The real reason why your battery won't balance

[Will Prowse]

A lot of people become obsessed with their BMS's balance current, thinking that if it is high, it will magically solve their balancing issues.

They also think that the passive dissipative balancer built into their bms with small resistors is not enough to keep up with the balancing requirements of a solar battery being cycled at low rates..

So they will implement active balancers with a high balance current so that every cycle, there is a solid top balance and their voltages stay within .01V.

The actual problem is that your cells are not matched properly by capacity, state of charge or internal resistance.

This is very common with cheap lithium iron phosphate batteries. Typically this occurs because:

1. The cells are not matched by capacity as well as they should be. This should be done at the factory. Cheaper batteries use cells that were obtained at lowest cost and sometimes there is a 1-3% discrepancy between cells.

2. The cells were not charged to full before putting them together. They were shipped at 50% state of charge or stored before they were assembled, which means they will not be at the same state of charge when they are put together. This is very common. Good cells that are matched, but take a few months to balance.

3. And more rare, the internal resistance is not matched. Especially true with grade b cells. Or large parallel cell packa. If battery is used at high c rates, balancing issues will occur. Especially in excessive temperature environments.

4. You are not charging to 100% often enough. Probably the most important one here on the list. If you're hitting over voltage protection and you never charge your battery to the recommended charge volt, your packs will become imbalanced over time.

Something I want people to consider is that a Tesla EV battery is very large. If you open up the BMS you'll notice that it has very small balancing resistors. This is still true in the LFP packs (NCA packs are much easier to balance and the small balance resistors can compensate for cell drift over time).

The reason these 60kWh LFP batteries can balance without issue is because the packs are matched and assembled properly. That's it. Even at high c rates, if the cells are matched and built properly, they will not have balance issues. You still need to charge to 100% to compensate for cell drift and reset SOC indicator, but it takes a matter of minutes.

If your LFP battery which is only a few kilowatt hours in capacity cannot balance properly, you may have mismatched cells. No amount of balancing will fix this. One will always hit LVD before the others if you top balance it often.

If there is a major imbalance then you have a bad cell. Again, no amount of balancing will fix this.

The BMS balancing circuit is designed to work with these large batteries. It is plenty of balance current.

If your batteries were assembled with the cells at 50% state of charge and they need to be balanced, there is a fast way to do it. There's no need to wait for months.

Charge the battery to 100%. Pop off the top of the battery to access the cells. Then charge each one to 3.65 volts individually with the power supply. What's the current drops below 0.1 amps, disconnect power supply. Usually there will be one or two cells that are lagging excessively.

But keep in mind if you were pulling over 98% capacity, and this pack is built with high quality cells, don't worry about it and just cycle it. It will balance in a few months and you still have good capacity today, so it's not an issue.

 

[BarracudaBob]

So you buy a welded cell rack battery from 3 different manufactures and the first few cycles they don't achieve the top rated SOC or voltage because a cell has gone into OV and stops the progress.

You are stuck with some big heavy battery that is difficult to ship back. You own it and it is wired up.

This is where most of the complaints and frustration is. They reach out for help, call customer service, and feel that they just got ripped off.

What is the "Average Joe" to do? There is a very long history of numerous LP4 V1 post out there with advice to just do multiple charge/discharge cycles hoping that after two weeks their issue goes away.

The issue didn't go away..

Now most of us with experience totally agree to pop the lid (void the warranty) and top balance each cell.

And of course I have my fast method

 

[Mattb4]

For those of us that run Grade "Z" cells we simply pick a conservative voltage for Bulk , a reasonable absorption time and don't spend much time about the rest of it. Typically a new battery added to the mix will need some "seasoning" period before it gets along with the other ones. But buying cheap has a price. You don't expect perfection.

 

[BarracudaBob]

Typically a new battery added to the mix will need some "seasoning" period before it gets along with the other ones. But buying cheap has a price. You don't expect perfection.

Seasoning= Battery Boot Camp

Like a new boat engine. There is a break in period of time and a proper procedure that if done properly in the beginning you will have years of pleasure cruising.

break it in and real live use with the other will achieve "spontaneous synchronization"

 

[Lt.Dan]

I have 2x 16s CATL 271ah packs that are for sure grade B. They have given balancing problems for years. I originally had a Daly BMS that would only balance when charging. This is a BIG problem! You need a BMS to balance ANYTIME the cell is over 3.4v! Once I re-arranged them and put them in the Seplos DIY cases, which had the Seplos BMS with only 150a passive balancing current. I learned that the batteries just needed more time at 100%. I started giving it 1-2 hours per day at 100% to get the cells back to less than .040mv at my absorb voltage of 56v. This made my entire bank play nice.

