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  • Noob Solar help for RV questions , Please !

    I am a Commercial Electrician but Solar beginner, Had a few questions after reading some of the Stickies and some other sources ...

    The install is in 35' Toy hauler equipped with a Onan 5500 Genset and will be used for primarily Desert Dry camping sometimes in excess of 15 days. Budget not as important as longevity and reliability, but don't want to waste either.

    1. Is running a 3000 watt AC off Solar just never going to happen? just askin' , If went with a 3000-4000w system and a Soft start device ?

    2. Assuming that the AC off Solar is not going to happen, I cant imagine needing more than a 1000W system of panels and a 1000w Inverter / Charger device?

    3. Do panels need to be tilted and aimed? we usually park in one place for the entire trip and can leave them in proper position. I understand there will be a loss of efficiency

    4. are Lipo's being used alot in RV systems? I read they are good for dry camping because they charge faster ?


    I checked into Packages and they seem overpriced after reviewing the components by themselves, Looking for recommendations on all the components off a system and design . I have High-Press crimping tools, Wholesale wire sources and experience building control panels and motor control.



    Thanks so much in advance for any help!




  • #2
    A1. Batteries are sized to meet 2 conditions. 1, is they need to be sized to supply 3 to 5 days reserve capacity. Example if you use 1 Kwh per day, the minimum capacity for RV camping is 3 days or 3 Kwh. Two is the killer for you and burst your bubble. Batteries can only supply a finite amount of current expressed as C-Rate and for Pb batteries is roughly C/6 where C is the AMP HOUR capacity, and 6 is a 6-hour discharge rate. So a 3000 watt Inverter at 12 volts requires a 300-amp circuit which is deadly dangerous, and it also means you would need a 1800 AH, 12-volt 1250 pound, $3000 battery. Good luck with that and the 2500 watt solar panel required to charge it.

    A2. Charge device is the Charge Controller and for a 1000 watt panel requires an 80-Amp MPPT charge controller, Around $600 to $800 it would also require a 800 AH, 12 volt, 550 pound, $1400 battery. Good luck with that.

    A3. Yes and absolutely no shade from sunrise to sunset. Good luck with that in an RV in warm months.

    A4. Yes and they cost 400% more than Pb and do not last as long. Only thing you gain is lighter weight, and a much lighter wallet. As for faster charging is non sense and as an electrician can understand. Start with a battery size say 100 AH. It can be any type of battery like lead acid or lithium.

    Amp Hours = Amps x Hours
    Amps = Amp Hours / Hours
    Hours = Amp Hours / Amps

    If the battery is fully discharge, all 100 AH used, and I charge at 10 amps, how long does it take to recharge? 100 AH / 10 Amps = 10 Hours. What kind of battery is it? Makes no difference, the math does not change. What is true and correct is lithium batteries can be charged at a higher C-Rate up to 1C or 100 amps the 1 hour rate where lead acid varies from C/8 to C/3.
    Last edited by Sunking; 11-06-2018, 12:07 PM.
    MSEE, PE

    Comment


    • #3
      Thanks very much Sunking, I relate to you because I spend alot of time crushing peoples dreams and correcting bad information, if you have a chance see my followup questions, thank you again:

      Batteries are sized to meet 2 conditions. 1, is they need to be sized to supply 3 to 5 days reserve capacity. Example if you use 1 Kwh per day, the minimum capacity for RV camping is 3 days or 3 Kwh. Two is the killer for you and burst your bubble. Batteries can only supply a finite amount of current expressed as C-Rate and for Pb batteries is roughly C/6 where C is the AMP HOUR capacity, and 6 is a 6-hour discharge rate. So a 3000 watt Inverter at 12 volts requires a 300-amp circuit which is deadly dangerous, and it also means you would need a 1800 AH, 12-volt 1250 pound, $3000 battery. Good luck with that and the 2500 watt solar panel required to charge it.

      I figured that it was not going to happen

      A2. Charge device is the Charge Controller and for a 1000 watt panel requires an 80-Amp MPPT charge controller, Around $600 to $800 it would also require a 800 AH, 12 volt, 550 pound, $1400 battery. Good luck with that.

      See below

      A3. Yes and absolutely no shade from sunrise to sunset. Good luck with that in an RV in warm months.

      We never have shade where we go, So I assume their is a optimal angle and orientation to place the trailer for maximum efficiency ? most sites I have plenty of room and options....

