one battery bank electrolyte low

jonkmahljonkmahl Registered Users Posts: 5
Hi Folks,Looking for some advice on my new issue. 
I have a 13 year old off grid 4k system with a Xantrex SW4024 system and a C-Series DC controller model 40 as I remember. I have 8  6V Trojan L16 batteries.
This is in the Eastern Cascades of eastern Washington and I get there usually every 4-6 weeks as its a retreat. Sometimes its longer up to 2 or so months and I've had no problem. I top the batteries before I leave and so on.
I was recently over there after nearly 2 months and things seemed to be working fine, all the lights worked and the microwave worked fine., I used it intermittently. I got ready to prepare my place for leaving and checked the batteries and one bank was so low I used nearly 3 gallons of distilled water to top them off. I was totally shocked as Id never experienced anything as severe as this.
They lit back up as soon as I topped them off again but thee seemed to be a lots of charging activity going on even though my monitor said the batteries were full.
Now my first suspicion is that there is some faulty interconnects between the two banks and what might be the problem and seemd one was receiving more current than the other. I figure next time i head over Ill have to disassemble and reassemble the system. I am also being pushed by my wife to replace the batteries before winter as they are now 7 years old. I did shutdown the whole system while gone for the next few weeks.
I thought that the controller would protect the batteries from overcharging and wanted to see about some getting expert suggestions and opinions on what I am experiencing.


  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Welcome to the forum Jonk,

    First, do you have a hydrometer?

    That will tell you if one or more cells have "issues" (shorted/open cell, etc.).

    Next, I highly suggest a DC current clamp DMM (Digital multimeter--Really an AC+DC current clamp DMM). You can measure the current in any cable connection--For example figure out if one battery bank is drawing charging current, and the other is not (open cell, poor electrical connection--Or you can have a shorted cell in one bank that is making that bank 2 volts lower in voltage, and taking all the charging current, and effectively getting over charged because it is now a "22 volt" battery bank). (good enough for our needs around $50) (nicer mid-priced meter)

    And sometimes charge controllers have been known to fail shorted--I.e., the C40 is no longer regulating, but just dumping all available current from the solar array into your unhappy battery bank.

    In general, a battery bank that "boiled" enough water to expose the plates--There was something that went wrong (shorted cell, over charging, etc.). And once the plates are exposed, that is usually the end of the batteries.

    For "proper" wiring of parallel battery banks, this website does a good job of giving the reasons and options for wiring that supports proper current sharing during charging and discharging:

    13 years is good for your battery bank... And given that you have cold winters (and probably not too warm winters), that really helps batteries last a long time.

    Anyway--With a good voltmeter--Checking the voltage drop on each 6 volt battery--You are looking for batteries that are "different' from the other batteries (high battery voltage--Overcharging? Open cell?) Low voltage (under charging? shorted cell?). And checking current flow (charging/discharging) will help isolate problems too.

    You want to see reasonable charging voltages on the 24 volt bank (around 29.5 volts absorb set point). And you don't want to discharge much more than 23.0 volts under steady state load before getting them recharged).

    I assume you are using distilled water (or deionized water)?

    What is your solar array wattage? Normally, want 5% to 13%+ rate of charge. 5% can work for weekend/sunny weather usage. 10%+ recommended for full time off grid system:
    • 840 AH battery bank * 29.0 volts charging * 1/0.77 panel+Controller deratings * 0.05 rate of charge = 1,582 Watt array minimum
    • 840 AH battery bank * 29.0 volts charging * 1/0.77 panel+Controller deratings * 0.10 rate of charge = 3,164 Watt array nominal
    • 840 AH battery bank * 29.0 volts charging * 1/0.77 panel+Controller deratings * 0.13 rate of charge = 4,113 Watt array "typical cost effective maximum"
    A single C40 40 amp controller... That is already less than 5% rate of charge (5% * 840 AH = 42 Amps).

    Cannot argue that your battery bank is being undercharged--It has already lasted a long time. However--A new controller (possible larger current rating, larger array).

    You have a large battery bank and reasonably large AC inverter... And, I guess, a pretty small solar array. If your loads are low, you are only there during sunny weather, 5% can get by (perhaps using a genset when needed).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonkmahljonkmahl Registered Users Posts: 5
    Thanks for the info Bill, that looks better price-wise that what Ive been looking at for my Fluke DVM. Fluke's i410 attachment is ~$240.

    A minor correction though, the solar system was installed in 2003 and the batteries have been replaced once in 2010 or 2011.

    With the impending battery replacement, I find myself wondering wetherupgrading the system to 7 or 8k is a possibility, but looking at the expense plus, puts a stick in the wheel as we are considering selling our place. It is a 4-5 hour drive for us. Plus I'm 71 and hauling batteries and redoing the system is non-trivial but while my brain says "Oh heck yeah, let's do it!" my body is saying "Lets go soak in the tub." Reality can be harsh at times.

    I have 8 Kyocera KC120-1 cells bought in 2003 and always top off with distilled water.

