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  • Float voltage for Rolls S-550

    Hi,

    My recently installed system (not really yet in use) has been floating the batteries for the past couple of very sunny days - about 8 to 10 hours per day. The Conext SCP tells me (as you can see in the attached picture) the float voltage is 54.4 volts (factory default) at 0.7A. The PV in is coming from 12 x 280W panels, all in series, using a MPPT 80-600 charge controller.

    I have 8 Rolls S-550 (428Ah) batteries, all in series.

    My Conext Battery Monitor still tells me that the batteries are 97% full.

    So I have two questions:

    1. is it normal that the current is so low? I would expect more a 4-5 amps than 0.7-0.8A.
    2. should I change the float voltage and slightly increase it?

    Thanks,
    Attached Files

  • #2
    How can the Conext Battery Monitor actually [B]know[/B] that the battery is 97% charged?
    Can the Conext read the SG of the electrolyte?

    Did you do the "Initial Charge" per the User's Manual?
    Did you get three equal hourly SG Readings?
    So then you know the SOC, right?
    You need to keep detailed records for Rolls Warranty.

    If Rolls says Float at 54.4 Volts (temp compensated) then Float at 54.4 Volts, unless you know more than the Rolls engineers.
    Are you complaining that your Battery bank has a low self-discharge?

    Comment


    • #3
      Originally posted by extrafu View Post

      My Conext Battery Monitor still tells me that the batteries are 97% full.

      So I have two questions:

      1. is it normal that the current is so low? I would expect more a 4-5 amps than 0.7-0.8A.
      2. should I change the float voltage and slightly increase it?,
      OK you probable will not like the answers, but at least you will know what is going on.

      The Conext Monitor is useless hardware. You cannot use Voltage to tell you what the SOC is on a working system. Voltage can only be used on a Open Circuit battery rested for 24 hours. So if you want to use you Conext, disconnect everything from the battery except the Conext, wait 24 hours and then it will give you a Ball Park SOC voltage. Will not be accurate, but who cares. So as you can see as worthless as tits on a boar hog.

      A1. There is no Normal Current. When a battery is fully charged, there is little or no current because it is Floating. [B]Battery Charge Current = [Charge Voltage - Battery OCV] / Battery Internal Resistance[/B]. Now that may not jump out at you but look at [U]Charger Voltage - Battery OCV[/U]. If both are the same voltage = 0 volts difference right? Well if they taught math in your school one lesson you had was[B] 0/x = 0[/B]. Zero divided by anything equal 0. So as the battery charges up, it voltage rises and when charged up equals the charger voltage, thus no current will flow.

      A2. No one can answer except your battery hydrometer. Bulk, Absorb, and Float voltages are just names of ranges. There is no exact number. Bulk can be anywhere 2.45 to 2.50 volts per cell. Float 2.25 to 2.35 vpc.

      Try reading this [B][I][U]Sticky[/U][/I][/B], and [B][I][U]this one[/U][/I][/B]. Then come back with questions.
      MSEE, PE

      Comment


      • #4
        Originally posted by Sunking View Post
        A1. There is no Normal Current. When a battery is fully charged, there is little or no current because it is Floating. [B]Battery Charge Current = [Charge Voltage - Battery OCV] / Battery Internal Resistance[/B]. Now that may not jump out at you but look at [U]Charger Voltage - Battery OCV[/U]. If both are the same voltage = 0 volts difference right? Well if they taught math in your school one lesson you had was[B] 0/x = 0[/B]. Zero divided by anything equal 0. So as the battery charges up, it voltage rises and when charged up equals the charger voltage, thus no current will flow.
        Thanks! I indeed do get that But I guess my questions wasn't clear. I was more wondering where it came from and I think I know why. The inverter and charge controller consume 20-30W when idling and at 48V, it's about .4 to .6A. So I guess my batteries are pretty much full (and should be after being floated for so many days) but the CC is pumping a bit more in the batteries to compensante the usage from the inverter and CC since they never stop drawing power.

