Battery bank aging signs

WaterWheel

My 1st large battery bank that I actually put a lot of effort to maintain with an SG meter so I'm learning here.     I'm using Crown L-16s that are now a tad over 2 years old and average about an SG of 1.269 after 2 days of 3 1/2  hr solid absorb cycles under little load.     They show a resting voltage (6 hrs rest) of 50.5v so not as strong as when new.     Is this normal aging?      The cells use roughly the same amount of water although the batteries closer to the ends of the strings (2 strings of 8 batteries) tend to use a tad more water     Got a few weak cells (weak cells SG 1.262 after EG) but all within .018 SG.      Longer EQ doesn't seem to get them any closer.

Crown spec sheet  recommends 58.1v absorb but in an effort to get SGs above 1.265 most days with manufacturers consent (called a year ago) I'm running 58.7v absorb.

Is this normal battery aging? 

mcgivor

With my bank I noticed a similar decline, although I have no manufacturers recommendations, I used others as a guide, one change which turned things around was following the Schneider manual recomendations, were it states that increasing the bulk to a higher voltage in the custom settings, wIll hold this setpoint for the first hour of absorption, then drop to the regular voltage for the ballance of absorption. The voltage I used is 30V for boost, 29.3 absorption, 24V nominal, the slightly lower SG cells came up to ballance over time, water consumption is supposed to be higher but as yet I've not needed to water, 8 months, but it would be logical since the electrolyte gassing. All SG are now 1.280 and have not done an EQ in 4 months, morning voltage also improved, inverter connected 24/7. Is what you're seeing a sign of aging? Could be, but 2 years is not that old, assuming no deep dischargeing and no high temperatures, they should be in their prime, mentioned the boost charge because you have a Conext 80 600 and L16's, which would benifit more electrolyte stirring, I would contact the manufacturer and check if it's something they would endorse. 

WaterWheel

I've used "Boost charging" set .2v higher than absorb for the last year.     The batteries in GA are generally over 85 degrees 6 months of the year and I've seen then break 100 degrees (while charging) for about 10 days each year (104 highest I've ever seen).      I leave the battery box top open during the summer months in an effort to keep things cool.

They are cycled down to about 77-85% most nights but have never been below 50%.

I've found it extremely hard to get all cells close to 1.277, usually requires 3 days of low evening consumption (above 88% SOC by next morning),     This is something I do about every 4- 6 weeks before equalizing.       I have gone as long as 2 months before watering but the batteries were getting pretty low on water, requiring 4 gallons instead of the normal 2 gallons for all 48 cells.     No cells were exposed.     
During the summer months with mini-split running into the night the sixteen L-16 batteries may use almost 3 gallons a month,    During the spring or fall (low power demand months) the batteries require about 1.5 - 2 gallons a month.    

mcgivor

The high temperatures are a real factor, but we have to deal with the environmental conditions we have, it is said a rise in temperature 10°C over25°C is equivalent to a 50% decline  of the life expectancy, sorry about the use of metric, just makes sense to me, but it appears you are in the high 30's to 40°C at times, which will have a detrimental effect on life expectancy, every morning I check the battery temperature, no box on a concrete floor, 28°C is average, morning rising to 30°C  charging, the increase in bulk of 0.7V has really made a difference, temperature compensated of course. What works for me may not nesesarally work for you, and of course I'm still learnig, as we all are, only wish there was a winter season here, it usually gets hotter come April, May where 40°C plus ambient is not uncommon, a water bath with cooling by refrigeration is planned, after all the batteries are the most important component in a system.

WaterWheel

My battery box is lined in anticipation of possible using a water bath sometime in the future but there is a lot of plumbing to get water to the box and installing a drain that would feed to a drain in the garage floor.

