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  • Batteries wont hold Voltage...

    I have a fully off-the-grid setup at my rural property.

    - 6k watts worth of solar panels
    - 4k watts magnum inverter & controller

    - a 24v battery bank of "Full River AGM" batteries that equate to 830 amp hours of storage
    - and a Honda 7k generator


    Ive had the system for about 9 months.

    During the spring/summer months the batteries do not get used much at all. During the winter it wouldnt be much different but Im spending a lot of time up at my place doing maintenance on the property so Im running heaters in the living quarters of the shop I built.

    Here is the situation/problem...

    I normally would run about 2000-3000 watts worth of equipment (heaters mostly). I could get 5-7 hours out of my battery storage during the day before needing to turn the generator on to recharge the system. At night, from a full charge at midnight, I could get about 5 hours out of the system before the low voltage would kick the system into protection mode and shut everything down. It'd be at that point I'd have to get up and go turn the generator on (about 5 in the morning).

    That started to suck. So I had my solar company install a generator auto-start so the generator would kick in once the system reached a low "state of charge" and charge the system back up from 5am to however long it took, and then by 10am the natural sunlight could take over from there.

    The concept was to go from having to manually run the generator twice a day (9pm-midnight & 5am-9am) to instead the auto start kicking on and all I need to do is make sure the generator is topped off with fuel.

    Here's where the problems started... Immediately after the auto-start was installed, I can no longer get the 5+ hours of usage out of my batteries with a 3000w load. It takes about 15 minutes for the voltage to sink to unsafe levels so the auto-start kicks on to protect the batteries. The geni runs for 20 minutes or so, bringing the voltage back up to a healthy level and then the generator shuts down. 15 minutes later the cycle repeats itself.

    I lowered the load to 1500w to see if that would preserve the voltage. No dice. It maybe bought me an extra 2 minutes before the voltage hit it's minimum level again.

    It doesnt matter if I start from a fully 100% charged battery bank. The state of charge might only drop to 97% before the voltage is so low that the geni auto-start kicks on. So I tried turning off the auto-start. The system then shuts down at 23volts as predicted. Reminder, before the auto-start was installed, I could run my batteries all the way down to as low as 45% state of charge before the low voltage protection kicked in and shut the system down. Now? The state of charge is barely used at all as the system simply bounces between low & ample voltage.

    I use software to track my solar system's setup and at one point, at it's worst, the generator had kicked on 40 times in one day!!!

    I called my solar company that has done all my installs, they instantly tried blaming the batteries and said that the batteries have gone bad/run their life cycle. Because Ive apparently cycled my batteries too much.

    My batteries are less than a year old. Due to my software, I can track the number of cycles. The batteries have maybe been cycled 200 times at most. They are rated to get at worst 1000 cycles how I use the system.

    But again, everything ran just fine BEFORE the auto-start was installed. I find it HIGHLY UNLIKELY that my battery bank just took a **** the day after the auto-start was installed.

    So after much fighting with the solar installers, they sent their guy out to diagnose the system. He said that a short in the system could be drawing the voltage down faster than normal. He went thru the system, found no short. He checked the voltage of all 8 batteries, none were "bad" per se. He then proceeded to do the math (for the 30th time) for me on what my battery bank is made to handle and that Im asking too much of it. He said that at my load, I should only get about 4 hours of use out of it before the state of charge/voltage is too low and the auto-start kicks on. This is where I start to get super frustrated because it's like he's not listening or acknowledging the issue at hand.... IF I COULD GET 4 HOURS OUT OF MY BATTERIES ON A 3300w LOAD, I WOULDNT BE CALLING HIS COMPANY WITH ANY ISSUES. Im only getting about 15 minutes before the voltage drops too low. This is a new problem, that only started AFTER the geni auto-start was installed.

    I have no idea how the auto-start could be causing the problem. Im not well enough versed in solar or electrical to diagnose the problem myself. All I can do is point out the symptoms and hope the "experts" can fix it.

