Battery connector wire

Skip3
Skip3 Registered Users Posts: 13 ✭✭
edited December 2019 in Solar Beginners Corner #1
I plan to have a 12 100ah battery bank for a total of 1200 amps.  I will be using a 4000 Watt inverter.  I know that I need to keep the wire as short as possible and will be using 4/0 wire to the inverter.  My question is about the individual connecting wires.  I plan on using 12" connections.  Since 4,000 wats/333amps is the most that can be pulled would 1/0 wire be sufficient?  Would I lose to much current or should I go larger?

Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    In theory, I think each parallel connection should provide 1/12th of the current.  At the inverter low battery cut-off voltage of ~10.5v, and assuming the 4kw is the sustained (not surge) rating, 4000w ÷ 10.5v = 381a ÷ 12 connections = ~32a per connection.  In actual use, there will likely be variances in current.

    Each parallel connection should be fused so a short-faulted cell/battery can't be fed by the other 11 batteries, with the fuses sized to protect the parallel wire size used.

    With 12 batteries and 12" wires, I assume you're connecting to substantial copper + and - busbars?  If not, you may want to consider wire layout:

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

    Keeping 12 parallel batteries evenly charged/discharged will likely be challenging, especially with such a large inverter.  A DC clamp meter may be helpful in monitoring current and catching differences before batteries are damaged.
    Off-grid.  
    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
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    You may also want to reconsider the system voltage and/or battery choice.  Ideally, you want to use big enough batteries so no more than two parallel strings are needed.  For 1200ah@12v you could use 6 individual 1200ah 2v cells, for example.  This prevents problems with under/overcharging in parallel, and has only 6 cells to check/water (vs 72 in a 12 x 12v parallel bank).

    If a 4kw inverter is really needed, a higher system voltage may make more sense.  Besides reducing/avoiding parallel issues, you get more bang for the buck with charging gear.  1200ah@12v is the same storage as 300ah@48v for example.  A single 45a charge controller might work at 48v, but a 12v bank would want 4 of them.
    Off-grid.  
    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: 33,431 admin
    More or less, the minimum recommended battery bank size (typically for flooded cell batteries--AGM, Li Ion, and others can sustain a higher surge current)... So:
    • 12 volts ~ 100 Amp*Hour per 250 Watt inverter --- 4,000 Watt / 250 Watt per 100 AH @ 12 volts = 1,600 AH @ 12 volt minimum FLA battery
    • 24 volts ~ 100 AH per 500 Watt inverter => 800 AH @ 24 volt FLA battery on 4kW inverter minimum
    • 48 volts ~ 100 AH per 1,000 Watt inverter => 400 AH @ 48 volt FLA batt+4kW inverter minimum
    Note, the above use the same amount of stored Energy (Energy = Volts * Amp * Hours = Watt*Hours of storage). So, physically, all of the above battery banks are (roughly) the same size and weight (and similar costs for the "whole bank" of batteries).

    Placing 10 batteries in parallel, using 12 volt @ 100 AH batteries for a 12 volt, 1,200 AH battery bank--I would highly suggest to not configure a bank that way... I suggest that more than ~3 parallel strings becomes more difficult to buy (expensive for wiring, connections, fuse/breaker per battery) and lots of connections to check, and if flooded cell, lots of cells to check electrolyte levels/specific gravity on.

    If nothing else, I would suggest 6 volt @ ~200 AH "golf cart" batteries. Easier to check cells (instead of 72 cells to check on 12x 12v @ 100 AH batteries, only 36 cells to check on 6 volt @ 200 AH batteries in 6 parallel strings). I like to use 2x 6 volt batteries in series--Makes it much easier to do a "sanity check" of your battery bank health--You can check the voltage of each 6 volt battery. With 12 volt batteries in parallel, you cannot use a voltmeter to check "each battery voltage" without having to discussion each battery for a voltage sanity check.

    If you are after low cost, 6 volt @ 200 AH golf cart batteries are hard to beat. Otherwise, there are other batteries (and cells) that are >>100 AH capacity. They are typically a better solution, but probably will not be cheap.

    Of course, designing your battery bank really depends on your loads (Watt*Hours, peak Watts), charging system (solar/genset/AC Mains), etc...

    If you run/start the load only a few times per day, then a small(er) battery bank may work for you... If the load(s) run many hours per day, then you (probably) need a much larger battery bank.

