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  • AGM charging versus Flooded

    Hello all. First post. Looking for help regarding a problem I'm having with slow charging of 6 volt AGMs.

    I have two systems on two RVs parked side by side. The systems are identical other than one has 4 Trojan T105 flooded (total of 450 AH) while the other has 4 Crown AGM (total of 420 AH). Both systems are comprised of three 160 watt panels in parallel feeding Borgart Engineering SC2030 charge controllers communicating with 2030 Trimetrics.

    With the Trojans (they're two years old) this setup has always worked well. With about 15% DOD I reach absorb of 14.8 vdc followed by full charge and float by noon most days, even before getting max charge amps. With the same charging rate going into the Crown AGMs (they're 2 months old) I rarely reach absorb of 14.6 or full charge by day's end. Voltage just rises to about 13.5 and hangs there for a long time.

    Put simply the AGMs take forever to charge while the flooded Trojans behave as expected with the same charge rate. What would cause this? Wiring is correct and both charge controllers seem to be working as designed and have correct programming.

    My second question is something I've never been able to get a good answer to: if the AH removed during a discharge is replaced (plus a little more) is the bank full even though absorb voltage was never reached and held there until current falls below 2%? With flooded the SG and open circuit voltage after resting seems to indicate it is but I'm unsure about AGMs.

    Thanks in advance for any insights.

  • #2
    What are the chances that the RV with the AGM, has some sort of parasitic draw, like a LPG leak sensor, or smoke alarms, or it's AC inverter is turned on?
    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

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    • #3
      There could be any number of reasons the AGM batteries are not holding a charge.

      As Mike stated you may have some additional load on them that slowly discharges while you are charging or there is a possibility that you have found out why the Trojans are just a better battery for the type of system you use. Or the AGM's are just looking for a more aggressive charge rate then the Trojans.

      Have you tried swapping the battery systems to see if the problem is with the RV loads?

      Comment


      • #4
        Thanks for the input. The AGMs are holding charge fine, the problem is taking the charge. Once there capacity seems normal.

        Parasitic loads have been reduced to near zero. Also, the Trimetrics display the amount of current flowing into the banks during charge and both are near identical at around 30 amps.

        I have not tried swapping the banks as that would be a job.The AGMs looking for a more aggressive charge is an interesting theory though. I'll give Crown a call and see what they say.

        Any thoughts on my second question?
        Last edited by Mitch Carbide; 05-15-2017, 11:10 AM.

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        • #5
          I want to say you are comparing apples-to-oranges, well more like tangerines-to-oranges.
          Flooded vs AGM - they are very similar but they are different.

          Do you have the same exact same Charging Profile selected on both Bogart Engineering SC2030 Charge Controllers or
          o you have different Charge Profiles selected?

          Can you ... physically measure the Net Bulk Charging Amps flowing into the Flooded Battery Bank vs the AGM Battery Bank
          to verify the Trimetric Net Amps reading?

          Flooded Lead Acid can be charged at 10% - 15% of the C-20 Hour Rating = 45 Amps vs Solar Panels generate 27 Amps.
          When the voltage during Bulk Mode rises to 14.8 Volts and the Charger transitions from Bulk Mode to Absorb Mode
          then your flooded batteries are near 90% SOC, not 100% SOC.
          Absorb Mode then charges the final 10% SOC ( 100% SOC when below 2% Amps )

          AGM Batteries can be charged at 20% of the C-20 Hour Rating = 84 Amps!
          Your Solar Panels only generate 27 Amps - way too low.
          When the voltage during Bulk Mode rises to 14.4 Volts and the Charger transitions from Bulk Mode to Absorb Mode
          then your AGM batteries are near 80% SOC, not 100% SOC.
          Absorb Mode charges the final 20% SOC ( 100% SOC when below < 1% Amps )