It sounds as though you've got similar temperatures to mine.      During the coldest months the battery bank is in the low to mid 50's.
How long have you been running your batteries?

mcgivor

The batteries are now 9 months old, temperature wise they have remained in the 85 to 90°F range, BTS sensed temp, ambient wise the coldest it gets here is 60°F overnight 80°F days, but the batteries being in a concrete room remain higher, somewhere between the max, min. During the hot period is when I experience high battery temperatures, for the same reasons the latent heat in the concrete keeps them unacceptably high, my plan is to use a water bath with a small 90w refrigeration unit from a water cooler, using excess production from a separate system to power it during the day, hopefully the chilled water will at least keep temperatures at acceptable levels. Then again, the complexity, bacterial growth problens and other unforseen issues, have me thinking about lithium technology, which is less sensitive to the temperatures  experienced here. For about double the cost of LA, a lithium bank of equal capacity is available, which theoretically will outlast LA > 3:1, so it's a matter of economics, an added benefit would be less maintenance, so much to ponder. Another twist is the grid is now only 500 meters away, albeit I would be 1400 m from the transformer, will speak to the authority soon to see what options are available.

WaterWheel

The first 6-8 months I saw no major signs of battery degration.    After that I saw things going very slowly south with the batteries so I 've called the battery manufacturer twice.      They wanted me to keep the battery absorb at 50.1v but suggested going to 50.5v since batteries needed more power during absorb       Battery spec sheet wants 50.1v absorb.  As mentioned before I'm currently at 50.7v absorb (50.9v boost) and still seeing resting voltage (after 3-5 hrs rest) drop to 50.5 or 50.4v.    Verified by a separate meter.
  Both strings show similar amps during charging ect.       All cells are similar in temperature when charging.

mcgivor

Although the boost charge is recommended, there is no suggested voltage this should be set at, my choice was not as high as EQ but the middle between absorb and EQ which is ~30V or 60V if 48V nominal. Although I haven't tested rest voltages, I did notice morning voltage, with just the inverter as the load, dropping after 5 months, the cell SG was drifting apart slightly and generally lower than they should have been. After an EQ and the introduction of the boost, everything seems back to where it was when the batteries were about 2 months old. 

Battery manufacturers more than often are not taking off grid charging and dischargeing into account when testing, with grid charging and a long float between cycles, the ideal situation, off grid is far more demanding, limited hours of charge followed by immediate discharge. For this reason I believe a more aggressive approach is needed, almost lost my first bank due to being too conservitive, for this reason you may want to increase the boost voltage  to see if there are any changes after a week or so, as an experiment. By no means do I claim to be an expert, but experience has taught me a few lessons, along with reading, the input of others, and their experiences.

The grid here has its issues, being on the end, with frequent outages, I would definitely keep a battery bank if I ever connect, ironically, family members come to my farm, from the village, to shower during extended outages, the prime reason to connect would be to have AC at night, hard to sleep when it's 34°C, 96°F at midnight, that is the extreme admittedly, mostly a fan suffices, in the birthday suit of course. Nothing happens fast in Thailand, so off grid it will be for some time.

WaterWheel

Tell me what happened with the first set of batteries.

mcgivor

The first set were charged at too low a voltage, the default of the PWM  CC was 28.8v, the DOD was ~40%, everything seemed ok but the SG's began drifting, so had to EQ about every 30 days, in my absence of 3 months something went wrong and one cell had dropped to about  1.100, the voltage at rest was right on the money despite this. Equalization had no effect other than producing heat, so it appeared to be a lost cause, then I came across a technique called water treatment, where the electrolyte is diluted to almost pure water, repetitive EQ'S are performed until the SG rises and cannot go any higher. The next stage is to withdraw electrolyte and add acid slowly until the SG rises to the correct level, I must add it is a very time consuming exercise, long story short the cell was recovered, by this time I aquired the Conext 60 150 and set a more aggressive charging regime and the battery performance was brought back to normal, with the bad cell using the same amount of water as the others.
Shortly after this I purchased new batteries and inverter, the old bank is still in use as a backup, with light loads and the PWM CC, the 28.8V algorithm seems to keep it happy  ~30 Ah daily from the original 260Ah capacity, so always in the 90% SOC area, which I'm sure would not be the case with deeper discharge values, they are 3 years old now and consume much more water than previously.