    At the end, he handed me a estimate for $5000 to have my batteries replaced. With the batteries he recommends for my setup. Mind you, I bought this system FROM HIS COMPANY. He said I'd need to replace the current batteries so the old ones could be sent in to the mfg for warranty inspection and then I'd be given a fraction of what I paid as a refund. So in the end it'd be a net loss as I'd have to spend MORE money on new batteries, installed by the same ****tards that caused this problem in the first place. I will NOT be giving them any more of my business. But I need to diagnose this battery voltage issue in the meantime.

    Any thoughts?

  • #2
    Here are my settings options and what I have had them set too:

    Auto-Start on State of Charge: originally set to 60% and to shut off at 85% (assuming the panels could do the rest)
    Auto-Start on Voltage: originally set to 23.8v and to shut off at 28.8
    Auto-Start on Load: originally set to 3600w or 30amps


    Ive got the SOC to auto-start currently at 80% and shut off at 95% as to protect the batteries. But again, this function doesnt ever see use. The voltage drops way too fast.

    I lowered the Voltage auto-start to 23.2 and have tried it as low as 23 to see if when under load, the system would hover in the low 23's. It doesnt. I just continues to drop.

    And I never put a 3600w load on the system so that function has never had to kick in.

    Typically in the past, the voltage would correlate with the SOC. Now? They dont correlate at all.

    Comment


    • #3
      You cannot use voltage to determine SOC. Only way you can use voltage as an indicator of SOC is if the batteries are Open Circuit and allowed to rest a day. Even then is only a Ball Park value. Only way to determine the true SOC in real time is Specific Gravity.

      Lastly you have abused your batteries from deeply discharging them multiple times per day, compounded by parallel strings. Now have lost significant capacity. Lastly you should not be using 24 volts at this power level, 48 to 96 volts. Why are you using 3 charge controllers? That should have told you something is terrible wrong with your design.

      Good luck.
      Last edited by Sunking; 01-10-2017, 08:50 PM.
      MSEE, PE

      Comment


      • #4
        Well, looks like the heaters are a pretty heavy load, AND the auto gen box is not allowing any absorb time.
        Do you have any data of system settings [ Bulk/Absorb voltage, Absorb time, Float voltage ] from the original, pre-auto settings?
        You should have an absorb time of about 2 or 3 hours in the solar, and half that for the generator (to save fuel)
        The new generator settings have likely not allowed the batteries to fully charge and they have sulphated and are shot,

        The Big question, is why are you not using propane heat? Generators are only 30% efficient, charging batteries 80%
        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
          Originally posted by Sunking View Post
          You cannot use voltage to determine SOC. Only way you can use voltage as an indicator of SOC is if the batteries are Open Circuit and allowed to rest a day. Even then is only a Ball Park value. Only way to determine the real SOC is Specific Gravity.

          Lastly you have abused your batteries, and now have lost significant capacity.

          Good luck.
          Im not using voltage to determine SOC. I get the SOC reading from the digital readout. It's separate from the voltage reading.

          Can you please clarify how the batteries have been abused?

          Comment


          • #6
            Originally posted by Jabroni View Post

            Im not using voltage to determine SOC. I get the SOC reading from the digital readout. It's separate from the voltage reading.

            Can you please clarify how the batteries have been abused?
            Read out from what? The only way to determine SOC that means anything is by using a battery hydrometer to measure the Specific Gravity by sucking electrolyte out of the battery with a hydrometer. I am absolutely certain you are not doing that. Coulomb Counting will not work on lead acid batteries. That only leaves voltage.

            So whicch of the three methods are you using? Only one method will work.

