Bad Battery?

Anyone have any thoughts on how to determine a Bad Battery? Or bad cells?

Three nights in a row, about two weeks ago, my system died. Two MPP's LV6548.
Three Husky Big Batteries (48v), Battery SOC was around 70%, and dropped to 10% SOC in less than an hour.

My only diagnostic is Solar Assistant, (Love it).

Batteries when Low Voltage at 44v, system cutoff. About 3AM each time. By the time I got to the system, the battery voltage was down to 14V. In the past because of not much sun, and cloudy days, they would be at 44V but the last three failures down to 14V.
I isolated one battery, and attached my battery charger, the batteries would climb from 14V to 46V in less than 5 minutes, unheard of.
Ran system on two batteries, and same failure happen next night. Put the battery back in the loop, and disconnected another battery.
Charging again from the 14V back to 46V happened quickly again.
Ran system next day, same failure. So that told me the third battery was the culprit. Isolated that one, and system ran all night.

Now, have had all three running the system, without failure for about ten days, so what's up.

Hence, my question, how do I find out a battery that has a BMS that only communicates internally. No way to see any info?

Anybody have any suggestions?

Thanks for any ideas.

First, what is reporting SoC?

Are you regularly attaining at least 55.2V for at least a couple hours a day?

SoC can become very inaccurate without regular full charges.

14V is a non-voltage. That's being reported by the BMS and isn't real, or something is horrifically wrong. Charging to 48V should be relatively quick.

Sounds like the 14 volts is a ghost reading from when the BMS has turned off. The 44 volt reading sounds correct for when the batteries have decided they've had enough and the BMS shuts them down.
As sunshine eggo says above, make sure that the batteries are getting a full charge and being held for at least half an hour to allow for full cell balancing and genuine 100% charge at least once a month if not every week.

sunshine_eggo said:

First, what is reporting SoC?

Are you regularly attaining at least 55.2V for at least a couple hours a day?

SoC can become very inaccurate without regular full charges.

14V is a non-voltage. That's being reported by the BMS and isn't real, or something is horrifically wrong. Charging to 48V should be relatively quick.

Click to expand...

Sorry for not responding. Didn't get a notification that you commented.
Yes, Batteries get up to 58v on good sun days. Cloudy days at least 53 to 55v.

As far as SOC, I use Solar Assistant daily, and that is where I base my assumptions on. I go to the battery shed, and numbers there match what Solar Assistant shows.

I agree the 14v is not correct, and I am working with the supplier as to the faulty voltage.

I do have a Victron smart shunt, and use it when I am within Bluetooth range, but use Solar Assistant much more than the shunt.

Quattrohead said:

Sounds like the 14 volts is a ghost reading from when the BMS has turned off. The 44 volt reading sounds correct for when the batteries have decided they've had enough and the BMS shuts them down.
As sunshine eggo says above, make sure that the batteries are getting a full charge and being held for at least half an hour to allow for full cell balancing and genuine 100% charge at least once a month if not every week.

Click to expand...

14v is strange. As soon as I can get to the failing system, I attach my charger and batteries climb faster than normal. Other times it failed to 44v and cutoff, it might take an hour or two to get up to 52v, then the 14v failure, voltages rises to 52v in about 30 minutes. So I know there is a BMS problem, just can't determine which battery is at fault.
Hoping the supplier will help determine which one is failing.
Also, as 100% battery charge, the system can get to 100% for two to six hours a day, on cloudy days, lucky to get to 80% SOC.

The 14V is likely normal for when the BMS enters protection. It's simply an arbitrary value.

It's still not clear what's reporting SoC. Where is solar assistant getting that value?

Is your smartshunt properly programmed?

I don't believe the Husky batteries report their SoC, do they?

Can you get access to the cell data?

Is it possible that you're simply over-using your system and depleting the batteries?

sunshine_eggo said:

The 14V is likely normal for when the BMS enters protection. It's simply an arbitrary value.

