Brand new setup and 1 cell out of balance? Not sure how to fix this

[interestingfellow]

Victron Multiplus 24/3000
Eve280 2p8s array
Daly 250 Smart BMS w BT
BVM712 Shunt

This is my first attempt at building an off gird power system like this. I'm about to add 2kw of solar to it, too.

I these cells were all close to each other on delivery but i did let them sit for 2 days all in parallel.
I did not top or bottom balance (I don't have a power supply and was hoping to get away with not, but now I see that maybe I should have)

I built the battery and hooked everything up.
I did set the daly to 0* low temperature cutoff, HVD of 3.65, LVD of 2.5v, and capacity to 560ah
I set the Victron to lifepo, 29.2v absorption , 27float, 52a charge limit, and 3 hour absorption time (I just saw that I set "repeated absorption time" to 3 hours by accident. I am going to go correct that right now)

I hooked everything last night and left it to charge. I woke up to the victron on float, and bvm says %100/27v, but cell #1 is at 3.5 and everything else is at 3.36v
How do I fix this? Or is the float charge driving up cell no1 while charging?

I did get all the computer and BT programs setup and working last night. When I checked today, the Daly BT was not found by SmartBMS app and I had to wake the Daly up. Does the Daly still balance when the BT goes to sleep? Isn't balancing kind of the whole point of a BMS? (/sarcasm)

I thought I had done enough reading and viewing over the last several months, but apparently there were some things I missed!

What did I do wrong to cause this? and
What do I need to do to fix this out of balance cell?

Thank you!

 

[mikefitz]

3 hour absorption time

Are you going to set lower? I would set absorption time to zero

What do I need to do to fix this out of balance cell?

Assuming its actually a high cell and not a poor connection/incorrect reading by the BMS, (check with a meter), pull the volts down with a DC load. Use any DC load that will pull a few amps, ( I use a car headlamp bulb). Connect temporally across the 'cell' for a few seconds whilst monitoring the cell volts, repeat as necessary.

Or just carry on using the battery. The BMS did not report an over volt cell and one would expect the BMS to gradually get balance. Most MBS are programmed to balance only when charging and the cell voltage is over 3.4 volts per cell. I think once you load up the complete battery, cell 1 will quickly become more equal to the rest.

Mike

 

[interestingfellow]

I am ignorant: why would you set absorption time to 0? I followed directions from a battleborn page and it recommended .5hrs for every 100ah of capacity. that is where I got all those settings

I ran the camper ac for a couple minutes and all the cells are back down to .005v of each other. I turned everything off until I can wrap my head around what's going on.

Is this issue because i didn't active balance them?

 

[upnorthandpersonal]

I these cells were all close to each other on delivery but i did let them sit for 2 days all in parallel.
I did not top or bottom balance (I don't have a power supply and was hoping to get away with not, but now I see that maybe I should have)

This is the main reason why you're seeing what you're seeing: putting cells in parallel without a power supply does nothing. Voltage is not a state of charge indicator: 3.3V could be at 40% or 70% state of charge, no way to know. That's why you top balance. It's most likely not just one cell either.
You can try to individually charge the cells to 3.65V with a supply so you don't have to take the battery apart.

 

[Bob B]

Yep .... you have demonstrated why top balancing is recommended.

You can either start over and top balance or manually balance the pack by individually loading high cells or charging low cells.

 

[fafrd]

Victron Multiplus 24/3000
Eve280 2p8s array
Daly 250 Smart BMS w BT
BVM712 Shunt

This is my first attempt at building an off gird power system like this. I'm about to add 2kw of solar to it, too.

I these cells were all close to each other on delivery but i did let them sit for 2 days all in parallel.
I did not top or bottom balance (I don't have a power supply and was hoping to get away with not, but now I see that maybe I should have)

I built the battery and hooked everything up.
I did set the daly to 0* low temperature cutoff, HVD of 3.65, LVD of 2.5v, and capacity to 560ah
I set the Victron to lifepo, 29.2v absorption , 27float, 52a charge limit, and 3 hour absorption time (I just saw that I set "repeated absorption time" to 3 hours by accident. I am going to go correct that right now)

I hooked everything last night and left it to charge. I woke up to the victron on float, and bvm says %100/27v, but cell #1 is at 3.5 and everything else is at 3.36v
How do I fix this? Or is the float charge driving up cell no1 while charging?

