Offgrid-House: Battery bank suddenly losing power rapidly?

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #32
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    Think ~1400 watts of panel can maintain a ~450 amp hour bank @ 48V?

    Well, converting that power back to 12 volt equivalent, I get 1800 AH at 12 volts for the same amount of energy. The rule of thumb of 1 watt of battery per 12volt AH of capacity leaves you a little short. But I would be more concerned about the panel wattage and sun hours compared to your average energy usage.

    BTW, 450 AH at 48 volts does not match the 8 x 6 volt x 225 AH in your signature line. That would be 225 AH at 48 volts. Did you buy more batteries?
    Increasing the size of the battery bank will not make up for insufficient panel wattage for your load. If anything it will make it worse.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #33
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Without reading through the whole thread again--How do you "know" the battery bank is 100% charged? Charge controller going into float, battery monitor, or what.

    Saying the system is 100% charged when the specific gravity says not--And the fact with lots of charging you got back to "full" specific gravity seems to indicate that the Charge Controller is not properly reading/understanding the battery bank capacity (too much voltage drop in charger to battery bank wiring, wrong voltage set points, too short of "absorb" time, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #34
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    I'm with Bill here, What is making you think the battery is fully charged?

    I'd say short on the array to battery bank, with mostly light loads I have a 1700watt array feeding a slightly smaller battery bank,...but as others have said it's not the problem, you have something else going on, I wouldn't buy more batteries to solve the problem, rather solve the problem, then...

    New/More batteries might mask a problem, or at least have new variables to contend with.
    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.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #35
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    spend the money on the clamp meter from sears. it's worth every penny
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #36
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    inetdog wrote: »
    If the SG was low across all of the batteries, I would say that the problem was not lack of equalization but rather a chronic undercharging leading to sulphation. (The trapped lead sulphate cannot get back into solution to allow the SG to rise.) I would run the numbers on available charge amp-hours versus use and look at the settings of the CC before risking a second set of batteries.

    inetdog -- thanks. I didn't think about the chronic undercharging. Below are the charge levels programmed into my CC. I would be surprised if they were undercharging, however, because I actually upped my some of my voltage levels, absorb and float, from what they were for ~6 months or so based on feedback from earlier in this thread. If anything I thought I might be overcharging them.

    Equalize is 61V
    Absorb is 57.6V
    Float is 54.4V
    inetdog wrote: »
    BTW, 450 AH at 48 volts does not match the 8 x 6 volt x 225 AH in your signature line. That would be 225 AH at 48 volts. Did you buy more batteries?
    Increasing the size of the battery bank will not make up for insufficient panel wattage for your load. If anything it will make it worse.

    Yes, I currently have 225 amp hours and my question was should I double it to 450 amp hours with another 8 batteries. Sorry for the confusion. I am hoping to wire in an electric start generator and get the Auto Generator Start function activated on my Outback inverter. I think that would solve any issue of letting the batteries drop too low ever again.
    BB. wrote: »
    Without reading through the whole thread again--How do you "know" the battery bank is 100% charged? Charge controller going into float, battery monitor, or what.

    Saying the system is 100% charged when the specific gravity says not--And the fact with lots of charging you got back to "full" specific gravity seems to indicate that the Charge Controller is not properly reading/understanding the battery bank capacity (too much voltage drop in charger to battery bank wiring, wrong voltage set points, too short of "absorb" time, etc.).

    -Bill
    Photowhit wrote: »
    I'm with Bill here, What is making you think the battery is fully charged?

    Bill and Photowhit, thank you for the help. I realize a battery with that low of an SG is not full, but I was referring to the 6.34 voltage of the battery, which x8 is 50.72V or near the theoretical 50.8V which indicates a 100% battery bank. So my voltage says 100% but my SG is saying dead or near-dead. I mentioned adding more water to the batteries, I wonder if after checking my EQ's today the SG will be back to full charge.

    Do my charging levels, mentioned above, look good to you? They match US Battery levels mentioned earlier in this thread.
    Photowhit wrote: »
    New/More batteries might mask a problem, or at least have new variables to contend with.

