How do You Raise SG on Single Cell

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How do You Raise SG on Single Cell

Postby EvKar on Thu Jan 30, 2014 1:14 pm

I have one cell out of 24 that is giving me trouble. If you follow my thread in the Off Grid forum, I have been working on getting my battery bank up to 100% SOC. By upping the absorption hours and some lengthy equalization, I have achieved a100% SOC, (according to the SG readings), in all my batteries, with the exception of one cell read 1.250 SG. This lone cell, I can't get it up higher than 1.250 SG. At the last three hours of the EQ, the other cells stayed at 1.277, and this cell stayed at the 1.250 mark... wouldn't move. The batteries were manufactured in November of 2013. Did I damage this one cell? Any ideas on how to get it's SG up?
Thanks, EvKar
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Re: How do You Raise SG on Single Cell

Postby Vic on Thu Jan 30, 2014 5:16 pm

In general, EQing the entire bank is the recommended way to try to raise the SG of lagging cells.

Often, battery banks, composed of a number of cells will have a or a few lagging cells. Battery manufacture is never perfect. Some variation is not bad. This one cell is quite a bit lower than the others. The Trojan battery manual probably has guidance on when to EQ the bank. However, if the SG of this cell did NOT rise at all during the final three hours of that last EQ, then the general wisdom is that it never will.

Cycling batteries to about 50% State Of Charge is good for them. Sometimes a couple of these cycles COULD possibly help the battery bank in general, and perhaps this one cell.

Have seen cells with too-high SG (with adequate electrolyte levels) come more into line with the rest of the bank with a couple of these deeper-than-normal cycles. It could not hurt to try.

Also, Trojan may have something to say about this level of SG variation, EQ, and warranty parameters.
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Re: How do You Raise SG on Single Cell

Postby BlackCherry04 on Thu Jan 30, 2014 7:49 pm

I'd pretty much agree with what Vic posted to you. Without the equipment to allow you to do that one by it's self your kind of stuck. I have a couple old GC-2 6 v batteries and I'll tag a one onto a battery like your's and EQ them at 16 V. With a variable Power supply you just leave the battery in the string and hook up the +/- battery and give it 7.75 v till it comes up. The other option would be to pull it and take to someone that has the equipment.
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Re: How do You Raise SG on Single Cell

Postby vtmaps on Fri Jan 31, 2014 8:27 am

One way to look at batteries is stochastically. The individual cells come off the assembly line and if you graph their lifespans you will see a normal bell-shaped curve. Half the cells will be below average. When you assemble a 6 volt battery from three cells, the only way you can get an above average battery is if all three cells are above average. (Remember, a battery is only as good as its weakest cell). There is virtually no chance that you can assemble 48 volt bank of above average cells. The average life of a battery bank is the life of its shortest-lived cell.

Calculating the average life of a multi-cell battery is very complicated. It depends on how wide the bell-shaped curve is. For example suppose the average cell life is 7 years, and the outliers are no less than 6 years and no more than 8 years. In that case, the minimum lifespan of the battery would be at least 6 years, and the average lifespan would be a bit longer.

A battery manufacturer sets its charging recommendations so that more than 99.9% of its cells will be charged by that protocol. This means that if you follow the manufacturer's protocol more than 99.9% of the cells are being overcharged. The reason that they can get away with this is because flooded lead acid batteries are tough and can take quite a bit of (overcharging) abuse. Remember, if 0.1% of a company's cells fail during warranty, then almost 0.3% of its 6 volt batteries will fail and almost 0.6% of its 12 volt batteries will fail.

This manufacturer sanctioned overcharging is why many of us can ease back on the manufacturer's charging recommendations. If you can maintain your particular bank with less overcharging, you will benefit with longer than average life. If you need the full charging protocol to keep the cells working, you will get the manufacturer's warranted life from the battery. If you can't keep the battery working using the manufacturer's protocol, they should replace the battery.

No discussion of battery stochastics is complete without mentioning parallel battery banks. Parallel batteries means having two or more times as many cells as is required to supply the voltage you need. It increases your chance of having an outlier among your cells. An outlier with a longer life does you no good because only the weakest cell determines your battery life. An outlier with a shorter life does harm to your entire battery bank.