            Yes you are abusing your batteries. They should be sized to run 2 to 3 days without need recharged on a generator. or in other words 5 day capacity of which only 3 days are usable.
            Last edited by Sunking; 01-10-2017, 08:58 PM.
            MSEE, PE

            Comment


            • #7
              Battery calcs
              830 ah @ 20hr rate = 41A load is the max the batteries can sustain when brand new

              2000w load for 7 hr = 83 amp drain for 7 hours = 600 ah consumed
              3000w load for 5 hr = 125 amp drain for 5 hours = 625 ah consumed When you add Peukert's Law, you likely were doing 95% deep cycles

              So you have hit your batteries really REALLY hard, combined with the auto-box not fully recharging, and the dealer better split the battery replacement cost with you - his fault for not configuring the Absorb time, which finished off your batteries,

              wikipedia.org/wiki/Peukert's_law
              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


              • #8
                Originally posted by Mike90250 View Post
                Well, looks like the heaters are a pretty heavy load, AND the auto gen box is not allowing any absorb time.
                Do you have any data of system settings [ Bulk/Absorb voltage, Absorb time, Float voltage ] from the original, pre-auto settings?
                You should have an absorb time of about 2 or 3 hours in the solar, and half that for the generator (to save fuel)
                The new generator settings have likely not allowed the batteries to fully charge and they have sulphated and are shot,

                The Big question, is why are you not using propane heat? Generators are only 30% efficient, charging batteries 80%

                I have a ton of data from the original system settings.

                Ive thought maybe the batteries were sulphated. But how does that happen instantly? This issue started IMMEDIATELY the first day I had the auto-start installed. Voltage just sunk and I couldnt run the identical load I was running just the day before.

                Never thought I'd need propane heat. I put $30k into a solar system. When the installers tell me I can run up to 4000w for multiple hours on a full charge, I assume the system will indeed do that. And it has just fine until the auto-start was added. What I cant seem to figure out is how the auto start would change the performance of the batteries overnight.

                Furthermore, my facility isnt typically made to be lived at. It only experiences these sorts of heavy loads (at night using the batteries) every 3 to 4 months for short periods of time. The majority of the year the batteries sit in float and at night might discharge down to 92% at worst.

                Comment


                • #9
                  Time for new batteries and a whole new design.
                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by Jabroni View Post
                    Never thought I'd need propane heat. I put $30k into a solar system. When the installers tell me I can run up to 4000w for multiple hours on a full charge,
                    You battery capacity at the 20 hour rate is 24 volts x 830 AH = 19.9 Kwh. If you slam them with an abusive rate of 4 hours the capacity drops by 40% or 12 Kwh. Do some simple math.

                    4000 watts x 4 hours = 16 Kwh and your gas tank only holds 12 Kwh. You should never discharge your batteries more than 50%, and that should not happen until 3 days with no sun shine. Whoever sold it to you did what they had to do to make a sell. They lied to you. Your batteries are shot and your system is improperly deigned and grossly undersized.

                    Never ever use off grid solar for any kind of heat. That is going to be a very expensive lesson you learned.

                    Sorry.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      Read out from what? The only way to determine SOC that means anything is by using a battery hydrometer to measure the Specific Gravity by sucking electrolyte out of the battery with a hydrometer. I am absolutely certain you are not doing that. Coulomb Counting will not work on lead acid batteries. That only leaves voltage.

                      So whicch of the three methods are you using? Only one method will work.

                      Yes you are abusing your batteries. They should be sized to run 2 to 3 days without need recharged on a generator. or in other words 5 day capacity of which only 3 days are usable.

                      Im trying to post a picture of my system's digital readout. It looks similar to this: http://www.invertersupply.com/index....33waAv1r8P8HAQ

                      But mine shows SOC, voltage, ADC, etc.

                      Now if that is not an accurate SOC and just some BS figure my system is telling me, I have no way of knowing that would be the case. Either way, it doesnt really address my issue. My system worked fine one day, the auto-start was installed, and then it didnt work as it once did. Kinda odd, no?



                      from the Full River website:
                      "Each Fullriver DC Series, Full Force and Full Throttle batteries are designed to be deeply discharged and recharged hundreds of times. With the sealed, maintenance-free aspect of all our AGM batteries, you can simply "Set it" and Forget it"."

