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  • New member, building off grid in a Volvo XC70

    Hi all, new here and wanted to introduce myself.

    They call me Wander. Im currently working to outfit my vehicle for off grid camping/living and trying to design a system that fits in the spare tire well of a 2004 Volvo xc70 with the eventual goal of being able to expand and use it with a small travel trailer and/or a small cabin. Im schedule to work a volunteer position in CO with wolves, and its completely off grid in the sticks. My current 120w inverter to 12v outlet is ok, but having killed the battery in the car multiple times in 2 weeks i need something more fitting.

    Sustainable energy is something thats interested me for years now, and now i find myself with time and reason to build. For now i want to keep it small, enough to run the essentials (laptop, cell phone, small space heater, electric cooler) and serve as a closed loop redundant charging system that can also jumpstart my car battery if necessary. The goal is to keep this as cheap as possible while learning about solar setups (read: Harbor Freight cheap).

    My current thoughts are to use 12v powersports batteries from Deka in parallel due to space. i can fit 6 to 8 batteries in the spare well in a 2x3 or 3x3 configuration and each battery is about 400cca/28aH. For the price i can get 6 for just shy of $250 out the door and they are the largest PS battery Deka offers (factory store is local). I would like to run these with a small 2 stroke generator for charging when solar isnt available and also be able to piggyback into the vehicle's 12v battery to slow charge off of the alternator while driving.

    Its been a long time since ive done any electrical engineering type of projects, and solar is new territory for me. The math and science is giving me a headache lol. Figuring out my panel watt needs is where im running into trouble and im hoping you folks can assist with the build specs/proper hardware recommendations to make this work. Eventually it will move out of the spare well and become hitch mounted on a cargo basket.


    ​​​​I'll post up soon with basic schematics, looking forward to learning what i can from y'all!



  • #2
    Hello Wander Wagen and welcome to solar panel talk, I think you have a lot of reading to do, start in the off grid section and read all the off grid stickies this should start to clear things up for you, cheers.

    Comment


    • #3
      Thanks Pete! Im excited to learn what i can while keeping it as simple as possible.

      my biggest issue is figuring out the power consumption vs how many batteries and what solar panels to go for, as well as if i should use a charge controller/isolator/capacitor in line with everything. My current 120w inverter to 12v port works but i have to start the car every hour or so for 20 min to make sure not to kill the battery.

      when factoring in total power consumption vs how many watts/number of batteries do i use inverter watts or do i use individual device power? For example, say im pulling 200w but using a 400w inverter, real world power use would be device based correct?

      Comment


      • #4
        Your real power is
        Device power + Inverter losses + inverter overhead (and then maybe PF losses if you use anything other than incandescent lamps)

        140W TV + (inverter running 85% efficient) 21w + 12w (overhead load whenever inverter is ON) = 173 actual consumed
        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


        • #5
          Thanks Mike. That helps a bit. Im so lost on this stuff, the words are running together in a jumble and making my head spin lol.

          ultimately, im looking at keeping it stupid simple. Start with my battery bank and work solar in from there, then add the harbor freight 900w 2 stroke genset.

          so heres where im at: my vehicle has a 150a alternator and a Deka agm installed (original factory alternator was 120a). If i recall correctly its an MF776 (stamped M6 on top) rated at 70aH/770cca. Due for replacement in about a year or so.

          my current power use off battery, vehicle off is a laptop rated at 19v/3.95a for the power adapter and a cell phone with a 3300maH battery charging at 2.1a. Running a 120w Everready model 70000M inverter rated 13.8vdc/12a input. This inveter will be swapped out with a 400w soon. I have a 1.5a 12v solar panel hooked up right now to help trickle charge the battery during daytime when not drawing power.

          my goal is to build a battery bank that will sustain recharging of the laptop battery and cell phone (4400maH, with plans to double that with an extended battery) at about 8 hours a day for 14 days before having to recharge. Bare minimum i need 5-7 days worth of power at 8 hours a day with room to add a 12v 200w rated (harbor freight) space heater on very rare occasions for 8 hours by itself. Possibly a small 12v piezo cooler down the line. 12v 400cca 28aH FLA batteries to start out with.

