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Discussion Starter #1
I bought 10 FLA 12 V, 105 AH crown deep cycle batteries, got 8 replaced due to bad cells (after some months of arguing).

I have now 10 new batteries (configuration is series, a 120 V pack). I can go shorter distances without trouble (about 10 km is fine), but suddenly two batteries are out of energy, while the other have more than half the charge left! This is the same scenario as with the other batteries...

All batteries were of course balanced and fully charged. (I use 10 smaller charger to top of the charge of each battery from time to time). They have enough water - but not too much. I also have a voltmeter for each battery so I can se the voltage drop as I drive. This is how I found the bad batteries (and because I could not get home...). At first, voltage drop is about the same for every battery, and then, quite suddenly two of them drops.

Why do I keep getting bad batteries? What am I doing wrong? These are supposed to be new, and have only about 10 cycles! I have contacted the company who sold them, and they have no clue... Was thinking about the cold (weather is about -3°C right now), but the failing batteries are insulated and in the middle of the pack, thus not the coldest ones. The batteries are next to each other, but I think it is a coincidence.

Max current is less than 250 battery amps, and the mean is less than 100.
 
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Have you checked the specific gravity of each cell when fully charged and when fully discharged from a drive? Did you top or bottom balance your batteries? Were they the same voltage from the start? You need to balance your batteries when you add in new ones to a used pack for sure and bottom balance is actually pretty good. I did. I know they are flooded but balancing from the low end is the better end. The SG is very important for floodies. Check them. Do not add water until you charge up full and don't over fill.

Check out all the information here on Lead Acid Batteries.

http://www.evdl.org/lib/index.html

Pete :)
 

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Discussion Starter #3
Have you checked the specific gravity of each cell when fully charged and when fully discharged from a drive? Did you top or bottom balance your batteries? Were they the same voltage from the start? You need to balance your batteries when you add in new ones to a used pack for sure and bottom balance is actually pretty good. I did. I know they are flooded but balancing from the low end is the better end. The SG is very important for floodies. Check them. Do not add water until you charge up full and don't over fill.

Check out all the information here on Lead Acid Batteries.

http://www.evdl.org/lib/index.html

Pete :)
I have not checked the specific gravity, have to rush and buy the tool first... :( But I still know that I have bad cells, the problem is that I cannot figure out why! When charged, they reach the same voltage. I does not seem likely to get so many poorly manufactured cells (although I got 8 ones replaced by warranty... I am actually trying to get the company buying back their batteries, so I can later buy lithium!).

As the batteries are very new, I have not yet had to fill up on water. Also, I cannot fully discharge all batteries because of the series configuration. When the bad batteries are drained the good one(s) still have a lot (maybe half) of charge left.

They were top balanced: Old batteries were charged full, and new were charged full by using the 10 small chargers have.

After driving, at the end of charge, with the batteries almost fully charged, I disconnect the main pack charger and turn on the 10 small chargers, one for each battery, which brings them to the same voltage. My BMS also shows a very similar voltage for each battery when driving, until the bad ones are drained and plunge. So driving about 10 km shows nothing wrong, voltage differences appear quite suddenly.
 
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So driving about 10 km shows nothing wrong, voltage differences appear quite suddenly.
Yea! at the bottom where you don't want that to happen. On top its not quite so bad because floodies can handle over charges easier than over discharges. Those batteries that are showing lots of power when it starts to crap out will suck the low ones dry and reverse them and kill them and you won't even know it. Drain your good batteries and balance at the bottom. Find a good low voltage setting and make them all the same then charge them up. Be sure you check your water and SG. New or not don't depend upon the battery company to make a perfect set for you. After a drive you want you batteries to be in the same zone. Keeps things alive. Never add water to a discharged cell. Make a list of all your cells SG both charged and discharged. It's a pain but you need to get your batteries back in line.

Pete :)
 

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Discussion Starter #5
Yea! at the bottom where you don't want that to happen. On top its not quite so bad because floodies can handle over charges easier than over discharges. Those batteries that are showing lots of power when it starts to crap out will suck the low ones dry and reverse them and kill them and you won't even know it. Drain your good batteries and balance at the bottom. Find a good low voltage setting and make them all the same then charge them up. Be sure you check your water and SG. New or not don't depend upon the battery company to make a perfect set for you. After a drive you want you batteries to be in the same zone. Keeps things alive. Never add water to a discharged cell. Make a list of all your cells SG both charged and discharged. It's a pain but you need to get your batteries back in line.