I did get all the computer and BT programs setup and working last night. When I checked today, the Daly BT was not found by SmartBMS app and I had to wake the Daly up. Does the Daly still balance when the BT goes to sleep? Isn't balancing kind of the whole point of a BMS? (/sarcasm)

I thought I had done enough reading and viewing over the last several months, but apparently there were some things I missed!

What did I do wrong to cause this? and
What do I need to do to fix this out of balance cell?

Thank you!

I built an identical-size battery (8S2P) though I did top-balance first.

You’ve either got a rough road or a long road ahead of you.

The rough road is it disassemble the battery, properly top-balance with a power supply, and reassemble.

The long road is to pick up a Heltec 5A Active Balancer: https://www.amazon.com/Heltec-Equal...cphy=9032080&hvtargid=pla-1196266193651&psc=1

Once the ‘high cell’ charges up to 3.5V while the other 7 are down at ~3.36V, 5A will be discharged from that high cell and redistributed to ‘boost’ the SOC of the other 7 cells.

All 8 cells will settle at 3.36V overnight and next time you charge, the same high cell will reach 3.5V while the others remain at 3.36V.

After enough days / cycles, you will see that all 8 cells have settled to 3.37V, and you will know you are actually making progress.

Then you’ll settle at 3.38V and after enough days/weeks/months, all 8 cells will be settling around 3.4V and you’ll be too-balanced.

I have one of these little Heltec Active Balancers and I’m impressed with it.

As long as you are not in a big rush to get to full battery capacity ASAP, they will eventually get you there without the need to disassemble & reassemble…

 

[interestingfellow]

Yep .... you have demonstrated why top balancing is recommended.

You can either start over and top balance or manually balance the pack by individually loading high cells or charging low cells.

I unplugged from shore power and ran the AC for a few minutes. The cells are now all down around 3.29x and all within .005v of each other. I've turned everything off until I can figure out what I need to know.

Is there any reason I wouldn't want to disassemble and top balance from the current SOC (it's close to %98 now) as Will described in this video?
I've watch this video before but apparently certain things were not clear *to me*.

 

[fafrd]

Yep .... you have demonstrated why top balancing is recommended.

You can either start over and top balance or manually balance the pack by individually loading high cells or charging low cells.

If tried all of these methods over 2 different battery builds, and unless you value your time below $0.01/hour, investing a few $10s of dollars in an Active Balancer is a much easier, cheaper, and safer way to get there (though not faster, as I just posted).

 

[interestingfellow]

I built an identical-size battery (8S2P) though I did top-balance first.

You’ve either got a rough road or a long road ahead of you.

The rough road is it disassemble the battery, properly top-balance with a power supply, and reassemble.

The long road is to pick up a Heltec 5A Active Balancer: https://www.amazon.com/Heltec-Equal...cphy=9032080&hvtargid=pla-1196266193651&psc=1

Once the ‘high cell’ charges up to 3.5V while the other 7 are down at ~3.36V, 5A will be discharged from that high cell and redistributed to ‘boost’ the SOC of the other 7 cells.

All 8 cells will settle at 3.36V overnight and next time you charge, the same high cell will reach 3.5V while the others remain at 3.36V.

After enough days / cycles, you will see that all 8 cells have settled to 3.37V, and you will know you are actually making progress.

Then you’ll settle at 3.38V and after enough days/weeks/months, all 8 cells will be settling around 3.4V and you’ll be too-balanced.

I have one of these little Heltec Active Balancers and I’m impressed with it.

As long as you are not in a big rush to get to full battery capacity ASAP, they will eventually get you there without the need to disassemble & reassemble…

TY.
Not that I'm in a rush, but I just want it done and off my mind. I think I am going to disassemble and top balance correctly. My only question is if I can/should do it from the ~%98 SOC that I am at, now?

