Xiaoxiang BMS settings help, please

[Zentenx]

Hello, I recently bought a 400ah Winston cell lithium battery bank for my van from a seller who also professionally configured the BMS for me cause I’m no expert. Things were good at the start, even though the battery only came 58% charged. It didn’t cut off charging from solar. P.S the seller balanced all the cells for me before I picked the battery up. I will double check all the connections are solid.

My problem lately is that I installed a 40a dc to dc charger and my BMS keeps killing the charging (from 40amp dc to dc charger plus little solar) because of single cell overvoltage (seems to be cell #1 of 4 every time). Even when the battery is only 50-60% charged but reads slightly over 14volts, cell balancing doesn’t seem to help much. When there’s 2amps of solar coming in after it balances the one cell it shuts off again a few moments later due to cell overvoltage. And every time it kills charging it displays 100% charged… I’ll post my settings and would greatly appreciate any help or advice.

I want to be able to charge my battery to 100% but have not been able to yet (after having it installed for a month). Thank you in advance for your time and assistance!

 

[Rednecktek]

Your cells are not balanced, #1 is hitting its top end cutoff which is telling the BMS that it's 100% full. You'll either have to tear the pack apart and re-top balance or just keep it on the charger for a week or so and hope the internal balancing can even things out.

 

[Bob B]

The cells are out of balance ... and the reason for it is probably the balance settings.

The start voltage in the Balancer Configuration part of the menu is set WAY too low. At 1050 mv, your pack will be trying to balance when a cell is a little over 1V .... and with "balance only when charging" set to off, the BMS will be trying to balance the cells at the top and at the bottom and will be balancing all the time as long as the differential is over 50 mv .... and if the battery sits too long, the BMS could run the cells all the way down to a little over a volt.

You need to change the start voltage setting to around 3400. With a 400 AH pack, it may take a long time for the cells to get back to a top balance. It may be necessary to speed it up by doing some manual balancing .... or use an adjustable power supply and hold the pack where the highest cell is a little over 3.4V and let it balance .... it will take a LONG time.

 

[mikefitz]

Your cells are slightly out of balance. The BMS will correct over a relatively short time, but these values need changing,
Ballance settings: start voltage 3400 mv, delta 15 mv
Set switch, 'balance only when charging'
Protection values, cell over volts 3650 mv, release 3500mv

With your chargers reduce the charge voltage to 14.20 volts, float 13.40 volts, absorbtion period 30 minutes, for normal charging.

The readings you have shown indicates the cell volts and pack volts show an almost full battery. The fact it reached 14.34 volts shows almost full. The battery will suffer less stress and ageing by charging to a voltage in the region of 14.0 volts rather than 14.4, 14.6.

I am afraid your 'expert' did not set up the BMS correctly. The cells have been pulled out of balance by the incorrect balance settings.

You could speed up the balance process by setting either a long absorption perion or set the charge and float voltages to same voltage, 14.2, ( or lower if the BMS shuts down on cell overvolts). After several hours you will see an improvement. Once the cells are more evenly balanced revert to the charge settings for normal charging.

Despite the 'doom and gloom' about cell inbalance your cells are not that bad, and perhaps better than many ready built batteries.
You don't need to take the battery apart, hopefully the BMS will correct the issue.

If you feel adventurous you can manually reduce the voltage on the high cell with a DC load, car filiment headlamp bulb.
Whilst the battery is under charge and a high cell is indicated, apply the load across the cell whilst watching the cell volts via the app. Connect the load for several second bursts and evaluate the voltage change.

Expect you battery to settle to a resting voltage after a full charge to 13.5 volts+/- 0.1 volt.
Under charge once the battery exceeds 14.0 volts its very near full.

Mike

 

[psolver]

What should the max voltage spread be between cells?

 

[HRTKD]

Ideally, we want to see zero volts difference between cells.

Most of us have the BMS setup so that it tries for .015 mV difference. If the difference is less than that, the BMS calls it good.

 

[Zentenx]

Thank you all very much for your support in trying to help fix my issue. It’s seriously, greatly appreciated!

