12V batteries in parallel. Any scientific documents?

lazza

HI All

Well it's been a long time since I lasted posted on the forum. Mainly due to work and family committments.

We're invovled deeply in a court-case where we were sold some very dodgy 12V AGM batteries, which all failed within a year! Dozens of other companies in Spain have also affected, but didnt dare take the culprits to court. I've had previous discussions on the forum: http://forum.solar-electric.com/discussion/comment/358349#Comment_358349

Well we've just a received a report instigated by the battery company conducted by a so-called "independent specialist", who said the reason they failed is because we put them in two parallel strings and batteries fail in parallel !!! So it's all our fault.

To summarize, they were small installations (2 or 3kW inverters), 4 x 12V 250Ah monoblock batteries, of 2 strings in parallel for 24V inverters (2x2). A textbook, 12V battery installation.

I know it's absurd what their report is saying, but it's our word against theirs, and the Judge is unlikely to have prior battery knowledge unless they are caravan or RV fanatics.

So it would be great if anyone has any documents that very simply explain parallel operation using 12V batteries. Preferrably, from a highly reputable scientific organisation. Could you share that with me? Or any arguments that you may think useful?

Thanks in advance, I hope to write on something more interesting soon

Cheers
Lazza

Estragon

IMHO, destructive expert testing of the actual failed batteries is your best bet. AGMs will obviously have no routine SG readings in maintenence records to evidence a charge/discharge regime meeting manufacturers specs.

A risk in running batteries in parallel is unequal resistance in connections, or in the battery itself, leading to unequal charging, and discharging. It wouldn't be difficult for the maker to make a case that wiring faults and/or charge/discharge regime (eg high current charge/discharge relative to wire and battery sizes magnify the differing resistances) *can* lead to failure.

Assuming the civil case turns on a balance of probabilities, and you're claiming a manufacturing defect without actually demonstrating the nature of the defect, I suspect the balance might well fall to the defense. They can quite plausibly claim alternate reasons for the failure, and you will have no evidence to support your manufacturing defect claim. Even if you find examples and/or theoretical evidence to support the idea that parallel operation *can* be done sucessfully in general, those can't and won't refute a claim that miswiring or misuse in this or these particular installations didn't lead to the failure. In order to have a chance of refuting that defence, I think you would need need, at a minimum, regular records testing resistance under load of all batteries, wiring, and connections, to demonstrate the charge/discharge use of all batteries was likely to spec. Even then, the records would be suggestive, not definitive.

If destructive testing shows sulfation and no clear sign of manufacturing defect, you can probably save a lot of legal and court costs. If testing shows a design/manufacturing defect, you will have a much better case.

All IMHO.

lazza

Thanks Estragon for your input

Their report has no detail on how parallel connection can cause failure, he simply stated it as the cause per se. And as i am aware, no more evidence can be brought now we are past first hearing.

Their batteries failed in insallations with just one series too. We have a report from an independent engineer that states that our design, wire sizes/fuses etc are spot-on.

At the time we looked into laboratory testing, but it was so expensive, and would probably prove inconclusive anyway, that we simply couldnt afford it.

Balance of probabilities- mmm one shall see 

BB.

You can check with our host NAWS, or Trojan directly... I think their 2 volt L16 battery is actually 3x cells in parallel (a reason to be a little unhappy is that one has to check all three cells for SG and Electrolyte levels--Unlike a true single cell 2 volt Lead Acid battery).

https://www.solar-electric.com/trl111ah2dec.html

When the batteries were running OK, did anyone have a DC current clamp meter to measure that charging and discharging currents were similar between strings?

Where these 12 volt batteries in 12 volt parallel connections, or were they something else (2/4/6/12 volt adding up to 24 volt or higher battery bus voltages)? I like small batteries adding up to one higher voltage string because it is so simple to take a volt meter to each cell/battery and check its individual "health". Any cell that is higher or low with respect to the rest of its mates need further investigation.

When cells fail in parallel connections (2-3 or more parallel strings), it is possible for the remaining "good strings" to supply sufficient energy during sunny weather/low power usage to "hid" the failing cells. So--it is possible for failing cells to look "worse" in parallel installations as they keep getting charged/discharged/etc. and the failure process to proceed further down the road (possibly to catastrophic cell failure, over heating, etc.).

Also, you have different failures... Cell open--The string "disconnects" from the battery bus--And nothing much happens to the rest of the cells (they slowly self discharge).

You can have a cell fail shorted--This can cause your 12 volt battery to become a 10 volt battery and the rest of the cells become overcharged ("good" cells overheat, vent and dry out).

I would push back on every statement that the Lab/Mfg gives you and make them prove it... No "expert" says parallel battery strings cause cell failures without a documented physical/electro-chemical explanation and laboratory/failure analysis documentation.

Many Failure Reports are deemed "company confidential/trade secrets". Different countries have different laws on disclosure--So your lawyer(s) will have to figure out how to pry the information from the company.

I guess my last question--Even a single cell battery is "parallel" in construction... The surface area of the plate (different sizes for different batteries) are, more or less a bunch of very small chemical reactors that add up in parallel to the one large AH capacity of the cell. There is the plate grid (similar to exterior wires and cables). Part of a plate can fail (low electrolyte levels cause "exposed" plates to oxidize, variable sulfation across surface of plates, grid corrosion, etc.).

