Xiaoxiang BMS Settings with Xuba 3.2V 280Ah LiFePO4 Lithium Batt

[Fosse]

I am using the iPhone version Xiaoxiang BMS app and some places it mentions 3.400 volts.

For example Under Capacity configuration: Full Chg. Voltage and Balancer configuration: Start Voltage



Is this wrong for a 3.2v Cell?

If not please enlighten me

Does someone have an example setup for these batteries?

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Randy

 

[Ampster]

That looks conservative and is where I will stop charging my cells. The 3.2 volts is the nominal voltage of the cells. Normally after a charge they settle to 3.35 volts. I think the 80% SOC is just a guess and on the low side because if you charge them to 3.65 or 3.4 volts they still settle at 3.35 volts
The balancing will start at 3.4 volts and if your charger set point that is when it goes from Constant Current to constant volage mode and the current will begin to taper. Remember this is just the BMS settings and the charger voltage has to be set for the entire pack which will be number of cells times 3.4 volts.

 

[heirloom hamlet]

That looks conservative and is where I will stop charging my cells. The 3.2 volts is the nominal voltage of the cells. Normally after a charge they settle to 3.35 volts. I think the 80% SOC is just a guess and on the low side because if you charge them to 3.65 or 3.4 volts they still settle at 3.35 volts
The balancing will start at 3.4 volts and if your charger set point that is when it goes from Constant Current to constant volage mode and the current will begin to taper. Remember this is just the BMS settings and the charger voltage has to be set for the entire pack which will be number of cells times 3.4 volts.

What does the balancing at a voltage between 3.4v and 3.65v accomplish if they always settle around 3.35v regardless? I've noticed this in my own case as well, and they never charge above 3.4v / ea, or 27.2v / pack.

 

[Ampster]

What does the balancing at a voltage between 3.4v and 3.65v accomplish if they always settle around 3.35v regardless? I've noticed this in my own case as well, and they never charge above 3.4v / ea, or 27.2v / pack.

Not much if they are already balanced well. I often leave my balancing off. If you never see one cell above the others when charging then your pack is balanced. Do the same when discharging and see if there are any significant cell voltage differences.

 

[heirloom hamlet]

Not much if they are already balanced well. I often leave my balancing off. If you never see one cell above the others when charging then your pack is balanced. Do the same when discharging and see if there are any significant cell voltage differences.

Why do we have all these people recommending charging figures like 28.5 or 29.2 and such. They'll never get there. Not talking forced for "balancing". Just standard SCC or BMS settings. 27.2, that's what you get. And that immediately settles to 26.8. Last forever when its there so its fine, but why all these conflicting number recommendations?

 

[Ampster]

but why all these conflicting number recommendations?

Different opinions based on experience, particular use and charging circumstance, and risk management preferences.
Do you feel that you have enough information to make a decision that is right for you?
As you may already know from my posts, my view is conservative, favoring long life over getting the last Watthour of capacity out of my pack. I also believe that once a new pack is balanced it normally stays that way and ongoing balancing is not necessary. That is the nature of a DIY install, each one is going to reflect the builders preferences.

 

[heirloom hamlet]

Different opinions based on experience, particular use and charging circumstance, and risk management preferences.
Do you feel that you have enough information to make a decision that is right for you?
As you may already know from my posts, my view is conservative, favoring long life over getting the last Watthour of capacity out of my pack. I also believe that once a new pack is balanced it normally stays that way and ongoing balancing is not necessary. That is the nature of a DIY install, each one is going to reflect the builders preferences.

Yes, I've noticed that, and of course your answer makes sense.
However, I have 4 of these packs and, in my experience, it is not a matter of wanting more or less voltage. At their "top" I can't see how anyone could pry any more amp hours out of them if they wanted to.
No matter the settings or desire or approach... they simply do not charge higher. My four are what they are, they go to 27.2 and perform exactly the way you described from there.
I don't know what others are doing differently to get another other result. Different component sizes or manufacturers ? I guess that has to be it. Because it seems from here impossible to play the Lifepo4 game any other way.

 

[Ampster]

Are you talking about finishing voltage or the voltage that they settle at? If settled voltage is what you are talking you are not going to see the difference. You will see that you can put more Amphours into a cell beyond 3.4 but it will settle at the same voltage as the cell that was only charged to 3.4 volts. Do you understand that?

I don't know what you mean buy playing the Lithium game. To me it is science and physics.