    We are there at all times of the year as we try to get over there every 6 weeks give or take a couple of weeks. Summer temp can be 110 while winter temps can be 0. I use a Generac 7k telecom backup propane generator to recharge when I approach 80-85% capacity.

    I use the solar for all lighting, some microwave usage, occasional washing machine usage and very rarely power tools but thats during daylight.

    The eastern side of the cascades in Washington state is similar to Flagstaff, where I moved from to here, BTW.

    Thanks .

  • jonkmahljonkmahl Registered Users Posts: 5
    BTW yes, I do have a hydrometer.
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Seven years of life from lead acid batteries is not bad, 3 is about all I got from both banks I've previously had due to high ambient  temperatures, 400Ah in 2 strings of 4. The progression of failure in both cases was one cell became weak which caused an imbalance in current to the string with the weak cell. This causes longer absorption times which consumes water, the good string meanwhile draws little to no current thus remaining in relitivly good condition.

    The progression occurs slowly over time often going unnoticed until it's too late to perform corrective action, if at all possible. Usually the cell in question becomes shorted by sediment accumulated in the well below the plates therefore rendering the battery useless. Having the correct tools to measure will help determine if there are imbalances but will do little to prevent natural deterioration as the plates are sacrificial. As part of general maintenance it's a good idea to measure the voltage drop across all terminals with a meter capable of 1mV resolution as a high resistance connection can have the same effect as a bad cell.

    Getting 13 years from the electronics is respectable as well, that is the average life expectancy, some fail well before others exceed by far, probably depends on how hard the use is and environmental conditions.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Do you think you can find 4 good batteries--Put them in a string, and (probably) replace the solar charge controller?

    For charging... If your bank typically was cycling >75% state of charge--You should not need the genset during that time. A good/fuel efficient use of the genset is to recharge from ~50% to ~80%, and let the solar panels take the rest of the charging cycle.

    That would get you going for the short term while you figure out what you want to do next.

    I am not sure that you can recover your money spent upgrading your solar power power system if the property went up for sale.23

    By the way, what do you mean by saying you have a "4k system"? Is that a 4 kWatt AC inverter or something else (4kWH per day energy usage, 4kW array or 4kWH battery bank--Neither which seem to match your system)?

    Debugging and running an off grid solar power system is really a game of numbers.. WH (or AH) of daily loads, hours of sun per day, 29.5 volts charging set point (for flooded cell), 2-6 hours of Absorb charging time (deeper cycling, longer absorb time), Solar Array Wattage (good sun, no shading), etc.

    If you keep the same size battery bank--I would be very tempted to install a 10%+ solar array--Should cut your genset runtime back a bunch--But, that involves installation racking/panel/wiring/and a not-cheap MPPT type charge controller, issues of mixing and matching old panels with new panels, etc.).

    I am a big believer in a balanced system design... Your loads -> battery bank AH and voltage. Your battery bank -> solar array size and backup charging capacity. Your loads + location + seasonal usage needs -> solar array.

    You have a relatively large battery bank, and a very capable DC genset. The solar array is small. The C-40 is too small for present battery bank (if installing a larger array). MPPT charge controller allows you to purchase larger format panels (200 Watts+), and run a higher voltage solar array (smaller wiring, allow array to be farther from solar charger+battery bank.

    And going back to the beginning--Looking at conservation. Reducing your loads usually is more cost effective and less expensive in the longer term. Just to give you some numbers... A "smaller" solar power system would be something like 3,300 WH per day... Enough for a very efficient/conservation minded smaller home/cabin. LED Lighting, Energy Star 120 VAC refrigerator, solar friendly well pump, washer, LED TV, laptop computer type system. A 2 day storage/50% max planned discharge (for longer battery life system) may look something like:
    • 3,300 WH pe day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    Charging for full time off grid--10%-13%+ solar charging. Again 5% can work for a weekend/sunny weather time (and/or more genset usage):
    • 647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "typical" cost effective maximum
    And you should look the larger panels available these days with an MPPT type charge controller. Larger MPPT charge controllers are expensive, but large format (200-350+ watt or so) panels are cheap ($0.50 to $1.00 per Watt is doable--Watch shipping chargers--Large glass panels are not cheap to ship).

    Looking at sizing your array for you location Wenatchee WA, 45 degree, facing south:
    MonthSolar Radiation
    ( kWh / m2 / day )
    Toss the bottom three months, and February at 3.92 hours of sun per day looks very good:
    • 3,300 WH per day * 1/0.52 off grid system end to end efficinecy * 1/3.92 hours of sun per day = 1,619 WH array for February "break even"
    A 2,437 Watt array will generate more energy and take you deeper into winter with less genset use:
    • 2,437 Watt array * 0.52 system eff * 3.92 hours of sun per day (Feb) = 4,968 WH per day (February)
    • 3,300 WH * 1/0.52 system eff * 1/2,437 Watt array (10% rate of charge) = 2.60 hours a day "break even"
    Anyway--That is how the math looks, and a very rough sizing of a system that could meet your needs. Energy usage is a highly personal set of choices that has to work for you--The above is just a quick set of rule of thumb design.