    For a "reliable" off grid inverter system--Typically suggest around a 1,200 to 1,800 Watt maximum AC inverter. It is very difficult to send heavy current at 12 volts over any distance (voltage drop issues would require very short/heavy copper cable).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    edited December 2019 #5
    Thanks to everyone for the information.  This system is for a motorhome. There will be 1600 watts of solar panels on the roof in two parallel strings of 800 watts each.   (8 200 watt panels)They will go into two 85 amp charge controllers in parallel.  It is going to be difficult to balance the bank. I haven't got that all figured out yet. I was using a 4000W inverter because it is split phase and I can run it straight in to power the 50 amp panel. Although it would be rare there is a possibility that there will be a 3000 watt draw particularly with start ups. I was staying with 12 volt so I didn't have to step down to power all of the existing 12 volt circuits.   The load will be 24\7  although during the night much less.  CPAPs, tv and furnace mostly but still enough to need to do some pretty good recharging and I tried to take in consideration cloudy days.  I will take another look at a higher volt system.  The batteries will be AGM  
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    If you have not already bought the batteries, consider looking at 2V AGM cells, and wiring in series.   Much less hassle
     Or going to a 24V system, much safer to wire.
    You could use a "small" 12V 200ah system with a 300w pure sine inverter, to power the small things (CPAP, fan ....) and reserve the huge bank for the larger loads.

    Something else worth looking into is a small inverter generator to recharge at selective times, instead of trying to take a big drink of solar and ration it out over a couple of days.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Skip3 said:
    ..... Since 4,000 wats/333amps is the most that can be pulled would 1/0 wire be sufficient? ......
    1/0 wire good for 150A,  sometimes 170A with hi-temp insulation.
      NO


    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    Thanks Mike.  I have been toying with the idea of also installing a second smaller pure some wave inverter but running it to dedicated outlets to power those items at night and also for tv and laptops when there will be less loads (no microwaves etc). I had planned on connecting it to the same bank with a transfer switch between it and the larger 4000 watt pure some wave inverter.  The smaller inverter would have a much smaller draw just for itself.  If I was running them off the bank, I wouldn't have to charge two separate systems. That would work, right?
  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    edited December 2019 #9
    Oh also originally I had planned on using 4\0 wire for battery connector and connection to the inverter. Then I started reading here and on other forums where others had used smaller wire for the connectors. Didn't make sense to me but I thought I should ask.  Thanks

  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    I am concerned about where to connect input from the charge controllers and output to the inverter for balance.  I have limited space in which to place the battery bank in the motorhome. Right now I am planning to have two levels of 2 rows of 3 batteries side by side, one level directly above the other in one of the outside (basement) storage compartments. I will be combining the output from the two parallel controllers and using 4 gauge wire to the bank.  Even though I am using agm batteries and they will need little maintenance other than replacement, I am using 12 - 100 ah instead of 6 - 200 ah  because of the weight. I am old (76 lol) and it will be hard enough installing 68 lb batteries but impossible for 120 lb batteries which the 200ah weigh.  
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Wiring specifications for current capability has quite a wide range of acceptability... For example, here is the NEC chart:

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    And a marine wire chart:

    https://baymarinesupply.com/bosns_corner_wire_sizes

    For 14 AWG wire, NEC has a maximum of 15 amps, and Marine has 35 amps.

    Both have deratings for temperature, number of conductors in a bundle, etc... And Marine SAE gauge is slightly smaller than AWG gauge.

    NEC tends to be more conservative, and seems to be more "exact" (classes of insulation/temperature) than Marine (at least the quick charts I could find).

    Note that wire heating equation is Power=Current^2 * Resistance... So if you have 2x the current going down the same wire, you have 4x the heating (or you need 4x heavier wire for 2x the current).