I’ll adjust my settings specifically as Mike suggested and see how it goes while charging with both solar and dc to dc.

The seller recommended I stop charging by solar and dc to dc until the battery voltage gets to 11.8-12v to “bottom balance”? My bank is actually 440ah but I confirmed that the settings he set were only using 30%(low end)-75%(max charge) of the capacity so I would get 5000+ cycles but I’d prefer getting more use of my capacity and only like 4000 cycles as I go off grid for days at a time.

I have the 40A Renogy dc to dc charger dip switch settings to 1 OFF 2-3-4 ON 5 OFF, should I change it to get the recommended charge/float voltages or is this correct?

Will post an update tomorrow after changing the recommend settings. Any further advice would be also appreciated, thank you all again. I will bottom balance the battery bank if the setting changes don’t seem to help over the next day or two. To the sellers credit, he is a great guy and did offer to replace my whole bank if bottom balancing didn’t work, should I just do that?

 

[mikefitz]

Bottom balancing is only uses for traction , motor drive, applications. For solar and RV charging top balance is used as the batteries will normally be in a high state of charge. The fact that bottom balance was used accounts for the inbalance neat full charge. You cannot have both, its either top or bottom balance.
For practical purposes you can ignore cycle life, for good service life, charge to 14.0 volts and stop discharge at 12 volts.
The Renogy allows charge voltage settings via the switches. If you select the lithium option there is no float mode and its possible to set the charge voltage to 14.0 volts. Don't worry about float, it's not needed. Refer to the manual for the settings.
I suggest, S1,2,3 off, S4 on, S5 off. This should charge at 14 volts.
Your original settings were charging at 14.4 volts, too high for an inbalanced battery.

Note its almost Inpossible to limit SOC at the top, best option is to charge no higher than 14.0 volts and stop charging.
With low charge currents you will be at well over 90% SOC. Stop discharge at 12.5 volts on load, around 20% SOC

Mike

 

[Ampster]

You cannot have both, its either top or bottom balance.

I agree and since you have a BMS which typically would top balance, that should be your choice of the two.

 

[Zentenx]

Bottom balancing is only uses for traction , motor drive, applications. For solar and RV charging top balance is used as the batteries will normally be in a high state of charge. The fact that bottom balance was used accounts for the inbalance neat full charge. You cannot have both, its either top or bottom balance.
For practical purposes you can ignore cycle life, for good service life, charge to 14.0 volts and stop discharge at 12 volts.
The Renogy allows charge voltage settings via the switches. If you select the lithium option there is no float mode and its possible to set the charge voltage to 14.0 volts. Don't worry about float, it's not needed. Refer to the manual for the settings.
I suggest, S1,2,3 off, S4 on, S5 off. This should charge at 14 volts.
Your original settings were charging at 14.4 volts, too high for an inbalanced battery.

Note its almost Inpossible to limit SOC at the top, best option is to charge no higher than 14.0 volts and stop charging.
With low charge currents you will be at well over 90% SOC. Stop discharge at 12.5 volts on load, around 20% SOC

Mike

Thank you very much for sharing your time/knowledge. I’ll update soon.

 

[Zentenx]

UPDATE: I changed my BMS settings and the cells are all staying in close voltages with each other, even with solar charging (13amps+) today, no cell overvoltage alarms average battery voltage stayed around 13.4v 54% charged.

However, I changed my Renogy dc to dc charger dip switch settings to 1/2/3 OFF, 4 ON, 5 OFF as recommended but when I tested it to charge my bank it wouldn’t charge at all. Zero amps going through BMS/battery, ran it for several minutes but nothing at all.

Should I change my settings back to charge at 14.4v instead of 14v?
Why is it not getting any charge now with these settings set to 14v?

Will always appreciate any advice, thank you all!
Looking forward to your responses.

 

[Ampster]

Why is it not getting any charge now with these settings set to 14v?

Perhaps the batteries are full since you charged them to 14.4 v earlier. Give them time and they might settle to 13.2 v but you might not be able to put much energy in to them until you put some load on them and take some energy out of them.

