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  • New Solar on Conversion Van Questions

    Hi All. New to the groups here. This is fascinating stuff and I can’t get enough of it. Thank you to everyone who posts and those who reply. It’s really helpful!! I recently installed a new system in my conversion van (2004 Chevy Express Quigly 4x$). I installed 2 x 100 watt 12v Renogy flexible solar panels on the roof with one VMAX AGM 12v 155ah battery. I have an Epever 4210 MPPT solar controller as well and all of this is wired with 6-8 Gauge wire (6 gauge to/from battery and 8 gauge to panels).

    Here’s my issue, when I connect the battery to the controller first and then the panels, the controller shows that the panels are producing quite a bit of power (approximately 15.9v / 8.2a). However, after minute or two, this drops down drastically to about 19.2v and 1.9a and remains fairly constant around this level. The battery is now fairly well charged at 14.2v 2.7a, although took a bit to get there. I would have thought that the controller would show that the panels are putting out a much higher amount of power (as it did initially). Clearly there is enough sun here in Los Angeles to produce more power and the panels are putting out that power, but when it gets to the controller it seems to be cut down somehow. My question is whether the display on the controller with respect to the panels is only showing what it is using to charge the battery, which may be lower after it is up and running, seeing that the battery is mostly charged already. However, this display of lower power was also showing when when the battery was less charged at 12.4v. If you don’t mind, I would very much appreciate your thoughts on this issue. I’m wondering if there is something wrong with the controller. Everything is brand new, just installed a couple of weeks ago.

    Also, I’m debating to add a 3rd panel to ensure that the battery is charged fast enough while I’m using it. I use it for a TV, charging several other RC batteries and some light tools (dremel, heat gun, soldering iron). Not sure if that is misguided, but figured I’d mention.

    Last question, is it normal for the battery power to show that it is fully charged at about 14.7v during the day when the panels are getting sun, but then it drops down to 12.7v at night without any power. Is there some sort of resting energy, although the battery is fully charged. That is another issue that I’m not sure about. In other words, why does the battery show fully charged with the solar controller charging, but then not fully charged when at night resting; both without having any power draining from tools or the TV?

    Thank you for your help and consideration in advance.
    Last edited by TStein; 03-02-2020, 09:10 PM.

  • #2
    Originally posted by TStein View Post
    .........

    Last question, is it normal for the battery power to show that it is fully charged at about 14.7v during the day when the panels are getting sun, but then it drops down to 12.7v at night without any power. Is there some sort of resting energy, although the battery is fully charged. That is another issue that I’m not sure about. In other words, why does the battery show fully charged with the solar controller charging, but then not fully charged when at night resting; both without having any power draining from tools or the TV?

    .
    The resting voltage of a battery is always below the charging voltage. The exact numbers depend on your battery type.

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    • #3
      Thanks very much! That makes sense. So then how do I determine if the battery is fully charged at rest when resting voltage is lower.

      Comment


      • #4
        Originally posted by TStein View Post
        Thanks very much! That makes sense. So then how do I determine if the battery is fully charged at rest when resting voltage is lower.
        You would find out from the manufacturer what the resting voltage of their particular battery is when it has been fully charged. They may give you a period of time for it to settle to the resting voltage after charging. It sounds like you are in the ballpark anyway if you can't get the answer right away.
        Last edited by Ampster; 03-04-2020, 03:07 AM.

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        • #5
          The battery voltage is unfortunately not completely analogous to a fuel gauge with respect to how "full" the battery is. I believe the specific gravity of the battery electrolyte is the most analogous parameter, but that's not as convenient as resting voltage. Having said that (and bear in mind that I'm no battery guru, just an internet keyboard warrior ), I certainly use voltage to get an idea of the battery state. But as pointed out, don't confuse charging voltage with battery resting voltage. Once you remove the charging source, the battery voltage will begin to settle down to its resting voltage. But there are things like surface charge and other stuff that affect this process. Basically, you would need to let it rest with no load for quite some time before you get to its true resting voltage. For a 12V battery, I think 12.6-12.7V is a good ballpark value for "full." Google "battery soc chart" and you'll get a lot of charts for how full the battery is based on state of charge (SOC).

          During charging, I still use the measured voltage to get an idea of the battery SOC. If it is at a value less than the absorption setpoint (mine set to 14.8V for 12V deep cycle batteries) and gradually increasing, then the controller is in bulk charging mode and the battery is <90%-ish charged. The further from 14.8V, the further from 90%-ish. If it is steady state at 14.8V, then the charger is in absorption mode and the battery is between 90-100% charged. This final 10% of charging is what takes the longest and is most difficult to achieve with solar. If it is steady state at 13.6V, then the charger is in float mode which means the battery is fully charged and the controller is maintaining it with a lower float voltage.
          I'm an RV camper, mine has 280 watts of solar

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          • #6
            Thanks very much! This is incredibly helpful. I have no clue how to figure out specific gravity, and barely know what that means... My fault for finding these things fascinating later in life. Too bad these things don’t come with a volt meter built in or some sort of gas gauge... I guess I could buy meters, but none of them available seem to measure full v empty in the same way. I’m thinking of buying multiple voltage monitors, one for solar power in, one for battery charge, and one for battery load. Although, that seems like a lot when you add up the amount of space required for all three of them, when I only have on battery. Any thoughts on a monitor that does it all? Thanks again for everyone’s great responses!!