          Summary ...
          Bulk Mode for your AGM should be a much shorter time, at a much higher amps rate vs Flooded
          Absorb Mode for your AGM is a much longer time, from (14.4v) 80% to 100% SOC vs the Flooded from (14.8v) 90% to 100% SOC.
          Absorb Mode for an AGM is about twice as long, as Absorb Mode for a Flooded.
          The Charging Profiles are similar, but they are not identical.
          If you expect the Total Charging Time for AGM and Flooded to be the same then you must speed up Bulk Mode for your AGM,
          because AGM Absorb Mode is much longer than Flooded


          Answer to your 2nd Question ...
          If you can, then it is best to reach and HOLD the Absorb Voltage daily.
          Flooded - Reach and HOLD the Absorb Voltage (14.8v / 90% SOC) until the Amps drop to 2%, or mfr specs for 100% SOC.
          AGM - Reach and HOLD the Absorb Voltage (14.4v / 80% SOC) until the Amps drop < 1%, or mfr specs for 100% SOC.

          If you don't reach 100% SOC daily then you might need to Equalize more often - I treat lead sulfate like it is cancer.

          It is extremely difficult to get to 100% SOC using Bulk Mode only, which is why Absorb Mode exists.
          Use your hydrometer on the Trojans & stay in Absorb Mode until the SG stops rising for 2 consecutive measurements, 1 hour apart.
          Your hydrometer will tell you exactly how long the Trojans need to stay in Absorb Mode to get to 100% SOC ( 1%, 2% or 3% Amps ? )
          Using the voltage of the battery to estimate the State-Of-Charge is just not accurate enough.

          After Absorb Mode, I use a third mode called Finish Mode.

          The guys at "RV dot NET" are extremely knowledgeable about Solar, RV and Flooded vs AGM related issues.
          Last edited by NEOH; 05-15-2017, 11:31 AM.

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          • #6
            NEOH, thank you for the detailed reply. I will try and answer your questions:

            1) I am not using the same charging profile on both systems. The flooded goes to 14.8 and holds until 2% then switches to a 15.5 vdc finish until replacement charge equals 110%.

            The AGM is set to reach 14.6 vdc (Crown's recommendation) and hold until 2% then continue there until 105% charge is replaced. I don't see how that matters however. The problem is getting the AGMs to rise to 14.6. Takes forever compared to the flooded reaching 14.8. Many hours longer. Again, both banks are the same AH and both are charging at the same rate.

            2) I have measured both charging currents at the battery using an amp clamp. Both are the same. And does the shunt on a Trimetric not show net flow into the battery anyway?

            I suspect I could connect any charging source to the two banks after discharging the same amount on each bank and still see the AGMs lag. In fact, when using the RV converter (65 amps to 14.4 vdc), charging still seems slow. This goes against everything I know about AGM.

            Fwiw I'm a BSEE and have installed 4 other similar systems all using flooded Trojans with all behaving as expected. This is the first one I've done using AGM which the owner agreed to on my recommendation. It's why I'm trying to puzzle this out. I do understand I'm not charging them at the rate I should and that could be an issue. Still, they're both lead acid chemistries and I don't feel it should be so slow compared to flooded. I've been wrong before though.

            As for my second question, are you saying that if the same number of AH (plus a bit more) are flowed into the bank that were taken out the bank is NOT fully charged if it doesn't reach absorb? Put another way, will long term "trickle" charging do it? SG readings on my flooded indicate it does.
            Last edited by Mitch Carbide; 05-15-2017, 05:23 PM.

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            • #7
              Crown 420AH at 12 Volts = 4 @ 6CVR215 or 6CVR220?
              So, that means you have two banks in series and those banks in parallel?
              Load & Charger at opposite diagonal connections?


              Issue #1 - Slow Bulk Recharge
              ========================

              What is the Voltage of each 6 Volt AGM battery during Bulk, Absorb and Float?
              Crown states, "All four (4) batteries should be within 0.25 volts"
              I would disconnect the AGM battery pack, let it rest for 24 hours, and then measure each.
              Is one AGM battery weaker than the other?
              Swap the two battery banks and swap the Charging Profiles...
              a) Did the problem follow the AGM Battery bank and the Charging Profile?
              b) Did the problem stay at the same RV?
              This will PROVE whether it is a AGM Battery Bank / Profile issue or an RV issue.
              You need to know what is actually functioning properly and what is not functioning.
              Send an email to Bogart Engineers - have they seen this "13.5 volt plateau" issue with their AGM Charge Profile.
              If you really only consumed 15% of the 420 AH Rating then Bulk @ 27 amps should not last more than 3 hours.