It's still not clear what's reporting SoC. Where is solar assistant getting that value?

Is your smartshunt properly programmed?

I don't believe the Husky batteries report their SoC, do they?

Can you get access to the cell data?

Is it possible that you're simply over-using your system and depleting the batteries?

Click to expand...

I have found about 5 different configurations for the shunt. They all work, and have found the one that works best. But, really, don't use the Victron shunt. It is not able to view remotely, hence don't use it much.
Solar Assistant is plugged into the MPP inverter. The MPP reports all the info to Solar Assistant.
Husky's report nothing.
The system has run fine for three years. SOC runs flat at about 80% all night. Really nothing attached that would drain it. Hot summer evenings, the A\C might pull SOC down to 50% overnight.
Bug I am trying to solve happened about 3 weeks ago, and has not failed since using all three of the batteries.

OleMan2765 said:

I have found about 5 different configurations for the shunt. They all work, and have found the one that works best. But, really, don't use the Victron shunt. It is not able to view remotely, hence don't use it much.

Click to expand...

There is really only one correct configuration. When charging with solar it should be set for 0.2-0.3V below absorption voltage. Tail current should be 6% and Peukert 1.05.

FWIW, I believe there is a means of connecting the smartshunt to SA.

When you check the shunt, does it read within a few % of what SA reports?

OleMan2765 said:

Solar Assistant is plugged into the MPP inverter. The MPP reports all the info to Solar Assistant.

Click to expand...

Where does the MPP get it's SoC value? I don't see that it can be programmed for battery capacity, and it can only track SoC when connected to a BMS capable of feeding it SoC:


So is this a Solar Assistant function where you've told SA how big your battery is, and it's calculating SoC based on the inverter's reported draw from the battery?

(I know essentially nothing about Solar Assistant).

Do the

OleMan2765 said:

Husky's report nothing.

Click to expand...

Thought so, but hoped otherwise.

OleMan2765 said:

The system has run fine for three years. SOC runs flat at about 80% all night. Really nothing attached that would drain it. Hot summer evenings, the A\C might pull SOC down to 50% overnight.

Click to expand...

Context helps.

OleMan2765 said:

Bug I am trying to solve happened about 3 weeks ago, and has not failed since using all three of the batteries.

Click to expand...

The act of isolating and individually charging (you didn't say you did, but I'm assuming you did) the "culprit" may have improved the balance of the cells and restored lost capacity.

Without gaining access to cell data at cut-off and full charge, it's very difficult to definitively say what went wrong, or why it's fixed now.

sunshine_eggo said:

There is really only one correct configuration. When charging with solar it should be set for 0.2-0.3V below absorption voltage. Tail current should be 6% and Peukert 1.05.

FWIW, I believe there is a means of connecting the smartshunt to SA.

When you check the shunt, does it read within a few % of what SA reports?



Where does the MPP get it's SoC value? I don't see that it can be programmed for battery capacity, and it can only track SoC when connected to a BMS capable of feeding it SoC:

https://www.mppsolar.com/manual/SPLIT%20PHASE%20LV/LV6548%20split%20phase%20manual-20210416.pdf

So is this a Solar Assistant function where you've told SA how big your battery is, and it's calculating SoC based on the inverter's reported draw from the battery?

(I know essentially nothing about Solar Assistant).

Do the



Thought so, but hoped otherwise.



Context helps.



The act of isolating and individually charging (you didn't say you did, but I'm assuming you did) the "culprit" may have improved the balance of the cells and restored lost capacity.

Without gaining access to cell data at cut-off and full charge, it's very difficult to definitively say what went wrong, or why it's fixed now.

Click to expand...

sunshine_eggo said:

There is really only one correct configuration. When charging with solar it should be set for 0.2-0.3V below absorption voltage. Tail current should be 6% and Peukert 1.05.

FWIW, I believe there is a means of connecting the smartshunt to SA.

When you check the shunt, does it read within a few % of what SA reports?