    I think my problem is how I brought the whole 48V bank this winter down to below 6V with a phantom load (I believe it was the inverter being left on, and then the panels getting caked with ice/snow while I was gone for 3 months). This permanently damaged the batteries and I am trying to get them to recover long enough to replace the battery bank. It seems I can run anything I want during the day and the panels are floating just fine, but after the sun goes down my battery bank drops voltage fast, even with minimal loads.

    Ideally I want to live with these batteries until I can save enough for 3 more 240W panels and to double my bank. Which will probably be 2 months or so.

    I guess the big question is would low water levels lead to undercharging and/or fast drops in the charge level of the batteries? I am hoping adding distilled water and EQ'ing will breath some life back into them. Thanks again for all of the help.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #37
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    if under charging is occurring with 8 batteries, the solution would be to add more panel, not more batteries
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #38
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    I am surprised to hear that you guys think under charging is occurring. During the day we have plenty of sun and the bank will drop quickly at night. Even with low loads I wake up in the bank is down to 40 percent. This is even with floating for a few hours.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #39
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    Below are the charge levels programmed into my CC. I would be surprised if they were undercharging, however, because I actually upped my some of my voltage levels, absorb and float, from what they were for ~6 months or so based on feedback from earlier in this thread. If anything I thought I might be overcharging them.

    Equalize is 61V
    Absorb is 57.6V
    Float is 54.4V

    US Battery and Interstate Battery (made by US Battery) have unusual charge profiles. They do not use bulk and absorb the way that folks in the renewable energy business use them. US Battery recognizes that in each charge cycle there should be bulk, absorb, finish, and float. The finish voltage for your batteries is 61.2 volts!

    see: http://forum.solar-electric.com/showthread.php?14738

    Interstate batteries are very popular here in Vermont. Most RE installers around here use an absorb voltage of 59.2 volts on these batteries.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #40
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    When was this 6.3 volts/battery measured? Was it while they were still tying to charge, or while they were under load, or was it after the batteries had "rested", neither charging nor discharging for at least 3 hours before the voltage was checked? Were the batteries fully charged before EQ was started and how do you know, or was the "EQ" actually just trying to bring the batteries up to full charge?
    I also strongly suspect the batteries have not getting properly charged for quite some time, if ever.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #41
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    Even with low loads I wake up in the bank is down to 40 percent. This is even with floating for a few hours.

    If with low loads you are down to 40% in the morning, that tells me that the batteries are not fully charged to start with. The other authoritative indication is the low specific gravity.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #42
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Using battery bank voltage to estimate state of charge is only "Valid" after the battery bank has been resting for 3+ hours (no load, no discharge).

    At 77F, the equation that relates S.G. to battery cell voltage is:

    • Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
    Or
    • Single-cell open circuit voltage = specific gravity + 0.845

    Since resting voltage is supposed to be Specific Gravity plus an offset... Then something does not sound right (measured while charging, meter not accurate, temperature not ~77oF, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #43
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    As others have pointed out, I think you really need to be able to accurately measure your battery bank's SOC.

    It won't be free - but one way to determine what is going on is to get an Outback Flexnet DC battery monitor with shunt to precisely measure/track amps in and out of your battery and to monitor SOC.

    If you also purchase an inexpensive data monitoring program like WattPlot ($50- requires a Windoze computer and serial cable a DB9 (serial) to USB adapter if no serial port on computer) - then with the FNDC hooked up you can precisely measure and record what is happening with your overnight loads in conjunction with the changes in your battery SOC.

    Without keeping track of SOC and loads it may be difficult to track down what it going on. With a FNDC and WattPlot you'd have in figured out in 24 hours.