Then I noticed as more months and years went by, it needed less and less time each day. Its almost as if the more time the cells were together, the more time they got "in sync" if that makes sense? Almost as if the internal resistance and capacity is getting closer together with more age. Now these Grade B cells, that are 3 years old with close to 1000 cycles on them, only take 30 min to an hour to get within balance. I don't even remember the last time I looked at them, so I couldn't even tell you how long they need. I still just give them an hour and my entire battery bank has been problem free.

 

[BarracudaBob]

Nature is truly amazing. There is also the McClintock effect and even Tesla's theory with the proper vibration at the proper placement you can cause a bridge to fall apart.

It seems that you need to get them close enough so that the coupling efficiency is strong enough the system will self synchronize.

So what are the evils of Active vs Passive balancing if done at the 3.45V or higher? It works. Even if it is only done for a short period of time. Enough for it to start self synchronization.

Resonance of Simple Harmonic Motion

 

[DougL]

A lot of people become obsessed with their BMS's balance current, thinking that if it is high, it will magically solve their balancing issues.

They also think that the passive dissipative balancer built into their bms with small resistors is not enough to keep up with the balancing requirements of a solar battery being cycled at low rates..

So they will implement active balancers with a high balance current so that every cycle, there is a solid top balance and their voltages stay within .01V.

The actual problem is that your cells are not matched properly by capacity, state of charge or internal resistance.

This is very common with cheap lithium iron phosphate batteries. Typically this occurs because:

1. The cells are not matched by capacity as well as they should be. This should be done at the factory. Cheaper batteries use cells that were obtained at lowest cost and sometimes there is a 1-3% discrepancy between cells.

2. The cells were not charged to full before putting them together. They were shipped at 50% state of charge or stored before they were assembled, which means they will not be at the same state of charge when they are put together. This is very common. Good cells that are matched, but take a few months to balance.

3. And more rare, the internal resistance is not matched. Especially true with grade b cells. Or large parallel cell packa. If battery is used at high c rates, balancing issues will occur. Especially in excessive temperature environments.

Something I want people to consider is that a Tesla EV battery is very large. If you open up the BMS you'll notice that it has very small balancing resistors. This is still true in the LFP packs (NCA packs are much easier to balance and the small balance resistors can compensate for cell drift over time).

The reason these 60kWh LFP batteries can balance without issue is because the packs are matched and assembled properly. That's it. Even at high c rates, if the cells are matched and built properly, they will not have balance issues. You still need to charge to 100% to compensate for cell drift and reset SOC indicator, but it takes a matter of minutes.

If your LFP battery which is only a few kilowatt hours in capacity cannot balance properly, you may have mismatched cells. No amount of balancing will fix this. One will always hit LVD before the others if you top balance it often.

If there is a major imbalance then you have a bad cell. Again, no amount of balancing will fix this.

The BMS balancing circuit is designed to work with these large batteries. It is plenty of balance current.

If your batteries were assembled with the cells at 50% state of charge and they need to be balanced, there is a fast way to do it. There's no need to wait for months.

Charge the battery to 100%. Pop off the top of the battery to access the cells. Then charge each one to 3.65 volts individually with the power supply. What's the current drops below 0.1 amps, disconnect power supply. Usually there will be one or two cells that are lagging excessively.

But keep in mind if you were pulling over 98% capacity, and this pack is built with high quality cells, don't worry about it and just cycle it. It will balance in a few months and you still have good capacity today, so it's not an issue.

I built 3 Basengreen DIY battery packs from 314Ah cells and the balancing took a few weeks but it tricked me when I saw it stopping charging from the EG4 inverter before it was at 100% SOC. It was stopping early because a few cells hit the BMS over voltage trigger level earlier than most of the rest of the battery cells. But the balance start and stop trigger voltages were pretty high so the balance bleeding of power from the high cells were not active for very long because the battery would only be at 100% for an hour or 2 and then it was being drained running the house.
It would have eventually balanced on its own after a few weeks of running this way since my system was such that it could and would hit 100% around 4 out of 7 days of the week. But I sped up the process by lowering the balance trigger starting voltage and once my battery VDiff at 100% was less than .030 V( 30mV ) changed the setting back to balancing at only the higher cell voltage. Basengreen had updated their balancing board to a 2A setup and that's what I have bit it still didn't move much power out of those high cells after being used to working with JK dynamic active balancing which pulled power from high cells and moved it into low cells. Strictly bleeding power from only the high cells takes a long time.
But as Will stated, once a matched battery pack gets balanced it'll hold it for a long time.

