Battery Issues

basewindow

I think I have a battery issue. I have 2 x 250ah 12v AGM batteries in parallel ( LFP12250 ) and 480w array. Yes I know that I am ‘over batteried’ or ‘under arrayed’ but my theory was this. I actually use very little power under normal circumstances, 8 x 6w LED lights, 4W water pump, LED TV using 46W, and a few phone chargers etc. Maybe I’d draw 16A with everything going at once which would happen rarely and even if they were it wouldn’t be for long. On a big night perhaps I’d draw out 50ah from  the battery or 10% according to the Trimetric. Usually that’s replaced by the solar even on an average day. So they don’t get a hard life.

These AGM batteries have a Bulk Charge recommend by the manufacturer of 14.8v, a float of 13.6 and when are 100% full sit at 12.8 to 12.9 at rest. Even by the next morning they are still at or around 12.6v to 12.7v. Yes I know they are not ‘Solar Batteries’ as such and are generally used for UPS but I get them cheap 2nd hand and are usually about 2-3 years old when I get them.

I’ve had them installed now for almost 4 years and have worked flawlessly and to be honest haven’t been watching them too closely lately, however this week when I came up on the Friday night (I’m usually up there 2 to 3 nights every week) I happened to switch the Trimetric over to Volts (From % , it was showing 100%) and noticed it was showing 12.6v, this was after about half an hour of being there and had a few lights on and TV on. I didn’t think too much of it but watched it over the next few hours and noted it dropped to 12.5, then, 12.4 and finally down to 12.3 by the end of the night. Under load 4a it would drop to 12.2v. Switching it back to % on the Trimetric show around 92%. I had never seen the voltage drop this low before. The only constant load is a 4w fan in the composting toilet and I’m fanatical about turning everything else off before i leave.

The next day was reasonably sunny and I put about 90ah back into the battery according to the CC. Now i could have sworn it was flashing as Charged Status on the CC and was sitting on 13.2v. The Trimetric was showing 103% charged, but now I’m not sure it was in Float or charged. I use very little power during the day, so the majority went into the battery. Anyway I watched the voltage again and noticed it dropped almost immediately to 12.8v under load, around 6a and half an hour later 12.7v. I watched it like the night before and it acted almost in the exact same manner, dropping to 12.2v again by the end of the night. Trimetric was showing 92% again.

At this staged i was beginning to think my batteries were stuffed, but I thought I’d give it a blast with the generator the next day. By the time I had to leave, I had pumped about 130ah into the battery via gen and solar at about 20a on the gen and 10 to 15a on the solar, so up to about 35a going in at any one time. This time i watched the CC and noticed it always stayed in Bulk and the battery only ever got to about 13.6v even with 35a going in. Bulk is set via CC  at 14.8v and Float 13.6v. The % on the Trimetric was showing 105% I think. I reset it back to 100. It now has 3 to 4 days to recharge via the solar before i get back to check. Even on a bad to average day it puts back 15 to 30ah and the fan uses maybe 6ah. 

Anyone want to hazard a guess as to what’s happening here? Have I somehow discharged my batteries badly and the Trimetric hasn’t picked it up? Even though my solar array is about half the desired or recommended size for my battery, i use only about 10% of its capacity a night/day and it usually is fully charged every day. Occasionally after a series of really cloudy days its only ever been down to 79% according to the Trimetric and sitting at 12.5v. I’ve never been concerned about it and by the time i get back after 3-4 days its behaving as normal.

Is it possible that it has developed a surface charge that is fooling the CC into thinking it’s charged because of insufficient charging current over time? We’re just into winter over here now and there hasn’t been much sun. If its had a low but constant charging current of only 4 or 5a per hour for the last few weeks with only the occasional sunny day could this happen? 

Secondly are my batteries junk or will a few days of heavy gen charging cure things eventually? 

Obviously I’ll see how things are next time I’m up there and report back. In the meantime any obvious ideas? 
Cheers,
Cam.

littleharbor2

Your batteries are probably on their way out, losing capacity. The Trimetric is programmed to reflect the amp hour capacity of your batteries when new to you. Now that the capacity is diminished in the older , used up bank you're dod is dropping faster than the Trimetric thinks it is. The Trimetric counts amps in and amps out. Your battery is acting like a smaller battery now that it's capacity is diminished. Using voltage alone in an active system is a poor way to gauge the batteries SOC. If you do a capacity test and determine the bank's current capacity you can reprogram your Trimetric's Ah. capacity and get a closer idea of SOC.  Then again, it sounds like you're ready for a fresh set of batteries. You ought to do a capacity test to the replacement  set of batteries and set your Trimetric Battery Ah. capacity accordingly.

Estragon

Getting 6-7 years out of a battery designed for float/stand-by service suggests to me they don't really owe you much.

That said, it may not hurt to try to get a bit more use out of them, but I'd do so with caution. In some failure modes, the battery will be turning available current into heat rather than charging, and too much heat can make for a really bad day.

The TriMetric SOC value is only an estimate, and is based on values you set. Two key ones are; the efficiency of the battery, and the current and voltage settings at which the bank is considered full and SOC is reset to 100%. These settings may have been about right in the past, but efficiency can drop over time, end-amps may increase, etc., causing misleading SOC readings.

