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  • #16
    Everyone,

    paulcheung is partially correct. I don't have a faulty volt meter, I am a faulty volt-meter-reader I think. I have an analog meter and after his comment, I just now went and tried it again. I think I had read the wrong scale. I re-measured and they were all reading at about 6V and the total battery bank was at about 51V. My apologies to everyone, and yet again, I feel pretty stupid. I double checked the volt meter on my newish truck battery and it read 12V. So, I think the volt meter is OK. You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.

    In the meantime, I was getting ready to post these thoughts about the discussion to date.

    Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

    Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
    So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?

    I see where a 370Ah rated battery isn’t quite big enough to allow for a 70% SOC, and certainly wouldn’t allow for any real storage for those cloudy days. In theory, if we reduced our usage to 3.5 – 5.3 Kwh, couldn’t we get away with the same size battery we currently have if we maintain it properly. Conversely, if we want to maintain our “extravagant” lifestyle of 6Kwh, then we would need at least a 420Ah rated battery, as suggested.

    I just now saw that you posted hoping I’d get back to you soon, so here it is.

    Dan

    Comment


    • #17
      Originally posted by dalyxxdj View Post
      Everyone,

      You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.
      Dan
      The two tests that Sunking suggested were open circuit and with C/10 load. Open circuit is simply measuring the voltage with nothing connected - there should be a disconnect in your system. C/10 means a current through your 48V bank of your AH capacity divided by 10 - in your case 370/10 = 37 Amps, @ 48V, or a load of about 1800 Watts.

      Comment


      • #18
        Some other things to factor in

        Daytime usage needs to be subtracted from the power available to recharge the batteries, with some clever timing, you can charge batteries, run the dishwasher and fill 3,000 gallons of water in the tank. Don't try any 1 of those things at night, on a cloudy day, or 2 at the same time. it's all about load management

        Any loads you can shift to solar hours (10am -3 pm) are loads the battery does not have to carry. nighttime, it's only 2 fridges, 1 freezer, and about 100w of incidentals - lights, TV & bidet.
        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


        • #19
          Originally posted by dalyxxdj View Post
          Everyone,

          paulcheung is partially correct. I don't have a faulty volt meter, I am a faulty volt-meter-reader I think. I have an analog meter and after his comment, I just now went and tried it again. I think I had read the wrong scale. I re-measured and they were all reading at about 6V and the total battery bank was at about 51V. My apologies to everyone, and yet again, I feel pretty stupid. I double checked the volt meter on my newish truck battery and it read 12V. So, I think the volt meter is OK. You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.

          In the meantime, I was getting ready to post these thoughts about the discussion to date.

          Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

          Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
          So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?

          I see where a 370Ah rated battery isn’t quite big enough to allow for a 70% SOC, and certainly wouldn’t allow for any real storage for those cloudy days. In theory, if we reduced our usage to 3.5 – 5.3 Kwh, couldn’t we get away with the same size battery we currently have if we maintain it properly. Conversely, if we want to maintain our “extravagant” lifestyle of 6Kwh, then we would need at least a 420Ah rated battery, as suggested.

          I just now saw that you posted hoping I’d get back to you soon, so here it is.

          Dan
          6000 WHs, if the load is spread out evenly, it is about 250 watts, which is less than 6 Amps at 48 volts., that is about 50 hours rate on a 370 AH FLA battery, it is equal to 394 AHs at that rate. remember, during sun hours the load is from the panels not the batteries, so you only draw about 16 to 18 hours from the battery, the Watt hours you draw from the battery is about 4000 to 4500 WHS. that is about 25% DOD for a 394 AHS from 48 volts system.

          The battery Sunking suggest is one of the best battery which could easily last you over 10 years for your application if you take care of them, but you can also buy the Trojan L16RE-B 370 amp hours battery which can yield you 394 AHs when you only discharge them at 6 amperes.

          My battery system is 750 amp hours at 48 volts, I consume 20 to 23 KWH each day. I do a lot of load during the day , my nightly consumption without sun is around 10 KWH. My battery bank voltage in the morning under 15amps load is around 48 volts before sun comes out. it gone 18 months already and I wonder how long my batteries will last.

