Bleedingblue
Solar Enthusiast
- Joined
- May 12, 2020
- Messages
- 564
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.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.
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
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).
You can easily put Float to 55.0V and get the full use of the working range charged & topped.My inverters are set to
55.2v bulk charging
54.0v floating charge voltage
Should I raise it up?
Float voltage should be above 16x start balance voltage.My inverters are set to
55.2v bulk charging
54.0v floating charge voltage
Should I raise it up?
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.
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.
Don't believe SOC until you KNOW the battery has charged to at least 55.0v.This is one thing I don't understand. I have full sun right now 7 of the 10 packs are full.
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).