Am I get EVE MB31 314Ah Grade A?

[Jollysingle]

DIYers,

I bought two battery packs connecting parallels in 4/0 DLO cable from Alibaba for $1,350 each, including 16 cells, a BMS, and a stand case, batteries come with fully assembly.

They told me that the batteries are EVE 314Ah MB31 Grade A, but after using them for a month, the charge jumps from 93% to 100% within minutes. When I checked the battery cell voltage at full charge, it was only about 3.4V (see the picture below), which is different from the specifications of the EVE 314Ah MB31.

Since the batteries came pre-packaged, I do not want to open them unless necessary.

Could you please provide guidance or input on what might be causing this issue?

Thanks.

 

[kommando]

Your cells are not balanced, you have a cell delta of 0.046 and the 3.432 one will no doubt be a runner and spike in V during charging.

What BMS is fitted and what are its capabilities ie does it have an active balancer, what are the settings for the BMS.

 

[Jollysingle]

I don’t know what BMS my batteries have. I bought them fully assembled from China, and the seller did not provide that information.

This is the inside of the BMS, and I did not see an active balancer.

If my cells do not have an active balancer, what would be the best way to balance them without disassembling the battery? Or, would it be possible to add an active balancer?

 

[kommando]

My JK PB with active balancer has all the balancer integrated onto the main board and not separate.

I suspect based on the price you have the most basic BMS which will ruin your cells but until you provide more info this is just a guess.

Yes there are separate balancers available but first check the cells are what they say they are by removing the cover and taking a photo of the top of the cells.

You paid less than I pay for the parts to make a DIY battery, that comes with corners being cut.

 

[Jollysingle]

Since I am not assembling the batteries, do you know what would be a good way to disassemble them so I can see the cells on their own?

The price I am paying does not include DDP yet; it is $1,850 with DDP. I hope they did not cut corners on the battery cells by not giving the right cells that I am asking for.

 

[kommando]

Well neither you or I have x ray eyes, if it needs updating by adding extra balancer or a new BMS with active balancer you need to find out if the cells are worth the investment.

 

[upnorthandpersonal]

$1,850

That's still pretty close to DIY costs at the moment.

What charge voltage are you using on the charge controller?

 

[Jollysingle]

That's still pretty close to DIY costs at the moment.

What charge voltage are you using on the charge controller?

I use the SRNE-12k-UP All in One to charge at a maximum of 56V, but I do not know how to read the charge voltage. Is it the bus voltage, which is about 500V? Usually, I set my inverter to charge at 3,000W for two batteries at the same time and discharge at about 4,000W.

 

[Jollysingle]

Below are few snapshots I got from Solar Assistant.

 

[upnorthandpersonal]

Is it the bus voltage, which is about 500V?

I think that needs to be divided by 10.

Take a screenshot of your cell voltages when it reaches that.

 

[Jollysingle]

Yes, I will check later tonight for the most accurate information. Below are the 100% readings on other nights for two batteries.

Furthermore, would it be a concern that after fully charging, my inverter keeps discharging at around 21W? So the 100% full charge only holds for an hour, after which it drops to 99%. Should I disconnect the battery breaker after it reaches 100%?

 

[Jack1985]

voltage of LiFePO4 cells will back to around 3.3 slowly after fully charge. This is a chemistry feature of LiFePO4 battery.
So these 3.4V make no sense about quality.
Grade A EVE MB 31 Grade A cells with case and ddp shipping will not less than 1800usd ++

 

[Jollysingle]

I think that needs to be divided by 10.

Take a screenshot of your cell voltages when it reaches that.

I took those pictures yesterday, please see figures below,


Figure 1. Battery voltages when it is about 40%



Figure 2. Battery voltages when it is 94%

voltage of LiFePO4 cells will back to around 3.3 slowly after fully charge. This is a chemistry feature of LiFePO4 battery.
So these 3.4V make no sense about quality.
Grade A EVE MB 31 Grade A cells with case and ddp shipping will not less than 1800usd ++

I paid about $1,850 (including DDP) for these batteries. Does my cell voltage not make sense for Grade A EVE MB31?