          Comment


          • #20
            Originally posted by dalyxxdj View Post
            Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

            Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
            So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?
            You are on target Dan. But perhaps the wrong approach. A Off-Grid Battery system is designed based on how much energy you use in a day worse case. In practice two designs are done. One for Summer loads, and another for winter loads. Example if you use say 4 Kwh per day in winter and 6 Kwh per day in summer, the battery is sized to largest daily usage of 6 Kwh per day or a 30 Kwh battery.

            Same with panels but things can reverse because of winters short days. If you only had say 2 Sun Hours in winter and 5 in summer the winter panel power is 3000 watts and summer is 1200 watts. You use worse case of 3000 watts.

            As for batteries yes I know they are expensive, but which is cheaper? Buying the same battery you have now every 1-1/2 to 2 years, or the Trojans every 5 or 6 years? So what you need to get a handle on is how much you use each day. Once we know that we can zero in on batteries. As you are finding out be careful what you ask for. Solar battery is not cheap. That unfortunately is the choice you made going off-grid. You might not have realized that when you first went off-grid, but now you know and have to live with it. Hang in there, put a pencil to some paper, no rush, but figure out how much you use in a day in both winter and summer. You do no twant to have to go through this every 18 months and may not be as bad as you think. But you will not know until you have done your homework.

            So once you figure out the daily wattage here is how you find your battery capacity (daily watt hours x 5) / battery voltage. Example 5 Kwh per day: ( 5000 wh x 5) / 48 volts = 520 amp hours. A good 5 to 7 year battery will cost you $200-Kwh so a 25 Kwh battery cost $5000. Or another way to calculate is $1000 x Kwh-day. Like I said be careful what you ask for, it gets expensive real fast.

            With your panel wattage you have now of 2000 watts in winter can provide you up to 5.3 Kwh per day. 2000 watt panel can support a battery as small of 320 AH and as large as 480 AH @ 48 volts. You reall do not want to go outside that range with your panel wattage. Smaller batteries can be damaged by too much charge current, and larger will stratify.
            MSEE, PE

            Comment


            • #21
              Hi again,

              1) If my batteries are dead/useless, why do I still have any power at all? Today and tomorrow are going to be rainy/snowy/cloudy. I can run the generator now and then and get enough power to run my basics. When the sun comes back out on Tuesday (or yesterday when it was mostly sunny), I seem to be able to manage throughout the day until the next day, albeit the day starts out at 48 - 49 volts.

              2) From my last post, I did get a handle on our usage. At most it is 6,000 watts per day. Usually less than that, but hardly ever more. Most of that is during the day. We have one fridge, one well pump and not much else. We probably get 5 hours of sun in the winter (maybe only 4.5 on December 21) and 7 hours or more during the summer. If my current set up can handle 17.76 Kwh a day, 6 Kwh a day is about 65% SOC each day. Is that correct?

              3) I understand that going off-grid wasn't going to be cheap or easy. Money isn't the issue per se -- understanding the basics is what is important. If my understanding from above is correct, my current setup, given my usage of 6,000 watts a day is 5% less than ideal if I want to maintain no less than a 70% SOC. Correct? It also doesn't leave me much/any room for cloudy days.

              4) If I went with the batteries Sunking recommended, my watt hour capacity would be 22,272 watts, or 22.27 Kwh (464AH X 48 volts). Correct? Assuming my usage stays at 6,000 watts a day, or 6 Kw a day, my SOC on any given day only gets me to 73-74% SOC? Correct?

              5) We are assuming that my current batteries will only last 1 ½ to 2 years. I’ve admitted that I didn’t care for them like I should have. None of the cells are or ever were dry, but it is true that I didn’t EQ them like I should have and probably there are other things I should have done. However, I am assuming that 1 ½ - 2 years is atypical and that even these batteries should have lasted longer with proper maintenance and charging. However, how likely is it that my DOD, which was likely in the 35-40% range for most of the time would wear out any battery too quickly, even if I had maintained them properly? Are these batteries that much worse than many others?

              As always, thanks again for all your help. Let’s hope the sun will come out tomorrow!

              Comment


              • #22
                If my batteries are dead/useless, why do I still have any power at all?
                Any time your charging a set of batteries that can't carry your design load for the specified time, they are useless. That is usually when their capacity reaches 75-80% in the real world, but most RE folks keep on trying to 50% or so like you are.