      A4. Yes and they cost 400% more than Pb and do not last as long. Only thing you gain is lighter weight, and a much lighter wallet. As for faster charging is non sense and as an electrician can understand. Start with a battery size say 100 AH. It can be any type of battery like lead acid or lithium.

      Amp Hours = Amps x Hours
      Amps = Amp Hours / Hours
      Hours = Amp Hours / Amps

      If the battery is fully discharge, all 100 AH used, and I charge at 10 amps, how long does it take to recharge? 100 AH / 10 Amps = 10 Hours. What kind of battery is it? Makes no difference, the math does not change. What is true and correct is lithium batteries can be charged at a higher C-Rate up to 1C or 100 amps the 1 hour rate where lead acid varies from C/8 to C/3.[/QUOTE]

      Takeaway is not worth the money yet?

      Ok, From your answers and my research , I Will stick with a 1000 watt system and AGM 6V batteries. Could you recommend and suggest a system layout? Brand names you trust etc, etc? I am all ears and very open to guidance....... ?

      Comment


      • #4
        Originally posted by JJV777 View Post
        Thanks very much Sunking, I relate to you because I spend alot of time crushing peoples dreams and correcting bad information, if you have a chance see my followup questions, thank you again:
        Not trying to crush your dreams, just bring you back to reality. But I will glad to help with you being a Sparky, I do not have to go into all the details.[/QUOTE]

        Instead of shooting things down, allow me to offer another way and more realistic goals here. First thing you got to work through and accept in a RV application solar is nothing more than Supplemental power, not your primary source. Solar is not capable of fully charging batteries in a daily use, there are not enough Sun Hours to get the job done. Having said that think of solar as extending run time or time in between full charges. Change your logic and attack.

        So here is what I would do. Determine how many wat hours you need in a day. Being a Sparky you should know how. Be careful what you ask for because it gets real expensive real fast. Say that number is 1.0 Kwh. Once you have that number multiply by 3 or 3 day run time and divide by nominal battery voltage. In practice this gives you 2 full days run time without sun. Using the example you get [3 x 1.0 Kwh] / 12 volts = 250 AH or a pair of 6-volt golf cart batteries that will cost you $300.

        As for solar could not be simpler. All you need is a C/10 charge current of 25 amps. Panel Wattage = 13.3 volts x 25 amps = 332 watts. Just call it 300 to 400 watts with a minimum 25 Amp MPPT charge controller. Here is the logic. Will 300 watts of panels generate all th eenrgy to recharge th ebatteries? Not likely, there is no amount of power that will work. So why throw money down a hole knowing it will not work?

        What you do is take all that money you would throw away on something that will not work, and use it for something that cost less and will work. Example install a $75 Electronic Battery Isolator so your engine alternator will charge the batteries. 2 hours engine run time is worth several days of solar. If you are only out for 2 days, you do not even need solar or the isolator. However you said you dry camp and stay parked for a week or longer. No problem because that is why you have a 2 KVA generator and battery charger you run every 3rd day to get fully recharged and save your butt. Just be sure to use LPG which you need for cooking, hot water, and heat.

        So you can use solar, just scale it back for show-n-tell, and take those savings and buy you a Royal Flush hand to play with. It is cheaper and better than solar. A pair of 6-volt golf cart batteries can just handle a 1 KW inverter barely.

        Your a Sparky and should be able to understand what I am saying. You do not need a 1/0 AWG copper THHN to run a 20 amp circuit 10 feet. Let your competitor go broke trying.

        FWIW are you a member on Mike Holt Code Forum? You should be. There you will get the best answers from real pros. You will find me there, I am a Moderator. No DIY's are allowed there. Only pros.


        Last edited by Sunking; 11-06-2018, 06:15 PM.
        MSEE, PE

        Comment


        • #5
          How often do you pack up and move ? (15 days I read)

          3000W of PV takes up quite a bit of space, even if you have $unpower panels. Doubtful you want enough roof holes to mount them, and still avoid all the vents and stuff on a roof

          You ALREADY have a 5Kw genset ! Consider swapping it for a honda eu7000is inverter genset, quieter, more fuel efficient .is it reliable as onan ?

          and most importantly - how much do you want to spend ?

          Me, in your shoes. I'd go for the eu7000, a 30A 12V battery charger, a pair of 6v batteries wired for 12V, and a efficient 700w inverter to run gear off of. Maybe only a 400w inverter - what loads will be on the inverter ? Inverters (especially cheap ones) have high internal losses, usually burning as much or more power then the loads on them. Something like the suresine 300, which runs my lights for a week in rain off a 12v deep cycle. is really miserly.
          Powerfab top of pole PV mount (2) | 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

          Comment


          • #6
            Sunking
            Makes sense, The Solar will just be one way to charge the battery bank which is the main power source . I have a 5500 Onan genset to charge the bank also and of course my Truck .