 

[interestingfellow]

If tried all of these methods over 2 different battery builds, and unless you value your time below $0.01/hour, investing a few $10s of dollars in an Active Balancer is a much easier, cheaper, and safer way to get there (though not faster, as I just posted).

So, I just hook this up, check my cell's balance daily ,and let it do it's thing for several weeks/months? Is there any danger/downside to using it?
(this are oversimplified questions)


I am going to look into this more, later this evening when I have time.

 

[upnorthandpersonal]

~%98 SOC that I am at, now?

How do you know you're at 98%? That one runner cell, yes, probably. All the rest? Not so sure.
You have to take your time to do this right. Either you properly top balance (preferably one cell at the time even) - and be patient, many people have destroyed their cells by being impatient and setting the voltage on the power supply wrong (while connected to the cells).
Other method is installing an active balancer. It will take weeks to get balanced; there is no quick lunch.

 

[interestingfellow]

How do you know you're at 98%? That one runner cell, yes, probably. All the rest? Not so sure.
You have to take your time to do this right. Either you properly top balance (preferably one cell at the time even) - and be patient, many people have destroyed their cells by being impatient and setting the voltage on the power supply wrong (while connected to the cells).
Other method is installing an active balancer. It will take weeks to get balanced; there is no quick lunch.

According to the BVM712 shunt I was at %100
and
According to the Daly, pic posted above

I know it's maybe not %98, but it's certainly closer to %98 than it is %50. The reason I asked is *because* I don't want to make another mistake; not because i'm in a rush.

In fact, I just want to know that I'm getting it right. If a manual top balance is what will do it, then I will buy a supply, disassemble, and do it

If I find out that an active balancer will do it in a few weeks with a high level of confidence, then I'm cool with that, too.

I just don't want to **** this up.

And I very much appreciate the help from you and the others.

 

[fafrd]

I unplugged from shore power and ran the AC for a few minutes. The cells are now all down around 3.29x and all within .005v of each other. I've turned everything off until I can figure out what I need to know.

Is there any reason I wouldn't want to disassemble and top balance from the current SOC (it's close to %98 now) as Will described in this video?
I've watch this video before but apparently certain things were not clear *to me*.

Top balance can only happen up above the ‘knee’ (>3.5V), so the higher SOC you start from, the faster you’ll get there.

But having been in your exact same shoes (well, almost), I strongly suggest you consider picking up an active balancer.

Your system is working, it’s just not giving you the full capacity you expected.

If you are not in a rush to have that full capacity ASAP, an active balancer will increase effective battery capacity each and every day until you get to 100% (without needing to disassemble / reassemble).

I decided to switch from a top-balanced battery to a bottom-balanced battery (for reasons I won’t get into here) and had one cell delivering only ~90% capacity to the other 7.

So after discharge to LVD, one cell was at 2.5C while the others were at ~3.2V.

It only took ~10 overnight balance seasons for my little Heltec 5A active balancer to get all 8 of my cells to be within 10mV of each other at LVD (25.25V or ~3.15V / cell).

My imbalance was only ~10% or ~56Ah, so a mere 5.6 hours at a full 5A should have been enough to correct that. The balance current drops as soon as the voltage mismatch drops under 100mV, so each of my 10 overnight balance ‘sessions’ probably moved only ~5.6Ah and the period with which the >100mV difference between my low cell and the others was probably less than an hour.

You have no idea how much of an underlying SOC mismatch c1 you are dealing with and if much greater than 10% SOC / 56Ah, it will take you more than 10 sessions.

But an active balancer will get you there (relatively painlessly).

 

[Bob B]

I unplugged from shore power and ran the AC for a few minutes. The cells are now all down around 3.29x and all within .005v of each other. I've turned everything off until I can figure out what I need to know.

Is there any reason I wouldn't want to disassemble and top balance from the current SOC (it's close to %98 now) as Will described in this video?
I've watch this video before but apparently certain things were not clear *to me*.

The cell voltage differential is only relevant above a cell voltage of 3.4V or so when trying to top balance. You probably are somewhere near the upper knee if you decide to charge to the level the BMS cuts off and then parallel top balance.