WaterWheel

I'm already charging at .6v higher than factory specs and the boost is at .8v higher than factory specs.     I don't want to push the charge too hard but I may have to.      But 60 v boost (equivalent to your 30v boost seems awfully high for a battery when factory specs calls for a 58.1v absorb.   

The factory technician whom I spoke with last year ok'd a 58.5v absorb but wasn't very happy about that (3 calls over a month while he spoke with the Crown testing department).     He wanted me to get the SGs over 1.265 at a minimum most days and to do that I had to go to a 58.7v absorb and a 58.9v boost. 

mcgivor

During my quest for information on the subject of charging voltages, I came across this article from Home Power Magazine, this along with recommendations from various manufacturers who state a voltage of around 29.6 v, or 59.3V for 48V nominal i made a choice, as I mentioned previously I had no recommendations from the manufacturer, the  Crown pdf I downloaded  really didn't have a clear outline clearly a voltage, but if the recommended value is 58.7v, it is what it is. The article below I found helpful in that it deals with off grid application as opposed to standby, which I believe many recomendations are based on, it also addressed the 14.4v / 12v issue, which  I discovered through experience, was not adequate.

Battery management and maintenance are significant concerns in off-grid PV systems.

Many of the user problems associated with these systems can be traced to improper treatment and misunderstanding of battery performance.

Modern battery chargers use three charging stages— bulk, finish (absorption), and float. Bulk brings the

batteries up to the high voltage regulation point; finish holds it at this high voltage regulation point based on

time. In the absorption stage, the voltage is constant, and the current tapers off as the batteries are filled.

Float trickle charges the battery to a lower, userdetermined voltage to keep it full.

From my experience, the most common battery problem is undercharging, leading to sulfation, loss of storage

capacity, and shortened service life. Sandia National Laboratories recently published “PV Hybrid Battery

Tests on L-16 Batteries” (see Access). Their tests represent several years of systematic testing of a PVgenerator

(hybrid) system. The Sandia report is very thorough. Four different brands of batteries were tested. They were all flooded, L-16 type batteries, the most common battery used in residential-scale RE systems. Tests were repeated so that the data represents good averages, and the conclusions are based on good data and methodology.

The study has four conclusions:

1. The finish voltage (sometimes called the absorptionvoltage) for a flooded lead-acid battery operating at

12 VDC nominal should be about 15.3 volts (2.55 per cell) rather than the customary 14.4 volts.

2. Finish charge time should be at least 3 hours and often longer.

3. The maximum interval between finish charges should be about five days.

4. Not all brands of L-16s are the same (though the report names no names).

The general conclusions of the Sandia report are consistent with the number one problem experienced in

off-grid PV systems—undercharged batteries. Richard Perez has for many years advocated higher finish

voltages for PV-engine generator systems. As he says, “I like to run them hot.” Home Power technical editor Joe Schwartz adds some good advice regarding flooded lead-acid batteries: • Higher finish charge rates result in significantly more gassing and potential for hydrogen buildup. Before you crank up the finish voltage to 15.3 VDC (for a nominal 12 volt system), make sure that the battery containment is well ventilated. The use of powered

battery vents is recommended.

• Batteries charged to a high finish voltage produce a significant amount of waste heat. Depending on the

type and location of the battery containment, in warm climates or seasons active ventilation may be required

to keep battery temperature in check. Optimal operating temperature for lead-acid batteries is 78°F

(25°C). Higher battery temperatures (90°F plus; 32°C) result in increased self-discharge. Temperatures over

120°F (49°C) can damage lead-acid batteries. • Batteries charged to a high finish voltage consume a

lot of water. Compared to charging at the traditional 14.4 VDC finish voltage, the time period between

battery watering can easily be cut in half. Automatic battery watering systems greatly simplify the process.

• Use temperature compensation on all charge controllers and inverter/chargers. Finish Charging Is Inefficient

There is one significant downside to the battery management strategy presented in the Sandia report.

Due to battery charging characteristics, efficiency is very low during the finish charge phase. Very long

engine generator run times were reported, sometimes from 6 to 20 hours. These long run times were required

to completely refill the batteries to the manufacturers’ stated ampere-hour capacity.

