What do you think is going on with this bank?

Forgot to post a few pics I took. The battery bank is on the bottom as far in as you can get of course. So hard to get too. The verticle packs are the envision 305s.

1. Did you swap BMS to see if the problem moves with the BMS or stays with the battery pack.
2. What fire safety plan do you have in place ?
3. Did you read the fire thread ?

what are your charge settings for bulk, absorb, float?

your battery with the 500 cycles looks like its doing the same thing as mine, where there is a spread in cell capacity that causes the active balancer to actually unbalance the battery during bulk charge. it causes two cells to run away from each other, you can see it in cells 11 and 12. cell 11 may be failing

you may need to manually balance with a power supply to bring those two cells back up

Bleedingblue said:

After getting home from work I cut the bms off from discharging.
The pack said 0% left. The #12 cell said 2.7 volts on the bms and the others were around 3.24.
Checked with the voltmeter and it was dead on what the BMS said.

Click to expand...

Once a Cell reaches cutoff voltage (set in BMS), the BMS will set to 0% SOC and shutoff Discharge. Depending on what is set for Power Down Voltage it may completely shutoff, this is correct behaviour for the BMS. If not powered down, it should still have Charge Enabled.

Cell 12 appears to be a Runner at 1st blush. BUT rule out the busbar & sense lead connection and ensure it is clean & tight first, that can be a contributor ! If you can, charge the entire pack up keeping an eye on #12's behavior and see if it deviated & by how much while charging... Slower or Faster than other cells are more indicators of a "cell issue".

Edit - re pics
Ahhhhaaaaa ! Better to see the whole !
a Couple of oopsies (OK I am a nit picker with this stuff but got there for good reason) seems straight forward but it isn't !


The devil is always in the details !
Pack imbalances can happen far too easily due to small things that are missed.

The Charge profile is another thing that needs looking at to make sure your not pushing the cells "just that bit too much" and not allowing the Active Balancer to transfer off the high volt cells. I always recommend to NOT exceed 3.450VPC (55.2V) for Bulk/Absorb and to set FLOAT at 3.440VPC (55.1) to allow the cells to fully saturate at the set voltage so when they settle they hover around 3.400 (Max of Working Voltage Range).

With two inverters lines, I would put at 1/4 and 3/4. Just my preference to minimize amps through any segment of the busbar.

Quattrohead said:

1. Did you swap BMS to see if the problem moves with the BMS or stays with the battery pack.
2. What fire safety plan do you have in place ?
3. Did you read the fire thread ?

Click to expand...

No hadn't seen a fire thread yet.
I dont think it's the bms the bms read exactly what the multimeter said on voltage

rustyrotors said:

what are your charge settings for bulk, absorb, float?

your battery with the 500 cycles looks like its doing the same thing as mine, where there is a spread in cell capacity that causes the active balancer to actually unbalance the battery during bulk charge. it causes two cells to run away from each other, you can see it in cells 11 and 12. cell 11 may be failing

you may need to manually balance with a power supply to bring those two cells back up

Click to expand...

Got my settings up above in some screen shots. I'll repost.

those are your bms settings, can you check your charge controller for charge settings

I’d be pulling the buss bars off to either side of the affected cell and twist some Scotch bright on the contact surfaces then wipe off the surface with acetone and assemble. If you use NO-OX-ID A Special do not get it on the threads as the reduction of friction will increase the tension force of the fastener. Always remove the balance connector from the bms before assembling or disassembling cells. Pry it out straight and evenly a little at a time gently.

There’s a really good chance that the cells are just really out of balance and didn’t spend enough time in balance voltage to get it done because the cell over over voltage is disconnecting before it gets there. An endless, increasingly worsening loop. This can happen when two things occur. A long period of several weeks or more where the batteries don’t get to a high enough voltage to balance and when it does balance the absorption time is too short to be any good. How I’d attack the problem;
After charging as high as it can go by itself, you may have to intervene and rig up a resistive load on the high cell to bring it down to just below the others manually. A bench top power supply can boost the low. This will take time and constant observation. Ideally you need a stable controllable (reduced current) supply or control of current to go further. Perhaps take the other batteries off line or use a generator. Remember to bring batteries to similar state of charge before paralleling them again.

if you look at the 2nd set of screen captures, which show resting voltages, cell 11 and 12 are actually lowest state of charge, even though cell 11 surges the highest during bulk, which hits ovp and ends charging early. makes me think something wrong with cell 11 or connections need cleaning. bms resistance values seem ok though, cell 15 is a bit high. based on the unloaded voltages, cell 11 looks to be about 20% down and cell 12 40% down

Steve_S said:

Once a Cell reaches cutoff voltage (set in BMS), the BMS will set to 0% SOC and shutoff Discharge. Depending on what is set for Power Down Voltage it may completely shutoff, this is correct behaviour for the BMS. If not powered down, it should still have Charge Enabled.