    But this is getting way beyond the "I want to put up my feet and enjoy the scenery @ 71" point in your life (???).

    If you are thinking about selling the property (or even possibly sub-dividing), might be an interesting time to see if you can bring utility power to the property. It is only getting more expensive and more difficult (utilities seem to be avoiding undeserved/unprofitable remote locations these days)--Wonder if the cost of having utility power at the property would increase property value (or at least value to you) more than a possible $10,000-$20,000+ solar power system rebuild(???).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonkmahljonkmahl Registered Users Posts: 5
    Thanks for all the greet information, didn't realize how much I had forgotten and didn't know!
    So to answer a few questions;
    Bill asked about 4 good batteries. Ill check when I head back over there in a couple of days or weeks.

    I mostly use the genny to run my well pump but also in the winter when we have low sun and much cloudy consecutive days. Ill keep the 75% in mind.

    When I say 4k, I only say it as such due to the inverter I am using, the 4024 inverter.

    As I only use the system when I am there, average usage varies. All lights are LED, the washer is only used in the daytime on a sunny day, microwave is used sparingly, laptops used all the time, occasional keyboard use, rare power tools.

    The 8 120W Kyocera panels are in full sun nearly all day. They are on a polar mount but it is not tracking. The present situation of it is set to lower wind resistance as we do get some significant straight line winds plus random as hell winds and it seems to do ok as is.

    We get an average of 8 hours of daylight in Dec-Jan (seems like much less due to clouds) to 16 hours in Jun-Jul. We are at Longitude: -120.004, Latitude: 48.1302 so we get quite a swing in hours.

    Thanks for the math gotta do some more calculating to get it square. Do you have a link to a site where I can calculate? Otherwise Ill fire up the solar powered calculator!

    Lastly bill, we had a check for bringing in line power to out place, 4 miles away from nearest feed, ~$90k! So out of the question for a second get away home. It is very sparsely populated there perfect for a get away.

    Thanks a bunch,

  • jonkmahljonkmahl Registered Users Posts: 5
    Sheesh, Great information. Its early for me!
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Hours of sun per day (sun above horizon) is not the same hours of sun per day we use here (which is hours of noon time equivalent sunlight at 1,000 Watts per sq meter).

    Using PV Watts and your gps coordinates at 48 degree tilt:

     48.1302, -120.004

    Solar Radiation
    ( kWh / m2 / day )

    Less than 3 hours per day is not great... Less than 2 hours per day--Either lots of panels and/or using a genset more than you probably want.

    And for a 24 volt battery bank with lead acid batteries, around 500 Watts per 100 AH (@ 24 volts) is about the max AC inverter and (cost effective) solar array:
    • 420 AH (single string of batteries) * 500 watts * 1/100 AH = 2,100 Watt typical "useful" AC inverter and max solar array
    So, using 1x string of batteries will give you significant limitations on power usage (at least you limp by until you decide what to do next).

    You can do a larger solar array than 2,100 Watts--But you should ensure you have a remote battery temperature sensor (for the solar charger) to make sure you do not overheat the battery bank (and optimal charging for your very wide temperature spread).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    jonkmahl said:
    A minor correction though, the solar system was installed in 2003 and the batteries have been replaced once in 2010 or 2011.
    I'm arriving pretty late to the party, but things have had time to level out...

    So batteries that are 9-10 years old, half of which likely had exposed plates needing 3 quarts each...
    To me it's a no-brainer, time for new batteries.

    You describe your system as being;
    jonkmahl said:
    I have a 13 year old off grid 4k system ...
    Usually this describes the size of your array, but I think you are stating you have a 4 kW inverter? As you added;
    jonkmahl said:
    The 8 120W Kyocera panels are in full sun nearly all day. 
    If you are serious about selling, I'd scrap the battery string you had to add so much distilled water to, and I'd see if you can charge them in the morning off the generator and do equalizing charge for a couple hours and then check the Specific Gravity. 4 - L16's should be fine for the described use if they are healthy and you are using the generator for the well pump. I might shift the clothes washing to daytime so you have the added support of the solar array. If you want to sell and the batteries aren't usable, you might replace them with 8 golf cart batteries. This would be a reasonable size for weekend use, with the array. You even have all the cables!, 4 golf cart batteries might be used, though this would be a bit small for a 4k inverter, but would allow you to demonstrate a functioning system while not being ugly if the new owners wanted to be full time residents and go with a larger battery bank.

    I think if you would like to increase the size of your inverter to 7-8K would pretty much be building the whole system from scratch. Indeed if your battery bank was healthy, it's about the only part that would be a good size. Don't think there are any 7-8K inverter that don't want at least 48 volts, I'd want a larger array just to service the current battery bank/inverter for weekend use through the winter, though you appear to use the generator for support there (That is a viable option)
    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, 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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