The state of charge (SOC) of a battery is most accurately measured with a hydrometer, and is

indicated as specific gravity (SG). Most RE users rely on amp-hour meters to provide convenient (although

slightly less accurate) battery SOC information. During the Sandia tests, full batteries had a SG in the range of

1.290. The long, engine generator run times needed to achieve this SG translate into dollars and pollution (both

audio and atmospheric). Perhaps there is a “middle way” that preserves the lifetime of the batteries while

reducing the time and cost of engine generator finish charging.

Revisit the Assumptions

The batteries tested at Sandia were discharged by 60 percent of capacity (to 40% SOC) and then charged

back to rated capacity. In these tests, the rated capacities were determined empirically, and in most

cases were close to the manufacturer’s stated value (in the range of 350 AH for an L-16).

These two points require comment. First, this depth of discharge is not typical of most well-designed, standalone

PV systems. This point is clearly stated by the author of the study. Most stand-alone PV systems, by

design, cycle batteries by about 25 percent daily, not 60 percent.

Second, the manufacturer’s rated battery capacity and the way it is determined should be understood. All

manufacturers recharge batteries on the grid. Using the grid, they can finish charge the batteries for long periods

(on the order of 8 to 12 hours), cramming maximum ampere-hours into them. For a manufacturer, this

method makes sense because it results in greater AH capacity figures for their product.

The long engine generator run times required by PV hybrid systems must mimic the finish charge conditions

the manufacturers use to rate the battery’s capacity. Perhaps batteries should be rated based on their

application. For instance, a battery used in a standby application (such as utility backup system with grid

recharging) might specify a full charge SG of 1.290. The same battery used in an application that regularly

cycles the batteries (such as a PV system with engine generator backup) might have a recommended SG of

1.250 to be considered full. It is true that a battery with a SG of 1.290 holds more

charge than the same battery with a SG of 1.250. 

However, the shorter finish charge time required to achieve the lower SG reduces the engine generator runtime.

WaterWheel

Mcgivor,     Ok, You've convinced me.     Back when I got these batteries spec sheet (another member on this site told me where I could get them) I was surprised at the 58.1 absorb since most battery manufacturers were wanting closer to 59v absorb.      So I used 58.1v for the 1st 6-8 months before calling the manufacture who reluctantly agreed to 58.5v.     As you know I'm already a bit above that.       His big desire was to obtain at least 1.265on all cells with an absorb of no more than 4 hours and preferable within 3 hours.

I'm going to compromise a bit and set boost at 59.3v and absorb at 59.1v and watch my SGs.      During the hottest summer months I'll monitor battery temps.     This gives me a higher "finish" absorb that you're using but well below the 61.2v the article advises.  "12 VDC nominal should be about 15.3 volts (2.55 per cell) rather than the customary 14.4 volts."

I'll give it a few weeks and report back.

mcgivor

Actually I'm not trying to convince you, just pointing out the observations seen along the way, what works for me may not nesesarally work for you, but taking a more aggressive approach, which  in my opinion, is the way to go, may resolve the issues observed, if some imprrovement is observed, with the boost set at 59.3 V, but not what is expected, it's easy enough to up the voltage to 60V boost, remember it's just for the first hour of absorption, temperature  compensated.  

WaterWheel

I suspect that many battery manufacturers want a lower absorb voltage to minimize rising battery temperatures.      As stated previously may reduce the voltage a bit when the weather gets hot.   

mcgivor

The voltage would be inversely proportional to temperature, with a remote temperature sensor, so heat build up shouldn't be an issue, the voltage would simply drop to acceptable limits during higher ambient, or battery temperatures, so even if a set-point of 60V was selected the actual voltage would  be significantly less, that's the beauty of compensation.