 

[Zentenx]

Almost 100% my bank is not full at 13.4v and reading 54% charged, I’ve never been able to charge this bank to 100%. The most I’ve ever charged it to was like 70% but cell #1 was causing cell overvoltage alarms with dc to dc charging + solar charging and it finally seems to be staying at the same voltages of the other three cells now with the new BMS adjustments.

I’ll post some more pictures of my current settings and readings for more information. Very sure it’s not full, but want to solve the Renogy 40a dc to dc charging issue now (after changing the dip switch settings to what was suggested).
- Old settings charged at 14.4v (1OFF 234ON 5OFF)
- Suggested new settings 14v charging but won’t charge at all now (123OFF 4ON 5OFF)

 

[HRTKD]

BMS says it's never seen more than 13.6 volts. Have you checked the voltage during charging at the battery posts?

 

[Zentenx]

I reset my session values after changing the BMS and dc charger dip switch settings. Haven’t been able charge via dc charger yet with the recommended setting (zero amps when on/running). May set the dip switch settings back to the old config (14.4v charge) to see if it even charges, or if cell #1 has an overvoltage alarm again as it used to to test it still works.

Is there a different dip switch setting I should use?

No, don’t have a multimeter with me currently, will have access to one Friday.

 

[Zentenx]

Perhaps the batteries are full since you charged them to 14.4 v earlier. Give them time and they might settle to 13.2 v but you might not be able to put much energy in to them until you put some load on them and take some energy out of them.
I am pulling 4-10amps average per hour for most of the day currently. Saw between 6-13amps charge from solar today at prime time without clouds. I think the 14.4v was cause by the cell overvoltage alarm that tricked the bms to thinking it was full and display 100%, after an hour or so I reloaded the app and it displayed the proper voltage and total bank charge status.

 

[Rednecktek]

May set the dip switch settings back to the old config (14.4v charge) to see if it even charges, or if cell #1 has an overvoltage alarm again as it used to to test it still works.

This and let it sit. When the voltage drops and it starts charging again the balancer will kick in. A few shallow cycles and it should resolve itself.

 

[Zentenx]

UPDATE: changed the dc to dc charger settings back and it’s charging again. Was fine yesterday with very little solar as it was a cloudy day, ran the dc charger for 2x 30min periods.

But I got the cell overvoltage alarms again today cause my solar was pulling 13-17amps plus I tossed on the dc charger for a short drive so it was charging 55amps… now it doesn’t seem to be balancing the cells while it has “balance only when charging” turned on as the system kills charging after an overvoltage alarm. And the balancing when charging wasn’t enough to prevent it from alarming.

Am I missing something here? Is there a way to have cell balancing on when charging and on after an overvoltage alarm? I’ll add a picture for review. Thanks all, looking forward to any responses!

Also: my BMS application is showing 13.7-13.8volts but my voltage display unit is showing 14.4volts?! Any ideas why?

I’m getting weird discharge spikes too for some reason, although I only pull a max of like 10amps with everything turned on. But max discharge spikes recorded on BMS application to 40-50amps?!

 

[Zentenx]

This and let it sit. When the voltage drops and it starts charging again the balancer will kick in. A few shallow cycles and it should resolve itself.

How long should I let it sit? And is that with turning off all charges (solar/dc to dc)?

The cell balancing doesn’t happen unless I’m getting a charge now. I set that on the BMS because it was recommended.

Thank you for your advice!

 

[Rednecktek]

How long should I let it sit? And is that with turning off all charges (solar/dc to dc)?

The cell balancing doesn’t happen unless I’m getting a charge now. I set that on the BMS because it was recommended.

Thank you for your advice!

Disconnect all the loads and charging and let it sit for a few hours at least before trying to charge again. The chemicals inside the battery will drop in voltage a bit as the electrons shuffle themselves around inside. When you go to reconnect it you'll find that the voltages have dropped a bit even with no load, that's what you want to happen.

Think of it like filling a cup of soda at a fountain. It fizzes up, settles down, add more, settle down, etc.