New guy needing assistance with RV solar system

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340driver
340driver Registered Users Posts: 11 ✭
in Solar Beginners Corner #1
Hey guys. I should start off by saying that I have no previous experience with solar, but I am excited about my project. I do have a fairly strong mechanical aptitude and will be installing the system myself. However, having read A LOT of information about solar, I feel that without proper guidance, I would make unnecessary mistakes in selecting the components and the overall design of the system. So, thank you in advance for those who take the time to share your experience with me.

I will start by telling you what I have and how I want to use it. My vehicle is a Ford diesel E350 cutaway box truck that has been converted into an RV. It has all of the components, to include: heater, fridge, vent fan, water heater, sit down shower, microwave, etc. I may be forced out of my current occupation (medical issue) and a divorce (2 kids) is on the horizon. I am being proactive in setting this vehicle up "just in case" things don't go well and I have to live in it for some period of time. My ultimate goal is to make it as "self sufficiant" as possible. What I mean is, I would like to design it so that I have as little need for shore power or a portable generator as possible. I would like to get the absolute most power from the system and plan to adjust my lifestyle (by modifying my need for electrical convieniences) to fit within the limitations of the system.

So, if any of that made any sense, the space I have available to me would allow for: (2) 140-150 watt panels and (4) 6 volt golf cart batteries. I also know that I can also utilize the alternator to assist in charging the batteries.

Where I am lacking, is in my understanding of the charging and use of the battery power. I believe I understand that a solar/alternator system will not "top off" the batteries and that the batteries should not be drained to below 50%. What I am having trouble grasping is how that will relate to my particular living situation. In other words, with the batteries not fully charged (ex. 80% and not being able to drain them below 50%, how does that translate into available power for the life necessities in the RV (lights, heater, water pump, radio, etc). What charging ability does a (2) 140 watt/(4) 6 volt battery ststem have? Would I be better off with only (2) 6 volt batteries (with a higher charge) or (4) 6 volt batteries with a lower charge? I relize that some of what I am asking is very broad and vague, but I am just trying to understand if the solar/alternator and available batteries will be enough to sustain my lifestyle (I do understand the concepts of amperage, watts and voltage) throughout the dark night-time hours and then replenish the system the next day to do it over and over again with only the occasional need for shore power or generator. Bottom line, is what I have available a possibility or is it a "pipe dream?"

Since I have a difficult time explaining it, I am sure that it is even more difficult understanding what I am looking for. Any advice would be greatly appreciated. I can provide as much information as possible to make things more clear. Thanks again for your help.
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  • Desert Rat
    Desert Rat Solar Expert Posts: 138 ✭✭✭
    #2
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    Re: New guy needing assistance with RV solar system

    A properly sized solar electric system WILL fully charge your batteries as long as your loads aren't excessive. The solar panels need to be pointed at the sun, so that means parking in a non-shaded area and tilting the panels to the proper angle. You might also consider having a panel or two on a moveable ground mount which could be positioned for maximum output. Lots of pertinent info in this thread: http://forum.solar-electric.com/showthread.php?18225-So-I-m-Confused-(what-a-concept)-)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: New guy needing assistance with RV solar system

    Welcome to the forum.

    Sorry to hear that life has "gone sour" on you. Most of us have been through similar situations and somehow survived, albeit not without scars. :blush:

    You've got one bit backwards: 280 Watts of solar panel would be able to top off the 440 Amp hour 12 Volt battery bank. What it will have trouble with is Bulk charging from a low SOC.

    What you could expect from that battery bank would be about 2kW hours AC power per day. What you could expect from 280 Watts of panel would be about 500 Watt hours AC per day. Here's the kind of ratio that works well: 220 Amp hours of 12 Volt charged at 10% = 22 Amps peak charge current. Multiply by 12 = 264 Watts / 0.77 (efficiency factor) = 342 Watt array. If the depth of discharge is limited to 25% the solar would handle it all then (providing good weather with at least 4 hours of good sun). But that would limit you to about 600 Watt hours of power per day.