WaterWheel

true,    but harder charging does increase battery temps and water usage.

mcgivor

Agreed, that is the tradeoff, my battery temperature is currently 28°C mornings, ambient 23 low, 32 high, after bulk/absorb, the battery is 30°C, boost charging voltage is compensated to 29.7V - 29.5V, absorb 29.2V, still have not added water since new, 9 months, levels have dropped a few millimeters, gassing occurs but not hissing like in equalization, I expect with age they'll use more water.  

bsolar

my opinion is depends on your usage .. if you dont need that much batt they would stay in better shape charging in smaller groups at slightly reduced spec voltages .. pounding them all the time to try to make them 'equalize' will speed their demise ..

westbranch

Sorry if I missed it but have you tried extending the ABSORB time from the 3 hr to 4 or 5 ?
Have you confirmed that the Absorb time you  are now using gets you to a 'flat line' at the end of that time period?

WaterWheel

westbranch said:

Sorry if I missed it but have you tried extending the ABSORB time from the 3 hr to 4 or 5 ?
Have you confirmed that the Absorb time you  are now using gets you to a 'flat line' at the end of that time period?

I usually have the absorb at 3 1/2 hrs but if the batteries get below 75% SOC (according to meter) I'll bump it up to 4 hrs.     I've got the absorb stop set at 1.3% charging rate (as a safety measure) but it rarely if ever gets low enough to stop the charging.     Usually when the charging rate gets below about 1.9% the charging rate barely decreases since the batteries are roughly 92% full at that point (average SG about 1.262).
A typical early morning SG reading is around 1.238, a bit lower if I used the mini-split to provide some heat through the night.

I'm not shooting for 1.270+ SG every day but I'd like to be above that level at least once a week, a level I rarely can obtain.

To get a SG average that high we need 3 sunny days in a row with minimal use during that time, like never dropping below 89% SOC (according to the meter) for 3 nights in a row and using 4-5 hr absorb each day. 

I don't want to cook these batteries but at the same time I don't want them chronically undercharged.

Dave Angelini

I do not want to sound flippant but I think you are overthinking this. The battery is going to probably last X number of years unless you really do something weird. Typically checking the SG once a year will get you 5 to 7 years with a battery system. There is only so much you can do after the system is set-up correctly. I speak from many, many systems experience. Eventually you will lose capacity and have to replace them.

If I  (or my clients) had to spend this amount of time on batteries I would go into another business. The charger should go to float at 2% of the 20 hour rate. The SG should be close to normal for the absorb time and V recommended. Be very careful of the battery monitor as they are the path to doom for many because of the calibration assumption. Make sure you get 2 to 4 preventative eq's a year and try not to miss to many happy hours

mike95490

 Perhaps there is a “middle way” that preserves the lifetime of the batteries while reducing the time and cost of engine generator finish charging.

I suggest using the generator early enough in the AM, to complete the high energy (Bulk & part of Absorb) so you get the most watts per gallon of fuel.  Then let the sun handle the long slow part.

Dave Angelini

He is tied to the grid Mike!

WaterWheel

Thank you Dave.     I'll stop stressing and enjoy the energy.

WaterWheel

Interesting older article that matches McGivor's ideas with the most interesting observations on page 3 and the top of page 4.   http://forum.solar-electric.com/discussion/17076/trojan-industrial-batteries-not-working

Anybody know how long/well Chris Olson's or North Guys's batteries held up?      

Considering that my battery manufacturer seems to be more of an industrial battery manufacturer that's fairly new to RE battery manufacturer I wonder if my batteries are closer to forklift batteries with calcium in the plates so a higher absorb/bulk voltage.     My bubbling at the factory recommended 58.1v is almost non-existent (a small bubble every few seconds), a bit better at 58.5v.    My bubbling at 58.9v is there, mostly large sets of bubbles every 8-15 seconds in some cells or a bb sized bubble or two per second depending on the cell.

All 16 batteries show a voltage within .1v while charging and water consumption is fairly even between cells (over the long term) but the older string (2 strings about 10 months apart in age) gives and draws a bit mire amperage.
I have no intention of using a 62v absorb like Chris uses but it makes me more comfortable with trying a 59.5v bulk and a 59.1v absorb.     I will watch the temps and water.