            I think its all a bit clearer now. Just a couple more questions ?

            - is there any harm in using say , a 500 AH battery bank just To buy myself some more charge time and saving some of my gas on long trips

            - In a different post you said that paralleling batteries is dangerous, should i always try to configure in series? we always want 12 V right?
            Last edited by JJV777; 11-06-2018, 07:24 PM.

            Comment


            • #7
              Mike thanks for replying also , after Sunpower gave me reality I am thinking about a much scaled down system .
              I want to keep my onan 5500 , we go out riding In the desert and places for 2,3, 7 and 15 ish day trips . We need all the gas we can keep to run the toys 🏍.
              I would rather put money into a really quality system then overbuy a huge system I guess I don't need and may not be practical.
              All ears on what everyone likes, uses and what to stay away from
              Last edited by JJV777; 11-06-2018, 07:23 PM.

              Comment


              • #8
                Originally posted by JJV777 View Post
                Makes sense, The Solar will just be one way to charge the battery bank which is the main power source .
                Received and understood. My point is you are throwing away good money trying to make solar your Prime Mover and I know you understand that term if you are a sparky. What I am telling you is consider changing logic and tactics to something less expensive and will work. I suggest you change your logic and call Solar Supplemental or Power Stretcher to extend run times between charging. Your bread and butter comes from the genny and alternator.



                Originally posted by JJV777 View Post
                I have a 5500 Onan genset to charge the bank also and of course my Truck .
                OK you are 66% there already. Scale back the solar to Supplemental, and use the savings and by a good battery charger for the Genny and Isolator. Much less expensive than depending on unreliable solar.

                Originally posted by JJV777 View Post
                - is there any harm in using say , a 500 AH battery bank just To buy myself some more charge time and saving some of my gas on long trips
                That is fine, just remember it gets expensive and HEAVY real fast. That is why I suggest you take time and calculate your daily wh usage. Once you got that you need a minimum 3-day reserve. So with a 3-day reserve capacity here is what the wallet and your back need to know so that can help you decide. For Each daily KWH you want will cost you $450 and weighs 175 pounds of dead weight. As 12 volt 500 AH battery will cost you roughly $850 and weigh 300 pounds.

                Originally posted by JJV777 View Post
                In a different post you said that paralleling batteries is dangerous, should i always try to configure in series? we always want 12 V right?
                I hope I did not say that, if I did point it out please. What I think I said is 3000 watt Inverter is dangerous at 12 volts because that requires a 300 amp circuit, which is dangerous. Ever seen a terminal in a Distribution Panel with 300-amps flowing through a loose connection. Not pretty huh? An RV is constantly in motion loosening connections.

                There is a problem with parallel batteries. Not a safety issue, more economic than anything else. I call it a Stuck Inside A 12-Volt Toy Box mentality. Most consumers like DIY's only know of 12 volts. So when they go battery shopping and they need 500 AH cannot find a 12 volt 500 AH battery, no one makes them because it would weigh 300 pounds. So they buy 5 x 12-Volt 100 AH 60 pound batteries and wire them in parallel. What they do not know is by doing that cuts cycle life in half for each parallel string. So instead of the batteries lasting 4 to 5 years only get 1 or 2 years out of them. If they only knew they made batteries in 2, 4, 6, 8, and 12 volts. To get 500 AH in a battery is going to be 6-Volts and 4-Volts wired in series to whatever voltage you want. Use a Single string. If you need 500 AH, buy 500 AH batteries. They will not be 12 volt batteries.

                Now having said that you can get away with parallel batteries in an RV application because it is not a daily cycle application like a home where used everyday. You can get away with 2 parallel strings because you have long periods between uses and thus the batteries have time to equalize between uses. RV application use is so infrequent age and abuse kills the batteries before cycles kill it. So if you must, you can use 2 parallel strings, but I encourage you to use 1 string if possible. Battery Fuse Blocks are expensive and each string needs its own Dual Fuse like you see below. One connect from the Charge Controller, and the other to the Inverter.