Cell 12 appears to be a Runner at 1st blush. BUT rule out the busbar & sense lead connection and ensure it is clean & tight first, that can be a contributor ! If you can, charge the entire pack up keeping an eye on #12's behavior and see if it deviated & by how much while charging... Slower or Faster than other cells are more indicators of a "cell issue".

Edit - re pics
Ahhhhaaaaa ! Better to see the whole !
a Couple of oopsies (OK I am a nit picker with this stuff but got there for good reason) seems straight forward but it isn't !
View attachment 213267

The devil is always in the details !
Pack imbalances can happen far too easily due to small things that are missed.

The Charge profile is another thing that needs looking at to make sure your not pushing the cells "just that bit too much" and not allowing the Active Balancer to transfer off the high volt cells. I always recommend to NOT exceed 3.450VPC (55.2V) for Bulk/Absorb and to set FLOAT at 3.440VPC (55.1) to allow the cells to fully saturate at the set voltage so when they settle they hover around 3.400 (Max of Working Voltage Range).

Click to expand...

My inverters are set to
55.2v bulk charging
54.0v floating charge voltage

Should I raise it up?

Bleedingblue said:

My inverters are set to
55.2v bulk charging
54.0v floating charge voltage

Should I raise it up?

Click to expand...

You can easily put Float to 55.0V and get the full use of the working range charged & topped.
I found the "Sweet Spot" for the active balancing to start @ 3.4 so it can do it's work while in float. BUt by the time my packs reach float, there isn't that much difference usually.

Bleedingblue said:

My inverters are set to
55.2v bulk charging
54.0v floating charge voltage

Should I raise it up?

Click to expand...

Float voltage should be above 16x start balance voltage.

Steve_S said:

You can easily put Float to 55.0V and get the full use of the working range charged & topped.
I found the "Sweet Spot" for the active balancing to start @ 3.4 so it can do it's work while in float. BUt by the time my packs reach float, there isn't that much difference usually.

Click to expand...

Changed my float to 55.0v

What happens when you have 10 battery packs and they are no where close to same voltage. How does the inverter go into float mode if it's still charging the other 9?

Update on the pack that had cell 12 really out if kilter.

What should I set that charger to to top off everything? Do I let it set there at that charge voltage and balancers on until all cells are exactly the same? How long should it sit?

It takes time. as the packs reach the set point voltage and the cells level up the Voltage will remain same but the Current will drop. When you have multiple packs in lay like this, they will slowly flip on/off (so it will appear) as it continues but they start taking charge as all packs charge. Keep in mind that LFP can charge happily @ .5C or 140A for a single 280AH Pack. The 50A charge you're charging with is divided between them.

Steve_S said:

It takes time. as the packs reach the set point voltage and the cells level up the Voltage will remain same but the Current will drop. When you have multiple packs in lay like this, they will slowly flip on/off (so it will appear) as it continues but they start taking charge as all packs charge. Keep in mind that LFP can charge happily @ .5C or 140A for a single 280AH Pack. The 50A charge you're charging with is divided between them.

Click to expand...

This is one thing I don't understand. I have full sun right now 7 of the 10 packs are full. When they are all charging they usually get 20-22 amps of current going into each one of the 10. How come I'm only seeing 15 amps when they should be getting like 60 amps each since the others have stopped charging?

They are still taking charge and will do so until they are all at a matching voltage more or less. It's never perfect. The reason they are taking such low amperage is the internal resistance of the cells within the packs. One thing you can do is to increase the absorb time when charging and that should help pick up the slack a bit.

Bleedingblue said:

This is one thing I don't understand. I have full sun right now 7 of the 10 packs are full.

Click to expand...

Don't believe SOC until you KNOW the battery has charged to at least 55.0v.

Set start cell balancing to 3.38v
Set Cell OVP to 3.640v
Set Cell OVPR to 3.639v

Charge at 58.0v until the first BMS cuts out due to Cell Over Voltage. Note the voltage at cutoff, and which BMS is cutting out.

Charge at 0.10v below cutoff voltage until the highest cell is under 3.630v.

Increase charge voltage by 0.10v.

Repeat until you get to 57.60v (3.60v/cell).

DIYrich said:

Don't believe SOC until you KNOW the battery has charged to at least 55.0v.

Set start cell balancing to 3.38v
Set Cell OVP to 3.640v
Set Cell OVPR to 3.639v

Charge at 58.0v until the first BMS cuts out due to Cell Over Voltage. Note the voltage at cutoff, and which BMS is cutting out.

Charge at 0.10v below cutoff voltage until the highest cell is under 3.630v.

Increase charge voltage by 0.10v.

Repeat until you get to 57.60v (3.60v/cell).

Click to expand...

If I have a runaway cell will it damage it? I have had cells in the past say 3.7 when it was set to 3.45

Don't you have a BMS?