 

[heirloom hamlet]

Are you talking about finishing voltage or the voltage that they settle at? If settled voltage is what you are talking you are not going to see the difference. You will see that you can put more Amphours into a cell beyond 3.4 but it will settle at the same voltage as the cell that was only charged to 3.4 volts. Do you understand that?

I don't know what you mean buy playing the Lithium game. To me it is science and physics.

The finishing voltage. No matter the settings, my 4 packs do not charge higher than 27.2v. My 3vBYDs before these were the same.

 

[Ampster]

The finishing voltage. No matter the settings, my 4 packs do not charge higher than 27.2v. My 3vBYDs before these were the same.

Finishing voltage is a setting in your charge controller or BMS. Earlier you demonstrated that you could take a group of cells to 3.7 and before that a single cell higher than that. Your packs do notcharge higher than 3.4 volts presumably because that is where they were set to stop at. I am not sure what you are saying or why it is significant. If you want to go to 28.5 like others you would need to change some settings.
It has taken me a while to understand the cause and effect relationship between the settings and the result but everything in physics has a relationhip.

 

[heirloom hamlet]

That voltage was only accomplished when forced to in parallel by that little charger, not when connected to a SCC.

The settings have no impact on the voltage beyond 27.2v. Bulk 28.5, Float 27.4 for instance, still produce a 27.2v max charge. No load or for my use a normal load don't change that. It may decline a bit, but the sun always brings it back to 27.2v. I've followed the lead of many, made many settings adjustments, but the voltage does not rise.
It's fine, it works great the way it is. I agree, it's just science and admit I'm only beginning to learn. I reserve the right to learn something new about the chemistry and settings, hopefully soon, and make a full retraction with the new revelation. But my personal experience does have me wonder why make a career out of them. If they are so rocking and refined right out of the box and are naturally so powerful, why put so much time and effort into changing their nature, pushing them. I'm personally ready to just enjoy them organically and dive into growing in some new endeavors.

 

[Ampster]

Float 27.4 for instance, still produce a 27.2v max charge. No load or for my use a normal load don't change that. It may decline a bit, but the sun always brings it back to 27.2v.

There is your answer. The float setting. Have you measured the voltage at the end of Bulk? The pack will start settling after Bulk until it hits your float setting. Then as long as the sun is shining it will remain at 27.2 until the sun sets.

 

[heirloom hamlet]

There is your answer. The float setting. Have you measured the voltage at the end of Bulk?

It never hits the bulk setting. It never exceeds Float.

 

[Ampster]

Perhaps it is the BMS that is terminating the voltage. Other than that your pack is doing well I presume and the overchargec cells a behaving well?

 

[heirloom hamlet]

Perhaps it is the BMS that is terminating the voltage. Other than that your pack is doing well I presume and the overchargec cells a behaving well?

They sure are. They all harmonize and balance very well while charging and under the loads I use. I don't have a BMS.

 

[tictag]

@ecualibrium, I could be wrong here but I sense a possible misunderstanding between the nominal voltage of a Lithium-ion cell and its recommended charging voltage. These two things are entirely different. The nominal voltage of a LiFePO4 cell is generally between 3.2V and 3.3V (or 12.8V - 13.2V for a 4S battery or 25.6V - 26.4V for a 8S battery). This is the mean average terminal voltage of the cell across its discharge curve and depends on battery spec, components, materials used etc.

This has nothing whatsoever to do with the charging voltage.

In order to overcome the battery's own potential you need to provide a higher voltage in order to force a current 'the wrong way' through the battery, which reverses the chemical reaction and, therefore, charges the battery. If, for example, you supplied 26.4V to an 8S battery what would happen? Nothing. Nothing at all because the charge voltage equals the terminal voltage resulting in a 0V potential difference - no current flows. No charging occurs.

So now you apply 26.5V and you have a 0.1V potential difference across the battery's own internal resistance and some current (tiny!) starts to flow. Increase that to 26.6V and more current flows ... you get the picture.

The optimal charging voltage for a LiFePO4 chemistry cell is 3.65V i.e. around 0.35V potential difference between the nominal and charging voltage. Because the internal resistance of Lithium-ion cells is so low (usually measured in milli-ohms), this relatively small potential difference actually creates a big current that will often need to be current limited (this also happens to be the reason you shouldn't charge a Lithium-ion battery from an alternator, but that's another story...), this is also known as the 'Bulk' charging stage.

Why do we have all these people recommending charging figures like 28.5 or 29.2 and such.

Now do you understand why?