    And then there is voltage drop... Say you want to run your battery down to 11.5 volts (12 volt bus). And you assume that your AC inverter has a 2x surge rating and a 10.5 volt cut off voltage (low battery shutdown). That means a 4,000 Watt inverter with 8,000 Watt surge, and 1.0 voltage drop (for surge). And lets guess you have 4 feet (one way wire run for this drop calculator, some use round trip length)... Playing with the numbers for a 1.0 volt drop:
    • 8,000 Watt surge * 1/0.85 inverter eff * 1/10.5 cut off voltage = 896 Amps (surge)
    Using 896 amps, 4 feet one way run, and 1.0 volt max drop:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.4066&voltage=11.5&phase=dc&noofconductor=1&distance=4&distanceunit=feet&amperes=896&x=66&y=23

    1/0 AWG cable, 4 feet, 896 amps, 11.5 volts at battery:
    Voltage drop: 0.89
    Voltage drop percentage: 7.72%
    Voltage at the end: 10.61

    The same thing at 48 volt battery bus, 42 volt cut off, etc.:
    • 8,000 Watt (surge) * 1/0.85 AC inverter Eff * 1/42 volts cut off = 224 amps
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.634&voltage=11.5&phase=dc&noofconductor=1&distance=4&distanceunit=feet&amperes=224&x=48&y=12

    7 AWG cable:
    Voltage drop: 0.89
    Voltage drop percentage: 7.76%
    Voltage at the end: 10.61
    • 4,000 Watts * 1/0.85 inverter eff * 1/42 volts cut off = 112 amps max continuous
    From NEC table, would need around 2 or 1 AWG cable minimum for 112 Amps continuous (I like to multiply the current for battery wiring by 1.25 to derate the wiring a bit more--Both to keep the cable cooler, and to rate the fuses and breakers (a 15 amp breaker will eventually "trip" at 15 amps and at 1/1.25 or 0.80x current not trip at 12 amps).

    Note that a smaller AC inverter mixed with a larger AC inverter (such as the nice 12 volt 300 Watt MorningStar and a 4 kWatt 48 volt inverter) is not "easy"... You should never "tap" 12 volts from a 48 volt battery bank... The 12 volt batteries will discharge more than the whole 48 volt string and cause your batteries to be "unbalanced" and give you charging problems.

    These days, there are smaller 48 volt inverters available, so you can mix a 48 volt 250 Watt to 600 Watt smaller inverter (for your normal lower power loads) and a 4 kW 48 volt inverter for when you need some power tools:

    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_input_voltage=439

    In any case, having a large battery / AC power system in an RV for random usage--Many times, it is just better to fire up the genset for those times you need the high current, and use a smaller/lighter/cheaper solar power system for the other 95% of the time.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    You really need to start with your loads... And conservation is key. For example, your CPAP can use a fair amount of energy overnight if it has a "boiler" to increase the humidity. There are portable units that are designed to run from batteries that use much less power.

    And then there are the hours of operation per day... For example, you may use a 1,500 Watt Microwave 15 minutes per day, and a 30 Watt laptop computer for 12 hours per day (work, watch a movie, browse the web). Vs a 300 Watt desktop computer system:
    • 1,500 Watt microwave * 1/4 hour per day (15 minutes) = 378 Watt*Hours per day
    • 30 Watt laptop* 12 hours per day = 360 Watt*Hours per day
    • 300 Watt desktop computer * 12 hours per day = 3,600 WH per day
    Use a Kill-a-Watt type meter to measure your AC loads (and pick the most efficient) over a ~24 hour period at home... You can see a heavy load used a short time can be relatively small total energy usage per day vs a small laptop or full size desktop computer 12 hours per day.

    https://www.amazon.com/s?k=kill+a+watt+meter

    There are similar meters for DC bus equipment too.

    Not trying to tell you how much energy you need in your RV... Your choice and needs dictate your needs (energy usage is a highly personal set of choices)... Just trying to show you how those choices can affect your power system.

    Just to give you some round numbers...
    • 500 WH to 1,000 WH per day--Small cabin (LED lights, 12 volt RV water pump, charge cell phone, run small laptop)
    • ~3,300 WH per day--Add a full size refrigerator, clothes washing machine, "solar friendly" well pump, LED TV, etc.
    • 10,000 to 30,000 WH per day--Typical North American home
    For the smaller system, 12 VDC usually works OK. For the 2nd, 24 or 48 volt bus, and any larger, generally 48 volt bus.

    Not to say that something cannot be done, but suggest that you build a few "paper" system designs first and see how they would work for your needs (energy) and how much they cost/weigh/space for your RV.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Skip3 said:
    ...
    , I am using 12 - 100 ah instead of 6 - 200 ah  because of the weight. I am old (76 lol) and it will be hard enough installing 68 lb batteries but impossible for 120 lb batteries which the 200ah weigh.  
    Using lower voltage & higher capacity batteries doesn't necessarily mean too heavy.  For example:
    https://www.solar-electric.com/concorde-sunxtender-pvx-5340t.html

    62lbs for a 534ah 2v AGM battery.  To get ~1100ah@12v, you'd use two parallel strings of 6 batteries.  Still 12 batteries, but only 2 strings in parallel instead of 12.
    Off-grid.  
    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: 33,431 admin
    And a 12 volt @100 ah should weigh exactly the same as a 6 volt @ 200 ah battery  Same amount of stored energy.