Pete :)
I will try! :)

I have done my best no to reverse any battery, like never driving until I cannot get further... I always stop when a battery drops... and my father will tow me home :mad:

I cannot see why discharging all batteries to the same SOC and then charging them all to 100% would create a more balanced pack than just charging every battery to 100% individually, from different SOC (which is what I am doing right now)... Could you please explain?

I shall try equalizing charge a couple of times too!
 
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You want them to start out the same on the low side. The low side is the dangerous side. If you have one cell that is low when all the others are high you can kill that cell without even noticing. Do the same drive again with maybe one more cell going south and you can kill that one cell. Each battery has 6 cells for a 12 volt battery. Any number of those can go south but when charged up full they all look fine but the bad ones hold much less AH and when discharged they crap out and the others cover for that one bad cell and that one bad cell can go into reversal long before you ever notice and you think your well within your end voltage range. Bottom balancing is a smart thing to do. Yes you should also charge and balance your batteries from time to time but you need to keep an eye on the low side too. Not just the top side. I have a battery that when fully charged shows a good SG and voltage but when discharged one cell is just crap while all the others are fine. That battery got pulled. For low discharge uses its fine but for my EV it's toast. All others are fine.

Pete :)
 

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Discussion Starter #7
You want them to start out the same on the low side. The low side is the dangerous side. If you have one cell that is low when all the others are high you can kill that cell without even noticing. Do the same drive again with maybe one more cell going south and you can kill that one cell. Each battery has 6 cells for a 12 volt battery. Any number of those can go south but when charged up full they all look fine but the bad ones hold much less AH and when discharged they crap out and the others cover for that one bad cell and that one bad cell can go into reversal long before you ever notice and you think your well within your end voltage range. Bottom balancing is a smart thing to do. Yes you should also charge and balance your batteries from time to time but you need to keep an eye on the low side too. Not just the top side. I have a battery that when fully charged shows a good SG and voltage but when discharged one cell is just crap while all the others are fine. That battery got pulled. For low discharge uses its fine but for my EV it's toast. All others are fine.

Pete :)
I am with you on the theory, and thanks for reminding about the cells! To be honest, I did not think further than battery voltage (possibly because I cannot monitor cell voltage)... So probably the bad cell(s) of the bad batteries have taken some beating!

If I understand correctly, this bottom balancing is to find any bad cells, not some way to miraculously bring back my bad batteries to life, and not a better way to balance? Or is this bottom balancing something needed to keep batteries balanced, or will top balancing be sufficient for this? :confused:

Because, I already think I have identified the batteries containing bad cell(s), and I keep wondering why so many of my batteries keep failing! One of the other batteries, when returned, showed, according to the company something like 15% capacity, and I am having the exact same symptoms now, only I can go further!
 
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Bottom balancing starts your pack on equal footing. If you tap off a battery or two you need to keep an eye on those at the bottom side. If a cell goes bad and you continue to keep charging with out fixing the problem it will cascade as other cells become further out of bottom balance. When you charge it may look good if you only go by voltage. Floodies are not maintainence free.

Pete
 

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Discussion Starter #9
Bottom balancing starts your pack on equal footing. If you tap off a battery or two you need to keep an eye on those at the bottom side. If a cell goes bad and you continue to keep charging with out fixing the problem it will cascade as other cells become further out of bottom balance. When you charge it may look good if you only go by voltage. Floodies are not maintainence free.

Pete
Ok, thanks! Just as I though! Sorry, but what is "tap off"? Any suggestions on how to fix this? Or theories on why I get so many bad cells? :(

I was thinking of adding H2SO4, which should, in theory, increase AH if there is enough PbO and Pb left on the plates. Although that would be on the cost of battery life...

And other cells go bad... because they will have to do the work of reversing the already weak? just trying to understand!
 

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I hate to break into the tail of this thread, but thought I would throw in a few comments...

- floodies 'balance' at the top by gassing when they hit their peak. so charging until all are gassing pretty much top-balances. This is not a bad thing since this is how MOST chargers tell when you are 'done', when the pack voltage hits a target after a short gassing. You have to be a little careful if bringing mixed batterie back into balance as the gassing will deplete water more and you DON"T want to run any cells dry. If you suspect some cells/batteries were gassing more than others, be sure to water after charges to make SURE the water level is consistant.

- mixing different age batteries is problematic.... older ones charge slower and have lower capacity so the whole system gets out of balace rapidly and the weker ones get weaker.