I have seen posts where people are successful using an active balancer .... and posts where there have been disasters using an active balancer.
If I was going to use one, I would only connect it when needed and would disconnect it when the cells are in balance.

A proper top balance is going to be your best option in my opinion, but manual balancing or using an active balancer are options that will work.
You will have to decide which option gives you the most confidence in a good outcome.

 

[fafrd]

So, I just hook this up, check my cell's balance daily ,and let it do it's thing for several weeks/months?

Yes.

Is there any danger/downside to using it?
(this are oversimplified questions)

It’s an extra (modest) expense. It’s another wiring harness you’ll need to connect in.

The upside is that it is now capability you can utilize whenever your cells get out of balance.

Especially with these cheapo Chinese cells (which are sold as ‘matched’ but are not), I would never build another LiFePO4 battery without biking in a harness to connect an active balancer…

I am going to look into this more, later this evening when I have time.

 

[fafrd]

The cell voltage differential is only relevant above a cell voltage of 3.4V or so when trying to top balance. You probably are somewhere near the upper knee if you decide to charge to the level the BMS cuts off and then parallel top balance.

I have seen posts where people are successful using an active balancer .... and posts where there have been disasters using an active balancer.

If I was going to use one, I would only connect it when needed and would disconnect it when the cells are in balance.

I’ll second this. I only connect my active balancer after the sun has gone down and discharge is complete (so no currents flowing other than those being directed by the balancer).

They are designed to be connected ‘always’ but especially with the wonky, mismatched charge/discharge curves these cheapo cells exhibit, I think they cause more harm than good when active anywhere near the ‘flats’ or while other currents are flowing.

But very happy with how they work when the battery is setting anyway (near 100% SOC or LVD).

A proper top balance is going to be your best option in my opinion, but manual balancing or using an active balancer are options that will work.
You will have to decide which option gives you the most confidence in a good outcome.

There is no difference in capacity or quality between a ‘proper’ top-balance and a top-balance achieved incrementally through an active balancer (only possibly speed to achieve full battery capacity).

 

[Bob B]

There is no difference in capacity or quality between a ‘proper’ top-balance and a top-balance achieved incrementally through an active balancer (only possibly speed to achieve full battery capacity).

I don't think I said there was.

 

[fafrd]

I don't think I said there was.

what you said was:

A proper top balance is going to be your best option in my opinion, but manual balancing or using an active balancer are options that will work.
You will have to decide which option gives you the most confidence in a good outcome.

It’s clear you don’t have confidence in Active Balancers and I can only interpret your statement to mean you don’t think they work at all (poor quality) or they they deliver a balance which is somehow deficient (not ‘proper’).

Do you have any experience using an active balancer?

 

[Bob B]

I

what you said was:



It’s clear you don’t have confidence in Active Balancers and I can only interpret your statement to mean you don’t think they work at all (poor quality) or they they deliver a balance which is somehow deficient (not ‘proper’).

Do you have any experience using an active balancer?

I think I stated very clearly that any of the three options I mentioned would work ..... and I have seen bad things happen with active balancers .... hence, not my top pick.

You have had good results with your active balancer .... so, that understandably is your top pick of the three possibilities ..... but it may not be everyone's.

Too bad we have to get into the weeds over this.

 

[interestingfellow]

Yes.


It’s an extra (modest) expense. It’s another wiring harness you’ll need to connect in.

The upside is that it is now capability you can utilize whenever your cells get out of balance.

Especially with these cheapo Chinese cells (which are sold as ‘matched’ but are not), I would never build another LiFePO4 battery without biking in a harness to connect an active balancer…

LOL, done!

I don't plan for failure, but I do try to plan ahead! I figured at some point I would have some need for a second balance lead on the pack So I built it in from the get!

I'm kind of leaning towards the balance board over disassembly (still going to read more tonight).
So, with the active balancer, do I want that just near the end of the charge? or wait till the pack is empty and connect it for the whole charge?
I believe I've read that active balancers during bulk can muck things up?

Currently, I have only the Multiplus hooked up but I am mounting my solar panels literally today and will wait to hook up the mppt's until I know I should