 

[BarracudaBob]

I sped up the process by lowering the balance trigger starting voltage

I did the same thing and it really helped. I played around and even started at 3.35 then 3.40 then 2.42, ending at 3.45v

Someone needs to write a really good "how to get out of balance hell" book and put it on Amazon. (hint)

 

[robby]

Will-P pretty much said it all and I agree.
The only thing not mentioned is that Grade A EV Cells are all well matched but Telecom Cells are not all matched and that is why the Cheaper battery packs have so many balancing issues.
Always remember that your battery pack is only as good as the weakest cell in the link.

 

[BarracudaBob]

Will-P pretty much said it all and I agree.
The only thing not mentioned is that Grade A EV Cells are all well matched but Telecom Cells are not all matched and that is why the Cheaper battery packs have so many balancing issues.
Always remember that your battery pack is only as good as the weakest cell in the link.

We all agree if you buy the best most expensive cells they will work batter. So show me a rack battery that has EVE cells, good communications, at a fair price?

There is also good enough or more accurately said most efficiency of capacity vs price.

I have a beat up old rusty truck. It pulls my boat. My friends are pushing me to buy some big expensive monster truck. This trucks purpose in life is to pull my boat to the dock and back. It work perfect for its task. it is GOOD ENOUGH...

Ok, that makes me a cheap bastard

 

[robby]

We all agree if you buy the best most expensive cells they will work batter. So show me a rack battery that has EVE cells, good communications, at a fair price?

There is also good enough or more accurately said most efficiency of capacity vs price.

I have a beat up old rusty truck. It pulls my boat. My friends are pushing me to buy some big expensive monster truck. This trucks purpose in life is to pull my boat to the dock and back. It work perfect for its task. it is GOOD ENOUGH...

Ok, that makes me a cheap bastard

Fair price has become very relative since EW came on the scene
I would say that Pytes V5 is a really nice pack with EV cells in it plus a BMS that is just about flawless, at $1500 it's a good deal.
Those Vatrer Batteries also have EVE cells in them so they are also good and very cheap, but they lack Comms and the BMS is not on the same level as Pytes.

 

[BarracudaBob]

Fair price has become very relative since EW came on the scene
I would say that Pytes V5 is a really nice pack with EV cells in it plus a BMS that is just about flawless and it $1500 a good deal..
Those Vatrer Batteries also have EVE cells in them so they are also good and very cheap, but they lack Comms and teh BMS is not on the same level as Pytes.

It was assumed that the VTR had EVE but nobody ever proved it on the rack battery. Labels are under the plastic holders under the bolted cells. The bolted sells make that enclosure repairable now many years from now is that going to be something we want to do economically? Regardless I like the bolted cells.

The SOC on the VTR is tracking the E-W. I set up coms to the VTR JBD BMS so I can monitor it. Sacrificed the Bluetooth but it is on Solar Assistant and I love it.

I was looking at the big Midnight Solar with active balancing. Don't recall the specs but it seemed nice. The E-W 280 I added the ABS and it is running good. after a the first month I turned off the ABS and it held its own.

So $719 and free shipping for my first E-W and I would say it is still a good deal. Zero balance issues with all 4 types of batteries (now)

 

[740GLE]

A lot of people become obsessed with their BMS's balance current, thinking that if it is high, it will magically solve their balancing issues.

They also think that the passive dissipative balancer built into their bms with small resistors is not enough to keep up with the balancing requirements of a solar battery being cycled at low rates..

So they will implement active balancers with a high balance current so that every cycle, there is a solid top balance and their voltages stay within .01V.

The actual problem is that your cells are not matched properly by capacity, state of charge or internal resistance.

This is very common with cheap lithium iron phosphate batteries. Typically this occurs because:

1. The cells are not matched by capacity as well as they should be. This should be done at the factory. Cheaper batteries use cells that were obtained at lowest cost and sometimes there is a 1-3% discrepancy between cells.

2. The cells were not charged to full before putting them together. They were shipped at 50% state of charge or stored before they were assembled, which means they will not be at the same state of charge when they are put together. This is very common. Good cells that are matched, but take a few months to balance.

3. And more rare, the internal resistance is not matched. Especially true with grade b cells. Or large parallel cell packa. If battery is used at high c rates, balancing issues will occur. Especially in excessive temperature environments.

Something I want people to consider is that a Tesla EV battery is very large. If you open up the BMS you'll notice that it has very small balancing resistors. This is still true in the LFP packs (NCA packs are much easier to balance and the small balance resistors can compensate for cell drift over time).