                Have you never had a battery in a car that causes the starter solenoid click , but the starter does turn the engine over ?? Is that Battery dead ?? It has voltage, but no capacity the same as yours.

                Most people that take care would get more time out of the batteries you have, but your's weren't taken care of.

                EQ them, get them up to 62 V and see what you can recover from them. Use your hydrometer.

                Comment


                • #23
                  Originally posted by dalyxxdj View Post
                  Hi again,

                  1) If my batteries are dead/useless, why do I still have any power at all? Today and tomorrow are going to be rainy/snowy/cloudy. I can run the generator now and then and get enough power to run my basics. When the sun comes back out on Tuesday (or yesterday when it was mostly sunny), I seem to be able to manage throughout the day until the next day, albeit the day starts out at 48 - 49 volts.
                  I never said useless, I said toast meaning they have lost so much capacity makes them impractical. If your batteries are sized properly and good working order should last you 4 days. at 48 volts are near completely discharged. Assuming your battery reaches fully charged say by 2:00 in the afternoon, you should see 50 volts the next morning just before sun up.

                  Originally posted by dalyxxdj View Post
                  2) From my last post, I did get a handle on our usage. At most it is 6,000 watts per day. Usually less than that, but hardly ever more. Most of that is during the day. We have one fridge, one well pump and not much else. We probably get 5 hours of sun in the winter (maybe only 4.5 on December 21) and 7 hours or more during the summer. If my current set up can handle 17.76 Kwh a day, 6 Kwh a day is about 65% SOC each day. Is that correct?
                  That would be correct, but you really do not want to go that low in a day. It does not matter which part of the day you use the power. If you use 6 Kwh per day you want a 30 Kwh battery. That is what CYA to cover you for 3 cloudy days, and maximize your battery cycle life.

                  Originally posted by dalyxxdj View Post
                  5) We are assuming that my current batteries will only last 1 ½ to 2 years. I’ve admitted that I didn’t care for them like I should have. None of the cells are or ever were dry, but it is true that I didn’t EQ them like I should have and probably there are other things I should have done. However, I am assuming that 1 ½ - 2 years is atypical and that even these batteries should have lasted longer with proper maintenance and charging. However, how likely is it that my DOD, which was likely in the 35-40% range for most of the time would wear out any battery too quickly, even if I had maintained them properly? Are these batteries that much worse than many others?
                  DOD has significant impact on cycle life among other factors. Keep in mind manufactures greatly exaggerate cycle life claims. They test in a labe performing many cycles a day to gather data for their charts. But batteries also have a calendar rather they are cycled or not. The battery warranty gives you a very good idea how long they will last. Example a battery listed at 2000 cycles to 20% DOD daily (80% SOC) would make one think you have a 6 year battery. However it carries a 18 month full replacement and 36 month prorated warranty is a 2 to 3 year battery at best or roughly 600 to 900 cycles.

                  Anyway here is a chart from a good manufacture. It has a 60/90 warranty. Very expensive battery.

                  MSEE, PE

                  Comment


                  • #24
                    Thanks again for responding so quickly. Regarding my first question, I really did just want to know how it was at all possible we are getting anything at all. I’m grateful that we’re getting anything because it could be awhile until we get a new set of batteries. So thanks for clearing that up for me! Just to clarify, are you saying I should see 50 volts in the morning with good batteries, not with my current batteries? In my current situation, I’m happy when I wake up and see 49 these days.

                    Also, I want a 30Kwh battery because that is 6 Kwh X 5 hours of sun? Or? And how is that related (or is it) to the Ah rating of the battery? Finally, what is AH20 vs. AH5 or AH100? On the battery you have recommended, the AH20 rating is 464, but I didn’t see a spec for Kwh, although I did see the spec labeled Energy as 3.61 kWh?

                    I’ve assumed that a cycle is from Rest to Bulk to Absorb to Float and back to either Rest or Bulk. True? If so, it isn’t necessarily one day, but for us that seems to be what was happening back in the good old days when we actually got to Absorb and Float.

                    Thanks again and let me know on these final (for now) questions!

                    Comment


                    • #25
                      Originally posted by dalyxxdj View Post
                      Just to clarify, are you saying I should see 50 volts in the morning with good batteries, not with my current batteries? In my current situation, I’m happy when I wake up and see 49 these days.
                      The answer to your question is apparent in the chart in Post #12 in this thread. He means good batteries.