Not shooting for 100% but the factory techs wanted to see 95% SOC most days (1.265 SG).      I believe getting 98%+ too often may result in overheating and too much plate shedding.

mcgivor

Interesting read, it would seem there is no one size fits all value due to every situation, discharge, recharge, controller algorithms, temperatures, charging windows and so forth, being different. The manufacturers have to publish their recommendations, which are researched in controlled situations, making other recommendations, such as using higher voltages would make them liable if things didn't work out. The word "recommended" is open to interpretation, at least that's how I see it, the manufacturer has no idea how the batteries will be used. Since the prime cause of battery failure is cronic undercharging, it would stand to reason that the laboratory testing is not well suited to off grid applications. There are many reports  of manufacturers changing their specifications regularly, trying in vein to hit the moving goal posts. Only through close observation on site, with reliable tools and equipment can one really get a handle on what's actually happening, a little knowledge is also required. My thoughts and opinions.

Dave Angelini

I liked Chris and as boaters we have kept in communication over the years. I think he and I were polar opposites of living offgrid.
He had gen support running all the time and had huge electric loads that I would never even try at night. He would go for hours before a generator started and I go for many years. I used one with a pole saw last year

If you google search this Trojan stuff you will get different search results monthly and one manufacturer will be beat-up over users that probably were incompetent. That someone would base a buying decision on search results alone is a bit unfair.

The one thing that all battery manufacturers have in common is they are in the business of selling batteries. If you look at one company's service info you will notice that it changes over the years or decades. It is not so much as the info is improving, it is just changing

 They do use highly accelerated life tests but those tests are often lacking as the resting time element is just an approximation of offgrid use.

I think you guys will really like the Lions once they get priced/sized and built by someone like Crown,Trojan, Rolls or ?

WaterWheel

When I spoke with Crown techs (several times last year) they discussed the charging routine they used to develop their suggested absorb voltage ect.

Water bath to keep the batteries cool as they charged them up, limited float time, hard discharge (still using water bath) and do it again.       I doubt they (or most manufacturers) used charging that slowly ramped up and down as solar does or take a few years of real world solar charging to truly test the RE batteries in real world conditions.

That's why it's good when battery manufacturers have people like Dave do real world testing. 

WaterWheel

Update,
Spoke and emailed with Gary Sinko at Crown Battery for 3 days.        He seems to be their east coast battery expert (I also spoke with 3 other people at Crown before speaking with Gary).      Gary called me within an hour of my explaining the situation with the 3 previous people so strong customer service.

Firm Crown charging routine for these L-16s     58.2v absorb, 61.9v EQ     2 hr absorb per string of 8 batteries (48v)     4 hr absorb with 2 strings.    Documents from 2007 show 58.7v absorb.      2014 spec sheet shows 58.1v absorb.

With the strings separated (something I'd already done) 4 hr absorb and 3 hr EQ for each string.(saw very little improvement)
emailed all SG readings in.       Gary called within  a few  hours.

Gary then wanted the strings combined with another 4 hr absorb and 3 hr EQ. with numbers emailed back. (saw almost no improvement)      At this point he believes the batteries are fairly strong.     SG readings are fairly close so no "weaker than most" cells.       We discussed the low SG ratings and inability to get SGs up in reasonable absorb time but he didn't seem overly concerned.

With a 5140 watt array I'm charging at about a C/11 rate (what I see on the meter is 65-74 peak amps most days).        He suggested a few more panels.

Customer service,,,  very good,   Batteries a good fit for RE use?,,, the jury is still out.     Time will tell.

softdown

Krikey.....I wonder how much we pay for all the phone calls to battery manufacturers.

I wonder what placing the batteries in water within ~4" of the battery tops and blowing button fans, say 4", would do for temperature reduction. Distilled water would be best since electricity leaps from solid to solid. In *theory*, distilled water has no conductivity.

This is just an idea. No progress is made without trying ideas. 

Having extensive work on reef tanks back when strong lighting was hot, button fans were needed to make the tank livable. Do expect significant evaporation....and hopefully significant evaporative cooling.