    IMO this is well worth the modest investment - not just to diagnose this issue but for ongoing monitoring of your system.
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #44
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    vtmaps wrote: »
    US Battery and Interstate Battery (made by US Battery) have unusual charge profiles. They do not use bulk and absorb the way that folks in the renewable energy business use them. US Battery recognizes that in each charge cycle there should be bulk, absorb, finish, and float. The finish voltage for your batteries is 61.2 volts!

    see: http://forum.solar-electric.com/showthread.php?14738

    Interstate batteries are very popular here in Vermont. Most RE installers around here use an absorb voltage of 59.2 volts on these batteries.
    --vtMaps

    vtmaps -- If I use the numbers from this link for US Battery then I get the following specs:
    Bulk: 57.6V
    Absorption: 57.6V
    Finish: 61.2V
    Float: 52.08V
    Equalize: 61.2V

    The float value is lower than what I had programmed earlier, although when I program the MATE I don't see Bulk or Finish charging values to adjust. Anyone know how to adjust these to 'finish' at 61.2?

    My current values are here again:
    Equalize is 61V
    Absorb is 57.6V
    Float is 54.4V

    waynefromnscanada wrote: »
    When was this 6.3 volts/battery measured? Was it while they were still tying to charge, or while they were under load, or was it after the batteries had "rested", neither charging nor discharging for at least 3 hours before the voltage was checked? Were the batteries fully charged before EQ was started and how do you know, or was the "EQ" actually just trying to bring the batteries up to full charge?
    I also strongly suspect the batteries have not getting properly charged for quite some time, if ever.

    Wayne, I measured after I ran the generator and had sunshine for a 1.5 hours. My voltage, which I know is an inaccurate measurement, showed full and I no longer had sun on the panels. There were either no or slight loads on the batteries (like 1 LED lightbulb in a nightlight). I'm not sure how you guys can live off grid and let batteries sit for 3 hours without any load -- my wife would kill me if I tried doing that multiple times per day/night and she was home with our little kids. That may not be what you all want to hear, and I am sure it is not the most efficient way to measure capacity, but I work with what I've got.

    See the numbers above for the proposed charging levels from US Battery -- if these are accurate then I agree I have not been charing the batteries corretly.

    BB. wrote: »
    Since resting voltage is supposed to be Specific Gravity plus an offset... Then something does not sound right (measured while charging, meter not accurate, temperature not ~77oF, etc.).

    -Bill

    Bill, the batteries were ~94 degrees or so. The numbers I provided were not temperature corrected. With temp correction we are looking at ~1.116 SG.


    mtdoc wrote: »
    As others have pointed out, I think you really need to be able to accurately measure your battery bank's SOC.

    ....

    Without keeping track of SOC and loads it may be difficult to track down what it going on. With a FNDC and WattPlot you'd have in figured out in 24 hours.

    Thanks mtdoc. I have the FlexNetDC and have put off buying the serial to usb cable. You have given me renewed interest to just go buy the cable and WattPlot. We are building a new 12x24 shed that will house my solar equipment and I will mount the panels on the roof. This has taken up the majority of our resources. Pics to follow!
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #45
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    vtmaps -- If I use the numbers from this link for US Battery then I get the following specs:
    Bulk: 57.6V
    Absorption: 57.6V
    Finish: 61.2V
    Float: 52.08V
    Equalize: 61.2V

    The float value is lower than what I had programmed earlier, although when I program the MATE I don't see Bulk or Finish charging values to adjust. Anyone know how to adjust these to 'finish' at 61.2?

    My current values are here again:
    Equalize is 61V
    Absorb is 57.6V
    Float is 54.4V

    Most RE equipment uses a different charge profile than what most battery manufacturers recommend. You can't set a 'finish' voltage on your outback. see: http://forum.solar-electric.com/showthread.php?14738

    What you should do is set your absorb voltage to 59.2 volts. Your other settings look OK. When you equalize you are providing a 'finish' voltage, but you shouldn't do it every day. You may need several hours of absorb. Watch your current into the batteries during absorb... when it stops decreasing check your SG.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #46
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Originally Posted by waynefromnscanada

    When was this 6.3 volts/battery measured?
    PorkChopsMmm wrote: »
    Wayne, I measured after I ran the generator and had sunshine for a 1.5 hours. My voltage, which I know is an inaccurate measurement, showed full ...

