Is my 12v LiFePO4 Battery dead?

[joelshort]

yes you should and no you cant because then you are putting brand new cells next to older cells so the problem shifts again to the older cells.

i would order a couple balance boards and put those on each bock to keep them in check.

Any recommendations for the balance boards? I don't know where to start or even know what to look for, nor how to connect them. Do the balance boards work independently of the BMS? Also, I'd really like to be able to charge the battery at a high rate with a 20A LiFePO4 charger (I currently have a 10A charger). Given some of the above discussion about active balance etc, will I be able to use the 20A charger?

Thanks again for all your help.

 

[flippy]

http://www.bestechpower.com/balanceboard/HCX-D162.html

2 or 3 of these on each block and you are done.

there is a minimum order quanity for these so just order 12 of them. make sure you order for lifepo4 and not lipo.

you can buy nockoffs on ebay but those have very little balancing current so you need a lot more for the same effect.

 

[joelshort]

http://www.bestechpower.com/balanceboard/HCX-D162.html

2 or 3 of these on each block and you are done.

there is a minimum order quanity for these so just order 12 of them. make sure you order for lifepo4 and not lipo.

you can buy nockoffs on ebay but those have very little balancing current so you need a lot more for the same effect.

Alright I'll get these ordered soon.

I'll try to do my own research, but as you can tell I'm a complete newbie. Where do I connect these boards? Does the BMS still stay connected? If not, do I just connect the charger to a + and - terminal on the battery for charging?

 

[flippy]

these only provide a top balancing, they dont do anything to prevent over discharging.

but considering your use case i would just ditch the whole bms, it does not do much exept drain the battery.

connecting is simple, just match the symbols. black is positive and red is negative. same goes for the charger.

 

[joelshort]

these only provide a top balancing, they dont do anything to prevent over discharging.

but considering your use case i would just ditch the whole bms, it does not do much exept drain the battery.

connecting is simple, just match the symbols. black is positive and red is negative. same goes for the charger.

So there is no danger of overcharging without the BMS? This is the charger I have (or one nearly identical) The description states "Please ensure that the LiFePO4 batteries include a PCM/BMS when using this particular charger."

 

[flippy]

They they warn you for that then its a shit charger. The only thing it as to do is do a CC/CV charge up to 14.6v, just like any other lithium based battery. If it goes beyond that you need to get another one.

 

[dustNbone]

I'm pretty sure the warning is more about having some kind of cell level overcharge protection. A perfect charger can still overcharge a cell group if another cell group is very low, that's why you need some kind of BMS, not because the charger is incapable of CC/CV.

These boards will start bleeding off at 3.65V, but they will not cut off the charger entirely however. So if the charger is putting current into a high cell faster than the boards can bleed it off, a (temporary) overcharge is still possible.

A BMS is a bit different in that it will cut off charge current entirely while it bleeds off the high cells, and then turn the charge back on to continue filling the lower cells. It will also switch off output when it detects a that cell has gone too low.

 

[joelshort]

I'm pretty sure the warning is more about having some kind of cell level overcharge protection. A perfect charger can still overcharge a cell group if another cell group is very low, that's why you need some kind of BMS, not because the charger is incapable of CC/CV.

These boards will start bleeding off at 3.65V, but they will not cut off the charger entirely however. So if the charger is putting current into a high cell faster than the boards can bleed it off, a (temporary) overcharge is still possible.

A BMS is a bit different in that it will cut off charge current entirely while it bleeds off the high cells, and then turn the charge back on to continue filling the lower cells. It will also switch off output when it detects a that cell has gone too low.

OK, well, if I add the balance boards and keep the BMS, do I just wire up the BMS like it was before?

 

[joelshort]

What about this balance module for each block?

 

[999zip999]

How is that group of cells 3.22v. If that group is self discharging it will always cause trouble. You can still make a 12v 60ah battery without a group always giving trouble for the bms and other cell groups.

 

[joelshort]

How is that group of cells 3.22v. If that group is self discharging it will always cause trouble. You can still make a 12v 60ah battery without a group always giving trouble for the bms and other cell groups.

I need 80ah minimum capacity. In one use I discharge 55-60AH.

That one 3.22v block has recovered to at least 3.44v. After sitting on the 3.65v charger for a day and then resting for 20hrs it still read 3.44v. So it's back on the charger and I'm hoping to saturate it more.

 

[dustNbone]

You can keep the BMS as it was before, and use those balance modules to "help" the BMS do it's job balancing. They don't really interact with each other. That second module you linked is pretty much the same deal as the first, just bigger and with adjustable bleed current.

As for your low block, just keep it on the charger at 3.65V. There's no harm in that, but it's hard to say what it's actual capacity is now. Hopefully still enough to do the job you need your battery for.

If you're going to go the route of replacing those 4 cells, you need to find some that are ideally identical to the ones you're replacing, or at least very close in terms of capacity and resistance, as you're going to be charging and discharging them in series with the existing ones. Any large deviation is going to result in a pack that is constantly out of balance.

 

[joelshort]

So instead of using 3 of the original linked balance modules on each block I can just use one of the second linked module on each block, correct?