                      Comment


                      • #26
                        Originally posted by dalyxxdj View Post

                        I’ve assumed that a cycle is from Rest to Bulk to Absorb to Float and back to either Rest or Bulk. True? If so, it isn’t necessarily one day, but for us that seems to be what was happening back in the good old days when we actually got to Absorb and Float.
                        I use to run a 6 minute mile, now maybe a 15 minute mile if I was lucky and down hill. If your seeing 49V in the morning, your still getting over the hump. Your losing capacity and have sulfated plates, thats all. Everyone with a set of batteries goes through the same thing. You still haven't posted any SG level.

                        Comment


                        • #27
                          Originally posted by Living Large View Post
                          The answer to your question is apparent in the chart in Post #12 in this thread. He means good batteries.
                          Only if you believe that chart is correct, some manufacturers have a much different take on it.

                          Comment


                          • #28
                            Originally posted by Willy T View Post
                            I use to run a 6 minute mile, now maybe a 15 minute mile if I was lucky and down hill. If your seeing 49V in the morning, your still getting over the hump. Your losing capacity and have sulfated plates, thats all. Everyone with a set of batteries goes through the same thing. You still haven't posted any SG level.
                            Thanks for the analogy, that helps. When I get my hydrometer, hopefully this week, I'll take some readings and let everyone know where I'm at.

                            Comment


                            • #29
                              Originally posted by Willy T View Post
                              Only if you believe that chart is correct, some manufacturers have a much different take on it.
                              I answered the question as to what Dereck meant, based on the reported performance issues, Dereck's comments, the chart and the question. As to the accuracy of the chart, that is a different matter I can't comment on.

                              Comment


                              • #30
                                Originally posted by dalyxxdj View Post
                                Also, I want a 30Kwh battery because that is 6 Kwh X 5 hours of sun? Or? And how is that related (or is it) to the Ah rating of the battery?
                                Has nothing to do with Sun Hours, it has to do with battery autonomy or reserve capacity and maximizing battery cycle life. All Autonomy means is how many days the battery can supply you with power before completely discharged. FLA systems are designed for 5 days, so it is 5 days x 6 Kwh per day. In reality you do not want to take your batteries lower than 50% and one reason why you have a generator. It gives you roughly 3 cloudy days before you have to run the generator.

                                Additionally if you look at any FLA battery graph of cycle life vs Depth of Discharge you can quickly locate the economic Sweet Spot to get the most bang for your buck. The Sweet Spot is located on the flat part of the line where it starts to be linear. FLA batteries that Sweet Spot is typical between 15 to 30% with 20 typical. Here is a different graph from Rolls 5000 Series.


                                The graph is mirror image but the Sweet Spot is 30%

                                Originally posted by dalyxxdj View Post
                                Finally, what is AH20 vs. AH5 or AH100? On the battery you have recommended, the AH20 rating is 464, but I didn’t see a spec for Kwh, although I did see the spec labeled Energy as 3.61 kWh?
                                It is a description of Peukert Law which states: As the discharge rate increases, the battery's available capacity decreases. Rate is expressed in hours. Amps = Amp Hours / Hours. So when you see C/20 which is typically how a manufacture rates the battery is C is the Amp Hours and 20 is Hours. So if you have a 100 AH battery at C/20 is telling you that battery can deliver amps for 20 hours. 5 Amps = 100 AH / 20 Hours. However if you discharge at a higher rate say 5 hours or 20 amps the capacity is 75 AH. Look at this battery spec, Rolls S-600 and note AH at 100 hours, 20 hours and 1 hour. At 100 hours it is a 599 AH battery. At 20 hours is 450 AH and at 1 hour sis only 162 AH. That is Peukert Law.

                                Originally posted by dalyxxdj View Post
                                I’ve assumed that a cycle is from Rest to Bulk to Absorb to Float and back to either Rest or Bulk. True?
                                Not quite and cycle life solar terms is a day or one complete charge cycle. In the morning your system should go to Bulk, then Absorb, and then Float and hold there until the next day. When it gets to Float is 100% charged. Kicker is in a Solar System 3-stage charging is useless because there are not enough hours in a day. Set Bulk = Absorb = Float = 57.6 volts.
                                MSEE, PE

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