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Author Topic: Positive plate corrosion in opz batteries  (Read 10607 times)
Wingnut
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« on: March 26, 2013, 11:59:07 AM »


Has anyone ever seen such corrosion on a battery before?

This battery was part of a set of 12 on a solar system in the South of Spain (600 AH C10). My guess is that epic under charging, over discharging, stratification and quite possibly over heating, perhaps by the proximity of the generator. has caused this to occur, but I could be wrong. (abused and neglected) The battery bank had 20 amps of solar charge and a 100 amp Xantrex charger attached. This set of batteries are only 4 years old and 6 of the 12 batteries have partially or completly detached themselves. I did give some of them a helping hand by slightly turning / wiggling the bridge post that was bolted to the batteries that were showing low voltage. It does appear that there is not that much material to start with attaching the plates to the post bridge, or is this normal?

The remainder of the cells have responded to remedial charging and now show full SG and hold a rest voltage of around 2.07V.

Has anyone taken this type of battery apart and re welded the plates? I was thinking of giving it a bash and perhaps using them for some light duties, landscape lighting or the likes.




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Philip R
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« Reply #1 on: March 26, 2013, 12:36:20 PM »

Wingnut,

Back in the 1990s when I had responsability for several large Plante batteries at my workplace, I visited The Tungstone battery factory in Market Harborough, sadly no more.
I saw the process of lead burning to join the plate lugs to the battery post(s) by forming a lead puddle (group bar) within a mould inserted during the assembly stage.

Having done lead burning myself during my plumbing training, I would suggest that trying to reform the missing plate lug as very difficult without some kind of former to hold the Molten lead. For health and safety reasons I would not attempt it. Another reason is you have to get the lid off and support the group bar and post connector.

The reason for your failure could be; vibration,misuse, abuse, varying acid/electrolyte level, too high charge rate, excessive ripple current from the charger, ( broken rectifier arm) and good old failure of the group bar burn. Many of the cells I has responsibility for had burn cross sections well below 25% after 18/ 20 years of life, some even lower, although on load tests (about C2), they performed very well. Hence the need to replace the batteries as a complete unit.

Philip R
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Wingnut
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« Reply #2 on: April 01, 2013, 09:37:30 AM »

Thanks Philip I will take your advice and scrap them, you are correct the health and safety side alone makes it hard to justify the effort, but as a tight bodger it does niggle me a bit. It does seem odd that some of the cells have such high corrosion levels and others have very little. Leaves me wondering how much life the other cells have left in them. I will look out for "group bar burn" when I inspect other battery banks in the future.

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Eleanor
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« Reply #3 on: April 01, 2013, 09:57:25 AM »

Hi Wingnut, my guess (and it is only that) is that the major cause of corrosion is the electrolyte not being topped up and the plates being exposed to the air (must go and check ours!). As you and Philip have already said there would also be stratification resulting in high acid concentrations at the bottom of the cells. Has the active material gone walkabout just at the top of the plates or further down as well? They do look to be in a sorry state - I've seen articles on the internet about people refurbishing cells but it's not something I'd like to try unless I really knew what I was doing and I don't!
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Philip R
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« Reply #4 on: April 04, 2013, 12:35:10 AM »

Wingnut,

The group bar burn was ascertained by a tear down test.

The battery lid is removed after the acid decanted. The whole mass of plates is removed from the container and gently !!! laid on the floor.( Ours ware glass battery cases, removed with a hammer!!)  If you have SAN (Styrene Acrylonitrile) containers, removal of the lid will be a bit ackward as they are sometimes welded together.

Whatever, removal is a destructive process.

Then each plate is moved side to side to shear it off the group bar, hence tear down. The section of lead in the group bar that appears bright and metallic is the remaining active conducting and suportive structure. You will find that these cross sections can be much reduced before an increase in resistance is spotted, i.e. poor voltage regulation on high discharge rate.

The test is not elegant or have much finesse about it, but proved how good the group bar integrity was.

Be aware, if charged, the negative pasted plates will burned out as they oxidize, and water vapour will be produced from them.

Philip R 
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Wingnut
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« Reply #5 on: April 05, 2013, 11:45:20 AM »

Eleanor, Philip

That is what gets me, the corrosion only appears to have of occurred on 6 of the cells on the plate bars that attach to the posts. Most 2V cells that I come across that do not receive regular equalization charges have stratification problems. You would think that if the acid is stronger at the bottom of the battery the corrosion would occur at the bottom of the battery not the top?  The remaining 6 batteries I put on a 75 amp charger and all recovered full SG and voltage. I actually put 5 on the charger and gave them a good 2 hours of increased voltage, then swapped out the one with the best SG and gave them another 2 hours; this got rid of the stratification issue as well. I did keep a weather eye on battery levels and temperature. I will do a load test on them as soon as I have time.

On the remaining six batteries the plates appear to be in very good condition and the posts that attach to the plates are not corroded or "inflated" as on other broken 6 batteries.