The reason these 60kWh LFP batteries can balance without issue is because the packs are matched and assembled properly. That's it. Even at high c rates, if the cells are matched and built properly, they will not have balance issues. You still need to charge to 100% to compensate for cell drift and reset SOC indicator, but it takes a matter of minutes.

If your LFP battery which is only a few kilowatt hours in capacity cannot balance properly, you may have mismatched cells. No amount of balancing will fix this. One will always hit LVD before the others if you top balance it often.

If there is a major imbalance then you have a bad cell. Again, no amount of balancing will fix this.

The BMS balancing circuit is designed to work with these large batteries. It is plenty of balance current.

If your batteries were assembled with the cells at 50% state of charge and they need to be balanced, there is a fast way to do it. There's no need to wait for months.

Charge the battery to 100%. Pop off the top of the battery to access the cells. Then charge each one to 3.65 volts individually with the power supply. What's the current drops below 0.1 amps, disconnect power supply. Usually there will be one or two cells that are lagging excessively.

But keep in mind if you were pulling over 98% capacity, and this pack is built with high quality cells, don't worry about it and just cycle it. It will balance in a few months and you still have good capacity today, so it's not an issue.

So will you stop recommending cheap 100ah batteries?

Or at least call out unbalance issues in the next review?

 

[Will Prowse]

So will you stop recommending cheap 100ah batteries?

Or at least call out unbalance issues in the next review?

No I love them I don't think there's an issue. for the price, just use the stupid batteries.

Does everyone forget how long I ran grade b cells for without issue?

And the litime and wattcycle cell voltage deviation is lower than most of the higher quality packs. It's hilarious. It's so good

What recommendation do I have that you disagree with and you're trying to "call me out" on. Pisses me off when people ask questions like this when I literally open the packs up and show all the testing. What is the issue here? I use these cheap packs all the time and love them.

 

[jgh]

In short: Don't obsess over it. Your battery capacity will increase with use, after initial installation.

Terms and conditions may apply. Caveat emptor.

 

[Madcodger]

Now most of us with experience totally agree to pop the lid (void the warranty) and top balance each cell.

Ugh, no. Just wait. Be patient, and wait. Voiding warranties? No, thank you.

 

[BarracudaBob]

Ugh, no. Just wait. Be patient, and wait. Voiding warranties? No, thank you.

do a search on the Eg4 LifePower4 V1 battery balance and other issues. There were many complaining. You could waist months and never get it. E-W doesn't void the warranty if you open up the rack but EG4 wouldn't replace it and wouldn't let you open it.

It was so bad that you just couldn't ignore it.. I am very pleased with the results after I took maters into my own hands.

Top Balancing welded cell batteries

 

[fuzzmunky415]

No I love them I don't think there's an issue. for the price, just use the stupid batteries.

Does everyone forget how long I ran grade b cells for without issue?

And the litime and wattcycle cell voltage deviation is lower than most of the higher quality packs. It's hilarious. It's so good

What recommendation do I have that you disagree with and you're trying to "call me out" on. Pisses me off when people ask questions like this when I literally open the packs up and show all the testing. What is the issue here? I use these cheap packs all the time and love them.

I don't think he's 'calling you out' so much as hoping you dig deeper, especially when a battery doesn't seem to perform to your expectations. I think this thread demonstrates a need for a deep dive BMS vid, showing app/SA access, how to interpret the settings, discover if factory defaults are in line with the cell manufacturer recommendations, how to change a setting/how to determine if a setting needs to be changed, etc. IOW simplifying the brain that mysteriously controls our batteries, and how to deal with this brain when things go south..it seems more common than I would imagine.

 

[BarracudaBob]

Sounds like the crowd is raising the standards. We are all getting a little smarter every day. The simple capacity testing doesn't quench the thirst of battery knowledge anymore.

We want more and we want it now!

 

[740GLE]

No I love them I don't think there's an issue. for the price, just use the stupid batteries.

Does everyone forget how long I ran grade b cells for without issue?

And the litime and wattcycle cell voltage deviation is lower than most of the higher quality packs. It's hilarious. It's so good

What recommendation do I have that you disagree with and you're trying to "call me out" on. Pisses me off when people ask questions like this when I literally open the packs up and show all the testing. What is the issue here? I use these cheap packs all the time and love them.

It’s safe to assume all these cheap units have wildly different cells, none matched nor batched.

It seems like you do initial reviews of build quality and maybe peak current capability. I’d love to see a 300 cycle review. Simulate a basic system with generic charging profiles let it charge and discharge say 2-3 times a day. See which units are able to keep balance, which units can’t.

A simpler test would be just open the case, after verifying each cell is 100%, drain off 10ah from a single cell. Then start charging the battery and see how long/many cycles will it take for the BMS to straighten it out.