    I see said the blind man.... If the batteries are fresh off charge they should be close to 7v per cell so they are NOT fully charged. [54.4 (float voltage) / 6 cells] = should be around 6.8Volts and if it's 6.3Volts my guess is you haven't gotten -through- Bulk. Might get a cheap volt meter that will run off the current flowing through it and watch the voltage. It will slowly rise through the Bulk stage until it reaches absorb voltage (57.6) then as the resistance with-in the battery increases the amperage tapers off and after reaching a set level or time the CC will drop to the float level.

    Either your not getting out of Bulk or your capacity(due to damaged batteries) is so low it just flies through bulk and absorb and falls with any load very quickly once off charge.

    FWIW - I don't have a battery monitor set up, I think it's nice while your setting up a system, but can be misleading over time. I've just gotten use to understanding my loads. If I had a family and lots of unknown loads I might feel more out of control and feel I need to 'see' the wattage used. Once you get a feel for watching the voltage levels you can get a pretty good idea of where your at. I've never actually let batteries rest, though i have check the voltage in the morning before doing more than turning on a light and the fridge doesn't run much in the winter.

    I went out to check my cabin today, as I had forgotten to turn off the air conditioning timer, about an hour after sunset I checked the voltage input on my inverter, it was at 25.5 with a 5Amp load (the fridge running) I was comfotable with that, the batteries had been fully charged during the day. When I had a battery bank 1/4 the size it would read 25 volts under that kind of load in similar situation. I think a monitor might be the way to go, just so you can keep an eye on those loads, I mean kids...lol
    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.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #47
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    Photowhit wrote: »

    I see said the blind man.... If the batteries are fresh off charge they should be close to 7v per cell so (at 6.3 volts) they are NOT fully charged.

    EXACTLY! It surely appears that these batteries have, for a very long time, not been getting properly charged. Unfortunately it is probably too late for these batteries.
    To replace the batteries now, before the cause of undercharging is found and corrected, would be throwing money out the window, because the new ones will soon be ruined. Batteries seldom suffer an early natural death, - - they're murdered!
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #48
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    The batteries were fresh from a charge but with a slight load applied; powering the inverter and 2 small LED nightlights.

    If these golf cart batteries are so common why is it so hard to find the right charging parameters? I'm not complaining, just wondering why it is so hard to pin this down.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #49
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    The batteries were fresh from a charge but with a slight load applied; powering the inverter and 2 small LED nightlights.

    If these golf cart batteries are so common why is it so hard to find the right charging parameters? I'm not complaining, just wondering why it is so hard to pin this down.

    It's a matter of application. The battery companies expect golf cart batteries to be used in golf carts, not RE installs. As such they don't test them for that purpose and don't supply the right numbers.

    The Absorb Voltage is correct at 57.6 (temp compensated). Probably the Absorb time is too short (MX60 defaults to 2 hours maximum). Absorb time depends largely on how deep they are discharged.
    The Float Voltage should be 55.2, not 52.08 (in a golf cart they expect "Float" to be zero loads).
    Equalization can be done at 61-62.

    With any RE install you have to monitor closely to begin with and adjust your particular settings to meet the situation. It's a pain, but there's no such thing as an out-of-the-box install really.

    Give them a good, long Absorb charge (bulk up early with a generator if you have to). Check the SG per cell for discrepancies. Equalize for an hour to see if there's any improvement. If so, repeat. When improvement to the SG stops, stop equalizing. Generic advice I know, and probably too late. But that's the best you can do for now.
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #50
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Thanks Cariboocoot. I spoke to another member who has a near identical set up. He contacted a battery engineer at Deka/East Penn, who actually makes the batteries I have, and he gave specs near identical to yours:

    absorb at 58 for 3 hrs
    float at 55.2 for 2 hrs
    eq at 62.6 for 1.5 hrs

    I will adjust mine when I get home and give it a go. Hopefully that allows the bank to chug on a little longer.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #51
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Your Absorb time should end about when the battery is just beginning to vigorously bubble. On days where you use less power overnight--The absorb time can be shorter. Conversely, when the battery is heavily used, then you will need a longer absorb time.

