about 35-40ft. 

    Any notes on this? 

    Next black box is the iota and the batteries.... 


    1. I am attaching the diagram of how I believe I should wire my batteries together. Can someone confirm this is correct? if not - then how? 
    2. Whats size wire do I use between batteries? 
    3. Is a 10/2 wire between IOTA and batteries sufficient? distance will be about 2-3ft. 
    4. How do I correctly wire the iota to the a batteries? 
    5. Should I have any circuit breaker between iota and batteries? Or maybe a switch? If Iota dies on my one day and need to replace it? 

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