    12v x 100 ah = 1,200 wh
    6v x 200 ah = 1,200 wh

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    Bill, thank you for all your help and time.  I had figured my draw under the worst circumstances would around 8000 watts per day. Due to some of my wife's health issues we will  need to run the air conditioner at times even though we  will try to travel to the right climate to achieve that. But that would be worst case. I also know that 6 hours of bright Sun on 1600 watts of panels will not completely recharge a 1200 ah bank. On those occasions I will use the generator. Since we will probably boondock  90% of the time I want to use the generator as little as possible. 
    You have given me a lot to consider and I have some more questions which will show I still have some to learn. I hope I am not asking too much.  

    OK on the 2 volt batteries, I like that a lot  but by my calculations from the website the cost would be 4108 dollars.  Nearly twice what either the 12 or 6 volt batteries to achieve 1200 ah. So for me I can't make that choice. I have noticed that some do use the 6 volt 200ah batteries and I don't know the advantage so I hope you can fill me in on that. If I understand correctly you would have to run 2 batteries in series to get 12 volts then run each of those two in parallel to get the 1200 ah  I suppose that you could run two strings of six batteries and combine the strings. But wouldn't there be the same problem with the controller connection for balancing?  I know I'm missing something that makes the 6 volt 200ah serries/parallel system better.  Either system will require me to use two rows on two levels directly above each other. If you could help in how to connect them the best way to get a balance I would greatly appreciate it and why the 6 volt system might be better


  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Skip,

    Regarding the batteries... 6 volt @ 200 AH batteries are very high volume and tend to be low cost (Golf Carts).

    I also like them because if you are using a 12 volt system, you have 2x 6 volt batteries in series... So you can measure/estimate the health and state of charge of each battery in your 12 volt x YY parallel strings. With just a bunch of 12 volt batteries in parallel, you have one voltage you can measure--The "12 volt" bus. If you have "problem batteries", you cannot quickly find them with just a simple voltage test--Your other option is to disconnect each parallel 12 volt battery so you can measure the individual battery voltage and gauge health (or if Flooded Cell, measure the SG of each cell can also tell you a lot).

    For me, I have a rule of thumb that battery strings between 1 string and 3 parallel strings is, more or less, a suggested ideal battery bank configuration. Managing more than 3 parallel strings, you have more electrical connections, more cells/batteries, more fuses/breakers, etc. that can get loose, corroded, go bad, etc. And each string of 12 volt batteries is 6x 2 volt cells to measure SG and electrolyte levels.

    With 6 volt @ 200 AH batteries, you would need only 1/2 the number of parallel strings vs 12 volt @ 100 AH batteries (so 1/2 the cells to check, 1/2 the wiring, etc.).

    Placing 12x parallel strings of 12 volt @ 100 AH batteries in parallel--Sure it can be done... But it could be really difficult to maintain and find problems before they cause more problems...

    FLA batteries are still pretty good price/performance--But for RVs, they tend to be large and heavy. Li Ion (specifically LiFePO4--Lithium Iron Phosphate) are a popular alternative for RVs and other applications--But LiFePO4 batteries are not yet cheap--And they do have other issues that you need to understand before jumping in with both feet.

    Next post, some math...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Just to clarify a term or two... Watts is a rate, like Miles Per Hour. Watt*Hours is an amount, like Miles Driven (60 mph * 5 hours = 300 miles driven... 100 Watts * 5 hours = 500 Watt*Hours).

    So, let us look at what a 1,600 Watt solar array can produce. I know that you are talking about an RV, but I will pick Orlando Florida for the "hours of sun" math...

    We have two calculations we make for sizing solar arrays to battery banks... One is the rate of charge for the battery bank. The second is hours of sun and how much energy per day can be harvested...