 

[dustNbone]

If they're set to the highest (1.4A) balance current then you could replace 4 of the 300mA ones.

Just remember that 1.4A times 3.6V is 5W of heat each one could potentially need to get rid of. Not a lot of heat, but something to consider when you're placing them.

 

[joelshort]

Can 1 balance module be connected to more than 1 block?

 

[dustNbone]

No. They work on a single cell or group of paralleled cells.

 

[flippy]

Can 1 balance module be connected to more than 1 block?

you can ofcourse, IF you like a nice big ball of flames.

 

[999zip999]

The cc-cv charger is charging all cells the balance boards drains the highedt cell down well the second one catches up . Them the balnce boards drain the next 3 cells till all four are at 3.65v.

 

[dustNbone]

Yes one of the larger ones will give you more bleed capacity than 3 of the smaller ones. Also less parts is less to go wrong.

It really depends how bad the imbalance is, but if 1.4A of bleed capacity doesn't do it I'd say you should consider replacing the cells.

 

[joelshort]

Can 1 balance module be connected to more than 1 block?

you can ofcourse, IF you like a nice big ball of flames.

:lol: I told you I don't know what I'm doing...

Just remember that 1.4A times 3.6V is 5W of heat each one could potentially need to get rid of. Not a lot of heat, but something to consider when you're placing them.

So what is a good strategy for placing the modules?

Yes one of the larger ones will give you more bleed capacity than 3 of the smaller ones. Also less parts is less to go wrong.

It really depends how bad the imbalance is, but if 1.4A of bleed capacity doesn't do it I'd say you should consider replacing the cells.

I guess what I don't really get is if the 3.2v blocks are wired in series and all connected to get a 12.8v battery, how do I connect the balance module to an individual 3.2v block? Is it as simple as connecting the positive on the module to any positive on the block, and negative on the module to any negative on the block?

 

[dustNbone]

Yeah, you are just connecting + and - on the board to + and - on the cell group. Doesn't matter which of the cell terminals it is because when they're connected in parallel they're effectively one big cell. It's the same way the BMS connects to them.

As for placing them for heat rejection, just make sure the resistors are in open air if at all possible.

 

[jonyjoe303]

"Any recommendations for the balance boards? I don't know where to start or even know what to look for, nor how to connect them. Do the balance boards work independently of the BMS? Also, I'd really like to be able to charge the battery at a high rate with a 20A LiFePO4 charger (I currently have a 10A charger). Given some of the above discussion about active balance etc, will I be able to use the 20A charger?

Thanks again for all your help."

The active balancers and the bleeder type balancers work independent of the BMS, you still need a BMS, I wouldnt run a battery which has balance issues without a BMS. The charger you have is a constant voltage, it won't monitor the balancing. Your battery could be 14.3 volts and 3 of your cells over there 3.65 volt limit severely out of balance and it will still be charging it, the BMS will protect against that.

The small 1.4 amp balance modules won't be able to keep up with your 10 amp charger, technically your charger will be putting out 2.5 amps to each cell(some more some less), the high cell will have to bleed off 2.5 amps. But if you use 2x 1.4 amp modules on each cell you can do it, it will be bleeding off 2.8 amps which is just a little more then you need.

The one I use on my lifepo4 is a 4s module, but they also sale single modules that you connect with other modules, those cost 26 dollars each.They can balance at 6 amps constant (10 amps peak) if you need to charge at 20 amps, you need active balancers. I tested mine at 15 amps charging current. At 6 amps constant they can handle (6 amps x 4s) = 24 amps charge current. You connect red wire to plus of each cell and black wire to neg of each cell, then the connectors are connected to each module on every cell.

The active balancers cost more but for a battery with balancing problems, it will keep it usable. Without the active balancers my battery would only be able to be charged with a balance charger, and with its balancing problems it would be an all day affair. Right now I have it connected all day to a solar panel / mppt controller which charges by overall voltage like your charger, its been like that for over 6 months, I don't need to monitor like before, worst case BMS will stop the charging but its been perfect.

This is a picture of the single balancer and its specs. Same company electriccarpartscompany sells them.

 

[joelshort]

Alright guys, I am cautiously optimistic that the one low cell block has recovered sufficiently. After float charging the block at 3.65v for about 40hrs and resting for 16hrs the block now reads 3.51v So I'm hopeful that the block has recovered some capacity.

The balancers should arrive tomorrow.

Now, when it comes to assembling the the full pack back to a 12v 80AH battery, is there anything I need to know before doing so?

 

[999zip999]

Make sure all paralleled cells are of same voltage before connecting in series. With the 3.22v blck is there one or two cells that are dragging the whole block of four down

 

[joelshort]

Make sure all paralleled cells are of same voltage before connecting in series. With the 3.22v blck is there one or two cells that are dragging the whole block of four down

I checked each of the 4 cells in that one block. All 4 cells discharged at the same rate and maintained the same voltage over a 24hr period. So I don't think that there is 1 cell that is worse than the others in that block. I think that saturating the cells at 3.65v has definitely helped.