    What has your water usage been? Roughly watering every 1-2 months for the "average" storage battery seems about right. If you water once ever 3-6 months or longer, probably undercharging.

    If you water every 1 month of more often--probably over charging.

    Both are damaging to a battery bank--But in your case, I would be dumping a lot more charging current into the bank. And checking (temperature corrected) specific gravity in at least one cell every day or two. You seem to be able to force charge to fully charged specific gravity (~1.265 to 1.275) when you try... So, a "full charge" day should get you to at least 90% to 95% of full charge (trying to 100% charge every day is probably going to over charge your battery and hurt its long term life just as badly as undercharging would).

    Make sure you are seeing ~58 volts at the battery bank for your 4-6 hours of Absorb charging (again, temperature corrected--hot battery at 94oF would be less).

    You can use an accurate volt meter to check the voltage across each cell/battery at this time... Extra high or extra low voltage readings will need more detective work.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #52
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    BB. wrote: »
    What has your water usage been? Roughly watering every 1-2 months for the "average" storage battery seems about right. If you water once ever 3-6 months or longer, probably undercharging.

    If you water every 1 month of more often--probably over charging.
    I have only watered once, and that was ~1 week ago. When I got them new the water levels looked fine.
    BB. wrote: »
    Make sure you are seeing ~58 volts at the battery bank for your 4-6 hours of Absorb charging (again, temperature corrected--hot battery at 94oF would be less).
    -Bill

    This could be where I am seeing a problem. I did a cursory check last night and saw on the CC that, good news, my panels were able to pull in a peak of 1510 watts, which sounds amazing. The downside was I saw that the high voltage for the batteries was only 54 volts. That isn't good -- that means I am not hitting my absorb (58V) OR float (55.2) which is bad. I am picking up a used netbook this weekend along with the Serial-to-USB adapter. I will download WattPlot and see what is going on.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #53
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    If you are measuring ~54 volts at the battery, what is the voltage at the charge controller output (looking for what the charge controller thinks the voltage is, and what a DMM reads at the output of the charge controller--i.e., what is the voltage drop of the cabling and is the charge controller reading correctly)?

    You are not fully/quickly charging the battery bank until there is ~57-59 volts at the battery bank for a few hours straight.

    If the voltage drop on the wiring is too high, or the charge controller not calibrated/working correctly are two possible problem points. The other is simply not enough solar array/current to fully recharge the battery bank (size of bank and amount of power/AH used).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #54
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    The CC (and MATE) showed that the battery bank voltage was 50.7 under a 100 watt load at the time. I have shunts set up with the FlexNet DC so it shows when loads are occurring. The 54V was only shown on the CC as being the high point of the batteries for the day. So at some point the batteries were 54V and when I was looking at them they had dropped to 50.7V. I am going to monitor them tomorrow and see what is going on. Thanks for the help!
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #55
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Before we get too far here, are your panels set up in 3 strings of 2 or 2 strings of 3?
    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.
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #56
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    2 strings of 3. This works out just fine per Outback's configurator and is one of the reasons in went with 48V.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #57
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?
    PorkChopsMmm wrote: »
    2 strings of 3. This works out just fine per Outback's configurator and is one of the reasons in went with 48V.

    Sorry, just looking at the easy solutions first, worried you had 3 of 2 grid tie type panels (often sold as 24 volt) and were not producing enough voltage to properly charge...
    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.
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #58
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    No offense taken. I think these batteries are done. We had beautiful sun today AND I fired up a a large construction generator and could not get the voltage up above 55.2V. Both the CC and the MATE are configured for the higher voltages previously mentioned. Looks like it is time to schedule a trip to Sam's to exchange these.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #59
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    In general, unless you have shorted cells or other loads--You should always be able to get the battery bank up to absorb voltage.