    For charging an FLA battery bank, I suggest 5%-10%-13%-20% or so... 5% can work for a weekend/seasonal/sunny weather system... 10%+ suggested for a full time off grid system (RVs--many times space limitations for panels force a 5% array + genset/shore power usage to keep batteries properly charged--And many folks RV during good/sunny weather). With you, living most of the year in an RV, 10% minimum rate of charge suggested. That would suggest a FLA battery bank maximum size of:
    • 1,600 Watts * 0.77 panels+controller derating * 1/14.5 volts charging * 1/0.10 rate of charge = 850 AH @ 12 volt battery bank maximum
    • 24 volt bank => 850AH/2 = 425 AH @ 24 volt battery bank (same energy storage, better battery bus voltage)
    • 4x 6 volt @ 210 AH in series (24 volts) x 2 parallel strings (420 AH) battery bank suggested
    And for your solar charge controller, 24 volt battery bank saves you from having to get 2x MPPT solar battery chargers:
    • 1,600 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 85 Amps charging 12 volt bank
    • 1,600 Watt array * 0.77 panel+controller derating * 1/29.0 volts charging = 42.5 Amps charging 12 volt bank
    A typical higher end solar MPPT charge controller is around 60-90 Amps capability... So you would only need one medium size controller on a 24 volt battery bank.

    And then there is figuring how much energy per day you can harvest. Lots of things affect harvested energy.. Flat array to roof vs tilted, where you will be located, seasons, etc... For this example, assume you are using a flat array (to roof), Orlando Florida:
    http://www.solarelectricityhandbook.com/solar-irradiance.html
    \

    Orlando
    Average Solar Insolation figures

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

    JanFebMarAprMayJun
    3.21
     
    3.90
     
    4.86
     
    5.78
     
    6.24
     
    5.53
     
    JulAugSepOctNovDec
    5.43
     
    5.06
     
    4.52
     
    4.15
     
    3.47
     
    3.02
     

    Over 4-5 hours per day, is a "good harvest". Less than 3 hours per day during winter, is getting towards poor harvest. Typically, for an off grid home, suggest the poorer 3 months may need genset backup, leaving Feb at 3.90 Hours of sun per day as the "break even" month. Your array would harvest:
    • 1,600 Watts * 0.52 end to end off grid system eff * 3.90 hours of sun per day (February average) = 3,245 Watt*Hours per day
    And lets estimate your summer energy harvest at 5 hours per day (A/C needs).
    • 1,600 Watts * 0.52 end to end off grid system eff * 5.0 hours of sun per day (summer average) = 4,160 Watt*Hours per day
    And lets say you use a Mini-Split inverter type A/C system that averages 400 Watts for 10 hours per day:
    • 400 Watts * 10 hours per day = 4,000 WH per day
    So, pretty much (guesstimate) A/C system could use 100% of your daily summer harvest pretty easily.

    A  425 AH @ 24 volt battery bank (FLA) would support maximum AC inverter of (roughly):
    • 425 AH (at 24 volts) * 500 Watts per 100 AH (at 24 volts) = 2,125 Wattage suggested maximum AC inverter size
    And if your battery bank is planned for 2 days of storage and 50% maximum discharge:
    • 425 AH * 24 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 2,168 Watt*Hours of suggested max energy usage per cloudy (no sun) day (stormy weather, etc.).
    There can be other options--There are mini-split A/C systems that run only from solar (if hot and sunny, A/C system runs from solar panels directly)... Saves designing a battery based system to run the A/C.

    https://hotspotenergy.com/solar-air-conditioner/ (I don't know anything about company or product--Just a starting point for research)

    Anyway... Without "real energy usage" numbers--The above is really all just a guess. More or less, if you are running lights, water pump, small fan, laptop and phone charging... 1,000 WH per day is enough power for that. If you are running a full size refrigerator, closer to 3,300 WH per day (includes a washing machine, TV, etc.). Assuming otherwise propane for cooking/hot water and refrigerator (for 1,000 WH per day system).

    A/C--Even more power hungry that a full size refrigerator... Hard to do with an RV.

    Not saying you cannot do it--But the numbers are looking a bit bad unless you do lots of conservation (insulation, awnings over windows to keep summer sun out, etc.) and you have "real numbers" measured for your A/C system (pick the smallest/most energy efficient version you can).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
    Skip3 said:
    Bill, thank you for all your help and time.  I had figured my draw under the worst circumstances would around 8000 watts per day. Due to some of my wife's health issues we will  need to run the air conditioner at times even though we  will try to travel to the right climate to achieve that. But that would be worst case. I also know that 6 hours of bright Sun on 1600 watts of panels will not completely recharge a 1200 ah bank. On those occasions I will use the generator. Since we will probably boondock  90% of the time I want to use the generator as little as possible. 
    You have given me a lot to consider and I have some more questions which will show I still have some to learn. I hope I am not asking too much.  