Many people that complain about litime or wattcycle, rodeo, ecoworthy units is after a year or two and they unable to charge past 14.0v without over voltage protection kicking in. Is it user settings issues or internal BMS issues?

There’s excellent example of the 170ah Renolgy battery that had no balance feature enabled. People tried everything in the word to get them to balance, only solution was open the case and change out the BMS. Otherwise each unit slowly loses capacity due to cell delta.

An answer is to open the case and manually top balance each battery?

I don’t think this is something an average person who is looking for a simple “set it and forget it system.”

I agree a crazy high current balance system shouldn’t be needed if we all got pristine cells that quality OEM vendors demand. Sadly we get the cast offs and have to apply bandaids.

 

[BarracudaBob]

An answer is to open the case and manually top balance each battery?

That is exactly what I found. I wont buy a glued shut battery anymore. I have to be able to open the hood and get to the cells. As far as average Joe consumer they just don't know how bad it is.

 

[42OhmsPA]

This thread https://diysolarforum.com/threads/more-eg4-lifepower4-battery-woes.103919/ and the current thread...

My 4 DIY packs aren't spectacular either, what they looked like yesterday before dropping to float....

 

[Will Prowse]

It’s safe to assume all these cheap units have wildly different cells, none matched nor batched.

It seems like you do initial reviews of build quality and maybe peak current capability. I’d love to see a 300 cycle review. Simulate a basic system with generic charging profiles let it charge and discharge say 2-3 times a day. See which units are able to keep balance, which units can’t.

A simpler test would be just open the case, after verifying each cell is 100%, drain off 10ah from a single cell. Then start charging the battery and see how long/many cycles will it take for the BMS to straighten it out.

Many people that complain about litime or wattcycle, rodeo, ecoworthy units is after a year or two and they unable to charge past 14.0v without over voltage protection kicking in. Is it user settings issues or internal BMS issues?

There’s excellent example of the 170ah Renolgy battery that had no balance feature enabled. People tried everything in the word to get them to balance, only solution was open the case and change out the BMS. Otherwise each unit slowly loses capacity due to cell delta.

An answer is to open the case and manually top balance each battery?

I don’t think this is something an average person who is looking for a simple “set it and forget it system.”

I agree a crazy high current balance system shouldn’t be needed if we all got pristine cells that quality OEM vendors demand. Sadly we get the cast offs and have to apply bandaids.

10Ah imbalance would take a ridiculous amount of time to correct. I actually made some videos about this and tested it years ago. I used 30 and 40Ah cells in a pack. I showed active balancers cannot keep up with large imbalances. Would still only pull 30Ah with capacity test.

The active balancers also created a new failure point. I've destroyed a few of them in the past.

Charging them manually to 100% and letting BMS do its job is best.

No amount of balancing will fix mismatched cells. It will just continue to pull less capacity and one or two cells will be stressed more than the others and will have a different rate of degradation.

I've always said in the videos that if you're pulling full capacity, forget about it. Just run the pack.

What voltage nominal was the 170Ah pack? I don't know about that one. It was completely disabled?

Actually that's false, many of the batteries are batched and matched. That's why many of the cheaper ones now have lower cell voltage differential than many of the more expensive ones. again, litime and wattcycle are good examples. test any of them and look at the voltages.

Can you post links to the OVP kicking on after a year or two?

I think a big issue that a lot of people are not doing is their solar system is not charging the 100%. I mentioned that in my video and people lost their minds. They said that they never want to charge to 100% because it will ruin their batteries. But I think it's really good to charge these things to 100% so they can actually balance. I mean it's lithium iron phosphate. The iron phosphate lattice can handle it just fine. And so can the electrolyte at these voltages.

Still trying to find a cycle tester that's easy to use. Does anyone have any recommendations? Usually what I do is I put it in my system in cycle it 100 or 200 times and then I capacity test it.

 

[Will Prowse]

This thread https://diysolarforum.com/threads/more-eg4-lifepower4-battery-woes.103919/ and the current thread...

My 4 DIY packs aren't spectacular either, what they looked like yesterday before dropping to float....

What is your absorption voltage? When I have a lot of mismatched batteries connected I usually charge them up to 58 volts. And hold them there.

 

[Will Prowse]

Not charging to 100% often, running high c rates, and using pack in extreme cold can create imbalance pretty easily.

That's why all my new recommendation videos say you should charge these things to 100%.

For some reason people charge to lower voltages and they think it will allow their batteries to last longer. With these solar systems, they are rarely held at 100%. Usually they are at 50-70% for most of the time if days of autonomy is designed properly.