Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

Hello all, please forgive me....this is totally new to me, both the interenet and my new, well older 5th wheeler....anyways I have 4 six volt batteries hooked up and it runs all my electrics in the 5th wheeler but would like to get a solar power system to get them recharged...they are trojan 105s ...any suggestions to what type of solar system I need to keep the deep cycle 6 volt batteries I might not be be able to get back to this site please send my info to "".....thank you....we are trying to get off the grid....God Bless....Mike


  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    Hi Mike,

    Welcome to the forum--I moved your post to its own thread... It will be much easier to follow the discussion about your system instead of being mixed in with a bunch of other issues (and hopefully will not remain "lost").

    Lets assume your batteries are 6 volts @ 225 Amp*Hour each wired in series parallel for 12 volt bank @ 450 AH capacity.

    The normal rule of thumb for such a system would be ~0.05 to 0.13 charge rate (below 5% is not great for charging batteries. Above 13% tends to be a waste of solar panels). If we throw in a 0.77 derating factor for solar panel and charge controller losses, your solar panel range would be:
    • 450 AH * 14.4 volts * 1/0.77 derating * 0.05 = 421 watts minimum solar panels
    • 450 AH * 14.4 volts * 1/0.77 derating * 0.13 =1,094 watts maximum
    Now for an RV--you may not even have room for 420 watts of solar panels, let alone 1,100 watts.

    We have sized your array for your battery bank... But we really do not know how much load you have on your battery bank to know if it is sized for your needs.

    For an RV, space and weight is at a premium--so your bank may not be as large as one would use in a cabin with the same power usage.

    Anyway--Conservation is your starting point (LED/CFL lights, energy efficient appliances, using propane for heating/cooking/refrigeration vs solar electric) etc. are the usual suggestions.

    Also, measuring your power usage with a Kill-a-Watt meter (AC) or DC Amp*Hour/Watt Hour meter and/or a Battery Monitor are all very helpful devices (and each has its place in your system--if not your pocket book :cry:).

    I will forward this post to your email address--But will probably find posting in the forum is your better option. The Q&A of forum posting usually works out much better and everyone can see your responses.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    I will post Mike's email response (I will have to add my 2 cents later in the day):

    I thank you so much for this info as I am below novice about these things....went to a couple of RV stores and had almost four different versions of what was needed....I have a 31 foot 1998 HitchHiker II Deluxe.....the refrigerator and freezer as well as the water heater and heating are all propane.....we are just wanting a good system to recharge the 4 six volt batteries that I believe have been set up as two twelve volts, but not I am a dummy at these electrical things....just wanted to be able to take our RV to places and to our property up in northern Washington State for a week or I was hoping that the ac and lights and tv and laptop would work on the batteries as I was told when they installed the 6 volt batters at the RV sales park when I bought this.....(...) ....we are presently hooked up at an RV park here in Bozeman, MT but are leaving back to our home in Pocatello, Idaho, about 250 miles away tomorrow.....we are learning about everything......but my biggest thing is wanting to be completely off the grid for weeks or months at a time....this is why I am looking into solar and got those batteries..if you can suggest anything else I will greatly appreciate it....I am also going to the website to see if anyone posted anytthing...again thanks Bill, but now that I and the wife are retired, (,,,) we just want to travel a bit without worrying much......Mike,
    (some personal information redacted from email)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    Just as an FYI, We live off grid with 4 t 105s, and charge them just fine with 400 watts of panel into a MPPT controller.

    I second the notion of conservation first. We consume ~ 600 wh/day. It is nearly an ideal balance between PV/battery/size and loads.

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    it sounds like he will be semi-permanent for awhile when in the rv so whatever he can't fit on the roof of the rv can be remote ground mounted or all of it ground mounted if he likes. of course the security of keeping the pvs then becomes an issue if you must leave the rv alone as ground mounted pvs would be a delite for a thief.
    he still needs to size his loads to determine the pvs requirements. if lower than the battery min charge rate he should still go by the battery min charge rate. excesses over 13% can be consumed by loads running at the same time so this needs engineered in such a case as this.
  • bryanl
    bryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    A simple rule of thumb pertinent especially to RV's is at least a watt of solar for each pound of battery. Maximum is whatever you can get to fit.

    4 batteries at 60# ea implies a minimum of 240 watts solar.

    That would provide a maximum possible charge current of 20 amps and perhaps as much as a kWh usable energy per day or about a third to a fourth of the usable battery capacity.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    I wonder if this is really 6 V, or two banks of two 6's in series for 450 Amp/hrs @ 12 Volts.
    It'd make a difference.