    OK on the 2 volt batteries, I like that a lot  but by my calculations from the website the cost would be 4108 dollars.  Nearly twice what either the 12 or 6 volt batteries to achieve 1200 ah. So for me I can't make that choice. I have noticed that some do use the 6 volt 200ah batteries and I don't know the advantage so I hope you can fill me in on that. If I understand correctly you would have to run 2 batteries in series to get 12 volts then run each of those two in parallel to get the 1200 ah  I suppose that you could run two strings of six batteries and combine the strings. But wouldn't there be the same problem with the controller connection for balancing?  I know I'm missing something that makes the 6 volt 200ah serries/parallel system better.  Either system will require me to use two rows on two levels directly above each other. If you could help in how to connect them the best way to get a balance I would greatly appreciate it and why the 6 volt system might be better


    Perhaps a used lithium battery pack from a Chevy Volt? I think Bill Von Novak champions this idea. I don't know much other than that - lithium is super light. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    Bill, thank you very much.  I really appreciate the information on a 6 volt battery system. I do understand the problem of the current draw of an air conditioner and plan to move geographically so I can avoid it's use. I also plan on installing a split mini a/c or a 5000 btu  window unit just in case I would need to run it a couple of hours a day and will run the generator as necessary. I really wish I could afford lithium  being able to discharge more 50% and better weight would be nice. Maybe I'll win the lottery.😊  You have given me a lot to consider, thanks again. Do you live in the Orlando area?

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited December 2019 #20
    Hi Skip,

    I live just south of San Francisco, California. We only have "hot weather" for a few weeks a year in late summer generally... And sometimes not even that.

    I will leave it to folks that live in warmer climates and actually use solar off grid and see if they have anything to add... I use math a lot of "model" systems--So that the poster can then configure and price out a system with little other facts. It focuses the thoughts--But it is still not real life.

    You can discharge FLA storage batteries to as low as 20%--Just as long as you get them back on Charge ASAP (lots of solar, genset, shore power, etc.).

    Lithium have lots of good features--But cost, and building out smaller battery banks (because of high costs) are definitely a drawback.

    Just to finish up... Lead Acid work well in sub freezing installations (cold batteries do have less usable capacity). Li Ion typically cannot charge/discharge much below freezing (32F/0C). And Li Ion, if there is a fire, can output very dangerous fumes (hydrofluoric Acid--I guess depending on exact chemistry, heat of fire, etc.). If there is HF acid, having to dispose of everything that may have been near the fire (firemen have had to get rid of hoses and equipment after Li Ion house/grarage fires). And HF Acid, is really scary around humans/etc.

    I have a few Li Ion flashlights, and everyone has laptops (many with Li Ion batteries)... But otherwise, I still stick with NiMH because I don't want to run the risk with more Li based batteries (and I do not have any battery based solar anyway--Our power here is more than reliable enough--At least until California started the utility grid shut downs a month or so ago--So far, just genset and stored fuel for that at this time).

    -Bill

    PS: Because I can see posters' IP Address, I can guess (sometimes) roughly where they are posting from... Saves a back and forth asking for location when trying to model a system.

    You can try this link to see what your IP address location report is:

    https://www.iplocation.net/
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Skip3
    Skip3 Registered Users Posts: 13 ✭✭
    Bill once again, thanks.  You have me thinking a lot more about Li batteries. Although the cost would be greater the pros of having fewer batteries is significant. Almost 1/3 of the weight, 1/2 of the storage space required, easier connection for balanced charging and easier on this 76 year old back!  I will have to consider the cold factor since when we start traveling we will no doubt have some sub-freezing weather. But it looks like I might have to start buying those lottery tickets. Lol.   Regardless of I do not use Lipo I will use am not fla.  Thanks for the tip on IP addresses.

    It will be a couple of months before I start the install but I will definitely contact you and let you know how it goes. I have a daughter in Sacramento.  Maybe when I travel to see her next year I can swing north and show you the results. 

    3.5 KW, impressive!