There are many reasons I suggest that 1 string is easier to maintain, and 2-3 parallel strings is as high as I would suggest (unless larger AH batteries are not available/cost effective)--To reduce maintenance issues and points of failure. But, if all is working correctly and maintenance (and monthly inspections) are performed (to catch small problems before they become big)--I do not know if any reason that parallel battery strings "do not work".

I see that you are past the first hearing and further evidence/disclosures may not be allowed/requested... Hmm, I don't know what else you can do other than simply point out that they have no supporting evidence to their statements (and was there any warnings in their documentation that parallel battery strings were not allowed/warrantied?).

-Bill

mike95490

Batteries in parallel are inherently prone to become unbalanced, because of minute resistance variations in the cables, crimps and connector bolting, in addition to internal battery resistance.   With AGM, because the internal resistance is so low, ALL the aforementioned factors come into play to destabilize the bank.

If you have a solo battery, or series bank that failed, that can be blamed on the the battery or charging regime, if you can prove proper charging, it's therefor a battery defect

see the self disclosure in post 34 of this thread

http://forum.solar-electric.com/discussion/353087/load-pv-during-day

Estragon

I'm not a lawyer, and wouldn't admit to it even if I was, so again, FWIW.

You are the plaintiff, which implies a burden of proof. The defence has put forward an alternative mode of failure which, absent evidence to the contrary, is entirely plausible. As plaintiff, it seems to me you need to; a) provide evidence in the negative, disproving the defence the charge/discharge regime given was not as recommended by the defendent, and 2) provide positive evidence of a design or manufacturing defect.

Destructive testing of the batteries would certainly be expensive. To be persuasive, it may even need to be repeatable (and repeated) by multiple experts. Compared to the cost of pursuing a civil case to conclusion though, not so much.

In my experience, the case may be more about who has the resources to sustain a case than about who has the "better" case.

Assume you're the maker of a badly designed or badly constructed battery. You know there will eventually be warranty claims denied and civil challenges. You know initial challengers will make the same cost/benefit trade-offs, and won't test. Challengers would likely lose at least the first few rounds. You're ready for this. By the time someone figures it out, paid the price to pursue it, and got a judgement, you're in the wind.

These are the kind of decisions that get made in civil actions.

mcgivor

 @lazza said, Their report has no detail on how parallel connection can cause failure, he simply stated it as the cause per se. And as i am aware, no more evidence can be brought now we are past first hearing.

If the rationale for the failure is based solely on parallel configuration, which is not only common but described by some manufacturers, Trojan is an example there are likely others http://www.trojanbattery.com/tech-support/technology-information/ ,If this particular manufacturer makes the claim that their batteries cannot be paralleled for any reason, this should be a caution/warning in their documentation or website as a disclaimer, without such a disclaimer, the argument is weak to claim that was the cause. Just a thought.

mike95490

It's a known problem with any mfg parallel banks,

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

  simple math and ohms law is described on the above site

lazza

Brilliant. This is all great stuff, thanks to everyone. Please keep ideas and information coming.

I think we can request inclusion of documents dated after the first hearing, as long as the document provided is dated afterwards. Even if the document is not admitted by the judge, it could be used as ammunition for our independent engineer to have in his hand whilst supporting our case.

Trial is not until May 2019!! So plenty of time.

jonr

Note that the smartgauge site is absolutely wrong when it refers to "perfect  balancing".   To get close to that you should measure amps from each battery.  Also note that to a very large extent, parallel batteries (unlike series) self balance.  For two reasons - 1) during low load, voltages even out and 2) a more heavily worked battery drops in voltage at which point it contributes less current (even if it has lower resistance).   The smartguage figures do not include this effect, making the claimed "massive improvement" a  "small potential improvement for people who don't bother to measure amps".

If all your batteries failed equally, then parallel load sharing was probably not the problem.  And since parallel batteries is standard practice, I agree that it should be assumed to be OK unless the manufacturer specifically says otherwise.

> (2 or 3kW inverters), 4 x 12V 250Ah 

Is the battery rated for a  > C/4 peak load?  

mcgivor

After reading the attached thread, it would appear the issue was leakage from the vent caps, rather than a capacity loss or other failure. Sometimes there is a bad run in production, using production lot numbers could pinpoint if it is an isolated case, or a broad systemic fault, what I'm alluding to is a compromise, again just thoughts. 

lazza

In reply to Jonr, ratings were given for C1, and no discharge limit was stated. However, batteries failed in all installations including those with a couple of LED lights and a LED TV, as well as those with higher power use.

McGivor. Yes the vent caps seem to have dodgy seals. however, that's not a scientific analysis . 

Estragon

McGivor's comment about lot numbers is interesting. I don't suppose a list of warranty claims with lot numbers was requested in the dicovery process (assuming there is a discovery process). It might help if similar failures happened in single string applications.

Is there such a thing as a class action? Do you sue in Spain under Spanish law?

lazza

Failures were generalized and across Spain for at least 2 or 3 years- so it's not even a question of lots. We have letters of support from companies in Valencia, Madrid, Canary Islands etc etc. But unfortunately noone has had the courage (or be stupid enough ) to stand up to these people and take them to court. There is no confidence in the spanish justice system and most companies have already sold their evidence ie the batteries, for scrap, cutting their losses. We tried to convince them to launch a joint claim, but to no avail, most have said. "we"ll see what happens to you first".

The judge wouldnt accept their testimonies in court as she said they've already supplied supporting letters- dont know if that means she accepts the problems is generic, or some other reason.

jonr

You could pressure test a failed battery/case to verify that it holds pressure up to the relief pressure.  If not, then excessive loss of electrolyte would be expected.