Introducing new battery into old bank, and other questions.

Volvo Farmer

I'm still having problems with my Surrette S530 bank. The beginning to the story is in this thread.
http://forum.solar-electric.com/showthread.php?14068-Battery-equalizing-rotating

I believe I have one battery going bad in a eight battery, 2 parallel string, 24V bank @ 800ahr. I recently checked the cell that was giving me problems, and the SG is around 1200, even after a full 4 hours of absorb. Additionally the adjacent cell, which was measuring 1250 or so a month ago, has also dropped to 1200. These batteries are 5.5 years old. I was mistaken in my other post when I said they were 4 years old. Time flies!

I have consulted two experts. One who has been working with off grid systems and batteries for over 20 years, and another who works for a company that manufactures batteries. One expert advises not to replace a single bad battery because the internal resistance of the new battery is so much lower than aged cells. He said the parallel strings would be constantly out of balance and the entire bank would suffer. The other expert advised to round up 3 of the batteries with the highest SG, and put the new battery in that string, and it should be OK. My goal is to squeeze 2 more years out of this bank, and a spending $400 on a new battery seemed like a worthwhile investment.

I was also under the impression that sulfation was only a product of chronic undercharging. However I recently heard that overcharging (or charging too quickly?) can cause sulfate to harden on the plates as well. This is the first time I have ever heard of this. One expert advised me to drop the 29.2V absorb setting to 28.8V, yet I have also heard the opposite from other people, that is to raise the absorb voltage for older batteries that may have diminished capacity due to aging.

I believe I have exceeded the 5A per 100Ahr limit on equalizations a number of times, also I was not fully aware until recently that an equalization needed to be performed on a fully charged battery. I have always charged these batteries at the high end of the voltage scale as I was afraid of sulfation from chronic undercharging. Now I wonder if I caused sulfation due to charging too quickly and being too aggressive with my voltage setpoints.

For now, I'm going to take the 4 best batteries and try to live off 400Ahr. We are generally using 100-120ahr overnight. Since I have a 120 lb of scrap lead in a red and blue container, I think I might try a few things to bring it back somewhat, like a good long charge on a 6V charger, or pulsing, or EDTA, since I have nothing to lose.

niel

Re: Introducing new battery into old bank, and other questions.

i'm not going to look back at your previous thread, but if you followed surrette's guidelines on charging then the rest is bull crap. usually too high a charge has the ability to warp plates, heat up the battery and cause issues with the casing, and of course lose electrolytes faster. i never heard of sulfating a battery with being on the high end of the charging voltage range. a similar thing can occur that i believe rcinfla mentioned having to do with positive post migration (if i'm remembering correctly) and that might've been for agm batteries, but that's not sulfation. in fact, why do you think it was a fault of yours the batteries have failed as batteries can and do go at any time no matter the normal lifespan or warranty for a battery? you may be splitting hairs being just over the 5a limit and you were doing this to bring all cells closer in capacity to each other. that seems to be problematic with the surrettes as per what i have been reading as they are being difficult to eq.

if you are certain the batteries are bad then you can try things with those batteries, but keep a very watchful eye on things when you do. a number of things can happen with bad cells and it could affect the good cells.

Volvo Farmer

Re: Introducing new battery into old bank, and other questions.

Thank you. I also have never heard of sulfation occurring during the charging cycle. Perhaps the expert at the battery manufacturing company, the expert who told me I could put a new battery in with 66 month old batteries with little consequence, was incorrect. I am seriously thinking about spending my next three to five thousand dollars with a different manufacturer.

I appreciate the feedback.

Ralph Day

Re: Introducing new battery into old bank, and other questions.

It sounds like your a committed off-gridder, with the charging sources to back that up. Have you the space for a lift truck battery? Check out solarvic's thread regarding sizing/purchase etc of a lift truck battery. There's a little more losses incurred in their use, but they do seem to last a long time and are robust. I'd be out of luck for one unless I took it all apart and re-assembled it in my basement. Where's your battery bank situated, garage, power house?

I did put 2 new cells in my Surrette bank (2 of 24), and they aren't dragged down in SG, in fact they are 1.280-90 when the rest of the bank is at 1.265. Not cheap! $450 each, then shipping...and that was only 60% of the new price (warranty pro rating). Like building a car from parts, it would be cost prohibitive to build a battery bank one cell at a time.

Good luck

Ralph

Volvo Farmer

Re: Introducing new battery into old bank, and other questions.

Ralph Day wrote: »

Where's your battery bank situated, garage, power house?

It's in a outdoor shed. I have plenty of room out there. Current batteries are in an insulated box. I was thinking about going Solar-One, as the guy who sold me my system has nineteen years on his, but a I would also consider a forklift battery. I'd like to get about 800Ahr out of a single series string at 24V though.

I did put 2 new cells in my Surrette bank (2 of 24), and they aren't dragged down in SG, in fact they are 1.280-90 when the rest of the bank is at 1.265. Not cheap! $450 each, then shipping...and that was only 60% of the new price (warranty pro rating). Like building a car from parts, it would be cost prohibitive to build a battery bank one cell at a time.

So it appears that your new batteries are doing more than their share of the work, and also contributing to a higher voltage being shown to the charge controller than the rest of the cells. I guess that's what one would expect to see if the internal resistance of new batteries is in fact lower than old batteries. As I recall, your bank was around 24 months old when you replaced two cells? I would not be so hesitant to try it if I had a single series string, but with two parallel strings, I think things would quickly get out of balance between the strings. What is the configuration of your battery bank? Do you have any parallel strings?

