repetitive cell failure - specific location in bank

morpho

What are the usual suspects in repetitive cell failure in a specific location in the bank?

I have had the battery in position 3 go rogue on me twice now.

It seem to always be bubbling over, the terminals get the green monsters of corrosion on them regardless of terminal dope or vaseline or pennies or stern looks!, The SG of two of the cells never get past 1.225

Thanks for any insights.

Dave Angelini

I never have this happen BTW.  It probably is you or a bad cable, corrosion on or in a cable, use of terminal dope on the mating surfaces. Replacing batteries and not the whole bank. Maybe time to change your screen name? You did say any insights!

morpho

HAHAHAHA!
Dave...that "Solar expert" is not the classification I would have given myself... without a doubt!
My best guess is it is the way the fine folks who designed this forum decided to engage people and make em feel special. I have never ever claimed anything but "short bus special".

I have no problem claiming my ignorance.
Without people like me, the smug wouldn't have much to be smug about.

I know this place is absolutely full of smart folks who have all this completely sorted.
Then there are the 99% of people out there who just want to/need to run off PV and just need to keep it going.
I have about a million other things to worry about than having the perfect system. 

Herein lies the uptake problem for PV. Few people want to become Solar experts with a 4 star rating.
I own a car. I could care less to know how the transmission works to be honest. Yup...probably would help to know if it goes bad...but I have a job and it isn't mechanic. I'm not afraid to pull it apart and sort it out if I have to...especially with the insights of people who are really into transmissions. Bless em!

So your input is it's probably the cable. (I didn't actually use a penny or terminal dope....but... a bunch of stern looks have been given!)

Dave Angelini

No, I also said " , corrosion on or in a cable, use of terminal dope on the mating surfaces. Replacing batteries and not the whole bank."
Adding on measuring SG incorrectly or not at all, using more energy that is safe for decent battery life.  I am sure there are even more you can add on. The thing about living offgrid, I assume you are, there really is a learning curve and you eventually fail or learn. You do have to be an expert eventually.

morpho

Ok Dave,
Thanks.
Hope your day goes better.

Dave Angelini

My day is great, I just got 2,000 watts of solar for free because Fedex put footprints on solar panels.

BB.

If you are only replacing #3 battery in a series string--My guess would be that the other batteries are getting old and have higher leakage current--Causing too much current to flow through the new battery. That would give the new battery "high" SG readings and bubbling.

Another issue is that old batteries have higher self discharge... So, again, the new battery gets "over charged" as the old batteries self discharge and need more charging current to reach >90% State of Charge.

What I do not understand is the low(?) SG for the #3 battery? Started out with 100% SOC on bank, and installed new battery with 50% State of Charge? Or bubbling acid, cleaning, etc. got baking soda in cell(s) and weakened electrolyte? Or bad cables/connections heated up the battery terminal and overheated cells?

I do not know. Over the years, some folks here have said they have found they have to move batteries around be one battery at the end of a series string would always run weak SG readings (like once a year). I never understood a physical reason for this other than if a battery ran hot because of poor ventilation or engine heat next to battery, etc....

-Bill

littleharbor2

Wow, Dave. Why are you bothering to answer, if that's what you call your reply/

Dave Angelini

littleharbor2 said:

Wow, Dave. Why are you bothering to answer, if that's what you call your reply/

Well, I live in a free country and I can do what I want most of the time. Your reply does not seem very helpful to his problem, why are you bothering?

morpho

It's ok everybody...honest...I'm a big boy. Poor Dave is probably tired of answering the same dumb arse questions, or he had a bad day or whatever. I am happy with his response, he gave me a direction to investigate. Thats what I came for.

morpho

Hey BB,
Granted I am not a solar ninja or anything, but I have not done anything too stupid to the system. (honest, I didn't try to scrub the plates with baking soda) Other than - as Dave pointed out - failed to educate myself better on the how's and what's. Ok, cool. I am surprised my training batteries lasted this long to be honest. After reading other posts, most of us PV neophytes blow through our pseudo deep cycle batteries in 3 years or so. So I am learning...just slowly.

Is there a way to better balance the bank? Attach everything to two BUS bars? Not even sure that would work actually...

I think what I will do is sort out the settings and clean that up in my head. Then I will build a new box because this one is shot, go pick up another set of batteries, pull the cables, strip back the shrink tube and make sure the bits are properly attached. Commission the new bank and monitor like a mad man.

But maybe not for a few more months, we are currently running on 7 hours of daylight and dropping...maybe winter is not the time to sort it out.

When a bank goes, does it just "go"...one minute you have a more or less functioning bank and the next there is simply nothing?

BB.

Battery banks seem like a slow motion car wreck sometimes. In the end, when the bank no longer supports your needs and/or the costs of replacing one battery at time becomes too much for you--Then it is time for the new bank (paid from your savings account you have been building up over the last few years ).

I am on-grid--So I am not the best person to be answering battery bank questions. Good practices are always the place to start (common wiring lengths between parallel strings, getting larger AH batteries/cells to keep to 1 string ideally, or 2-3 maximum (if you can), good quality batteries, reading the Battery FAQs, using distilled or good/filtered rainwater, etc., checking state of charge, watching for over/under charging, etc.)...

In your case, I do not understand why the one battery position is failing. I know we keep making the same suggestions/asking the same questions--But not being there, it is where we start at. Lead Acid batteries, in general, are a pretty well known quantity--And failures should not be difficult to diagnose. However, there are times when very good battery companies seem to miss-place the recipe. And trying to figure out if battery company or operator error--I tend to start with operator error just because that is the most common cause of failure. But--Other things do happen.

-Bill

morpho

Slow motion car wreck!...perfect visual.
And I am in the back seat eating a sandwich ...thinking Cruise Control means Auto Pilot!
hahahaha!