              Issue #2 - Bulk Mode NEVER reaches Absorb Voltage
              ===========================================

              I would never do this.
              Not one Lead Acid Battery Manufacturer recommends doing this.
              If you continue doing this, your batteries will see an early grave.
              You have been warned ...
              Last edited by NEOH; 05-18-2017, 02:56 PM.

              Comment


              • #8
                Originally posted by Mitch Carbide View Post
                NEOH, thank you for the detailed reply. I will try and answer your questions:

                1) I am not using the same charging profile on both systems. The flooded goes to 14.8 and holds until 2% then switches to a 15.5 vdc finish until replacement charge equals 110%.

                The AGM is set to reach 14.6 vdc (Crown's recommendation) and hold until 2% then continue there until 105% charge is replaced. I don't see how that matters however. The problem is getting the AGMs to rise to 14.6. Takes forever compared to the flooded reaching 14.8. Many hours longer. Again, both banks are the same AH and both are charging at the same rate....
                I have to ask. Are they both getting cycled to the same DOD?

                While the systems are close to the same if the AGM have twice the load on them it will take twice as long to charge them.

                WWW

                Comment


                • #9
                  OK your first mistake is is using Bogart and Trimetrics to give you any useful information. You cannot use voltage on a working system to tell you the SOC of any Lead Acid Battery. It is worthless. SOC voltages can only be used on a fully rested battery disconnected open circuit. We are talking disconnected and rested for 12 to 24 hours. Even then it is only Ball Park and not accurate.

                  The correct algorithm for the T-105 is to charge at 14.8 volts on a 12 volt battery until charge current tapers down to 13 amps on a 450 amp stack (3% of C/20). At that point you float charge at 13.5 volts until the cows come home.

                  As for the Crown AGM batteries you did not specify model number but they only give generic specs. First AGM is extremely sensitive to heat and thermal runaway and thus should use Temperature Compensation. Colder the battery is the higher the voltage. That means the Bulk/Absorb ranges (temp comp) from 14.4 to 14.8 volts until current tapers down to 3 amps on a 440 AH stack (.07% of C/20), then Float at 13.2 volts. (much lower float than FLA)

                  Similar but different voltages and termination current. My guess is you are not using Temperature Compensation on your AGM batteries. Nor are you using a high enough voltage if you are not using Temp Comp. The Trojans need 14.8 volts, and the AGM needs 14.4 to 14.8 depending on Temp.

                  Here is the Spec Sheet on the T-105's Note the Bulk/ Absorb is 14.82 volts @ 12 volt battery. They can also be Temp Compensated (see spec for values) but FLA's are not prone to thermal runaway like AGM's.

                  Last 2 comments is AGM's need to be charged at much higher rates than FLA. Crown recommends C/4 so with your 440 AH battery is 110 amps. They need that fast rate to generate gas and pressure inside. If you go slower the ABSORB time increases greatly because it takes a lot longer time for the pressure to build up and thus saturate the battery to see the current taper down to 2 or 3 amps. Also as WWW hints at you might be discharging the AGM's a lot more than you think.
                  Last edited by Sunking; 05-18-2017, 05:55 PM.
                  MSEE, PE

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                  • #10
                    NEOH: I'm quite familiar with the owner/designer of Bogart. He hasn't a clue. As for the bank being charged by replacing the AH removed I don't do it but was merely seeking an answer. I can tell you without a doubt if I do this without ever reaching absorb the specific gravity shows fully charged as I've mentioned several times.

                    WWW: The Trimetric records AH removed. Does that not give me DOD? Or are you saying the rate of discharge matters?

                    Sunking: Your regurgitating stuff I already know and mostly agree with. Not helpful.

