Is it time for new batteries?

rgk1
rgk1 Solar Expert Posts: 134 ✭✭✭
My batteries are usually cycled very, very shallow. During the summer a box fan, radio and a few lights during the daytime and probably no net deficit to the batteries. During the winter mostly just the dusk to dawn LED light outside (13 watt on maybe 13 hours a day) as is the case right now.

Today is the 1st day in a couple of days to have intermittent bright sun. Has been cold (for my area) for about a week. Looking at the meter on the CC it was going back and forth between MPPT and Absorb with the passing clouds.

Would I be correct to assume the CC is on the border between bulk and ready for absorb? The big issue and reason for the post is the logged data so far today:

Battery min. voltage 24.6
Battery max voltage 30.0
Battery amps today 18.9
Battery temp 46F

Should it be entering absorb after less than 20 amps with voltage low of 24.6 for the day? (210ah bank)
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is it time for new batteries?

    It will drop back to MPPT (Bulk) whenever the panels are not able to maintain Absorb Voltage level. This will be a function of how much light the panels get and how much load is on the controller (including battery charge demand).

    As for whether you need new batteries the question is: how is it performing compared to history?

    If you want to test the batteries you need to full charge them, see how long they'll hold with no load, and then discharge them and see how fast they go down. A rapid drop with no load or typical loads indicates a loss in capacity (as best determined without an actual controlled load test). Unfortunately this is a pain to do on an in-use system.

    13 Watts for 13 hours is 169 Watt hours (not including inverter efficiency and consumption). That would be less than 10 Amp hours on a 24 Volt system and shouldn't phase a 210 Amp hour bank. If it's having trouble with that, the batteries could be bad. How old are they?
  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Re: Is it time for new batteries?

    The batteries have date codes of late '06 and early '07. It is no big deal to run the Iota charger tonight and turn inverter off and let the solar run through all the charge stages tomorrow as it is going to be sunny all day.

    What should I look for and do after that?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is it time for new batteries?
    rgk1 wrote: »
    The batteries have date codes of late '06 and early '07. It is no big deal to run the Iota charger tonight and turn inverter off and let the solar run through all the charge stages tomorrow as it is going to be sunny all day.

    What should I look for and do after that?

    Uh, I think the '06 and '07 pretty much tells the story since it is now '14. Those batteries are seven and eight years old. That's a pretty good life for AGM's.

    The battery condition is indicated by how fast they discharge with no or little load. Sounds like you are not getting anyplace near full capacity.
  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Re: Is it time for new batteries?

    I was afraid you would say that :D.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Is it time for new batteries?

    Since you are running minimal loads, if the batteries still support them (mostly if it will keep the LED lit all night) and don't drop too low in voltage, I'd keep them as-is.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Is it time for new batteries?
    rgk1 wrote: »
    The big issue and reason for the post is the logged data so far today:

    Battery min. voltage 24.6
    Battery max voltage 30.0
    Battery amps today 18.9
    Battery temp 46F

    Should it be entering absorb after less than 20 amps with voltage low of 24.6 for the day? (210ah bank)

    As the others have mentioned, the issue is whether the batteries still have the capacity to meet your needs.

    To answer your question... if the low voltage of 24.6 represents a resting voltage, then yes, it seems that 20 minutes is too short an absorb time.

    But if, for example, the battery voltage were at 25.4 and you started the fan (or some other load with a startup surge) there might be a transient voltage sag (coup de fouet) that might be captured by your data logger. In that case, the 24.6 does NOT represent the low point of the battery's SOC. On the other hand, AGM batteries have less voltage sag than flooded LA batteries, and if your batteries were good it is likely that they wouldn't sag very much. As the AGM gets old or sulfated, its internal resistance (and voltage sag) increases, and its capacity decreases.

    So either way, it doesn't look good for your batteries. The real question to ask yourself is whether sulfation is part of your battery's demise. If there is sulfation it means that you could have made them last a bit longer. If you have been charging those batteries to 99.95% SOC on a regular basis for many years, it means that you have some sulfation. After a few weeks, 99.95% becomes your new 100%. After a few years your battery capacity is 99.95% of 99.95% of 99.95% of 99.95%, etc.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is it time for new batteries?

    I agree with techntrek: if this is a non-critical application then 24.6 Volts after use indicates SOC >50% so run 'em 'til they drop before spending the big bucks on new batteries. I suspect the short Absorb time is indicative diminished capacity, although as I recall the TriStar has a fixed Absorb time setting not a counting clock so maybe you want to check its settings.
  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Re: Is it time for new batteries?

    Agreed. They do still fulfill my needs. Not a critical application. The only time the system sees any stress is if there is an outage. Even then all I need is about 1.4 kw maximum between charges.

    Think its time to test that before a real need arises. I will check resting voltage after a full charge, then put some load on and see how it recovers afterwards. Is that going to be my best way to get some indication of condition? If so, how much load for how long? How much of a role in capacity will the battery temp. play?

    Sorry for all the questions, but you guys got me up and going/growing and everything has been running good for a few years. I just think the used ($40 ea.) batteries are starting to show me their age. I know how they feel... a bit tired;)
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is it time for new batteries?

    Theoretically a load of about 20 Amps (240 Watts on the inverter) would drain them dead in 20 hours if they were brand new. I'd try about half that and see how fast they go down. Ought to be able to support that for 8 hours, but may not be able to now so watch the Voltage under load too. Your basically trying to simulate the lab test of constant current over fixed time, but you won't be able to do that so try for sustained load time that amounts to about 5% of capacity (which is how they get used in RE anyway).

    Yes, cold batteries will have less capacity, but this is not likely to be an issue as the current draw will make them warmer than ambient and they should be around 20-25C anyway.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Is it time for new batteries?
    rgk1 wrote: »
    If so, how much load for how long? How much of a role in capacity will the battery temp. play?

    The load should be whatever you would draw in an outage. The battery temp should be at whatever temp they will be at in an outage.

    After all, the purpose of your test is to see if the batteries will hold up in an outage... make the outage as realistic as possible.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Re: Is it time for new batteries?

    Well, did some testing over the weekend. After shutting off everything but the CC and letting it charge all day, the meter and logging showed the following after 4 hours of rest:

    Battery voltage: 25.9
    Absorb: 149 minutes
    Float: 239 minutes

    Then I hooked up the Killowatt meter that should have captured everything but the CC and inverter usage. Before shutting everything back off it read 21.51 hours and 1.39 KWh. At that time the batteries were reading 24.0 Volts. With everything off and rested a few hours the battery voltage was at 24.5

    So, as of right now the system is still capable of doing the most I ever expect to ask of it. But, still wondering if there is any way to determine a general condition of the batteries from this info?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    Re: Is it time for new batteries?

    6v x 210 ah x 4= 5040 watt hours

    I think the xp600 uses about 10 watts so 1600 watts = 5040 - 3440

    3440/5040 = 68% SOC

    24.5/12=2.04volts per cell which should be between 60 and 70% SOC

    I'd say they are in the ballpark, assuming you took the charge controller off line while discharging the battery bank.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    Re: Is it time for new batteries?

    I did leave the charge controller on the entire time. (Solar panel breaker off while discharging batteries)
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    Re: Is it time for new batteries?

    So that would draw a bit of current, also the inverter inefficiencies would add another 150 watts, I'd keep using them.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.