Thanks,

 

[upnorthandpersonal]

Figure 2. Battery voltages when it is 94%

What I want to see are the cell voltages when it stops charging (100%). The reason is that's where cell voltages can be used to find differences between cells. If they're not balanced, that would be the only time you can use voltage to see this, for example one cell at 3.4V while another sits at 3.55V.

Your 94% voltages are very low, so my guess is that the shunt to calculate the SoC is completely off. You need to charge full - not relying on the monitor, but on the cell voltages/current going in the battery.

 

[Jollysingle]

What I want to see are the cell voltages when it stops charging (100%). The reason is that's where cell voltages can be used to find differences between cells. If they're not balanced, that would be the only time you can use voltage to see this, for example one cell at 3.4V while another sits at 3.55V.

Your 94% voltages are very low, so my guess is that the shunt to calculate the SoC is completely off. You need to charge full - not relying on the monitor, but on the cell voltages/current going in the battery.

Can I disconnect the communication between the battery and inverter and then use the charging voltage to force the battery to fully charge?

Or do I need to open the cells and charge each one individually? Please guide me, as this is my first time working with this system.

 

[upnorthandpersonal]

Can I disconnect the communication between the battery and inverter and then use the charging voltage to force the battery to fully charge?

This should work. Your BMS should provide a disconnect, but be careful none the less. Do you have an app for the BMS to change its settings and monitor? (maybe you mentioned, don't remember).

Or do I need to open the cells and charge each one individually?

No, not at all.

Something is turning off your charger because the battery indicates its at 100%. It's not at 100%, the shunt likely needs a reset. To do that, you normally charge until you reach a total voltage of 56.8V or thereabout (3.55V per cell) and ignore whatever the indicator says.

 

[740GLE]

Can you hold battery voltage at 56.8v for 4hrs or so?

Note the cell voltages at the start then again after 4hr, see if active balancing is happening.

 

[Jollysingle]

Can you hold battery voltage at 56.8v for 4hrs or so?

Note the cell voltages at the start then again after 4hr, see if active balancing is happening.

I held the cells for 6 hours last night, but I overslept, so I didn’t see the voltage when it was at 100%. Since the BMS has a passive balancer, it drained the battery to 98% by the morning. I will try to catch the data tonight.

This should work. Your BMS should provide a disconnect, but be careful none the less. Do you have an app for the BMS to change its settings and monitor? (maybe you mentioned, don't remember).



No, not at all.

Something is turning off your charger because the battery indicates its at 100%. It's not at 100%, the shunt likely needs a reset. To do that, you normally charge until you reach a total voltage of 56.8V or thereabout (3.55V per cell) and ignore whatever the indicator says.

My batteries no longer jump from 93% to 100% when I push 5200W to charge them. On a daily basis, I push around 2000W, which is about 0.07 C. I read somewhere that some BMS units do not like slow charging, but I do not know if that is the case.

 

[upnorthandpersonal]

My batteries no longer jump from 93% to 100% when I push 5200W to charge them. On a daily basis, I push around 2000W, which is about 0.07 C. I read somewhere that some BMS units do not like slow charging, but I do not know if that is the case.

The shunt that records state of charge (coulomb counter) is only so accurate. It tends to be less accurate at low currents.

 

[Jollysingle]

The shunt that records state of charge (coulomb counter) is only so accurate. It tends to be less accurate at low currents.

Since my BMS is a passive balancer and the seller did not provide all the information, should I modify the case (cutting metal) and install another BMS (e.g., JK BMS)? Or wait until one of the BMS die then replace a good one later on. I am not sure if it is worth it or if we can properly use a passive balancer.

If I want to keep the passive balancer, what would be the best practice to maintain cell balance and extend its lifespan?

 

[upnorthandpersonal]

Don't make any modifications yet.

Once your cells are balanced, you should be good - BUT you have to get to true 100% state of charge (i.e., cell voltages at 3.5V or so) once in a while so the balancer can do its thing.