So, here I am with my relatively small bank of 8 batteries (48V 232 amp hour)
For 9 months of the year I have more power than I know what to do with. My typical SOC when I wake up and look at the remote is 85% - 83% as we come into the fall and I use more lights earlier in the day.

In the winter, if it is sunny I have enough power... when it's not sunny, I turn on my little generator and top it up. Last year I clocked 96 hours on the genset. Some years its a bit more but somewhere around there. So now I am trying to figure out if there is much point in buying fancy proper thick plate deep cycle batteries (scrubbers) with maybe a little more capacity for lets say...?...$3000... and in a perfect world with a DOD of 20% they will have 4000 cycles...so...11 years more or less. So I will round that down to 10 because life is like that.
Or do I buy another set of what I have at $1500 with cycle count of lets say 3000...8 years...round that down to 7.... I will do my best to not screw this set up....but...life is like that.

What is the benefit in a better built bank?

BB.

How long did this bank last? (first battery replacement, and how long since on replacement batteries?)

In the end, a bank that costs 1/2 as much and last 1/2 as long (say 3-5 years vs 6-8 years) ends up costing the same... Just 2x as much work for you (2x replacements instead of 1x over 8 years).

Down side with an expensive/long lasting bank is if an "oops" happens in year 3, you just flushed 5 years of expensive battery bank down the tubes.

As long as your battery strings are "balanced" (like below), not much more you can do.

http://www.smartgauge.co.uk/batt_con.html

1x string of larger batteries--24 cells to check
2x string parallel--48 cells to check, 2x wiring/connections, etc...
3x--You get the math (I tell people to avoid more than 3 parrallel strings unless they have no choice--they can work, just more maintenance/wiring costs, and possible secondary failure causes).

Your best bet--Perhaps get cheaper batteries and spend it on a larger solar array--Reduce genset runtime and less battery cycling in winter... Your non-winter sounds like an ideal setup. You could even cycle them a bit deeper (use more power at night if you wish).

-Bill

PS: Add missing link to Smartgauge.

SolarMusher

The benefit is to get the maximum from your oversized array and have a better autonomy to save on gen. 3kw array would ask for a 400/450Ah bank or if you want to go golf batteries, two strings.

morpho

Thanks for the info and link folks.

BB
So this bank as a whole has been going for almost 5 years in total. The first battery went in 1.5 years.
The replacement has been in slow decline since then....so 3.5 years more or less.

You said a funny thing: "...You could even cycle them a bit deeper (use more power at night if you wish). " 
I wouldn't know what to use the power on. The only thing I used to cringe at in the evening was the bathroom fan...but I just replaced that with one of those Broan 8 watt Bath fans. It's awesome! 

So, you advise a boost to the array size to possibly glean a bit more from the light in the winter and hopefully cutdown on the generator runtime.

SolarMusher says - if I am interpreting it correctly - it is already over sized and I have the option to up the bank capacity.

I guess it depends on how you look at it and want to use it, plus I need to do the math on gas and engine wear and tear. vs added battery and/or more PV. If it actually works out that more panels would add enough to make it worth it. Take today for example, It was cloudy and I had a max of 3 or 4 amps coming into the system, more typical was 2. This is normal for me probably 3 days a week on average during winter. Even if I doubled my PV array and I was now getting 4 amps into the system on a cloudy day, I'd still have to run the genset. What we should do is call it what it is in the winter Generator power with PV support!

Ok...I am going to read that link you sent.

Thanks SolarMusher and BB.

westbranch

More panels do not necessarily have to be oriented in the same direction as the first array...  you can build a 'virtual array' that mimics the effect of a tracker, gets earlier sun interception and later as well by facing in different directions,  ie SE, S and SW is a simple example, or you could go and add E and W facing panels as well.  You do not get the maximum output from the total arrays potential but you do get a longer period (more hours) of input to complete your absorb cycle and float.  Remember that Absorb and float use decreasing amounts of amps the longer the phase lasts... This of course depends on your solar window at the winter solstice, mine is ~ 2 1/2 hrs...  11 days and counting then everything starts to get better...

morpho

Yup Westbranch, I am right there with you. I am in Central Alberta.
Interesting point about the pseudo tracker effect. I will ponder that.

westbranch

search on 'virtual tracker', it been discussed here several times...  lucky you not being in a deep V valley unless it's Drumheller...

morpho

HA! I am actually in a little bit of a valley. I have to wait about 45 minutes for the already risen sun to break over the top of the ridge. But in the end it doesn't really make an impact on me. Except in winter...go figure...but missing out on 45 minutes of low angle sun isn't really the difference I suspect. I still think about closing up shop in the winter and swinging in a hammock for 3 or 4 months every year. Anybody want 2 big stinky dogs and three cats?

westbranch

gave up 2 large dogs and a cat for 1 good sized dog, mainly wife's allergies, dogs, cats, horses, house dust, etc.

you would be surprised about the winter PV output especially on a good old cold winters day, the refection from the snow is a real boost... as well as the PV's being cold.
Getting another 45 min is a +-30% increase for me

SolarMusher

Hey guys! I was thinking alberta was very sunny, if that can help Quebec is worst!
Morpho, the best tracker I know that really works in winter for us in canada is a standby Kohler + AGS .
Eric, did you think about giving up the wife, it would be much simple (joke)!
Erik

morpho

My wife and I haven't been able to go on vacation together in 5 years. The animals + the PV system + the composting toilet all add up to make it hard to find a competent house/animal sitter. First world problems.

Solar Musher:
it is pretty sunny here in the winter, but it is winter so the days are short and the snow days combine to make it just slightly less than ideal. But still pretty good overall. The advice I got from my system provider was spot on: plan for efficiency and you will have enough power.