- if all are about the same age, but out of balance badly, you MIGHT want to take the time to disconnect and wire in parallel for a coupe days and let them sit so they can self-equalize. Then charge, and then water.

- am suspicious that you are killing cells in the same position of the pack. Have you checked the cabling? connections?

- also it sounded like you are not using a normal single charger fo rthe pack in series... true? if so, are you SURE your chargers are charging to the same top voltage, and turning off correctly? perhaps one is high, or low, or gassing longer than others?
 

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I have one thing to add to Dan's advice. If you do not fully charge all the batteries regularly they will quickly die. A bottom balanced lead acid pack is not a viable option.
 

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I'd like to add another comment. I don't agree with gottdi's advice to bottom balance a flooded lead acid battery. This might be ok with Lithium but lead acid batteries will sulfate if left in a partial state of charge. Since you are monitoring all the batteries if you stop when one falls off the cliff you won't reverse a cell. As Dan said above, flooded batteries off gas when they reach full. This is why there are several stages to a flooded charging routine. My Zivan had a bulk charge phase where it would charge at full current, then a constant voltage stage where the voltage would be held constant until the current dropped back to about 6A or so and then an absorption phase where the current was kept at 6A for a set time period depending on how long it took to get the the last phase. There was also an upper voltage limit as a safety. As my batteries aged I could see that the voltage would climb and then start to drop again just before the end of the last stage of charging. As I understand it, the point where the voltage started to drop was when the batteries were full.
 
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I am not saying to leave your batteries in a lower state of charge but to start off balancing them on the bottom. With floodies the norm is to charge with a bit extra. If you put another battery in the pack to replace a bad one you need to balance it in on the bottom then go to the top from there. That is how it is done with lithium but lithium can be under charged so not to over charge. Floodies can handle a bit of over charge. It is good practice to start out balanced on the bottom then go up. It is also good to bottom balance the SG on the bottom too. That is where the most critical part is in a battery discharge curve. Not going to kill a floodie by over charging a but you will kill any battery if it is over discharged. Some more than others but over discharging is not the way keep your pack alive for as long as you can. Be sure you discharge your pack to a specific point then stop. Don't allow yourself to go that extra mile. It can kill a cell. If you top balance and only top balance you may never know you have a cell that discharges quicker than the others and you may find a cascade effect happening and your pack dying faster than expected. Range lessening and over all performance just in the crapper. Other cells will take over for a bad one and soon those will crap out too.

Sorry but bottom balancing at the beginning is what you want. I am not saying to bottom balance every charge. Neither is Jack saying that on his Lithium packs. He just says to bottom balance from the start. Damn good advice. Proven and irrefutable.

Pete :)
 

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Bottom balancing floodies is a waste of time. So, go ahead and bottom balance them. First of all, you can bottom balance only in a group of 6 cells with a 12V battery. Then on your first proper flooded lead acid charge you are top balancing them so you wasted the bottom balancing and further you ran them lower than you typically want to run them.

The voltage curve for lead acid is quite different than lithium. What Jacks contention is that people were applying flooded lead acid charging to lithium. Now you are applying lithium charging to lead acid.

When bottom balancing LiFePO4 type batteries the charge cycle should never run any cell voltage over its maximum safe voltage. With lead acid it naturally just "boils" off any extra charge. Lithium do not have such a mechanism.
 

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Discussion Starter #15
I hate to break into the tail of this thread, but thought I would throw in a few comments...

- floodies 'balance' at the top by gassing when they hit their peak. so charging until all are gassing pretty much top-balances. This is not a bad thing since this is how MOST chargers tell when you are 'done', when the pack voltage hits a target after a short gassing. You have to be a little careful if bringing mixed batterie back into balance as the gassing will deplete water more and you DON"T want to run any cells dry. If you suspect some cells/batteries were gassing more than others, be sure to water after charges to make SURE the water level is consistant.

- mixing different age batteries is problematic.... older ones charge slower and have lower capacity so the whole system gets out of balace rapidly and the weker ones get weaker.

- if all are about the same age, but out of balance badly, you MIGHT want to take the time to disconnect and wire in parallel for a coupe days and let them sit so they can self-equalize. Then charge, and then water.

- am suspicious that you are killing cells in the same position of the pack. Have you checked the cabling? connections?

- also it sounded like you are not using a normal single charger fo rthe pack in series... true? if so, are you SURE your chargers are charging to the same top voltage, and turning off correctly? perhaps one is high, or low, or gassing longer than others?