From a stochastic point of view, the best system will be composed of the fewest cells. Of course, a 2 volt system is not practical, so a good design compromise is to use a single string of cells at the lowest voltage that is practical.

Now, let's discuss your situation which also applies to my situation. I too have a weak cell (actually two in my L-16 batteries). What to do? Not sure... If I had 2 volt cells and a young bank, and one cell was weak (but not replaceable under warranty), I would replace it at my expense. In my case, I am not going to replace an L-16 battery in a 4 year old bank... I will just wait until its time to replace the whole bank.

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Re: How do You Raise SG on Single Cell

Postby EvKar on Fri Jan 31, 2014 4:01 pm

Thanks for the responses, there is a lot of information.
Cycling batteries to about 50% State Of Charge is good for them. Sometimes a couple of these cycles COULD possibly help the battery bank in general, and perhaps this one cell.


Vic, I believe at this stage of the game, I'll try the above suggestion.

Thanks, Guys
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Re: How do You Raise SG on Single Cell

Postby BlackCherry04 on Sun Feb 02, 2014 7:43 am

Your batteries are 3-4 months into service and have a cell with low SG that will doom it for life unless you raise it. The " Could " and " Possible " sound good but the reality is once the Sulfate crystallizes it will stay for ever and cannot be removed. That cell will be feeding on all the other cells and shorten it's life and the ones around it and expect a early end. During the charge and discharge cycle it's going be out of balance with the others, I'd be trying to raise it.
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Re: How do You Raise SG on Single Cell

Postby Solar Jason on Mon Feb 03, 2014 6:08 am

Raising SG on a single cell would be tough unless your batteries are single cell batteries. I had one three cell (6V) battery that was always lower than the rest when I started out. Rather than EQ the whole bank for a long period of time, I connected a power supply up to just that battery and raised the SG of just that battery.
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Re: How do You Raise SG on Single Cell

Postby EvKar on Mon Feb 03, 2014 6:42 pm

Solar Jason,
Rather than EQ the whole bank for a long period of time, I connected a power supply up to just that battery and raised the SG of just that battery.


This afternoon, I called the company that sold me the Trojan Batteries, and that was what was recommended. I'm going to do an EQ on just this one battery, then if that doesn't work.. bring it in and do an acid adjustment. Which he said was to dump part of the original acid out and replace with new. Anyone have any experience with this procedure?

Black Cherry, I pulled the warranty card, and he said that with a 15 point difference (85% SOC vs 100%), Trojan couldn't help him. But should it get to be 25 to 30 point difference, they could. But he wanted to try these other options, first.

Since the next 3 -4 days will find my PV Array under snow, I have nothing better to do then try the above. But the exciting part is, should this upcoming snow storm knock the grid down, our batteries are 100% charged... I'll just have to figure out how to get the snow off my panels that are high up on the roof, with out breaking them or killing myself (so I can keep them charged). :-k I'll search this forum for suggestions.

Later, EvKar
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Re: How do You Raise SG on Single Cell

Postby BlackCherry04 on Mon Feb 03, 2014 8:57 pm

There are reasons to adjust the SG level by adding acid or removing some. If you said I boiled a bunch out and added water to the cell , then you could understand it being low, in that case balancing would be called for. To me all I see here is a under developed cell based on the age of the battery. The Acid that was added when new ( 1.280 ? ) is still in there and sulfate needs to be driven off the plates and recombined. As long as your keeping the temperatures under 110-115 F at cell level there should be no harm to the battery. I wish you good luck on solving it, I can only tell you what I would do. If it is actually .27 ( 1.250 vs 1.277 ) I would hope the dealer would help you. At least they are aware of it now.
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Re: How do You Raise SG on Single Cell

Postby vtmaps on Tue Feb 04, 2014 3:43 am

BlackCherry04 wrote:There are reasons to adjust the SG level by adding acid or removing some
<snip>
The Acid that was added when new ( 1.280 ? ) is still in there and sulfate needs to be driven off the plates and recombined.


If you can get the SG up to spec with hard equalization, then adding acid doesn't sound right to me. All the acid is there, and there is some other reason the cell won't charge as easily as the others.