Philip, I found this brilliant piece of writing on the internet from the 30īs about how to start and run your own battery shop.  The health warning are just hilarious "drink plenty milk and take Epsom salts if constipated due to lead poisoning"  Have a look at the safety equipment being worn, dickey bow and trilby! Well worth a read to anyone interested in battery anatomy.
Link:

http://www.powerstream.com/1922/battery_1922_WITTE/battery_WITTE.htm#toc

That being said there is a mine of information in there; I do not think I have ever come across a more complete readable set of instruction on how to complete a technical task or run a business. This has inspired me to have a go at battery rebuilding. 

My plan of action is to, empty acid and replace with distilled water, remove the tops, not sure how, possibly with an angle grinder, drain the battery. Then lift up the plates slightly when the battery is on its side all together as they are still attached via the positive post.  Then burn some lead strips onto what is remaining of the plate bars. This will at least let me do some testing on the battery to see if it is worth continuing.

Would it be better to completly discharge the battery before I attempt any tear down?
Do you think I could use a butane micro torch to "burn" / weld lead strips onto the battery plates or will I need some oxygen mixed gas?
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Philip R
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« Reply #6 on: April 05, 2013, 10:06:55 PM »

When I did my lead fabrication, I used oxy acetylene. The guys at the former battery factory used oxy propane through a fine nozzle i.e. oxy acetylene type.

The plates they were burning had been formed, in a dry state before any of the charging / plate conditioning cycles had started. The plates were in an inert condition.

Please note, your plates are charged and the negative plate is almost pure spongy lead. Expose it to air, it will oxidise and "burn out", whether it can be recoverred from this, I do not know. If you discharge it, the plate will convert to lead sulphate, not desirable me thinks.

One other point, even if drained but wet, the cells can still be shorted circuited and go bang, if not, the liberated explosive gases to which you plan to introduce a nice hot flame may then go bang!!!!   BE CAREFULL!!

Philip R
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ecogeorge
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« Reply #7 on: April 05, 2013, 11:27:56 PM »

Lead fumes , charged plates , liquid acid , hmmmmmm  not sure I could think of a worse combination
 to work with. facepalm
Please be careful , lead poisoning is cumulative.
Why not just weigh them in , -battery scrap is good money at the moment.
rgds george.
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Eleanor
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« Reply #8 on: April 06, 2013, 12:17:56 PM »

Wingnut, you're far braver than I am! Just handling and storing that quantity of acid is enough to put me off without the other potential problems which could occur as Philip and George have said.

Thinking about how they could have ended up in this state : do you know if they were all connected in series as a 24V bank? Did they fail randomly or was it the first six in line that failed? Maybe there was a poor connection between cells 6 and 7 or something happened in cell 6 which effectively split the bank in two? Would Cells 1-6  then have taken all the charge causing overheating, excessive gassing, exposure of plates to the air and hopefully the popping of a fuse on the cable? Cells 6-12 would just sit there innocently with nothing happening? It's only a theory and someone may have a better one. I don't think higher acid ie sulpate ion concentrations at the bottom of the cell would cause corrosion but it would lead to more sulphation as the battery naturally wants to be in a discharged state with the plates covered in lead sulphate.

Without taking the orange separators off the plates you won't know the integrity of them. To be honest I'd just get rid of them - it looks they have already had one lucky escape  signofcross
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clockmanFR
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« Reply #9 on: April 06, 2013, 12:53:00 PM »

Hi Wingnut,

I have built a complete new cell when I lost one a few years ago.

I did not do any burning near the battery itself, but removed the cell and re-built it elsewhere.

I used a wood chisel to get at it and to disconnect it from the other cells; on re-build I bolted it back in with stainless steel bolts.

I have plenty of zinc sheet and plenty of lead sheet, and 80% sulphuric acid, (used for Jewellery/silversmithing), which I mixed down. I used bits of the plastic battery case top to make several combs to keep the plates separated.

However, the original plates are a matrix fabrication, and when I put my re-built cell back, I was only achieving 20% of the original amperage from that battery. Voltage was okay.

Conclusion:- Just not worth the effort and my time.

But it did prove that I could make a battery, but just a very very inefficient one.
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Wingnut
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« Reply #10 on: April 09, 2013, 03:05:04 PM »

mmmmmmmmmmmmm starting to wobble again.

Thanks for all your advice. I have just removed one of the tops of the batteries and after draining and flushing the battery I have realised that there is no correct way that I can dispose of the left over mess apart from chucking over the neighbours fence. What to do with all that lead gunk and left over contaminated water? Think it is back to the safe plan A and weigh them in 50 cents a kilo does not seem too shoddy. Pity I was just about to invest in a portable mini torch set up to add to my tools kit.  It seems a real shame, guess I will have to test my DIY skills elsewhere, perhaps a bit of grouting seems safer all round.

Thanks again folks, you helped me make the right choice and save the tool shed from Armageddon, I think!
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