I have had that problem before: An equalizing charge did not stop, because some cells did not reach high enough voltage, and I lost a lot of water, so I am careful not to let that happen again! These were the old batteries, and although they did not lose enough water do make any harm, they are replaced because of other reasons. The batteries kept failing one after another, so they just replaced them all! I am afraid the same thing will happen now again... Seems like the batteries cannot deliver the power for my EV (as I said, FLA, 105 AH (at 20 h), 120 V pack - should work).

The batteries as almost the same age, got 2 replaced first, then 8, so the two olders may have had 10-20 cycles more, or something like that. Also, these are not the batteries failing, but 2 of the 8 new ones.

I have checked the cables, no heat etc, but I will try going further and check again, because this was one of my theories. Also cables are 70 mm^2, so resistance should be negligible.

I do have a normal charger, china made, for 120 V FLA pack, charging at 8 A (takes some time to charge full...), but I have also 10 smaller battery chargers for balancing the pack. I will measure those today to check the voltage. I checked two of them before, showing the same voltage. Most charges, I let the 120 v charger to all the work, but sometimes I disconnect it just before charging stops, and let each battery charge full individually by means of these 10 smaller chargers, in order to balance batteries. Also, the 120 V charger have equalizer mode, used to balance the cells.
 
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What I said if you did not listen last time, Start with a pack bottom balanced. All on equal footing and yes you can bottom all the cells at least with SG which will be better anyway. A hassle for sure but a good thing to do. Can't hurt. Then charge as normal for floodies. I am not talking about charging as you would a lithium. I am fully aware about the charge and discharge curve of Lithiums and with the floodies you can get into very dangerous territory real fast if you decide to go that last mile. If your cells are not balanced or your batteries are not taken care of you will have problems. Your Floodies are not maintenance free. You must work with them like you would do with a VW gas engine. They are not plug in and forget type batteries.

I also understand that your battery has cells that you can not check the charge but you do get to use SG which is equally important. More than anything get your SG to match in each cell. So rather than balance with voltage also do so with SG since that is what you can do with each cell.

Like I said I can have two batteries side by side and charge each one to the proper voltage for a full battery but the capacity of one or more cells in the battery will be more or less than another and if you discharge to far you will loose a cell. Guaranteed and it is a proven and unarguable fact. Floodies, AGM, Gel, Lithium, NiMH, and any other you can think about to add to the list. I happen to have a battery that has cells that are down. I did not in the beginning balance them on the bottom before starting out. Now my floodies are sitting pretty. I charge the normal way for floodies and yes the top out balanced too. That does not knock out the bottom. I did mention that the floodies do top out balance during charging too.

Bottom balancing does not mean to take your pack to the utter low end of the voltage before you balance them. You do however balance them in a low range across the board. It is done ONE TIME. Done properly it helps keep the pack balanced. If you tap off any batteries you will knock out that balance.

I am also not talking about that drop off cliff like a Lithium battery during the discharge. The floodies don't do that but they do drop off and SAG like hell when you stress them and that hurts them too. Be careful.

A one time bottom balance is not a waste of time. Even a $1500 pack of floodies is expensive and an investment. Take care of them. Or not.

Pete :)

Don't forget you need to check water and SG every once and awhile too and you need to keep them clean. Can't just drop them in charge them up and forget about them. It won't work.
 
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For 6 volt Floodies

Open Circuit Voltage Electrolyte Specific Gravity @ 80°F State of Charge

≥6.3 ≥1.265 100%
6.2 - 6.3 1.225 75% - 100%
6.1 - 6.2 1.190 50% - 75%
6.0 - 6.1 1.155 25% - 50%
5.85 - 6.0 1.120 0% - 25%
<5.85 <1120 0%
 

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Discussion Starter #18
What I said if you did not listen last time, Start with a pack bottom balanced. All on equal footing and yes you can bottom all the cells at least with SG which will be better anyway. A hassle for sure but a good thing to do. Can't hurt. Then charge as normal for floodies. I am not talking about charging as you would a lithium. I am fully aware about the charge and discharge curve of Lithiums and with the floodies you can get into very dangerous territory real fast if you decide to go that last mile. If your cells are not balanced or your batteries are not taken care of you will have problems. Your Floodies are not maintenance free. You must work with them like you would do with a VW gas engine. They are not plug in and forget type batteries.

I also understand that your battery has cells that you can not check the charge but you do get to use SG which is equally important. More than anything get your SG to match in each cell. So rather than balance with voltage also do so with SG since that is what you can do with each cell.