    The good news is that you have a generator available. With some clever planning you can use that to do the Bulk charging stage and let the panels do the 'finish' (Absorb & Float if possible). You say you will have "shore power" available? If so, why not use it all the time? Or won't it be there all the time? Grid power is inevitably cheaper than off-grid in any form almost everywhere in the world.

    If you haven't already done so I suggest you read through the battery FAQ's to begin with: http://www.solar-electric.com/decybafaq1.html
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #4
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    Re: New guy needing assistance with RV solar system

    Sorry to hear about your situation.

    About 11 years ago I had a breakup, shortly after having a bunch of things stolen on a property where I was building an 'A' frame. What I did have was a camper on another property with a 200 watt array and a couple golf cart batteries, It was enough for minimal life enhancment things, light, some laptop time, and some TV/video. I had been use to an energy budget and that will be the hardest to get use to.

    Please note that,
    340driver wrote: »
    ...(lights, heater, water pump, radio, etc)...
    'heater' of any sort draw a good bit of current and don't belong in a small system, use propane for heating/cooking needs!

    Good Luck! Perhaps I can contribute more later. Holiday times are the hardest to deal with these things, For a day or 2, perhaps, think of the kids that represent the love you once had between you and not the current changes that creating the problems.

    All the best, Merry Christmas!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • 340driver
    340driver Registered Users Posts: 11 ✭
    #5
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    Re: New guy needing assistance with RV solar system

    Thanks for the kind words. It is interesting how things in life seem to come at you all at once. Ironically, I am writing this in the same room with my kids watching a Christmas movie and sitting 6 feet from our Christmas tree. My situation is advancing at a rapid pace and I feel it necessary to be prepared as quickly as possible. But, having said that, I am thankful that I have the opportunity and the resources (at least for now) to have a roof over my head. There are many that don't have that luxury.

    Well, it sounds like I may have a shot at making this work. I will address the heater issue with propane. The shore power that I refered to would be at the expense of staying in an RV camp ground. According to what I have read, the system needs to be fully charged "every once in a while" in order to keep the batteries hold a greater charge and have a longer life. I have read any where from once a week to once a month. My future financial situation is in question at best, so charging them at $25-$35 per night may be a struggle. On the other hand, mistreating the batteries and having to replace them prematurally would be much more difficult. How often should the batteries be "fully" charged?

    Does anyone have experience with having the alternator assist in charging the batteries? Is it very effective and worth the expense?
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  • 340driver
    340driver Registered Users Posts: 11 ✭
    #6
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    Re: New guy needing assistance with RV solar system

    I failed to mention that I have very little storage available (only a 10' box) for things like moveable ground mount panels. So, the ones that I mount on top will be all that I can have. I will have the generator as a backup and last resort (due to the expense to run it and not being able to run it at all in certain situations)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: New guy needing assistance with RV solar system

    It's more or less a matter of how long they sit below 75% SOC. This rapidly increases the rate of sulphation and thus severely shortens the expected lifespan.

    Standard off-grid practice is to plan on 25% DOD daily, with 25% "in reserve" for cloudy days. Then on the third day you start the gen if needed. I wouldn't want to be below 75% for more than three days, especially on a regular basis. You might want to consider a battery monitor http://www.solar-electric.com/metersmonitors.html to be on the safe side. Yes, I know: more money.

    It will be important to get some idea of how much power you need to supply. The more charging you can get from solar, the better as generators burn a lot of expensive fuel. I don't know how your budget is (probably lousy, like everyone else's) but the little inverter-generators are a better choice for over-all fuel consumption than the standard gens.

