sunshine_eggo
Victron's little biatch
IMHO, since you claim it was on float most of the time, this likely happened due to poor balance behavior on the BMS.
Depends on use, but 13.8-14.2V absorption, 13.5V float.
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Huge lithium degradation
- Thread starter 91cavgt
- Start date
IMHO, since you claim it was on float most of the time, this likely happened due to poor balance behavior on the BMS.
Depends on use, but 13.8-14.2V absorption, 13.5V float.
91cavgt
New Member
I’m not going to replace the BMSs. I’m going to get an adjustable power supply, disassemble the battery, charge each of the 12 cells to 100%, then upon reassembly I’m going to be adding a way to check each cell from the outside of the battery. That way I can also charge each cell individually if need be without disassembling the entire thing again.
Zwy
Emperor Of Solar
You do not need to disassemble the cells. Purchase the power supply and do the procedure I mentioned in this post 3 pages ago.
Charging each cell will take a long time as the voltage will be under 3.65V. Simply charge as a 12V battery at a fixed voltage and low current and give the BMS time balance the cells.
Maybe, just maybe if I repeat it 10 times, you will try it first. It is not that hard, but if you want to make it a harder task to accomplish, then proceed.
Drunkin Solar
Solar Enthusiast
Terminals???
You are wasting time and money. Are you planning to be your own BMS god with a multimeter and a BMS that is not handling your pack correctly?
91cavgt
New Member
Not at all. I have no means of monitoring each of the 12 cells without disassembling the entire assembly. So, I am creating a way so I can easily monitor those cells. And IF this imbalance does occur again, then I can easily remedy the situation. Once I get the cells back in balance and the charge settings adjusted properly then I don’t foresee this happening again.
91cavgt
New Member
Sorry, I was rushed when I posted this and so it didn’t make any sense.
Edit: Since I have no means to monitor the cell voltages, I am going to take it all apart anyway to add that capability. So, since it has to be taken apart to do this, I’ll just go ahead and charge each cell, then reassemble the pack.
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Drunkin Solar
Solar Enthusiast
This is where you are mistaken. It will happen again and you most likely and going for a ride on a imbalance merry-go-round
Highly doubtful charge settings alone will correct this but....
91cavgt
New Member
And you may be 100% correct. At this point, with how much prices have gone down over the last 3 years for batteries, it just doesn’t make financial sense to replace the 3 BMSs with new ones with 3+ year old cells that are questionable. So adding the capability to monitor individual cells with only time invested(I’ve already got the terminals and wiring needed), and then buying an adjustable power supply that I can use on other projects to get these cells back into balance makes sense.
I’m going to monitor the cells with my Fluke every month or two just to see how they are doing. If they start to get out of balance again then I can easily rectify the problem with the terminals I’m adding.
Zwy
Emperor Of Solar
You should be able to charge slowly and use a multimeter to monitor each cell.
We expect to hear an update from you about 3 months from now if you charge each cell individually.
sunshine_eggo
Victron's little biatch
May be more than you want to spend, but it also has a passive balancer you can activate:
91cavgt
New Member
My interest is peaked!!! And I’ve already got XT60 plugs too!
sunshine_eggo
Victron's little biatch
I had a dumb bms, and I wired this up in conjunction with it (two separate sense harnesses).
Brucey
Velcro Man
I think that's an 8 cell max.
TomC4306
Solar Obsessive
And how are you going to add that capability if you're not going to replace the BMS?
With a BMS that has Bluetooth capability to give you visibility into the individual cell voltages.
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Charge settings may not be the cause of your issue, I’m thinking questionable cells with BMS with low balancing capacity. JBD are known to have “balance while charging” enabled, so that means it only charges during a short time when current is still flowing into the cells above a threshold.
If you are determined to not buy a new BMS which I can see knowing you’d need 3 of them. At least look into an 4s haltec active balancer that you can wire in an on off switch. Soon as the pack rises above 13.8v turn on the active balancer and let it eat for an hour or so. Do that once a month and it should be good enough.
I used one of those haltec units with my JBD (even with Bluetooth) in a 2p4s config and it did a good job of keeping things in check.
91cavgt
New Member
I’ve already covered this multiple times. I’m going to add external terminals to the battery enclosure that are connected to each cell. This will primarily allow me to check each of the 12 cells to see their voltages, but it will also allow topping off each cell individually if the BMSs can’t keep up without disassembling the battery(which is time consuming) to do so. I won’t be checking the cell voltage every day, probably just once every month or two.
91cavgt
New Member
That is something that I am considering after I get the cells balanced and am able to monitor what the cells are doing. I want to see what the BMSs do first after I am 100% confident that the cells are top balanced. If they can’t keep the cells balanced after some time then I will look at getting active balancers for each of the 100 amp/hr batteries inside the enclosure.
91cavgt
New Member
The adjustable power supply came in today. It is 0-30 volt and 0-10 amp. Early next week I will be taking the enclosure back apart to top balance all 12 cells.