Like I said I can have two batteries side by side and charge each one to the proper voltage for a full battery but the capacity of one or more cells in the battery will be more or less than another and if you discharge to far you will loose a cell. Guaranteed and it is a proven and unarguable fact. Floodies, AGM, Gel, Lithium, NiMH, and any other you can think about to add to the list. I happen to have a battery that has cells that are down. I did not in the beginning balance them on the bottom before starting out. Now my floodies are sitting pretty. I charge the normal way for floodies and yes the top out balanced too. That does not knock out the bottom. I did mention that the floodies do top out balance during charging too.

Bottom balancing does not mean to take your pack to the utter low end of the voltage before you balance them. You do however balance them in a low range across the board. It is done ONE TIME. Done properly it helps keep the pack balanced. If you tap off any batteries you will knock out that balance.

I am also not talking about that drop off cliff like a Lithium battery during the discharge. The floodies don't do that but they do drop off and SAG like hell when you stress them and that hurts them too. Be careful.

A one time bottom balance is not a waste of time. Even a $1500 pack of floodies is expensive and an investment. Take care of them. Or not.

Pete :)

Don't forget you need to check water and SG every once and awhile too and you need to keep them clean. Can't just drop them in charge them up and forget about them. It won't work.
I was of course listening, and I am buying the gravity meter today, but how can I alter the specific gravity? I have heard filling up on acid is not exactly recommended (I have about 0,5 l sulphuric acid, and if needed I think I could easily get some at my university lab - I can already fill up how much distilled water I want there), and adding water will decrease specific gravity.

I think the problem is not balancing the cells, but rather that some of them holds less energy... what can I do about that? Or are you saying that if I equalize the troubling batteries enough the cells will get back to normal? If so, how do I do this? Equalizing charge a couple of hours? And, maybe the most important: why does some cells fall out of balance, or as I think the case is, decrease in capacity? Because I failed to bottom balance at the start? :confused: Have to prevent this happening again and again and again...

And I am sorry I am not actually doing this recommendations right now, but the car is at my parents place (I do not have a parking space, and even less charging opportunity at my apartment), but I will visit today! :)
 
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If you have cells in your battery that are weaker than others don't buy that battery. If your battery is charged properly your SG should be the same across all the cells. If not you can balance them out. You really need to check your batteries when you buy them. Just getting random batteries can lead to troubles. No cell will be perfect but you need to have them close. The closer the better. That is what balancing is all about at the top or bottom. Lots of things can knock out a flooded battery cell. Over discharging is at the top. Keeping your battery partly charged is another. Keep them fully charged. They are not Lithiums. Vibration, natural degradation, among others. You can buy batteries with weak cells. That is the problem. You can have a fully charged battery with weak cells and without checking SG you may have a bum battery. I can have a cell that looks fully charged but when checking SG it shows it may be lets say 90% but on the volt meter the battery looks fully charged. Much to your surprise you will if you take your pack to the utter low end while driving which many will do you will weaken that cell further and soon have a dead cell as the other cells will take over for the weak one and your performance will drop like a rock. I know first hand how that works. SG is very very important. It will show you a dead cell. So what do you do to prove it? Charge up a battery with a weak cell. It will show fully charged but your SG will be off.

Never add pure distilled water to a discharged cell. Never use any thing but pure distilled water in your battery. Any minerals will weaken or kill a floodie. If you happen to need to ad acid go by some premixed for the task. It is likely you won't need to do that. When you go buy your batteries you need to check voltage and SG. If they won't let you, go buy them somewhere else. Don't be half hearted about your investment.

Pete :)

SG. When you discharge your pack SG goes down. When you charge up it goes up. Most likely unless you spilled your battery you won't need to add any acid. After about a year or so you many need to ad a touch. Do so only with a full charged battery and only a tiny bit at a time. Get the premixed and you add like water when your water is low but your fully charged. Not too much. A bit at a time and check. Mix well before checking. In other words go for a drive and charge up then check. Do so until it comes back into balance but don't over fill your battery either.

If you loose water your SG goes up but low water can lead to plate damage. So watch your level and keep your water above the plates. That is the purpose of adding water. Too much water will lower your overall SG slightly. Just be careful and don't spill on your clothes. It will eat them up in a hurry. Wear old clothes while doing any work on your batteries.

Pete :)
 
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I don't need to add more about batteries because all the information is out there. You just need to hunt and read for yourself and learn as you go. Bottom balancing Floodies is not as critical as for lithium but still a very good thing to do. No amount of care for your batteries is a waste of time.
 
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