                    Trimetric...I've installed many and all including mine work flawlessly, especially when coupled to their solar controller. I and others in small RV solar consider it the best setup to be had and my experience bears that out.

                    The other rant of yours that always makes me chuckle is the "big inverter on 12 volts" thing. It's nonsense if one derates the unit. Makes it last longer too. As for "joe blow can't terminate properly" I've lost count of the proper 2/0 crimps I've made with a $35 hydraulic unit from Amazon. Not a one has ever given me a lick of trouble even when run @ 300 amps over time.

                    I've read much of your stuff here and while a minority is absolute nonsense the rest is solid. Not so your egotistic, self inflated, and condescending attitude. It's a pity someone with your technical knowledge possess such grossly obvious personality flaws.

                    Comment


                    • #11
                      Originally posted by Mitch Carbide View Post
                      Sunking: Your regurgitating stuff I already know and mostly agree with. Not helpful.
                      It appears to me you do not know what is going on. If you did you would not be here asking questions. I have forgotten more about Pb batteries than anyone on this forum will ever know about them. Certainly more than you do because I explained why it is taking so long to saturate your AGM battery.

                      AGM must be charged fast in order to develop gas pressure. Fast as in C/4 for your batteries. If you charge slow, when they reach Absorb stage, it will take a very long time to saturate and for charge current to taper to less than 1% C. It has to gas and build up the pressure. If you charge at C/4, the pressure has built up already when you go to absorb. When that happens Absorb happens very fast. That is what you do not know, and Using any voltage monitor is worthless on Pb batteries. Just a clever upsell item.

                      FWIW to put in your book of knowledge AGM charge efficiency at C/4 is 90 to 95%, It drops significantly at slower charge rates. FLA at any charge rate is around 80%. AGm have their place in a solar system where either high charge or discharge rates are encountered. But they do not charge exactly like FLA. It is apparent you do not know that.

                      Lastly I could care less what you think, Grow some skin and balls. It gets you through the real world and out of your make believe Safe Zone world.
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by Mitch Carbide View Post
                        .....

                        I've lost count of the proper 2/0 crimps I've made with a $35 hydraulic unit from Amazon. Not a one has ever given me a lick of trouble even when run @ 300 amps over time.

                        ......
                        I have lost count of the number of times I have crossed an active roadway in the middle and have not been hit by a car. That does not make it safe or smart.

                        Using a cheap hydraulic crimper from Amazon will work but there is still a chance that the connection will fail if it has been weakened by movement and sees too many amps.

                        Cheating death a dozen times does not make the 13th time any safer. So excuse us if we like to point out unsafe practices which may help others not so lucky to stay healthy.

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                        • #13
                          Originally posted by SunEagle View Post
                          I have lost count of the number of times I have crossed an active roadway in the middle and have not been hit by a car. That does not make it safe or smart.

                          Using a cheap hydraulic crimper from Amazon will work but there is still a chance that the connection will fail if it has been weakened by movement and sees too many amps.

                          Cheating death a dozen times does not make the 13th time any safer. So excuse us if we like to point out unsafe practices which may help others not so lucky to stay healthy.
                          Not one of those crimps would ever pass an Electrical Inspection. Anyone using such tools is not a professional, HACK would be accurate. Seem to recall users get banned advocating dangerous and illegal activity?

                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by Sunking View Post

                            Not one of those crimps would ever pass an Electrical Inspection. Anyone using such tools is not a professional, HACK would be accurate. Seem to recall users get banned advocating dangerous and illegal activity?
                            But, just to be clear, it must be OK if it's on the new idiot's bible - u-tube, right ?? I mean, isn't it ?? Really ??

                            Comment


                            • #15
                              LOL. So hydraulic crimpers are rocket science now?

                              1) Other AGM banks charge fine at that low rate.

                              2) Crown says the thing about pressure is nonsense. Their guy actually laughed at it. So much for "I have forgotten more about Pb batteries than anyone on this forum will ever know about them."

                              Thanks for all the "help" folks. I appreciate the effort if not the content. Adios...

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