Doing daily bulk charging with the generator and a long absorb with solar may restore some capacity, but I'd recommend taking along an IR thermometer to monitor battery temps. If you find the batteries heating too much (>~120°F) or hotspots, stop charging.

mcgivor

Personally I'm in agreement with both @Estragon and @littleharbor2, batteries are a consumable part of any system, with a limited life expectancy, given the use you've achieved so far that's actually quite impressive, even a battery in standby application will usually fail at, or before the 5 year point, they must be pretty good quality to exceed that.

softdown

mcgivor said:

Personally I'm in agreement with both @Estragon and @littleharbor2, batteries are a consumable part of any system, with a limited life expectancy, given the use you've achieved so far that's actually quite impressive, even a battery in standby application will usually fail at, or before the 5 year point, they must be pretty good quality to exceed that.

I have come to believe that much of a batteries life is dependent upon ambient temperatures. Aren't you in tropical Asia? 

My newish cell phone had an amazing battery until I spent a couple weeks in Florida. Perhaps I left it on the dash one day? At any rate, the battery is now about 75% of what it was. 

I still have about 1/2 dozen normal FLA 8D's built in 2011....though three may be replaced this year. Figure I may as well wait until a cell goes. I store my batteries cool and live in a generally cool to cold environ. 

basewindow

Thanks for the input. Pretty much what I figured. And yes I dont really expect more than 4 years from these type of batteries and that's about what i got from the last lot. I'll give them a good charge with the genny for a few days (watching the temp) and see what happens. I might even split them and try individually charging and discharging etc. I'll probably keep them if they're on the way out and use them for the lights in my shed. Not looking forward to moving them, they're 80kg each.

I previous had 2 x 2 100ah, which served me reasonably well but obviously got a deeper discharged each night and didnt give me the same amount of backup for cloudy days. The idea of going a larger bank was that it would be less depth of discharge each night and hence extend battery life. Flawed thinking perhaps. I can't easily increase my array without a bit of mucking around, as the shack it wired for 12v and my CC and incoming array cables are at they're limit.

So if I do replace the batteries with a similar type AGM used 12v battery around the 250ah capacity, is there any point getting two in parallel should I just stay with the one and save a few dollars?  As I said I can get them reasonably cheaply and they seem to work for my application.

PS. I could also get some 6 year old YUASA 2v 300ah x6 batteries, but don't know alot about them.

softdown

If the price is great, I might go parallel and see what happens. Cheerio mate.

I just replaced a 2009 truck battery today. Failed to turn over my 488 yesterday when the engine was hot. Resting voltage at 12.4 = time to go.

Thing is, the replacement marine battery may have been made in 2007 as far as I can tell. Held a good charge for 1/2 year in cold storage so should be good for a bit.

Batteries hate heat...generally speaking. Been moving them out of sunroom and into garage.

Estragon

I wouldn' t put a lot of faith in 6 yr old batteries, so I'd take a pass on the 2v. As far as (if I'm understanding the question correctly), doubling capacity by paralleling, I wouldn't. If it's worked for you, stay with what's worked.

littleharbor2

You should be able to double the array size and still use the same controller and wiring when switching to 24 volt as the amperage would be halved at twice the voltage. One of the benefits of going to higher voltage. If your controller does 48 volts you should be able to quadruple the array.

basewindow

Just an update. Got up there last night at about 9pm, bit chilly outside at around 4 degress C. Checked the batteries and same issue. Thought id physically check everything and noticed one battery was warm to the touch and the other cold. Temp sensor was attached to the cold one. Took note of it and left it for the night and noticed the same effect, voltage quickly dropping etc, down to 12.2 by morning.

Disconnected the warm battery from the system which left a single 250ah battery. Had a busy morning and left it for the solar to charge. Typical cloudy day and got back 2pm and only 35ah in to the battery. Ran the Genny for about 2hrs and noticed voltage up to 14.2 at the end and about another 35ah in.

Let it rest for 2hrs and noticed voltage down to 12.8. Had a steady 6A load on it now for about 2hrs and its sitting on 12.6. Had 11A on for about 10 minutes and noticed it dropped to 12.5. Came back up to 12.6 after switching back to 6A. Im guessing the battery I removed perhaps has a degrading cell? Hopefully this battery hasn't been destroyed and I'll try to get it up to full charge tomorrow and see how it goes. Maybe get a bit more out of it.

Haven't checked the condition of the other battery yet per charge and voltage etc, but will investigate.

Otherwise its new battery time.

Cheers All.

mcgivor

The warm one is probably at end of life, just being a parasitic load to both the charging, as well as to the apparent good battery. The voltages stated in the last paragraph look promising, but being old the life expectancy is probably limited but may allow time to prepare for replacement. Best of luck.

softdown

You are using a difficult method for ascertaining battery health. I think cell by cell specific battery is both much easier and more scientific. You have not mentioned doing that with a battery hydrometer.

Bad batteries do more harm than good. My experience, almost 100%, is that bad batteries are caused by a bad cell. 

Check specific gravity early in the morning before the panels are really engaged in charging. It is pretty common to have a cell with literally no measurable battery acid density. Measuring as "water". 

Another possibility is a faulty connection. Do you have access to an instrument that reads temperature? Bad connections get much warmer.

Which reminds me of an almost fatal flaw in using batteries with automotive type top posts. It seems to be difficult to achieve a great connection with automotive posts.  Yet many deep cycle batteries sport automotive posts. Which tells me that they were not thinking about solar applications during design and construction. 

Estragon

OP mentioned AGM type batteries - no way to check SG.

basewindow

Well it looks like it was definitely the 'warm' battery that had the issue. Seems like the other is holding reasonable charge. Will see how it goes over the next few days. Might squeeze a bit more out of it before i replace them all.