If you can't get the SG up to spec with hard equalization, then you should ask why. If they admit to underfilling it originally, or if some electrolyte spilled out during transport, then adding acid is the right thing to do. But if it was filled correctly to begin with and didn't spill out, something else is wrong. Where is the sulfur that was in the original filling? If its not in solution (as sulfuric acid) then its on the plates. If its on the plates, your battery is sulfated and adding acid is the wrong thing to do.

Generally, adding acid to a cell will raise its voltage and capacity a bit, but will shorten its life. Your cell is already having trouble taking a charge... If it still has all of its original electrolyte, then adding acid means it will need even higher voltages to charge it. You will need to overcharge (even more) all the other cells in the bank, or the weak cell with added acid will become progressively more sulfated.

Feeding it more acid is a low risk strategy from Trojan's perspective... it might get your battery bank through the warranty period, and if it doesn't, it at least delays the payout.

Bottom line, I suspect that your weak cell is an outlier. I think it is a good idea to equalize the one battery in isolation from the rest of the bank. If you can get its SG up to spec, it will be most interesting to hear how it behaves in the future when it is part of a bank again. If you can't get it up to spec, I suggest you push hard for a replacement.. I don't like the idea of just adding acid.

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Re: How do You Raise SG on Single Cell

Postby EvKar on Tue Feb 04, 2014 8:34 am

vtmaps,
I hear you and agree with your concerns. Currently I have that single 3 cell 6v battery out of the bank and attempting to EQ it with a charger that is a 6 or 12 volt charger, with max setting to 6 amps. This is the best I have for single charger. I'm not sure what amps are flowing into the battery, but last check it was at 7.92 volts. I do see some small bubbles coming to the surface, and the thermometer says the solution is only at 35 degrees... yes it is cold in that facility. I probably ought to bring the battery in the house, but the thing is so heavy and I worry about the venting.

Currently, 1 cell is at 1.300 SG, the other is at 1.280, and the "bad" one is at 1.260 SG. When I do temperature compensation of minus .014, that brings the SG to 1.246 or 85% SOC. I'll keep monitoring it and seeing if it rises, but I have a feeling my charger isn't serious enough.

Everyone, thanks for enlightening me on adding acid or not to add acid. I can't vouch for whether any had spilled out previously during shipment, but there was one time when I was taking a SG reading, and I got careless and missed the hole (hydrometer tube came out) and shot a couple of tablespoons worth of acid over the side of the battery. I did clean it up. But as that was a month ago or so, I can't remember if it was that particular cell. I didn't know that much about these batteries, and in hind site, I should of kept track. Can a couple of table spoons (or whatever fits in the straw portion of my hydrometer) be enough to lose SG? Now I'm thinking technically that it could, and as all the other cells are synced together, maybe that could be the culprit. If indeed that is enough acid lose, then would an acid transfusion be in order? Can the battery tech tell if I have 1.280 of acid in, or are they just going to put acid in just to put it in? Keep in mind that we aren't at the Trojan warranty point yet, but my main goal is to get a battery replacement... we will see.

EvKar
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Re: How do You Raise SG on Single Cell

Postby BlackCherry04 on Tue Feb 04, 2014 8:54 am

Your doing fine, and it's coming UP and thats a good sign. A few teaspoons lost electrolyte are nothing to worry about. This has to do with the porosity of the lead. That cell is lagging , the lead has way to much sulfate trapped in the pores of the lead. This EQ you are doing will clean them out and open new material to the acid. Once you start getting above 1.250 -1.260 the sulfate on the surface of the plate has re-combined and your working on a lower level. At that temperature ( 35 deg ) 7.92 V is probably a little low, but it will not keep you from getting results, it will just take longer.

I worked on a set of Rolls over the weekend, they were 40 deg and it took 17.2 V to get enough current to ever get to a good gassing level. After 6 hrs they had gone up to 58 deg and had gone from 1.210 to 1.265 and were fine. ( 1.265 fill strength )
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Re: How do You Raise SG on Single Cell

Postby EvKar on Wed Feb 05, 2014 10:47 am

Okay, Here is the update.
With my small 6 amp charger, generating approx. 7.9v, and leaving it on approx 24 hours and watching the SG and temperature, the SG came up to 1.270. And with my Temp compensation of minus .014 (cold), I'm at 1.256 which is 90% SOC for this battery. Now the other two cell rose in SG, of course. They rose to 1.300 (minus .014 for a total 1.286), way over the 100% of 1.277 SG mark.