                Last edited by Sunking; 11-06-2018, 09:29 PM.
                MSEE, PE

                Comment


                • #9


                  "There is a problem with parallel batteries. Not a safety issue, more economic than anything else. I call it a Stuck Inside A 12-Volt Toy Box mentality. Most consumers like DIY's only know of 12 volts. So when they go battery shopping and they need 500 AH cannot find a 12 volt 500 AH battery, no one makes them because it would weigh 300 pounds. So they buy 5 x 12-Volt 100 AH 60 pound batteries and wire them in parallel. What they do not know is by doing that cuts cycle life in half for each parallel string. So instead of the batteries lasting 4 to 5 years only get 1 or 2 years out of them. If they only knew they made batteries in 2, 4, 6, 8, and 12 volts. To get 500 AH in a battery is going to be 6-Volts and 4-Volts wired in series to whatever voltage you want. Use a Single string. If you need 500 AH, buy 500 AH batteries. They will not be 12 volt batteries."

                  Gotcha, Sunking, Qty 3, 4V (X)AH batteries in Series will give me (X)AH in with a 12V output . So once I am solid on my AH needs, find the Batteries to make up the Configuration I need.

                  Thanks very much for your help and perspective, Definitely learned a lot from this.

                  I have lurked in the Mike Holt Forum for decades and will join someday!

                  Comment


                  • #10
                    Originally posted by JJV777 View Post
                    Gotcha, Sunking, Qty 3, 4V (X)AH batteries in Series will give me (X)AH in with a 12V output . So once I am on my AH needs, find the Batteries to make up the Configuration I need.
                    Or 2 x 6-Volt cells.

                    12 volt ranges from a few AH up to 200AH but keep in mind weight and physical size come into play here. That is why 12 volt battery capacity is so limited. Don't allow yourself to get stuck in a 12 volt box. I work in Telecom and utility sectors and they primary use 2 volt cells up to 6000 AH. On a USN Fast Attack Submarine has three large battery banks, the largest being propulsion of 126 to 220 2-Volt 8000 AH cells weighing in at 2000 pounds each cell.

                    Originally posted by JJV777 View Post
                    Thanks very much for your help and perspective, Definitely learned a lot from this.
                    You are welcome

                    Originally posted by JJV777 View Post
                    I have lurked in the Mike Holt Forum for decades and will join someday
                    I have been with Mike since 1996. We hooked up at the 1996 NEC Conference.

                    On a closing note, There are two really good battery manufactures for you to look at. Trojan and Rolls. Be aware both have multiple product lines from entry level up to Industrial. There are 3 inportant things to look at:

                    1. Warranty
                    2. Warranty
                    3. Warranty

                    Did I fail too mention warranty? They will range from 1 year to 10 years, you get what you pay for. If some manufacture claims 1000 cycles and only offers a 1 year warranty like Lithium Manufactures try to get away with. Spit in their face and walk away. Look for something like a Rolls S-550, a 6-volt 428 AH battery with a solid 7 year warranty with first 2 years free replacement 5 years after that prorated.

                    Here are Trojan and Rolls Warranties. Avoid any with 1 year entry level. You get what you pay for.

                    Good luck.
                    Last edited by Sunking; 11-07-2018, 05:19 PM.
                    MSEE, PE

                    Comment


                    • #11
                      One word of caution. With you being a Sparky working with higher voltages, voltage drop has not likely been an issue you are use to dealing with. It becomes critical at low voltages, and 12 volts is the biggest PIA. Between your Battery Term Post and Inverter Input Terminals you want to limit voltage drop/sag to 5% or less. and all other conductors to 3% or less. At the moment may not sound like much, but pretty much makes NEC 310 tables worthless if 1-way wire distance is greater than 10 feet as they only give you minimum size wire based on OCPD's current rating. That turd does not fly in the punch bowl.

                      The battery is a killer because you have to control both Battery Voltage Sag when under heavy load, and wire/connector losses. It is 5% total between the two. If you recall I said there are discharge limits on batteries as in do not exceed some C-Rate Amount like C/8 or C/6? This is what I am talking about. You need to limit battery Voltage Sag to 3%. Just like the wires, batteries have Internal Resistance and that is what limits charge and discharge rates. Generically C/8 is the point where you reach 3% voltage sag. 3% of 12.6 volts only allows you .38 volts, and 2% is .25 volts for a total loss of .66 volts @ 5% loss. Stop and think what can happen?

                      Say I have a 12 volt 100 AH battery with an internal resistance of .01 Ohms.I have a 12 volt 3000 watt inverter drawing 300 amps at full power. Ignore wire loss for this drill, only consider Battery Sag. Open circuit Voltage = 12.6 volts indication 100% fully charged. Pretty easy to solve because we know we start from 12.6 volts, and we have a known current flowing through a known resistance and can calculate Voltage Sag = 12.6 - [300 amps x .01 Ohms] = 9.6 volts at the battery terminals. See any problem? Your Inverter had a Low Voltage Disconnect and tripped off line at 10.5 volts on a fully charged battery. Now you wana add wire loss on top of that? Be my guest.