    In a standard off-grid configuration this would require something along the lines of 800 Watts of panel to properly charge.
  • System2
    System2 Posts: 6,290 admin
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    Forgive me if I am as stupid as it appears, but we, wife and I, are totally new to this RVing and just want get things straight...from what I understand all four 6volt batteries are hooked up like one, well one to another and another, crap...I apologize but the diagram shows all 4 six volt batteries connected, if that is 240wats enough or 400 watts...again I do appreciate any help...right now we are in Bozeman, MT at a RV campground but leaving back home tomorrow....just want to get everything right before we begin our cross country one or two or more month journey then to our property to be off the gird for as long as we can......thanks...:confused:
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    It's a question of: are all the (+) posts tied together and all the (-) posts together, or is it like this:

    (-) Battery 'A' (+)---(-) Battery 'B' (+) [series connection]


    (-) Battery 'C' (+)---(-) Battery 'D' (+) [series connection]

    The the (-) on Battery 'A' and Battery 'C' are connected and the (+) on Battery 'B' with the (+) on Battery 'D' [parallel connection]

    It is possible the system is 6 Volt, but highly unlikely. It doesn't matter for the size of the array (Tony's calc is at the 5% minimum - he's something of a miser in power use :p) because the total Watt hour capacity is the same. It makes a difference for the charge controller or any battery charger.

    It is also possible (but unlikely) that all the batteries are in series, making it a 24 Volt system.

    The recommended and generally accepted charge rate for FLA's is 5 to 13% of their '20 hour' Amp/hr rating. In the case of T105's this is 225 Amp/hrs each. Parallel connections increase the Amp/hr capacity, but not Voltage. Series connections increase Voltage, but not Amp/hrs.

    My guess is it would be a 12 V 450 Amp/hr battery bank. 5% = 22.5 Amps minimum, @ 14.2 Volts (charge) which is 319.5 Watts. Panels do not put out their nameplate rating; usually you have to give them an 'averaged' rating in good sun. Normally this is about 80%, so 319.5 / 0.8 = 399.375 roughly the 400 Watts Tony uses.

    In and RV you have the difficulty of not getting good orientation, so you may need more panel. Long wire runs shouldn't be an issue here (it is in fixed locales) but heat can be. This is why I "shoot for" 10%. Merely replacing the "used" Amp/hrs is easy; the tricky part is hitting that charge rate (5-13%) to decrease sulphation and keep the electrolyte mixed.

    You have to remember that any loads used while charging (which is normal) effectively decreases the charge rate: 20 Amps in and 5 Amps out means the rate is really only 15 Amps.

    Clearer? Or more confusing?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    Usually RV systems are 12 volt DC (large trucks may be 24 VDC).

    Put two 6 volt batteries in series (+ to - like stacking cells in a flash light) and you get 12 volts DC.

    Take two 6 volt series string (12 volt total) and connect them in parallel (+ to + and - to -), the voltage stays the same, but you have twice the current output.

    Perhaps this link will help you understand series and parallel for batteries.

    Assuming your RV power system is 12 volts (more than likely), then we know know that you have a 12 volt (two 6 volt batteries in series) and 450 Amp*Hours battery capacity (two 12 volt 225 amp strings in parallel equal 450 amp*hours).

    Assuming that is all wired correctly for the moment (and you have a 12 volt system)... We can give you an estimated amount of solar power. From my first post, a good range for that size battery bank would be in the 400 watt to 1,100 watt range of solar panels. (we still don't know how much power you use in a day--but lets start here for now).

    Looking at our hosts website--for the best bang for the buck ($$$/watt), you would choose solar panels that are 100 watts or larger. Take a look at this link and find out what panels will fit your roof space (or some people mount the panels on the side of the RV and swing them out when parked -- aimed at the sun -- tilting towards sun can be helpful during winter/northern latitudes to generate more power).

    Say you can fit 4x Kyocera KD135GX-LPU 135 Watt 12 Volt Solar Electric Panel ($400 each currently).
    • 4x 135 watt panels = 540 watts total power.
    To mount the panels--ideally it would be great to get tilt kits so you can prop. the panels up during winter, and lay them near flat in summer. However, not everyone can/wants to climb on the roof to do the adjustments--so they simply mount flat.

    Depending on where you are located, you may range from from 2.5 to 6.7 hours of sun per day (Helena Montana, winter/summer). And an off-grid solar system with AC inverter is around 52% efficient (solar panel to charge controller to battery bank to AC inverter to AC power). So, a 540 watt system would generate:
    • 540 watts * 2.5 hours of sun * 0.52 = 702 Watt*Hours in December
    • 540 watts * 6.7 hours of sun * 0.52 = 1,881 Watt*Hours in July
    You will hear many people ask about Amp*Hours in regards to your battery bank... Watts and Watt*Hours divided by bank voltage (12 volts in your case) equal Amps and Amp*Hours:
    • 702 WH / 12 volts = 58.5 AH (at 12 volts)
    • 1,881 WH / 12 volts = 156.75 AH (again at 12 volts)
    To mount your solar panels, you can look around here:

    RV Panel Mounts

    For a 12 volt controller, you would be looking at:
    • 540 watts of solar / 14.4 volts charging = 37.5 amps
    A very nice solar charge controller for that range would be:
    The MPPT controllers are very nice--but if you are on a budget, the PWM will work OK for you too.