        I am aware the Conext Battery Monitor isn't 100% accurate but it should still do a nice job at showing good numbers to people not off-grid savvy when I'm not there for a few days.

        As usual, many thanks for your help [USER="2334"]Sunking[/USER] !

        Comment


        • #5
          If you haven't seen it yet, you mind find it useful to review the voltage guidelines Rolls has published (with the first sentence of the document providing the reminder that specific gravity is the truest measure of state of charge)

          http://support.rollsbattery.com/supp...acid-batteries



          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

          Comment


          • #6
            [USER="24105"]sensij[/USER] Yep, saw that - thanks though!

            Comment


            • #7
              Take note Rolls, Trojan, Crown and all leading manufactures have turned up the voltage significantly. Solar users are beating the manufactures up with warranty claims. The issue is not the batteries but solar and solar users.

              When it comes right down to it, solar is not capable of charging lead acid batteries unless over sized. What you will notice today from Trojan and Rolls is the so called 3-Stage Algorithm is really gone. That works great on AC powered chargers that are not power and time limited. The issue is the Absorb stage takes 6 to 12 hours complete. Solar does not have that luxury of time and power to do that.

              So what the manufactures are seeing is a lot of Chronic Under Charged batteries coming in for Warranty claims. Of course when they see chronic under charged batteries voids the warranty. To try to get out ahead of this and slow it down, they changed Voltage Set Points. Something I said and wrote about a few years ago here with Max Smoke settings and use a Hydrometer to set the voltage. Example both Trojan and Rolls upped Bulk/Absorb to 14.85 volts up from 14.2. Trojan does not even use the Terms Bulk and Absorb today. It is now called Daily Charge to 14.85 volts until current tapers down to 3% of C. Solar is still not capable of doing that, bu tit should slow down the claims.

              Now maybe you understand if you are off grid, you must have a generator to recharge your batteries at least once a week. Solar is not going to do it.
              MSEE, PE

              Comment


              • #8
                Looking at the latest Rolls manual from their website, They are now stating even higher Bulk/Absorb settings for off-grid use: http://rollsbattery.com/wp-content/u...ery_Manual.pdf

                For off-grid 12V battery I see 15V or 60V for my 48v system.

                What i am wondering is if I should follow their formula for calculating max Absorb time which gives me about 4 hours.

                I am also curious about the easiest way to have force a longer Absorb time for Generator runs once a week? Should I change the Absorb time for that cycle and then reset back to the 4 hours? I small pain in the rear but easy enough.

                I wasn't happy with my SG readings so I've cranked up my voltages and doing long charge cycles using my generator.
                :

                Comment


                • #9
                  Originally posted by Riley5781 View Post
                  Looking at the latest Rolls manual from their website, They are now stating even higher Bulk/Absorb settings for off-grid use: http://rollsbattery.com/wp-content/u...ery_Manual.pdf:
                  Yep, already stated, they did that a few years ago with all others.

                  Originally posted by Riley5781 View Post
                  What i am wondering is if I should follow their formula for calculating max Absorb time which gives me about 4 hours.
                  You can set it to anything you want or disable it. Absorb is not a timed event and can take 6 to 12 hours. There is not enough hours in a Solar Day to charge a battery. That is why you are not happy with you SG readings. You are like anyone else with solar, you have chronic under charged batteries.

                  Absorb is a metered event measuring current. For a normal charge you apply 14.8 volts until current tapers to 3% of C. Time has nothing to do with it other than it takes a long time When you set a Controller up, you will set the voltage for Bulk/Absorb to say 14.8 volts. When the sun comes up, your Controller will be in Bulk or aka Constant Current mode. As the day goes on, the voltage of the battery rises with a constant current with all the power the panels can muster. Then sometime later in the day or afternoon your batteries finally reach 14.8 volts, which starts the Absorb phase when current starts to taper off. as the battery saturates. So unless your battery are in Absorb before noon, there is just not enough sun light to fully Saturate the battery. Next day, same thing. You never get fully charged.