Thanks for the reply.

Vic

Re: Introducing new battery into old bank, and other questions.

Hi VF,

Well, looks to me like you are doing fine with your battery life. Would not worry too much about weather you have hurt that one battery or any of the others. 5.5 years off grid with two strings says (to me) that you are doing well.

Long ago, remember that BB Bill mentioned the 5A/100 AH twenty hour capacity was the EQ current max, and that the result of higher currents in EQ was the risk of hardening the sulphation, resulting in irreversible capacity loss.

IMHO, however, doing an EQ from Float let's say should not be that damaging to batts. The high current part of that cycle occurred well before EQ voltages are met. Have not heard/read of high Asorb voltages leading to sulphation issues.

Batteries are complex chemical/mechanical engines. There are many, many variables. Each manufacturer's battery may be a bit different than others, etc. FLAs ARE forgiving, especially if they are monitored fairly carefully. Everyone has opinions, and everyone can be correct, at least about some of the issues. But with so many small variables having some effect it seems nearly impossible to do a perfect job in managing battery care. Good thing that we do NOT need to be perfect at it.

66 Mnoths of good service from L-16 seems very good to me. Many of my neighbors seem to get a year or two from them. Altho, most of those banks are ignored until the lights go out at 11:00 PM.

WHatta I know (?)! V Good Luck, Vic

Volvo Farmer

Re: Introducing new battery into old bank, and other questions.

Thank you Vic.

I was really expecting to get 7-10 years from these, but I don't have any real world examples of them lasting that long. I took the bad battery to a local battery reconditioning shop that has access to several different types of 6V chargers. I'm expecting they will try charging it for a couple days and see if they can get the cells to even out. I'll have them load test it as well. Seems that it can't hurt. I'm missing that other 400AH when the fridge is running, the pressure pump is on, there are 4 lights on and the wife decides to dry her hair an hour before the sun comes up. Batteries drop right down to 22.6V with all that load on them.

I am learning a lot here! Maybe my next set will last longer.

bluz4evr

Re: Introducing new battery into old bank, and other questions.

my battery bank isn't that large -while traveling once I had trouble with a 6/125ah battery bank and after checking found dead cells in several bats.I replaced the whole bank -only using 4/115ah bats as thats all the store had.but never had any problems since.guess what am saying is I think its better to replace all instead of a few that way all are equal

Volvo Farmer

Re: Introducing new battery into old bank, and other questions.

Yeah, better, but also a $3000+ investment.

I took my weird Surrette S530 to the local battery guys and they determined that the center cell was bad. They got the SG up over 1250 after much effort, but the battery lost voltage overnight at rest. I guess I have about $45 back in warranty if I want to pursue it.

I have always heard that most batteries don't die prematurely, they are murdered. I don't know if I murdered them or not, but I am somewhat disappointed that I only got 5.5 years out of a supposedly premium set of solar batteries with a seven year warranty. I'm still undecided on what to do for my next bank. I'm torn between buying a $5000 set of HuPs, or trying to find a nice cheap forklift battery. Whatever I do, I'm going with one series string this time. Just hard to find 2V batteries in the 600-800 ahr range on the cheap.

niel

Re: Introducing new battery into old bank, and other questions.

bluz4evr,
i think you were undercharging your previous bank in light of the thread you starting stating what you have and what you're going to upgrade to. for the record and everybody else's benefit, you have 16 15w pvs and 3 7a controllers that you plan to upgrade to 420w of pvs and a mppt controller. generally one would want to be within the 5% to 13% charge rate range for the batteries and what you had previously was just way too much battery for the charge source and most likely resulted in sulfation destroying those batteries.

i should add that sometimes the vmp is low on small pvs which takes away from valuable charge time for the batteries too.

stephendv

Re: Introducing new battery into old bank, and other questions.

Page 17 of this paper describes 4 causes of pre-mature battery ageing: http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf
1. Discharging too deeply
2. Charging too quickly (during bulk) and not fully charging (during absorb)
3. Undercharging = sulfation
4. Overcharging

Sounds like you may have overcharged. From what I've read, overcharging doesn't cause sulfation, but causes corrosion of the positive plate - which is irreparable.

niel

Re: Introducing new battery into old bank, and other questions.

"Sounds like you may have overcharged."

stephendv,
who were you referring to for if you are referring to bluz4evr how do you figure that one when he had 6 125ah batteries?

6 x 125ah = 750ah battery capacity
pvs 15w x 16 = 240w.
240w/12v=20a this should also be reduced by 77% as efficiencies on pvs aren't 100%, but i'll initially show it as 100% efficient.
20a/750ah=2.67% charge rate and is about 1/2 of the 5% minimum. if the pv efficiency is accounted for it would be a 2.05% charge rate.

even if these were 6v batteries series/paralleled to get 12v they would still be on the low end of things.

stephendv

Re: Introducing new battery into old bank, and other questions.

niel wrote: »

"Sounds like you may have overcharged."

stephendv,
who were you referring to for if you are referring to bluz4evr how do you figure that one when he had 6 125ah batteries?

Oops, missed the quotes, was referring to Volvo Farmers first post in the thread.