    Lots of FAQ's to read:

    All About Charge Controllers
    Read this page about power tracking controllers

    Deep Cycle Battery FAQ

    Here is a nice thread about equipping a small trailer with a couple of solar panels and a 15 amp MPPT type solar charge controller. Also includes a youtube video -- gives you a good idea of what an installation can look like. Also includes a Battery Monitor so you can see how they work too.

    Again--without knowing your actual daily loads (Watt*Hours or Amp*Hours), these panels may be enough or not... For example:
    • 100 watt light * 6 hours = 600 Watt*Hours
    • 100 watt light * 6 hours * 1/12 volt battery bank = 50 Amp*Hours @ 12 volts
    Some rough rules of thumb running your battery bank:
    Basically, you need to ensure the battery is not over discharged (ideally, don't discharge often below 50% state of charge and never discharge below 20% state of charge -- running battery dead can kill them), and recharged back to over 90% at least a couple times a week (if you are living full time--for best battery life). Also, don't store your battery bank under ~75% state of charge for longer than a day or so... Will not kill battery but storing lead acid batteries below 75% state of charge for weeks/months will sulfate them (sulfate hardening is not usually reversible and reduces battery bank storage capacity).
    If you are not electrically inclined--you can specify/order the hardware you need and get somebody local to help you install (you drill/mount/seal--they wire and test).

    It is not difficult to wire up--but batteries pack a lot of current and it is easy to draw some big arcs/short circuits... Fire and damaged components are a real possibility if wired incorrectly.

    I cannot help you directly--You really need somebody local to help you with the install. However, NAWS or other retailers should be happy to put a kit together (and quote) if you give the basic hardware requirements (XXX watts of solar panels, YYY model of charge controller--the vendor supplies fuses, wiring, mounts, combiner boxes as needed, etc.).

    I gave you links to our host NAWS... But you are welcome to purchase anywhere that make sense for you. We are here to help no matter where you pick them up.

    Be careful of kits from places like Northern Tool and such... Check out the hardware closely. Frequently they are less expensive amorphous solar panels and simple 2 stage PWM charge controllers. And, many times, they really do not perform all that well (solar panels do not output rated power and such).

    Camper World may have kits that will work OK -- But price out their solutions vs other suppliers and see which works best for you.

    We have not discussed your 120 VAC power inverter... We can talk about that a bit later when you are ready.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    Re: Totally New at this needing HELP WITH RV 6volt battery Recharger Solar

    As I think you mentioned earlier, and as 'Coot suggests, it is likely that your four 6V batteries are in a series-parallel configuration. This would be common for a RV where most systems are 12V. Batteries connected this way double both the voltage (6 becomes 12) and the AmpHour rating (220 becomes 440) Which, by the way, can be converted to WattHours if you multiply by the system voltage, in this case 12, which yields 5280 WattHours.

    I don't mean to overwhelm you with electrical and mathematical concepts, but if you intend to do any of this work yourself (or want be confident that the work of those you may hire to do it is adequate and safe,) you will need some understanding of those concepts.

    You say that you are new to RVing and to solar. Those are two big bites that may be hard to swallow all at once. I suggest that you learn as much about your RV as you can ( seems like a good place to start) before doing the solar modifications. Try to stay at campgrounds that have 120V hookups (and perhaps potable water and sewers, called black water by RVers.) Then when you are comfortable in your new home and have a better understanding of your usage and needs it will be easier for you to size your PV system and avoid the READY, FIRE, AIM pitfall that memeber Tony has coined.

    To add some perspective, I do have some electrical and camping experience. Yet, I spent 6 months last year researching how to add a PV system to my tiny camper. This forum was the best resource I found to facilitate the completion of that project, but I did use others as well. I installed the system on August 1, 2009. It has been working very well, but I am still learning how it works and looking for bugs I may have missed.

    And my camper is parked. I have not taken it on the road yet, although at some point I intend to do so.

    Edit: Marc and BB. have chimed in and you should pay heed to what they have to say. They provide many more details about the way to do it than I do.

    But still, I recommend that you take some time with your RV. Get acquainted with it and while you do that, get acquainted with PV.

    Hope this helps.

    Good luck and.... Enjoy!