    Running the Ford to charge with sure wouldn't be economical unless you're using it to move on down the road at the same time. Typically you want to isolate the "house" batteries from the "vehicle" battery most of the time so that one system does not draw from the other. You can do this simply with a switch that will allow charging current to the house when driving (manually turned on/off - pain if you forget to) or an automatic battery isolator which does the same thing (but costs more). The vehicle alternator will not have the right charging profile for the deep cycle batteries, but it is capable of boosting them up through Bulk which is going to be the hardest part for the small amount of solar. With the parallel battery set (get the wiring right on that; it is critical to good performance. See this: http://www.smartgauge.co.uk/batt_con.html) you will need perhaps 60 Amps from the alternator at maximum charging. This shouldn't be a problem with most alternators, but it will require heavy wire (especially if the run is long) and proper fuse protection.

    Yes, it can be done. But there are a lot of options to wade through and a lot of trade-offs between cost/performance/convenience/longevity.
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  • johndowns
    johndowns Registered Users Posts: 4
    #8
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    Re: New guy needing assistance with RV solar system

    I am setting up a similar system and I am stuck on a few things. I have a 3800 international school bus and I'd like to use the alternator to bulk charge during the day while driving and a couple panels to top it all off. I have 4 t-105 6v 225ah batteries. So my questions to this point are...
    a) Are the batteries connected directly to the battery isolator or is there some sort of charge controller in between?
    b) Will the isolator always charge and maintain the starting battery first so there are never any starting/running problems?
    c) Can the alternator and solar panels both charge the batteries at the same time with no complications? If not what are the methods to deal with this?

    I'm really excited about this project but I don't want to waste money on some stupid amateur mistake. Thanks so much for any help.
    This is also the first time I've used a forum so I hope I'm doing it correctly and in the right place.
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  • westend
    westend Solar Expert Posts: 46 ✭
    #9
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    Re: New guy needing assistance with RV solar system
    johndowns wrote: »
    I am setting up a similar system and I am stuck on a few things. I have a 3800 international school bus and I'd like to use the alternator to bulk charge during the day while driving and a couple panels to top it all off. I have 4 t-105 6v 225ah batteries. So my questions to this point are...
    a) Are the batteries connected directly to the battery isolator or is there some sort of charge controller in between?
    b) Will the isolator always charge and maintain the starting battery first so there are never any starting/running problems?
    c) Can the alternator and solar panels both charge the batteries at the same time with no complications? If not what are the methods to deal with this?


    I'm really excited about this project but I don't want to waste money on some stupid amateur mistake. Thanks so much for any help.
    This is also the first time I've used a forum so I hope I'm doing it correctly and in the right place.
    I'll take a whack at this.
    A) your batteries will be in some way connected to an isolator, if done properly. For any kind of meaningful solar wattage, you will have a charge controller.
    B)An isolator doesn't charge, it is a switch, usually with relays. The purpose of an isolator is to switch charge current first to the starting battery and then to the "House" batteries. It interrupts current being delivered back to the house batteries so your starting battery isn't drained should those batteries drain completely. There are different types and functionality between different isolating devices.
    C) Yes, your alternator and the charge controller for solar will both limit current to the batteries as they are charged.

    A good place to read and learn: http://www.jackdanmayer.com/rv_electrical_and_solar.htm#The Golden Rules
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  • johndowns
    johndowns Registered Users Posts: 4
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    Re: New guy needing assistance with RV solar system

    Thanks for the whack. Let me try to be a little more precise with my questions.
    a) The isolator is wired and very close to the alternator. From there it is wired to the house batteries and starting batteries separating them. The question is, are the house batteries wired directly to the isolator? (are the house batteries self regulating as to how much current they accept from the alternator or do they need some sort of regulator? (no solar involved in this question)
    b) Does the alternator charge both battery banks through the isolator at the same time or does it switch back and forth? If it switches then does it prioritize the starting batteries? Here I am trying to determine whether or not I could accidentally starve the starting batteries of current from the alternator thus leading to under charged starting/running batteries.
    c) So the alternator and charge controller can be charging the house batteries at the same time with no complications from varying current (like driving through shade or slowing to an idle)? Also, does a charge controller only allow current one way so it could never back feed to the panels?

