Xiaoxiang BMS settings help, please

[Zentenx]

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.

Oh okay, thank you very much for explaining it.

I turned off the charge master switch in the BMS application to allow the cells some time to settle. Here’s a picture of my current status. Seems like the voltage did drop after a few hours and the cells balanced. It usually reads 13.8+ volts when I’m charging both solar and 40amps from dc to dc but now it’s at 79% 13.3volts, seems good and that’s the most I’ve ever charged the battery.

Any suggestions on the random discharge spikes that are showing 40-50amps?
My max draw is only ever around 10amps with everything I have on 12v/inverter 110v items.

Thanks again, cheers!

 

[HRTKD]

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

I'm going to use that analogy. That's great.

 

[mikefitz]

The voltage displayed on the blue led display is not accurate , these types can be up to 0.5 in error. You need a good quality multi meter to read accurate values.
You are getting cell over volts because the charge voltage is too high. Modify your charger settings to lower values. The Renogy manual is not very clear on set up for the switches. Note when using the lithium settings once the battery reaches the set charge volts, it will stop charging. It suggests a charge voltage of 14 volts is possible.
The capacity/cell volts settings inthe BMS seem too high, this is giving you under reporting of SOC. Many of the settings in your BMS have been adjusted away from default.
Once you stop charging the cell volts will settle, and appear to get back inbalance, there could be inbalance when charging over 3.4 volts per cell.
The random spikes may be caused by load, what loads are connect?
Your BMS is designed to balance cells near to full charge, this is where cells with a different SOC will show different voltages.
Thus the BMS is set to balance under charge only where cell volts exceed 3.4 volts per cell.
Because your cells are not top balanced you need time for the BMS to make corrections. If the charge volts and or current is too high then the cell volts will rise too fast and the battery will reach cell over volts before enough ballance action takes place.
Since the balance correcting current is low it could take many hours for the BMS to correct the situation.
Unless you want to invest in an AC charger or carry out a top balance, it will take some time with the solar charger to get the cells better balanced.
The aim is to get the cell volts over 3.4 but not high enough to get cell over volts, this is done by suitable charge volts and current.
The last set of readings show a battery over 80% SOC. If you can keep the charge volts in the range 13.8 to 14.0 volts is will allow balancing.
Your issues stem from a bottom balanced set of cells. When this technique is used top balance action by the BMS is effectively not applicable. Unfortunately you were not advised that this bottom balance technique would require careful set up of chargers to avoid cell overvolts.
Again with the full facts not being available BMS settings were changed on forum advice.

Bottom balanced cells are only normally used if the application frequently operates with the battery at a low state of charge or no BMS is being used. It's a fail safe situation since if the battery is completely discharged no cell can destroy others because they are all empty.

When you have a BMS that can detect low cell volts and an application that operates at mid to high SOC, like a solar charged system, top balance is a more ideal technique.

Renogy DC to DC settings, from the manual S5 off, S1 off, S2 off, should be 14.0 charge, no float.

Mike

 

[Zentenx]

Thank you all. I’ll try the new dc charger settings and let you know.

I’ve also been monitoring the cell voltages when I’m charging, and when they reach 3.500v I cut charging to give them time to balance and prevent cell overvoltage alarms. Pretty happy that I’ve been able to charge my bank over 60-70% for the first time.

Thanks for explaining things in detail as well. Feel like I’ve learnt a lot from this discussion and appreciate it. Will update soon. Have a great day all!

 

[squowse]

You probably want to use a lower charge voltage. I use 13.9V. It’s sufficient and you will have less problem with overvoltage cells. The balancing possibilities of that BMS are very limited.

 

[squowse]

Thank you all. I’ll try the new dc charger settings and let you know.

I’ve also been monitoring the cell voltages when I’m charging, and when they reach 3.500v I cut charging to give them time to balance and prevent cell overvoltage alarms. Pretty happy that I’ve been able to charge my bank over 60-70% for the first time.

Thanks for explaining things in detail as well. Feel like I’ve learnt a lot from this discussion and appreciate it. Will update soon. Have a great day all!