                  You cannot force Absorb. You do not have any control of it. It is a point at where your battery voltage reaches voltage set point. You do not even worry about. In solar applications, you do away with it by turning up the voltage set points. At the end of the day, check SG. If SG is low, turn the voltage up.

                  Battery Charge Current = [Charger Voltage - Battery OCV] / Internal Resistance

                  Charging Battery Voltage = OCV + [Ri x Current]


                  MSEE, PE

                  Comment


                  • #10
                    Only way to get more absorb time, is to increase the Bulk & Absorb voltage settings to push more power in the batteries, without cooking batteries or other gear. Try increasing by 0.1V daily till you get better SG or start reaching Float. Then prepare to enter winter with shorter solar days
                    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
                      Originally posted by Mike90250 View Post
                      Only way to get more absorb time, is to increase the Bulk & Absorb voltage settings to push more power in the batteries, without cooking batteries or other gear. Try increasing by 0.1V daily till you get better SG or start reaching Float. Then prepare to enter winter with shorter solar days
                      Yes Sir, called Max Smoke.

                      You want to disable Absorb time and force your controller to run CC/CV. You set Bulk = Absorb = Float = 14.8 volts on a 12 volt battery. At the end of the day, take a hydrometer reading. If it is low, turn the voltage up. If it is too high, turn the voltage down. When it is right, leave voltage alone.

                      What you will likely find is there is no voltage high enough, at least in winter. In Summer you might be able to fully charge a battery. If you never reach full charge means your panel wattage is to low and you are running out of day light. Bottom line it means your system is poorly designed. Even if properly designed you may never get your batteries fully charged because there is not enough Sun Hours. If absorb takes 12 hours, you are SOL. That is why you need a generator to fully charge your batteries once a week, and EQ them once a month. Solar cannot do that.

                      MSEE, PE

                      Comment


                      • #12
                        Thanks guys. Very helpful advice.
                        I am working my batteries harder now and everyday ending with a higher SG.
                        I am also doing a couple of hours of EQ each day as well.

                        Question - As I am working to breath life into these batteries, do I need to worry about an EQ cycle of 3 hours a day for 4 days or so?

                        Comment


                        • #13
                          Originally posted by Riley5781 View Post
                          ....Question - As I am working to breath life into these batteries, do I need to worry about an EQ cycle of 3 hours a day for 4 days or so?
                          Just until the SG stops climbing. Then let them do the daily cycle thing for a week, and then try EQ's again to get the SG up. It's going to take a while to condition the cells, just plan on it taking time.

                          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


                          • #14
                            Ok after about 9 hours of EQ (over 3 days) my cells are now up at 1.260 SG range.

                            The Rolls S-550 manual talks about 100% charge being in the range of 1.255 to 1.275 SG. However on the S-550 datasheet, they state the capacity at 1.280 SG. Obviously they will get better numbers when measured at 1.280.

                            My question is: should I push the batteries past 1.275 and try to get to 1.280? Or would that stress them too much with an over charge?

                            Today will be my first cycle without any extra generator help for long EQ cycle. I will just let it run and see what happens with my new higher voltages or Bulk, Absorb and Float.

                            Comment


                            • #15
                              Originally posted by Sunking View Post

                              ... snip ...

                              Absorb is a metered event measuring current. For a normal charge you apply 14.8 volts until current tapers to 3% of C.
                              So I have a S-550 Royals 428AH battery system (8 in series for 48 volt system).
                              I assume when it's recommended to exit absorb at 3% of C, that would be 428*0.3 = 12.8 amps.

                              That seems a little high to be dropping out of Absorb and thinking I should run longer to a lower current to get a higher level of charge.
                              In the summer time I find to get my SG up to 1.275, I don't drop out of Absorb until about 5 or 6 amps.

                              Note that in the summer months, I easily have enough sunshine to do this... but want to make sure I don't over charge.
                              I think my load is such that I don't discharge my batteries very much so doesn't take that long to get back to full charge.

                              Is my math correct? OR am I missing something.
                              .

                              Comment

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