    The solar side of things seems easier to me. The trouble I'm having is finding info specific to systems with solar and alternator.
    Thanks again. And thanks for your patience with me trying to convey my questions through text.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
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    Re: New guy needing assistance with RV solar system

    often times the alternator will not complete the bulk stage of charging, but this can vary depending on the charging system in the bus and the battery requirements. being you have a bus you then have quite a bit more room to allow for mounting of pvs. it would be a misnomer for anybody to think the alternator can be that reliable in providing all of your power needs too. for instance, if the alternator is rated 80a then don't expect it to provide that consistently for 8, 10, 12, etc. hours every day as that is most likely not happening and the current is somewhat of a max rating. the rating is a peak output that soon slopes backward as the initial charge surge is given. once the battery is charged in a vehicle this tapers to just a few amps when you are driving to just keep the plugs firing and your lights and small electronics like your stereo going.

    basically what i'm trying to say is that pushing any alternator to the max for long periods will cause a premature failure.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
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    Re: New guy needing assistance with RV solar system
    johndowns wrote: »
    T
    b) Does the alternator charge both battery banks through the isolator at the same time or does it switch back and forth? If it switches then does it prioritize the starting batteries? Here I am trying to determine whether or not I could accidentally starve the starting batteries of current from the alternator thus leading to under charged starting/running batteries.
    c) So the alternator and charge controller can be charging the house batteries at the same time with no complications from varying current (like driving through shade or slowing to an idle)? Also, does a charge controller only allow current one way so it could never back feed to the panels?
    The CC will regulate the current it send to the house battery (it should be directly connected to that battery only.)
    A battery isolator can be built as a pair of diodes, in which case the CC connected to the house battery cannot charge the starting battery.
    Or it can be built using relays, so that when the relays are all closed (the alternator is running) the current from the CC may go to both batteries.
    You need to know what kind of battery isolator you have. Disconnect all three terminals. Now if an ohmmeter measures a connection from the alternator terminal to each of the battery terminals with one lead orientation, but no connection when you reverse the leads, you have a dual-diode isolator.
    If you have a permanent connection from alternator to starting battery but a one-way connection to the house battery, you have a single-diode isolator, which will not perform as well. It will always deliver a lower charging voltage to the house battery than to the starting battery, and is rarely used for that reason..
    SMA SB 3000, old BP panels.
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  • johndowns
    johndowns Registered Users Posts: 4
    #13
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    Re: New guy needing assistance with RV solar system

    Here is a crude diagram of what I hope to do. The batteries and vehicle are the only things I have already so I can get whatever I need to make it work. I am thinking of a TS-MPPT-60 controller and 2 245W Helios HV panels
                             starting batteries
Alternator-----isolator--<
                          4 t-105 house batteries-------charge controller--------2 245w panels
                              /             \
                       battery meter      inverter-------load
    Does this seem like it would put too much strain on the alternator?
    Are the T-105s wired directly to the isolator? and what is the best kind of isolator? the alternator is 130 amp.
    Any other obvious flaws with my plan so far?
    Thanks everyone.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #14
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    Re: New guy needing assistance with RV solar system

    To make your text graphic look reasonable, paste it inside CODE tabs (Go Advanced from the Reply window, then the # sign from the format bar).

    Like this:
                               starting batteries
Alternator-----isolator--<
                           4 t-105 house batteries-------charge controller--------2 245w panels
                                  /                         \
                        battery meter                     inverter-------load
    SMA SB 3000, old BP panels.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
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    Re: New guy needing assistance with RV solar system

    i think you may misinterpret my previous post too negatively, but i wanted you aware the alternator charge may or may not work. you will have to see what your voltage can reach to when charging the batteries compared to what the batteries call for for a full charge. if the voltage is shy of being able to charge them fully then a pv system may have enough voltage to give the full charge, but only if enough amps are supplied too. if you are draining power in your loads while attempting to bring the batteries to a full charge this will stop the batteries from attaining their full charge status. often times this could mean a shutdown of your loads or supplementing them with another source while you try to get your batteries to their full charge. charging up with a generator for the final 20% or so of charge may not utilize the generator's capabilities very economically, but can be done. it may be better to run the loads with the generator and solar give the final charge to the batteries at that point, but it could be supplemented with the same genny too while running the loads. too many variables involved and ways to make it work.
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  • johndowns
    johndowns Registered Users Posts: 4
    #16
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    Re: New guy needing assistance with RV solar system