The State of Charge is probably inaccurate at the moment. You need to to a full cycle. Trip it at the top, bottom and top again. Its a pain tbh I wish they would make it simpler.

 

[Zentenx]

How do I do that exactly? Start at 100%? Run it down to 11.8volts or 20%? Then full charge? And everything will be better or more accurate?

Cause the seller setup the BMS so I can’t use more than 70-75% of the capacity I believe. I can post updated setting pictures if wanted?

I don’t have any complaints at the moment. Been running it down about 10%-15% everyday (reads 60-75%like 13.3-13.4v) then only charging 10%-20% every couple days. Been cloudy and raining a lot for a few days but I’ve been fine, probably get it back to 100% this week with more sun.

 

[mikefitz]

Just use the battery normally
Charging to full will set the SOC to a more accurate value, full whilst charging is over 14.0 volts , full after resting is 13.4 volts.
You can use almost the full range of your capacity, the 'total cycle capacity' in the BMS is set to 395000 mAh, the capacity is set to 400000 mAh. Nothing in the BMS limits you to 75%.
Most accelerated ageing occurs at a low SOC, limit the discharge to 12.0 volts.
Had another look at your BMS settings, comments,
The charge and discharge current limits are set at 100000 mA, is this OK you have a 100 A BMS?
The low temperature charge and discharge limits are set to - 55 degC. I understand Winston cells tolerate temperature but this seems excessive.
Further investigation found two data sheets with different limits, - 45 degC and -25 deg C. There will also be limits on the actual currents allowed, this I cannot find.
The data sheets also indicated the advantages of not taking g the battery to a low SOC. Discharging g to 20 % SOC gave 3000 cycles, discharging to 30% SOC gave 5000 cycles.

Mike

 

[squowse]

How do I do that exactly? Start at 100%? Run it down to 11.8volts or 20%? Then full charge? And everything will be better or more accurate?

Cause the seller setup the BMS so I can’t use more than 70-75% of the capacity I believe. I can post updated setting pictures if wanted?

I don’t have any complaints at the moment. Been running it down about 10%-15% everyday (reads 60-75%like 13.3-13.4v) then only charging 10%-20% every couple days. Been cloudy and raining a lot for a few days but I’ve been fine, probably get it back to 100% this week with more sun.

to rest the coulomb counting it's normally a full charge, full discharge then full charge. To sense top and bottom the instructions sometimes indicate that the cell over and undervoltage protection needs to be triggered, so I do this just to make sure.

 

[Zentenx]

Just use the battery normally
Charging to full will set the SOC to a more accurate value, full whilst charging is over 14.0 volts , full after resting is 13.4 volts.
You can use almost the full range of your capacity, the 'total cycle capacity' in the BMS is set to 395000 mAh, the capacity is set to 400000 mAh. Nothing in the BMS limits you to 75%.
Most accelerated ageing occurs at a low SOC, limit the discharge to 12.0 volts.
Had another look at your BMS settings, comments,
The charge and discharge current limits are set at 100000 mA, is this OK you have a 100 A BMS?
The low temperature charge and discharge limits are set to - 55 degC. I understand Winston cells tolerate temperature but this seems excessive.
Further investigation found two data sheets with different limits, - 45 degC and -25 deg C. There will also be limits on the actual currents allowed, this I cannot find.
The data sheets also indicated the advantages of not taking g the battery to a low SOC. Discharging g to 20 % SOC gave 3000 cycles, discharging to 30% SOC gave 5000 cycles.

Mike

Yes, it’s a 100A BMS. I set the low temps both to -35C. Thank you again for all your help! Hope your doing well.

Recently picked up a new German shepherd puppy so I’m a bit preoccupied, sorry for the delay. ?

Any idea why I get max discharge spikes (50-60A+)? I only pull 10-12amps with everything in my van on.

 

[Zentenx]

UPDATE: my battery was working fine for a week or so of some rainy days and partial sun. Now it’s been sunny for several days in a row and I keep getting cell over voltage alarms from just solar charging and it cuts charging port off. But it doesn’t seem to balance the cells very well and takes a while before turning charging back on, at which point it just happens again.