          What im having trouble figuring out is how to tie in the solar and how much. If my math is correct, a 200w panel should cover my immediate needs, correct? The laptop pulls 75.05w alone, the cell phone pulls another 25.2w. Also if math is correct im pulling 8.35a on a 70aH battery, which means i can run 8.38 hours to completely flat on this battery, correct? At this rate i would need 7 batteries to make it 7 days with no reserve?

          adjusted to 28aH batteries, i can get ~16 hours on 6 batteries (2.68 hours per battery@8.35a)? I feel like im missing something here, something to do with internal resistance of the batteries?
          Last edited by WanderWagen; 03-15-2019, 12:23 AM.

          Comment


          • #6
            So, I'm gonna give you the tools, and then do one example so you can do your own calculations

            Volts x Amps = Watts (laptops, batteries, TV's, Lights, everything , it;s Ohm's Law)
            Watts x hours = watt hours
            A PV panel produces 80% of nameplate when well aimed
            Batteries should never be drained below 50%

            laptop rated at 19v/3.95a
            That turns into 19 x 4 (always round up for worse case) 76 watts
            for 3 hours - it becomes 228 watt hours


            car battery rated at 70aH/770cca
            first, the CCA is a garbage number, second, a car battery can only be taken down 10% and must be recharged immediately, or it dies.
            a realistic figure is the 70ah x 12v = 840 watt hours in the battery, 84 of which you can use, so you can charge your laptop for just over an hour !!

            A 200W panel becomes a 160W panel, in great sun for 4 hours = 640 watt hours harvested *

            *Harvested is not the same as stored, as there are about 20% losses when recharging a battery, you take out 228wh and have to harvest 273.6wh to recharge

            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


            • #7
              Got it, thanks again Mike! That definitely simplifies things a lot.

              So by that then, laptop only for 8 hours a day (76w * 8h) im at 608wh. 61wh useable.

              cell phone would be 12v/2.1a for 8 hours, so 202wh, 20wh usable @ 10%.


              total for 8 hours a day i need 810wh. Adjusted for planned powersports batteries at 28ah*12v i have a total of 336wh per battery. To meet the need of my devices for just over 1 hour i would need 3 of these batteries (34wh*x3 gets me 102wh). 9 batteries will get me 3-4 hours without recharge. Thats about the max i can fit in the trunk and id be wedging them tight i suspect.

              now by that logic, if i increase to 400w solar i can harvest 1280wh in 4 hours of sun. Take out the 810wh for tne 2 devices combined and im harvestimg 470wh to recharge.

              does this look correct? By the math i have here i have room to add another small device (100w or less)





              Comment


              • #8
                > powersports batteries at 28ah*12v 336wh, 168 useable

                Please, don't use small batteries stacked in parallel. Too many connections to go bad, too many cells to water, and parallel lead acid banks inherently die sooner because of unequal charging.

                > laptop only for 8 hours a day (76w * 8h) im at 608wh. 61wh useable.
                I cannot figure what math you used I see 76w x 8h = 608wh consumed.

                A pair of 6V 200ah golf cart batteries will contain 2,400wh, 1,200 usable.



                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


                • #9
                  Maybe i misinterpreted your post. 608wh 10% is 60.8 rounded to 61wh.

                  so total power use then is actually 810wh for both devices. Id like to have a 25-50% reserve over and above that for SHTF purposes

                  the powersports batteries are sealed lead acid batteries. I figured on using 8ga wiring (as ive gathered from stickies in off grid forum) and doing 2-3 banks at 3-4 batteries parallel then series each bank together as ive read elsewhere in my research (putting each bank in series allows for reserve when one bank goes out). Cost is really the reason for these batteries, i can get 6 of the Deka/east penn batteries from the factory store in Lyons Station for $255 after discount (roughly $48 ea). Havent looked into golf cart battery prices yet but i suspect the cost goes up significantly.

                  is there a way (with either a charge controller or capacitors, etc) to equalize the charge rate on the smaller batteries that will keep the cost down? Say im running 3 strings of 3 batteries wired parallel with serial connections between each bank and put a 1k farad cap om each serial connection...that would in theory equalize it out so the 2nd and 3rd bank receive equal charge thru the circuit, correct? (Thinking in terms of car audio caps, since they are used mainly to provide steady power without fluctuations, ie, keeping the lights in car from flickering on heavy draw from the amp). I do plan to install an isolator between the vehicle battery and the battery bank when i hook up for mobile charging/using the vehicle as a generator until i get a 2 stroke...not sure if i should cap that connection also?