    Sorry, I didn't think of it negatively. I'm a novice so I am totally unaware of what works and what doesn't. It wont be practical to have a generator in my situation and i don't think I can afford enough panels to be only on solar, so I was hoping to use the alternator to help. I won't really be running loads while driving. does this sound like it could work
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  • westend
    westend Solar Expert Posts: 46 ✭
    #17
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    Re: New guy needing assistance with RV solar system

    "Workability" has to take into consideration "use". Your use is determined by the amount and duration of the devices you plan to power. Four Trojan T-105's and 490w of solar would power most users for all but excessive loads like Air Conditioners, Electric Heaters, and heavy Microwave use. You need to do an energy audit of all the loads on your 12v system to properly scale your solar system.

    The confusion about the vehicle alternator, isolator, and solar system can be befuddled.
    Think of your situation as having two charging systems. One is the vehicle alternator, the other is the solar system. The additional consideration is battery management, i.e. how will both chargers direct current to my batteries and how much will they deliver to the two banks of batteries? How does a battery isolator work with all this? First, your 130 amp vehicle alternator charges your vehicle starting battery until it reaches a certain set point. After that, it diminishes the current supplied to the battery. It does the same thing for your Trojans but is limited by the size of the wire to the house batteries, the state of charge of those batteries, and by it's own internal regulation. If you wish to get optimal charging from the alternator, you could install an outboard rectifier/diode regulator and increase the size of the wire to your house batteries. That removes a lot of the heat inside the alternator and affords a less resistive path for current. At the end of the day, as has been mentioned, the alternator will just supply so much charging and you'll have to determine if it meets your needs.

    The solar system has a charge controller that regulates similar to the alternator in that it determines the state of charge of the batteries and tapers current accordingly. Both charging systems can be operated simultaneously and without fear of failure to either. Solar modules have diodes to insure that they are not a drain to the battery.

    The isolator operates like a switch, it interrupts current flow between what ever is connected to it. In your case, that would be the vehicle starting battery and the house battery charge wire. Some isolators will let you switch between both battery banks and some are switched by relays that rely on solid state electronics. Some are combinations of these. All of them are an interrupter, as is a switch.

    Hope this helps.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
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    Re: New guy needing assistance with RV solar system

    "Solar modules have diodes to insure that they are not a drain to the battery."

    this is not true as most pvs do not have blocking diodes to stop current drainback. what pvs contain are bypass diodes and they perform a different function. most controllers do stop the drainback of current.
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  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    #19
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    Re: New guy needing assistance with RV solar system

    There are a number of parts of this equation. We have a large teardrop trailer with a 185W high voltage panel mounted flat feeding a Morningstar MPPT controller. I designed the trailer for serious boondocking and a big part of this equation is conservation. All of the lights are LED, the heater an Espar diesel, propane cook top and grill, a Waeco refrigerator and I used two three speed Antec computer case fans in place of a Fantastic fan. On our month long trip last summer we did not get below 73% SOC and reached 100% SOC each day even in heavily shaded camping spots. I have a 140W Unisolar flexible panel and another controller, but have yet to need it.
    I have a set of jumper cables with Power Pole connectors that connect to the 150 AH AGM battery. At idle the tow vehicle alternator puts out 90A and the Subaru uses .56 GPH
    one of the best sources for RV?solar is Handy Bob http://handybobsolar.wordpress.com
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