Is it better that I have “balance only when charging” setting on? Can anyone else recommend something that will help me avoid these solar only charging battery cell over voltage problems? I haven’t even been using my dc to dc charger cause with all this sun I charge back to 80% or a bit more before the alarms go off. Still have not been able to charge my battery bank to 100% since owning it for five months… kinda desperate for a solution after paying so much for this bank and 100A BMS.

I’ll include setting pictures for anyone who can help. As always, any input is greatly valued and appreciated. Thank you.

 

[mikefitz]

Some of your issues are due to the original bottom balance. When using a set of bottom balanced c.ells a 'full' battery is when one cell reached 3.65 volts. This is why I recomended you to just use the battery but limit the charge volts. This is how bottom balanced batteries are used. Having set the BMS conditions for top balance , time, perhaps several months will be required. It only needs a small difference in cell capacity for large voltage differences once the cell volts exceed 3.40 volts .

You are still charging to a higher voltage than necessary. Set your charge volts to below the value that causes cell over volts.
There is no need to exceed 14.00 volts. To give to time for balance to take place set a long absorbtion time and float value equal to charge volts. Revert to more normal charge value once better balance is found, charge 14.00, float 13.40.

The cell voltages shown indicate a near full charge , also shown by the BMS at 100 %, why are you stating its not fully charged, what is this based on?

Balance only when charging, cell volts over 3.4 volts, delta greater than 15mv.

Intermitant high discharge current pulses must be related to your loads, what DC and AC loads do you have?

Setting the low temp limit to - 35C does not allow high current charge at this temperature.

Mike

 

[Zentenx]

Hey Mike, thank you for your ongoing responses! I understand what is happening now after everyone’s support just don’t know how to fix it. If it takes several months for the BMS to adjust to top balance so be it. Sorry but the only charging I am doing recently is from my solar. I have 600w (3x 200w panels) of solar on my roof and a 40A Renogy MPPT charge controller set to charge lithium batteries, on sunny days I get 9-13amps on average, 19amps on perfect clear days. Don’t believe I can alter the charge specs for lithium batteries on the Renogy 40amp MPPT charge controller…?

It is not fully charged cause it was only at 83% and 13.2-13.4v charge before the slow solar charging eventually set off the single cell over voltage alarm at 9amps (with my current load subtracted) and that’s when the alarm triggers and it displays 100% charged and the voltage spikes to 14v or so for some reason…

It’s 70-80 degrees outside where I am currently and only gets to like -10 in my van at most with the insulation in winter, when I’m inside I run the diesel heater and keep it around 70degrees inside.

My inverter is powering a Mini dorm fridge with separate freezer compartment, extension cord with a laptop (40w) and a 40” new TV (like 60-70w max). The rest of my items are 12v… maxair fan, additional 12v fan, lots of USB charging devices, 6x LED puck lights and that’s basically it.

 

[Zentenx]

Hey Mike, thank you for your ongoing responses! I understand what is happening now after everyone’s support just don’t know how to fix it. If it takes several months for the BMS to adjust to top balance so be it. Sorry but the only charging I am doing recently is from my solar. I have 600w (3x 200w panels) of solar on my roof and a 40A Renogy MPPT charge controller set to charge lithium batteries, on sunny days I get 9-13amps on average, 19amps on perfect clear days. Don’t believe I can alter the charge specs for lithium batteries on the Renogy 40amp MPPT charge controller…?

It is not fully charged cause it was only at 83% and 13.2-13.4v charge before the slow solar charging eventually set off the single cell over voltage alarm at 9amps (with my current load subtracted) and that’s when the alarm triggers and it displays 100% charged and the voltage spikes to 14v or so for some reason…

It’s 70-80 degrees outside where I am currently and only gets to like -10 in my van at most with the insulation in winter, when I’m inside I run the diesel heater and keep it around 70degrees inside.

My inverter is powering a Mini dorm fridge with separate freezer compartment, extension cord with a laptop (40w) and a 40” new TV (like 60-70w max). The rest of my items are 12v… maxair fan, additional 12v fan, lots of USB charging devices, 6x LED puck lights and that’s basically it.

Here’s another picture showing 100% but lower voltage. This was taken now like 30mins after the first pics approximately.