                      The generator was only being used twice a day to recharge the batteries. If that is abuse, so be it. But it's nothing new to the company that installed the system. They knew what I'd be using the system for and how. All they said to worry about was the number of cycles the batteries went thru. Im not the expert here. I needed a solar system, I told the installer what I needed it to do, they designed a system that was supposed to work for that, I wrote the check. If the way Im using the batteries was destroying them (a) I wish I they wouldve told me that beforehand and (b) dont you find it just a bit odd that the batteries took a dump the day the auto-start was installed?

                      Comment


                      • #12
                        Originally posted by Mike90250 View Post
                        Battery calcs
                        830 ah @ 20hr rate = 41A load is the max the batteries can sustain when brand new

                        2000w load for 7 hr = 83 amp drain for 7 hours = 600 ah consumed
                        3000w load for 5 hr = 125 amp drain for 5 hours = 625 ah consumed When you add Peukert's Law, you likely were doing 95% deep cycles

                        So you have hit your batteries really REALLY hard, combined with the auto-box not fully recharging, and the dealer better split the battery replacement cost with you - his fault for not configuring the Absorb time, which finished off your batteries,

                        wikipedia.org/wiki/Peukert's_law
                        Ok. This is starting to make sense somewhat.

                        I can tell you for certain I was never using up 95% of the batteries. They were dropped to around 50% only a few times. I generally started recharging them at 60-70%.

                        And yes, he did not configure the absorb time. He mentioned that "mistake" yesterday. But again, that doesnt explain the batteries falling off a cliff instantly. They went from holding their voltage to not holding their voltage immediately after the autostart was installed. Not days later.

                        Comment


                        • #13
                          Originally posted by Sunking View Post

                          You battery capacity at the 20 hour rate is 24 volts x 830 AH = 19.9 Kwh. If you slam them with an abusive rate of 4 hours the capacity drops by 40% or 12 Kwh. Do some simple math.

                          4000 watts x 4 hours = 16 Kwh and your gas tank only holds 12 Kwh. You should never discharge your batteries more than 50%, and that should not happen until 3 days with no sun shine. Whoever sold it to you did what they had to do to make a sell. They lied to you. Your batteries are shot and your system is improperly deigned and grossly undersized.

                          Never ever use off grid solar for any kind of heat. That is going to be a very expensive lesson you learned.

                          Sorry.
                          FYI, this isnt simple math.

                          Im not an electrician or a solar expert, or even novice for that matter. As Ive said, the system ran just fine until immediately after the auto-start was installed. I cannot see how one affects the other in such a short time but that's the only correlation Ive got to work from. Had this problem started a week or just a few days into running the auto start, I wouldnt be barking up this tree.

                          If the batteries are indeed shot, wouldnt that show up on a voltage test? I watched at the installer was measuring each battery yesterday. Each were above 6v. And when put under a load by the tester, they barely dropped to 5.9v.
                          Last edited by Jabroni; 01-10-2017, 09:35 PM.

                          Comment


                          • #14
                            Originally posted by Sunking View Post
                            Time for new batteries and a whole new design.
                            a whole new design?

                            Why would I need new panels or inverters?

                            Comment


                            • #15
                              A new design is needed primarily because it is NOT SAFE at 24v first of all.

                              Just to be *sure*, you are pulling about 3K of power for heating, each-hour for about 4-6 hours?

                              Here's the breakdown for maximum limits just from a safety and efficiency standpoint.

                              Up to 1KW = 12v
                              1K to 2K = 24v
                              2K and up = 48v system (not much 36v gear)

                              So if it is true that you are doing 3Kw per hour, then yep, redesign time.

                              Comment

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