Replacing a Bad Battery in an 8 strong bank

muirhouse

Does anyone know how to find a good USED 6volt deep cycle lead acid battery Surrette s460 350Ah I have an 8 battery string, and one is bad, causing the whole string to refuse its charge! Plopping a new battery in the string is not advised, so I am wondering how one goes about this? Thanks for any assistance!

mike95490

Re: Replacing a Bad Battery in an 8 strong bank

At this point, adding a new battery is less than a new string. How old is the string with failed battery ?

The reason it's not recomended, is the new battery will be quicly degraded to the the age/capacity of the string.

Vic

Re: Replacing a Bad Battery in an 8 strong bank

muir,

Check with your neighbors if you are off-grid, there may some serviceable used batteries in your area.

However, if one in a string is bad, and all of the batteries are roughly of the same vintage, how will the other batteries know to not go bad, very soon. Is not the writing on the wall, ? Or, was this one battery abused in some manner ?

Good Luck, Vic

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

Thank You Vic and Mike,

Yes this battery was abused and the rest of the string tested under load test fine. Not sure how a new string of 8 at $300 per battery is more than a used one? Yes, neighbors are an option, so far no one has a used one hanging around!

icarus

Re: Replacing a Bad Battery in an 8 strong bank

One new battery is cheaper than a whole new string.

That said, if they are getting to the age where you really don't know, consider buying 1 new one, or if you are running 12vdc, cut a pair of them out, keeping the one for a spare, just using a smaller bank.

SOL or that idea if you are 24 or 48 vdc.

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

This is an OLD bank, 2002. But they are still testing at 6v like I said, except for this one that got zapped. This string is series/parallel stacked with another string of 8, which was added in 2005, so 48V. So already we had violated the 'all one age' rule of thumb, then made it worse by having a similar problem with the old string years ago, and plopping a NEW battery right in the middle. But that said... this whole kit n' kaboodle is charged through 2 Xantrex 4048 inverters, by 15kw genset.

Getting PV now and trying to minimize the high cost of this system by keeping these batteries a bit longer if they can be made to perform up to snuff again.

While I have your attention and re the cost focus, does anyone have an opinion on the differences between Trojan and Surrette for 6V batteries, isn't Trojan a bit less expensive?

niel

Re: Replacing a Bad Battery in an 8 strong bank

"This is an OLD bank, 2002. But they are still testing at 6v like I said, except for this one that got zapped."

the only good test is a load test to see what kind of capacity is really there. the stress from this test can actually force a failure on any battery that is teaterring on the edge.
just what do you mean by zapped? what actually happened or is going on with the battery you say failed and was it an original 2002 battery that failed? of course you know that all of the batteries can be considered 8yrs old because newer was used with older batteries which drags them down to the worst of the bunch and that is usually the older ones. newer ones, i concede, can fail prematurely too.

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

Niel,

I did test them all under load, all were a @6V, the bad one was @2. We are not sure exactly what happened, but when the electrician was cleaning the battery terminal, he put some resistance goo on the terminal which may caused something, but more likely it was because the parallel connector was touching the series connector, and when pulled apart, the problem went away. I do understand about the bad one pulling the rest down to its level. Which is why the whole string is now refusing to take a charge.

QUESTION: In the meantime I have found a good price on 16 new batteries, 10 s460s and 6 s530s, and I want to know if I can used these together, or do I have to have all 460s, or all 530s. The only difference is 50 amp hours more for the 530s.

mike95490

Re: Replacing a Bad Battery in an 8 strong bank

muirhouse wrote: »

QUESTION: In the meantime I have found a good price on 16 new batteries, 10 s460s and 6 s530s, and I want to know if I can used these together, or do I have to have all 460s, or all 530s. The only difference is 50 amp hours more for the 530s.

NO, you should NEVER mix capacities in a series string.

parallel mixed capacity, while possible, I'd avoid

niel

Re: Replacing a Bad Battery in an 8 strong bank

keep all batteries as identical as mixing is asking for trouble.
as to load testing, i don't think you are fully understanding what is involved with that. that is a controlled current draw that is run until the battery reaches 100% dod or simply dead which for a 6v battery is 5.25v. the time it takes to reach that point will be the current drawn x the hours drawn to get amp hours. the fact this goes down to being dead can cause failures in batteries that are close to failing already or it could shorten the life cycles further. at this point you need not worry about it if you are buying new batteries.

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

Quite right, not in the same string, but was considering it in the 2nd 8 battery string which is as you say then wired in parallel. Will investigate the hazards further.

niel

Re: Replacing a Bad Battery in an 8 strong bank

muirhouse wrote: »

Quite right, not in the same string, but was considering it in the 2nd 8 battery string which is as you say then wired in parallel. Will investigate the hazards further.

no, that is not good as that makes one string different than the other. keep them all the same no matter if in series, parallel, or both.

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

If the only caveat is that the longer ah batteries will be dragged down to that of the lesser amp hours, then I still might consider it. These batteries are basically a gift, and if I can possibly make it work, it saves me four thousand dollars. If anyone knows any Other reason that I should not use 8 s460s and 8 s530s, series kind to kind then parallel to each other, please let me know. I am going to check all the charging parameters to make sure they are otherwise exactly the same. Right now my one bad battery is leaving me with a constantly charging generator, and replacing 16 batteries on top of the rest of the new pv install is prohibitive. Thanks so far for everyone's input.

BajaGringo

Re: Replacing a Bad Battery in an 8 strong bank

I do agree that batteries in series should be exactly the same. In parallel the higher ah capacity units will drag down. A neighbor down the beach did what you are contemplating a few years back with 10 and 6 batteries of 200 ah and 250 ah capacities. He tells me that they are still going strong. He just programmed his battery monitor for sixteen batteries at the amp hours of the lower capacity and tells me that they have operated steadily.

If I were in your shoes I would do the same thing if you can get them at a great price!

muirhouse

Re: Replacing a Bad Battery in an 8 strong bank

Thanks for the example Baja, - are you saying he did NOT put his mixed battteries in series? Do you know how he did put them together? And thank you for the idea for programming the monitor to the lower battery ah to begin with. Battery monitor here, I am understanding as the inverter.

BajaGringo

Re: Replacing a Bad Battery in an 8 strong bank

I was thinking about my post last night on my way into town this morning so I drove out to his place on the way back home. Looking at his setup again I noted that he had 14 batteries not 16 as I had posted. He has them wired for a 24 volt output and the attached shows his wiring. He told me they have over three years on them and still going strong. The battery monitor is a Trimetric so he can monitor his SOC.

BB.

Re: Replacing a Bad Battery in an 8 strong bank

One thing too we try to recommend is "balancing" the wire resistances to have the batteries sharing the loads/charging current:

SmartGauge suggested battery layouts

-Bill