Click to expand...

Battery capacity is 315A
Charged voltage 56.0v
Discharge floor 20%
Tail current 2.00%
Charged detection time 3m
Peukert exponent 1.05
Charged efficiency factor 95%
Current threshold 0.01A
TTG averaging period 3m

SA has Battery voltage at 52.9v and SOC at 86%
Shunt thinks SOC at 93% all other numbers are the same

For LFP charging to 58V+, 2% tail current is a little low, but it's not bad.
Charged efficiency factor for LFP is 98-99%

7% difference isn't great, but it's pretty common. If the battery hasn't attained true 100% in a month, I wouldn't be surprised... if it's only been a week, something is amiss.

Did you program SA with the battery capacity? Does it have charge sync settings?

sunshine_eggo said:

o is this a Solar Assistant function where you've told SA how big your battery is, and it's calculating SoC based on the inverter's reported draw from the battery?

(I know essentially nothing about Solar Assistant).

Do the

Click to expand...

Interesting question. Have to look at MPP values again, but SA uses battery info from the MPP's.

sunshine_eggo said:

For LFP charging to 58V+, 2% tail current is a little low, but it's not bad.
Charged efficiency factor for LFP is 98-99%

7% difference isn't great, but it's pretty common. If the battery hasn't attained true 100% in a month, I wouldn't be surprised... if it's only been a week, something is amiss.

Did you program SA with the battery capacity? Does it have charge sync settings?

Click to expand...

No battery config in SA, points to MPP for data. Good point above about charging the isolated battery to reset the cells. Might have been the fix, and I didn't know it, as after the third isolated battery charged, the system is running like before.
As far as MPP configs for batteries, Bulk at 58.4 Float voltage at 58.0, but battery equalization is disabled, as the MPP cant communicate with the Husky's.

OleMan2765 said:

No battery config in SA, points to MPP for data.

Click to expand...

I just don't see where you can enter battery capacity into the MPP. Maybe you have a different model than that manual.

OleMan2765 said:

Good point above about charging the isolated battery to reset the cells. Might have been the fix, and I didn't know it, as after the third isolated battery charged, the system is running like before.

Click to expand...

Hopefully that's all.

OleMan2765 said:

As far as MPP configs for batteries, Bulk at 58.4 Float voltage at 58.0, but battery equalization is disabled, as the MPP cant communicate with the Husky's.

Click to expand...

I would lower float to 54V. The MPPs tend to have a long absorption period, and after charging to 58.4V, you need almost no absorption - like maybe 15 minutes. Floating at 58V just does damage by overcharge.

sunshine_eggo said:

I just don't see where you can enter battery capacity into the MPP. Maybe you have a different model than that manual.



Hopefully that's all.



I would lower float to 54V. The MPPs tend to have a long absorption period, and after charging to 58.4V, you need almost no absorption - like maybe 15 minutes. Floating at 58V just does damage by overcharge.

Click to expand...

Like your idea about float.
The Outfit I bought the system said to use 58.4v. I questioned them on that, and three different support techs said to use the 58v value.
I have always questioned that, and never had a good response from them.
I believe your assessment about float, and will lower it and monitor.
Thanks for all your valued input.

As far as MPP info for batteries, I have value for steps;
26 = 58.4v Bulk
27 = 58.0v Float
30 = disabled battery equalization

Big Battery is notorious for being clueless. Keep in mind that all batteries are constructed from CELLS. Big Battery has purchased cells and put them in a package.

Literally no CELL manufacturer recommends floating at elevated voltage. In fact, they specify charge to 3.65V and TERMINATE charge once the current has dropped to 0.05C or 5% of capacity. For a 100Ah battery, it's full when cells are at 3.65V and current has dropped to 5A. Any additional charging past that is overcharge and runs the risk of damaging the cells.

54V will hold that batteries at ~99%-ish SoC and prevent over-charge, lithium plating on the cathode/capacity loss.