So what is it that I should conclude from these results? I'm happy that the cell continued to rise, but should it have equalized with the other two cells? Or getting that high, good enough?

Although I saw small bubbles, I never got the battery to bubble like it does when connected in the banks and taking charge from the Outback system. Do I need to charge the individual battery more (didn't use much water)? Or buy a larger amperage charger (and what size)?

Let me know if over killing this whole EQ thing!
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Re: How do You Raise SG on Single Cell

Postby vtmaps on Wed Feb 05, 2014 11:17 am

EvKar wrote:Now the other two cell rose in SG, of course. They rose to 1.300 (minus .014 for a total 1.286), way over the 100% of 1.277 SG mark.

So what is it that I should conclude from these results?


It doesn't make any sense to me... if the other cells started at 1.277 they can never go higher... unless you've boiled off enough water to concentrate the electrolyte. I wonder if your hydrometer (or the temp compensation you are applying to it) is wrong.

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Re: How do You Raise SG on Single Cell

Postby EvKar on Wed Feb 05, 2014 11:55 am

It doesn't make any sense to me... if the other cells started at 1.277 they can never go higher


I was hoping it made sense to someone, because I don't understand half of this stuff (but I do find it fascinating). No, I didn't boil off any water. But these readings were taken right after I disconnected the charger, maybe I'm reading a spike and just need it settle down.

Are you saying that I can't rise above 1.277, as that is the quantity of electrolyte that was initially added?

Lets say my hydrometer is wrong, I still have a difference in SG of .03. Should I be concerned?

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Re: How do You Raise SG on Single Cell

Postby BlackCherry04 on Wed Feb 05, 2014 12:44 pm

Let the battery cool for 3 hours and the take the sg readings again. The difference you are seeing is due to temperature differences and the possibility of some acid that was used in the pre-forming of the plates. You batteries were filled with 1.280 and at 100 % charged it will have a range of 1.270 to 1.290 in SG to begin with . It is more than normal to see those high readings with the amount of overcharging the EQ is doing. I'd put the battery back in the bank and cycle it a few times and then take the readings again and see where they are. The question I have is, have you taken that cell as high as it will go ? At this point I think the cells will be about even after the cycles, if not you can work on it some more or let the dealer deal with it.
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Re: How do You Raise SG on Single Cell

Postby Vic on Wed Feb 05, 2014 1:03 pm

Several things,

1. Is your temperature compensation taken for the one battery that you are individually EQing, or that for the BTS on a different battery? The temp of the target battery is quite a bit warmer than the others in the bank.

2. The cells in this target battery probably have consumed more water than the lagging cell. Some of this high SG value can be due to this.

3. Based on my experience with Flooded batteries, it IS possible to raise the measured SG (with an accurate and repeatable Hydrometer) above the SG of the factory-fill electrolyte after temp compensation and with electrolyte at the specified fill level.

4. Your power supply voltage is at the high end of the recommended EQ voltage (IIRC). Although accurate voltage measurement is important on these things. At this voltage, obviously, this battery is drawing as much current as it will. Having more current available will cause no more current to flow into the battery, unless the voltage is increased.

5. And, just my opinion again, it IS good to cycle Deep-Cycle batteries, on occasion. Cycling this bank to about 50% SOC should be good for them. Just watch the bank voltage carefully, and often during these cycles, until you learn what is the nature of this bank. If one has a weak cell, also watch this cell/battery very carefully. In the initial art of these discharge cycles, battyery voltage will drop fairly rapidly (from full charge V). Then after surface charge is removed, and the battery impedance becomes lower at the broad, flat part of the curve, battery V is quite stable for a considerable part cycle. If the bank voltage or the voltage of this one battery begins to drop rapidly, compared to the flat part of the curve, TERMINATE the discharge cycle, and immediately begin recharge.

These cycles are best done on full-sun days, from a full charge. OR from a full charge at any time if one is willing to run a genset for recharege, to at least 80 - 90% SOC. The rest of the recharge could be completed on the following day, ideally from PV or other Renewable Energy source of power.