            The battery was showing 12.7v last night resting, which seems pretty good. I’m adding another 100w panel today and will let it run to ensure it’s topped off. Just found out that VMAX has a chart that shows float voltage in the range that you noted. https://www.vmaxtanks.com/assets/ima...arge_chart.pdf.

            Comment


            • #7
              Having run solar on our camper for nearly 10 years, I've actually become more comfortable knowing less than wanting to know more. I have one voltage readout that I installed, and it isn't taking a reading from an ideal location. But good enough for camping. if it is daylight out with good sun, then that value is the charging voltage. If it is after dark or there is no sun (overcast), it is more reflective of the battery's resting voltage. First thing in the morning before sunrise, I consider it to be the true resting voltage.
              I'm an RV camper, mine has 280 watts of solar

              Comment


              • #8
                A Bogart Tri Metric or Victron meter work fairly well for figuring your battery's state of charge. The bogart is the only one I have experience with and I like it. It's simple tom operate and straightforward to read. As with all these shunt based meters the accuracy is purely based on The info you input into it. Batteries will lose capacity as they age so you need to adjust the settings or just bear in mind that you likely have less in the tank as they age than the readout says.
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                Comment


                • #9
                  Before adding another panel check your usage. I have a single 100 watt panel and a MPT controller 2 35AH batteries(wheelchair), in the winter it will run my furnace(very low draw propane), power my lights and charge my phone, kindle and computer for a couple of days in cloudy weather.

                  One thing you might want to look into is a diverter for your vehicle charging system. I have an automatic one on my van where the vehicle battery is fully charged it will diver to the cabin battery and when the engine shuts down it disconnects to keep the cabin system from discharging the vehicle battery. I lived on the PNW coast and would travel a lot so I always had a full battery in the cabin. Here in the SW I just shut it off and the solar keeps up with everything.

                  My cheap system has a light that is on solid when charging and blinks when in float mode. Resting my meter reads 13.1v when fully charged and 13.6-14.5v when charging depending on the light available. When my resting reads less than 12.6v it is time to replace batteries as they run down pretty fast then. I replaced them this spring for the first time in 4 yrs. It is pretty much a simple system that I just forget about as there is no maintenance.

                  Comment


                  • #10
                    Originally posted by TStein View Post
                    Thanks very much! This is incredibly helpful. I have no clue how to figure out specific gravity, and barely know what that means...
                    Here's an example of a battery hydrometer you can purchase to measure your state of charge. This one has a correction chart for temperature because the density of the battery acid changes with temperature. This will give you a much more accurate reading of "state of charge" than the voltage will. Basically, you stick the end though the opened battery cap, suck of some battery acid, and read the floating stem to get a density reading. You can look up for your brand of battery what it's density is supposed to be at full charge, but it's usually around 1.265 to 1.285.

                    https://www.ebay.com/itm/Temperature...b84d5ab126035a

                    Comment


                    • #11
                      Originally posted by TStein View Post
                      Hi All. New to the groups here. This is fascinating stuff and I can’t get enough of it. Thank you to everyone who posts and those who reply. It’s really helpful!! I recently installed a new system in my conversion van (2004 Chevy Express Quigly 4x$). I installed 2 x 100 watt 12v Renogy flexible solar panels on the roof with one VMAX AGM 12v 155ah battery. I have an Epever 4210 MPPT solar controller as well and all of this is wired with 6-8 Gauge wire (6 gauge to/from battery and 8 gauge to panels).

                      Here’s my issue, when I connect the battery to the controller first and then the panels, the controller shows that the panels are producing quite a bit of power (approximately 15.9v / 8.2a). However, after minute or two, this drops down drastically to about 19.2v and 1.9a and remains fairly constant around this level. The battery is now fairly well charged at 14.2v 2.7a, although took a bit to get there. I would have thought that the controller would show that the panels are putting out a much higher amount of power (as it did initially). Clearly there is enough sun here in Los Angeles to produce more power and the panels are putting out that power, but when it gets to the controller it seems to be cut down somehow. My question is whether the display on the controller with respect to the panels is only showing what it is using to charge the battery, which may be lower after it is up and running, seeing that the battery is mostly charged already. However, this display of lower power was also showing when when the battery was less charged at 12.4v. If you don’t mind, I would very much appreciate your thoughts on this issue. I’m wondering if there is something wrong with the controller. Everything is brand new, just installed a couple of weeks ago.

                      Also, I’m debating to add a 3rd panel to ensure that the battery is charged fast enough while I’m using it. I use it for a TV, charging several other RC batteries and some light tools (dremel, heat gun, soldering iron). Not sure if that is misguided, but figured I’d mention.

                      Last question, is it normal for the battery power to show that it is fully charged at about 14.7v during the day when the panels are getting sun, but then it drops down to 12.7v at night without any power. Is there some sort of resting energy, although the battery is fully charged. That is another issue that I’m not sure about. In other words, why does the battery show fully charged with the solar controller charging, but then not fully charged when at night resting; both without having any power draining from tools or the TV?

                      Thank you for your help and consideration in advance.
                      This article is the answer for your question >> https://www.flexible-solar-panel.com/diy-solar-panels

                      Comment

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