                  ​​

                  And am i correct that a 400w panel (or 2x 200w panels in series) will cover my needs,while still allowing for that SHTF reserve? Realistically im estimating high at 8hr per day of use, and its more likely to be 4-6 hrs.
                  Last edited by WanderWagen; 03-15-2019, 09:26 PM.

                  Comment


                  • #10
                    Stop now.

                    Do not try to parallel that many sealed batteries. They will have problems with equal charging. Capacitors will not cure it, it's the very minor differences in milli-Ohm resistances in the connection cables, crimps, battery internal resistance. it's not solvable
                    Here's a lengthy article about the issues http://www.smartgauge.co.uk/batt_con.html

                    You are walking into this backwards. With earbuds on. you can't hear the alarm bells !

                    First - Calculate your loads in watt hours
                    Second - battery bank size at least 2x the watt hours of the loads
                    Third - charging source large enough to recover 120% of daily loads in 1 sunny day
                    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


                    • #11
                      Im not trying to argue your points, trying to get all the info for better understanding. this is all completely new to me again, i haven't done anything like this since my Vo-tech engineering class that was very limited....over 20 years ago.

                      to address your points:

                      first, lets plan a bank that will output 1000wh/1kwhfor simplicity sake (~20% over what has been calculated as my daily usage to allow for additional devices)

                      second would require a bank that outputs 2000wh

                      ergo third would require 1200wh for total recharge on 1 sunny day, correct? That bumps me up to at least 3, if not 4x 400w panels?

                      Would it make a difference to switch to a dry cell battery instead (i.e., odyssey style batteries)? How about wiring in series first for 24v then wiring parallel each bank of 2 batteries (say 4 total banks)? That brings my PS batteries to 24v at 28ah, bringjng me to 682ah per bank. That would mean 3 banks of 2 batteries in 24v config equals 2072ah, meeting requirement #2?

                      Comment


                      • #12
                        What is your fixation on tiny batteries ? 4 banks of batteries is still in La La land.

                        Maybe Li batteries will be compact enough for you to stash all over the vehicle and still not parallel
                        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


                        • #13
                          Originally posted by Mike90250 View Post
                          What is your fixation on tiny batteries ? 4 banks of batteries is still in La La land.

                          Maybe Li batteries will be compact enough for you to stash all over the vehicle and still not parallel
                          You've answered your own question sir...small batteries are what i can fit in the confines of the spare tire well, under the floor of the trunk. Have you ever looked under the floor of a 2001-2007 Volvo xc70 station wagon before? If not, I suggest doing so and perhaps youll see why im "fixated on tiny batteries". Physical dimensions of the batteries do matter here (for example, the original proposal of PS batteries are 6x5x6). As does cost vs available resources. Lipo4 batteries arent cost effective and unavailable locally. Dry cell Odyssey and Deka are what i have access to.

                          So maybe not 4 banks, but the # of banks is moot. We're talking hypothetical here right now and that still doesnt answer the questions I've asked in my last post, about using dry cell and/or 24v series configuration with parallel between the banks. There is room enough for 6-8 small batteries.

                          to be quite frank, this is a prototype setup. If its not the most efficient, who cares? Its about learning the ropes and getting my feet wet. Its only temporary until i can find/afford a better solution.

                          Comment


                          • #14
                            You can use dry batteries and put them where ever you like. The # of banks is bad, if it's more than 2.
                            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


                            • #15
                              Thank you. Running in 24v series doesnt make a difference?

                              so theoretically, could i run 2 seperate, isolated banks of 2 batteries (or 4x 6v) in 24v and wire up some sort of automatic charge switch to go between banks of 2 when the charge drops below a certain point? Some sort of relayed trigger comes to mind...2 banks at 24v would still give me almost 1000wh per bank (or more depending on 12v vs 6v)

                              Comment

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