6. Continuing to EQ this battery may be a fine idea. BUT, personally, I would cycle the entire bank at least once, before EQing further. Although, I am assuming that this battery bank has not seen very many (perhaps none?) cycles to about 50% SOC.

Just my opinions. Am not a battery engineer, just an abuser. Good Luck, please let us know how you are doing. Thanks Vic
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Re: How do You Raise SG on Single Cell

Postby vtmaps on Wed Feb 05, 2014 2:38 pm

Vic wrote:Based on my experience with Flooded batteries, it IS possible to raise the measured SG (with an accurate and repeatable Hydrometer) above the SG of the factory-fill electrolyte after temp compensation and with electrolyte at the specified fill level.


Vic, I don't doubt your observations/experience. But can you explain how the SG could get to be be higher than the factory fill?

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Re: How do You Raise SG on Single Cell

Postby Kent Osterberg on Wed Feb 05, 2014 4:04 pm

3. Based on my experience with Flooded batteries, it IS possible to raise the measured SG (with an accurate and repeatable Hydrometer) above the SG of the factory-fill electrolyte after temp compensation and with electrolyte at the specified fill level.

I have also observed this happening. Particularly when trying to equalize a battery with a low cell. For a L16 cell, I think it takes 1/3 liter of water to change the specific gravity by 0.03. So the water lost to electrolysis will change the specific gravity significantly.

I'd continue equalizing until the specific gravity stops rising in the suspect cell. Keep adding water if necessary. Then put the battery in service for month before checking it again.
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Re: How do You Raise SG on Single Cell

Postby Vic on Wed Feb 05, 2014 10:30 pm

vtmaps wrote:
Vic wrote:Based on my experience with Flooded batteries, it IS possible to raise the measured SG (with an accurate and repeatable Hydrometer) above the SG of the factory-fill electrolyte after temp compensation and with electrolyte at the specified fill level.


Vic, I don't doubt your observations/experience. But can you explain how the SG could get to be be higher than the factory fill?

--vtMaps


vt, I do not claim to know just how this happens, but have seen it in a number of different Flooded banks.

Think that there is some re-forming occurring. On new Flooded banks, some cells arrive with SGs a bit above rated electrolyte SG, and some a bit below. The low ones only get to rated SG when the fill level is low, and the high cells can go to 1.300 even when over-filled after an EQ. Cycling the bank will take the 1.300 cells back to about 1.270 - 1.275 when fully charged, but still over full.

The pilot cells in the two largest banks here were a bit low on day one, and still struggle to get them back to that SG.

But cycling deep-cycle Flooded batteries does reduce the total SG variation, particularly on the high SG cells.

You have read more on Flooded battery ins and outs than I. But know that you simply must cycle your bank more than I.

Am no expert. FWIW, Vic
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Re: How do You Raise SG on Single Cell

Postby EvKar on Wed Feb 19, 2014 6:12 am

Update:
After a long EQ and numerous days of absorption cycles (higher than recommended at 59.2V and 6 hr), I'm still getting a SG reading indicating an 85% SOC for the infamous one cell, while all the other cells are at 100%.
The good news is that my battery dealer is sympathetic to the issue, and although it isn't bad enough for Trojan's warranty replacement, he wants to look at the battery. Means he wants to see if he can't get that cell to respond, and it sounds like he'll replace if he can't. Which will be great.
So that is the update... but I have another question. While this battery is out of the string temporarily, can I slip my RV's Trojan T105 6V battery in it's place for a day, with out any harm? I know the AH is different, but will there be any long term issues with my L-16 batteries?
Thanks for your responses in the past and for any in the future,
EvKar
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Re: How do You Raise SG on Single Cell

Postby vtmaps on Wed Feb 19, 2014 7:08 am

EvKar wrote:So that is the update... but I have another question. While this battery is out of the string temporarily, can I slip my RV's Trojan T105 6V battery in it's place for a day, with out any harm? I know the AH is different, but will there be any long term issues with my L-16 batteries?


If you're careful it is probably OK. Your bank will have the capacity of the T105. Watch the voltage carefully... it will drop faster than usual and you could damage the T105. Be sure to recharge the T105 with a 6 volt charger when you are done, and then recharge and equalize the bank that the T105 came from.

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