    It actually may be a good sign that your battery bank is still reading low voltage--It should indicate that the battery bank is still accepting charging current.

    What was the charging current? Did it taper off or was it still at maximum while solar+genset was operating. And how many hours at YYY Amps did you put into the battery bank?

    Specific gravity readings?

    Did you have a chance to pick up a DC current clamp meter? How are you measuring charging current, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    #60
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    Bill, thanks for the help.
    BB. wrote: »
    What was the charging current? Did it taper off or was it still at maximum while solar+genset was operating. And how many hours at YYY Amps did you put into the battery bank?
    Ironically the charging voltage of the solar array was dropping while I was looking at the MATE. From ~90 volts down to 77. I need to check out the MATE tomorrow to check on how many amps went into the bank.
    BB. wrote: »
    Specific gravity readings?
    No, I don't think I have been able to get the voltage up enough to change the SG's from last time. I w
    BB. wrote: »
    Did you have a chance to pick up a DC current clamp meter? How are you measuring charging current, etc...
    No, no DC clamp meter yet. The MATE display, the FlexNet DC, and the shunts are showing me power that is coming in/going out.

    Below are some pics of my MATE display and CC.
    An example of power going into the batteries. This was with ~4 or 5 more hours of sun left.
    img20120728142510.jpg

    Trying to EQ the batteries. Array voltage dropped and the battery voltage did not increase to even absorb levels.
    img20120728140854.jpg
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #61
    Re: Offgrid-House: Battery bank suddenly losing power rapidly?

    I am not completely sure I understand the Mate display--But that is OK. Let us approach it from a different direction.

    You have a 225 AH @ 48 volt battery bank, and lets assume it is 50% charged and you want to get it back to full charge.

    From an Amp*Hour point of view, batteries are pretty nearly 100% efficient (in terms of Amp*Hours out~AH in) (except for near 100% charge and equalization where efficiency can drop to near zero percent as you end up, mostly, converting electricity to heat plus hydrogen and oxygen gases).

    So:
    • 225 AH * 0.50 to recharge = 112.5 AH to bring the battery bank back to "Full"

    Watt*Hour wise, where batteries are 80% to 90% efficient at charging (energy vs Amp*Hours):
    • 225 AH * 0.50 state of discharge * 59 volts charging * 1/0.80 eff = 8,297 WH = 8.3 kWH to recharge a 1/2 full bank

    It looks like you are getting ~21 amps into the battery at that time of day (almost 10% rate of charge--that is good):
    • 112.5 AH to recharge / 21 amps = 5.4 hours (plus 2-4 hours for Absorb)

    But, you really need to add a few hours for Absorb charging (once the battery hits 59 volts is Absorb set point, and current will taper from Imax-charge to a few percent of battery AH capacity after 2-4 hours or so).

    Of course, there is the question of how much load you have on the battery bank overnight--Is the battery bouncing between 50% and 75% state of charge, or between 75% and 100% state of charge (the second does not sound likely).

    You can start the genset in the early AM and run it until you get to ~59 volts on the battery bank (that is the absorb transition point and the battery bank should be ~80-90% full). Then let the solar panels carry the charging during the rest of the day.

    Or, you can start the genset in the evening (when you have loads and less than full battery bank--and somebody is home to operate the generator) to help get it back up to the ~59 volt Absorb point--then shut down. And let sun (or sun and generator) manage the rest of the charging the next day.

    By the way, what is the generator kWatt rating and the Amp rating (and voltage set point) of your AC Battery charger?

    Need to get a handle on the battery state of charge and where it tends to cycle during the 24 hour period. A battery monitor makes it easy, but an accurate hydrometer (if there is one:p) and logging data (AM before sun is up, and PM at sunset) for a pilot cell will be a great help. As will knowing your loads (AH/WH used) and charging (AH/WH from sun) (difference should be AH in/out of battery bank). The battery monitor will monitor AH in/out of the battery which is critical to understand right now.

    Sorry to be such a pest--But I am not sure I understand your needs/operating conditions yet.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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