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  • Beginner help with fixing bad installation

    We bought a pre-converted VW kombi campervan from what we now know is a very dishonest and incompetent firm in Mexico. We have worked a lot trying to fix everything they neglected or did badly. And right now I'm working on the electric system.

    First of all, the charging stopped many times and I found that almost all the cables are just twisted and taped, even cables between the solar panel, the charge controller and the battery. I have fixed it now with butt connectors and increased the charging a lot. But it still feels low so first of all I want to confirm if my numbers make sense.

    Panel is 100W from unknown chinese brand (can't ask, as we told that company to go to hell etc)

    The controller is a simple one called CMTD (I guess thats the brand at least)

    The battery is some brand called MS Battery (120Ah, deep cycle)

    When i first checked, the controller said 1.6A charge during noon in Mexico. After I fixed the cables I could find between the panel, controller and the battery and removed the protective film from the panel (no, they hasn't even done that), I now get 3.6A. I also disvonnected the panel and measured the voltage over it and it was 19.9. As i understand it, that means 71.6W, way below specifications, but maybe normal?

    Also, on our first trip without my fixes we discharged the battery way too much. But it has now been 2 days of good sun light and the charger shows 11.7V after sunset. It also only shows 2/5 bars full so far. Is it normal that it will take multiple days to charge it?

    I also wonder about cable dimensions, most guides use crazy thick cables, but playing with tools for this I assume if I want to replace their crap cables, they wouldn't have to be super thick for one panel and maybe 5m of distance (x2)? I'm thinking 8 awg is even too much, but would rather overdo it if I get more current. What do you think?

    Most guides say you should ground the battery to the car chassis, can't see that they did that anywhere except at some of the lights and the fridge. What effect could this have?

    And lastly, even though as far as I know, there is nothing on, the solar controller shows a load of 0.4A. I assumed it might be what it uses itself, but it doesn't really measure that right? So, what can I do to find out? Could it be their bad cable work leaking somewhere? Or maybe something is running I don't know about, but really can't think of anything...

    I'm extremely greatful for any help, our vacation is just ticking away while we are working with this piece of 💩... ☹



  • #2
    Hello UglyBob,
    I am no expert in solar, but to charge that 120Ah battery you need 12A for a C/10 charge rate. I would recomand fitting a second solar panel on the van wired in series. Also if you could write the exact model of the charge controller, that would help.
    If it's a 10A charge controller, you might want to change it to a 20A controller.
    Don't let the battery stay discharged or you will have to buy another one. If it's possible, use an outlet charger until you get the second panel fitted.

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    • #3
      Not sure if it's even possible to fit 2 panels on this small VW combi though... What does C/10 charge rate mean?

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      • #4
        Btw, can I mix brands of panels or do I have to figure out what this one is before I can get another one, IF I can fit it somehow?

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        • #5
          Originally posted by UglyBob View Post
          Not sure if it's even possible to fit 2 panels on this small VW combi though... What does C/10 charge rate mean?
          The letter C is used for Capacity (in Amp-hours). Since the number is lower at higher discharge rates, the common measure is what is written as C[SUB]20[/SUB], the capacity when discharged at the twenty hour (to full discharge) rate. If not otherwise specified, C by itself means C[SUB]20[/SUB].
          The charging current it then written in terms of C. Charging at C would recharge the battery fully in one hour (actually longer, because the charging process is not 100% efficient.)
          C/10 is one tenth that current. So for a 120AH battery, C/10 would be 12A.
          If you are a stickler for keeping dimensional units consistent, C/10 actually means C (in AH) divided by 10 hours, leaving just Amps.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            You'll never get full output with a panel mounted flat on top of a vehicle. The best output would come from a panel aimed at the sun on a cold day. Poorly aimed, hot panels give the type of output you are describing. If you get creative with your mounting system you can make your panels tiltable. That will help with your dilemma. Another issue being you need to keep your vehicle in the sun to capture that energy. Leaving you a hot vehicle. You might consider a couple freestanding panels that can be deployed away from the camper and aimed at the sun throughout the day while you are in camp.
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #7
              Ok, thanks for the input, I was expecting that 100W was probably a lab value, but I was hoping there was something holding it back. Freestanding panel could bee an option yes, at least when we are around...

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              • #8
                Btw, can I charge the battery with a normal charger while ut is connected to the solar controller or do I need to disconnect it first?

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                • #9
                  There shouldn't be a problem using two separate charging systems. The charging parameters probably aren't be exactly the same so when one charger is transitioning into absorb or float the other will not be done with its particular phase. If you have adjustable setpoints on both chargers set them the same.
                  2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                  • #10
                    It is normal below Standard Test Conditions ,
                    to gain just 2/3 to 3/4 to 4/5 of the Nameplate Watts .

                    So, 72 Watts are average jarvest for a 100 Watt panel .

                    The Voltage of around 20 V and the Amps of around 3,5 A are
                    in line .


                    When doing the Math , you will gain approx . 30 amps during
                    charging of the battery over 10 hours .

                    Your 120 Ah battery will need 4 days @ 10 hours or 5 days @ 8 hours
                    to be fully charged .


                    The voltage is good enough , so it would need 4 or 5 of
                    these panels in parallel to charge that battery in one day ,
                    if deeply cycled to low State of Charge (SoC) .
                    ​​​​​​

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                    • #11
                      Mmm, makes sense, thank you for the explaination. I will think about if we can fit another panel somehow. I replaced all the crap cables between the controller, the battery and the load now at least, and I think it is as effective as it can be right now. Not sure if they attached the panel cables correctly yet though or just more twisting with tape...sigh...

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                      • #12
                        Battery Isolator protecting between the starting battery allows a storage 12 Volt battery to be charged off the VW battery charging system anytime the VW is in use.

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                        • #13
                          Mmm, I was thinking about that too, if that ancient engine can handle charging 2 batteries...

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