 

[heirloom hamlet]

@ecualibrium, I could be wrong here but I sense a possible misunderstanding between the nominal voltage of a Lithium-ion cell and its recommended charging voltage. These two things are entirely different. The nominal voltage of a LiFePO4 cell is generally between 3.2V and 3.3V (or 12.8V - 13.2V for a 4S battery or 25.6V - 26.4V for a 8S battery). This is the mean average terminal voltage of the cell across its discharge curve and depends on battery spec, components, materials used etc.

This has nothing whatsoever to do with the charging voltage.

In order to overcome the battery's own potential you need to provide a higher voltage in order to force a current 'the wrong way' through the battery, which reverses the chemical reaction and, therefore, charges the battery. If, for example, you supplied 26.4V to an 8S battery what would happen? Nothing. Nothing at all because the charge voltage equals the terminal voltage resulting in a 0V potential difference - no current flows. No charging occurs.

So now you apply 26.5V and you have a 0.1V potential difference across the battery's own internal resistance and some current (tiny!) starts to flow. Increase that to 26.6V and more current flows ... you get the picture.

The optimal charging voltage for a LiFePO4 chemistry cell is 3.65V i.e. around 0.35V potential difference between the nominal and charging voltage. Because the internal resistance of Lithium-ion cells is so low (usually measured in milli-ohms), this relatively small potential difference actually creates a big current that will often need to be current limited (this also happens to be the reason you shouldn't charge a Lithium-ion battery from an alternator, but that's another story...), this is also known as the 'Bulk' charging stage.


Now do you understand why?

Well, I didn't have the nominal and recommended, BUT I know way more about the how's and why's now, so I sure thank you for that info.
I know more today than when I typed that response, however, I personally don't see the need in my own case to try and squeeze every drop out of these with such a limited upside and painful downside.
They perform exceptionally if my parameters are more balanced. No pun intended. But they do really well for my needs at 27.2v or MAYBE 28.2v. If it weren't for all the education I have received through posts like yours, it would be hard to justify the price paid for a little more aH. I wish I'd never pushed them to new 29.2v heights in the name of top balancing. I've learned a lot, though, at reatively low cost, so lesson learned, but I won't be doing it again.

 

[dsilver]

I am excited that I have my 8s-16S 100 Amp BMS functional with my 280AH batteries. The app I was given looks different than was listed previously in this thread. From what I can tell the app is defaulted to Lifepo4. But some settings are confusing to me. I have included a screen shot. I thought Will had some parameters in the forum, but I can't find it. The cell high protect seems too high. The app is called MaYi-BMS from the BMS manufacturer.
Could someone point to the right thread with parameters or tell me what should be set for the 3.2 280AH xuba batteries? I have them setup as an 8s 24v battery.

Also in Will's video on this BMS he said it does have a Lifepo4 profile. I am not sure how to find it.

 

[tictag]

These parameters are not suitable for LiFePO4 chemistry.

I am going to assume that:

• Alarm event happens before Protect event
• You are happy to de-rate your battery to a 100A maximum discharge, even though it is capable of charging/discharging at 1C or 280A
• You are happy to go with generic LiFePO4 parameters

Parameter	Value	Comment
CellHighAlarm	3.75V	Typical charge voltage is 3.65V
CellHighProtect	3.85V	Emergency shut-down
CellHighRecover	3.60V	1.5V below Alarm
CellLowAlarm	3.0V
CellLowProtect	2.5V	Emergency shut-down
CellLowRecover	3.15V	1.5V above Alarm
TotalVoltHighProtect	30.8V	3.85V x 8 cells
TotalVoltLowProtect	20V	2.5V x 8 cells
ChgOverCurrentProtect	100A	Battery can be charged at 1C, but limited by BMS
DisChgOverCurrentProtect	100A	Battery can be discharged at 1C, but limited by BMS

p.s. Note that your BMS is your last line of defence, not your first! Your SCC should be configured to ensure charging stops at 3.65V per cell (8S = 29.2V) and your design should ensure that you never consume more energy than your battery is capable of supplying.

p.p.s. There doesn't appear to be a low temperature cut-off parameter. Do be sure not to charge your LiFePO4 below 0℃.

Edit: added postscripts

 

[apctjb]

I am using the iPhone version Xiaoxiang BMS app and some places it mentions 3.400 volts.

Dumb question but does Xiaoxiang make a BMS or just and app? If they make a BMS can someone post link. If they make just an App, then what BMS can it be used with.


Thx