                      So here is my point. Calculate wire size based on Max Current vs Distance. Double check NEC 310 Tables to make sure it meets minimum requirements. I say this because many Voltage Drop Calculators do not cross check with NEC and you can get too small of a wire size on short runs like use 10 AWG with 200 amps is not going to fly. Only trick is what voltages to use. Panel voltages will be higher than battery voltage. Keep wire losses to 3% or lower.

                      Hint that is why we like high voltage charge controllers running on series high voltage panels used for Grid Tied System. Not only are they much less expensive than battery panels, with a 600 Volt input controller we can run 1000 watts down at 500 volts @ 2 amp using 14 AWG for several hundred feet if needed on any 12 volt battery system and up to 5000 watts @ 48 volt battery. You want a minimum 100 volt controller preferable 150 Voc Input
                      Last edited by Sunking; 11-07-2018, 05:59 PM.
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by Sunking View Post
                        One word of caution. With you being a Sparky working with higher voltages, voltage drop has not likely been an issue you are use to dealing with. It becomes critical at low voltages, and 12 volts is the biggest PIA. Between your Battery Term Post and Inverter Input Terminals you want to limit voltage drop/sag to 5% or less. and all other conductors to 3% or less. At the moment may not sound like much, but pretty much makes NEC 310 tables worthless if 1-way wire distance is greater than 10 feet as they only give you minimum size wire based on OCPD's current rating. That turd does not fly in the punch bowl.

                        The battery is a killer because you have to control both Battery Voltage Sag when under heavy load, and wire/connector losses. It is 5% total between the two. If you recall I said there are discharge limits on batteries as in do not exceed some C-Rate Amount like C/8 or C/6? This is what I am talking about. You need to limit battery Voltage Sag to 3%. Just like the wires, batteries have Internal Resistance and that is what limits charge and discharge rates. Generically C/8 is the point where you reach 3% voltage sag. 3% of 12.6 volts only allows you .38 volts, and 2% is .25 volts for a total loss of .66 volts @ 5% loss. Stop and think what can happen?

                        Say I have a 12 volt 100 AH battery with an internal resistance of .01 Ohms.I have a 12 volt 3000 watt inverter drawing 300 amps at full power. Ignore wire loss for this drill, only consider Battery Sag. Open circuit Voltage = 12.6 volts indication 100% fully charged. Pretty easy to solve because we know we start from 12.6 volts, and we have a known current flowing through a known resistance and can calculate Voltage Sag = 12.6 - [300 amps x .01 Ohms] = 9.6 volts at the battery terminals. See any problem? Your Inverter had a Low Voltage Disconnect and tripped off line at 10.5 volts on a fully charged battery. Now you wana add wire loss on top of that? Be my guest.

                        So here is my point. Calculate wire size based on Max Current vs Distance. Double check NEC 310 Tables to make sure it meets minimum requirements. I say this because many Voltage Drop Calculators do not cross check with NEC and you can get too small of a wire size on short runs like use 10 AWG with 200 amps is not going to fly. Only trick is what voltages to use. Panel voltages will be higher than battery voltage. Keep wire losses to 3% or lower.

                        Hint that is why we like high voltage charge controllers running on series high voltage panels used for Grid Tied System. Not only are they much less expensive than battery panels, with a 600 Volt input controller we can run 1000 watts down at 500 volts @ 2 amp using 14 AWG for several hundred feet if needed on any 12 volt battery system and up to 5000 watts @ 48 volt battery. You want a minimum 100 volt controller preferable 150 Voc Input
                        I actually deal quite a bit with voltage drop in a variety of applications, Recently did a project with Parking lot light Standards with 500' feeders in some cases. Even at 277v and LED heads, still had to upsize wire quite a bit. I also know that in DC , Volt drop is a very big problem, So will heed the advice for sure.

                        Comment


                        • #13
                          Originally posted by JJV777 View Post
                          I also know that in DC , Volt drop is a very big problem, So will heed the advice for sure.
                          Well DC has less loss than AC, but the issue is not about AC or DC, it is low voltage. 5% at 277 volts is 14 volts. 5% at 12 volts is 0.6 volts. Just want to make sure you know so it does not bite you in the butt.

                          MSEE, PE

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