In the meantime, like what ZWY had suggested, I’ve got the power supply connected to the battery right now. I had lowered the charge controller down to charge to a maximum of 13.8 volts. That started last week and is where it has been set since. So, I’ve got the power supply set to 14.0 volts right now at 5 amps. I’ll check on it in a day or two and once it is down to 0 amps then I’ll raise the voltage up to 14.2, and will repeat this process of slowly raising the voltage up until it hits 14.6 volts, or until I take the enclosure apart next week. This should test the BMSs to see if their balance function is in fact working or not. When I disassemble the enclosure, before top balancing the cells I will check their voltage and compare that to the previous readings. Of course, I will report back to what the progress is.
Thank y’all for your patience and help on this!!
In the meantime, like what ZWY had suggested, I’ve got the power supply connected to the battery right now. I had lowered the charge controller down to charge to a maximum of 13.8 volts. That started last week and is where it has been set since. So, I’ve got the power supply set to 14.0 volts right now at 5 amps. I’ll check on it in a day or two and once it is down to 0 amps then I’ll raise the voltage up to 14.2, and will repeat this process of slowly raising the voltage up until it hits 14.6 volts, or until I take the enclosure apart next week. This should test the BMSs to see if their balance function is in fact working or not. When I disassemble the enclosure, before top balancing the cells I will check their voltage and compare that to the previous readings. Of course, I will report back to what the progress is.
Thank y’all for your patience and help on this!!
Koyaanisqatsi
Electron addict
Don't go all the way to 14.6V unless you can be absolutely sure you are balanced to 0.000V. 14.6 is an unattainable absolute maximum that WILL push a cell into OVP, unless all cells are EXACTLY the same voltage, which is near impossible. Go for 14.45-14.5V maximum.
I'm willing to bet that the 25P construction is a big cause of the " cells' " propensity to become imbalance in the 1st place. Can OP post a pic of the construction. Anytime 3P or more cells are used to make the "1s" cell, the risk rises for the cell to become unbalanced.
Charging to 100% soc may mean different things to different BMS's. Some won't register 100% when a single cell goes over V protection while some do, so its always best to charge it to a reasonable 3.40 x 4 (13.60V) to start, and note the V of each cell as pack V approaches the larger #.
Most BMS I know count a cycle every time depth of discharge (dod) accumulates 80%, some adjustable to 100% btw. So you can discharge a total of 20% each time and on the 4th time (80%) the cycle will increase by 1.
And yes, don't just charge to 14.6V as others have written. Not sure what cell level ovp that bms is set to, but it might be higher than 3.65V so can damage small amounts each time. If you indeed were able to charge to 14.6V, it's 100% that some of the 25P cell have easily gone above 3.75V based on the individual Voltages you posted.
EDIT: BMS standards for cell protection a few years back were at 2.5V and 3.8V. This is due to the fact that no real harm is done to the cells at these levels and the manufacturers wanted maximum perceived performances so i wouldn't be surprise if your bms has cell ovp at 3.8V.
Charging to 100% soc may mean different things to different BMS's. Some won't register 100% when a single cell goes over V protection while some do, so its always best to charge it to a reasonable 3.40 x 4 (13.60V) to start, and note the V of each cell as pack V approaches the larger #.
Most BMS I know count a cycle every time depth of discharge (dod) accumulates 80%, some adjustable to 100% btw. So you can discharge a total of 20% each time and on the 4th time (80%) the cycle will increase by 1.
And yes, don't just charge to 14.6V as others have written. Not sure what cell level ovp that bms is set to, but it might be higher than 3.65V so can damage small amounts each time. If you indeed were able to charge to 14.6V, it's 100% that some of the 25P cell have easily gone above 3.75V based on the individual Voltages you posted.
EDIT: BMS standards for cell protection a few years back were at 2.5V and 3.8V. This is due to the fact that no real harm is done to the cells at these levels and the manufacturers wanted maximum perceived performances so i wouldn't be surprise if your bms has cell ovp at 3.8V.
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Worse case the power supply will go into CV mode and current will go to zero, at that point you’d know the BMS is detecting out of balance cells and protecting.
I’d wager if the cells saw 13.8v for a long time and was still unbalanced in minutes after raising the voltage the high cell will spike and current would stop.
TomC4306
Solar Obsessive
Make sure you disconnect one lead of the power supply before changing the voltage.
Adjusting the power supply while connected is a sure fire way to overcharge.
Adjusting the power supply while connected is a sure fire way to overcharge.
42OhmsPA
Who likes Electrical Gremlins?
And verify the voltage with a trusted meter before reconnecting.
91cavgt
New Member
So I set the voltage on the power supply to 14.0 volts, amperage to 5 amps, and confirmed voltage with my Fluke at 13.97 volts. Close enough for government work.
After 24 hours, when I checked on the power supply it was showing 0.14 amps and 14.0 volts.
After 24 hours, when I checked on the power supply it was showing 0.14 amps and 14.0 volts.
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