Why Does My Battery Bank Now Top Out at Only 88% Capacity?

[AgroVenturesPeru]

I've had this off-grid system up and running succesfully for about a year now. I used all new components. Here are the components and wiring diagram if you're curious... https://diysolarforum.com/threads/is-my-installation-plan-ok-pictorial.22812/

Looks like I've encountered my first hiccup. I have a touch screen display for my cerboGX, and check it every so often. Today I noticed the MPPT was not sending any more electricity to the batteries. It seemed to be treating 88% charged as if it were 100%. I confirmed this by running a pump in the house. The sun was shining outside. When the pump was on, I could read the (-) amp draw from the battery bank, and when the pump cycled off, the MPPT compensated accordingly and sent an equivalent amount back to the batteries, until it reached a full 88% charge again. Battery health on the monitor states 99%.

I certainly haven't changed any settings lately. Actually, I haven't made any modifications since the installation one year ago. The only thing I can think of that might be causing this is about a week ago, I was moving a floor fan in the room, and the back of it accidentally touched the switch on the inverter, which turned it off. I turned it back on promptly. Maybe I've been having this problem since then, but can't say, because today was the first day I payed attention to the display since then.

What do you think is causing the system to treat 88% charged as if it were 100% charged?

 

[rmaddy]

Do you have a shunt/battery monitor? If so, which one?

What's displaying the 88% SOC?
What monitor is displaying 99%?

What you describe sounds like a shunt that is drifting due to a lack of charging the battery to 100% at least once every week or two. The batteries may be getting charged but the shunt isn't showing an accurate SOC.

 

[RCinFLA]

Whether a separate battery monitor or battery monitor built into BMS, full reset is based on reaching the set trigger point voltage during charging.

The 'full' trigger battery voltage is usually set to be just slightly below your charger absorb voltage level.

If you have not charged up to absorb voltage during charging for some long span of time the monitor works on cummulative dead reckoning and will accumulate errors making SOC indicator more inaccurate over time. Fully charging zero's out the cumulation and sets SOC to 100% giving a fresh full reference point to work from.

With LFP battery BMS balancer you usually also need to charge to absorb voltage at least periodically to give some balancing time on all cells.

 

[AgroVenturesPeru]

The display is the touchscreen display from victron, which is linked to the Victron cerboGX. The Pylontech batteries have their own BMS.

The victron display shows 88%, and then charging stops completely. The LED indicator lights on the front of the batteries (there are six lights on each battery) show that charging stops when only 5 out of the 6 lights are illuminated.

I'll probably have to get out my mk3 to usb and run veconfigure to see if something is wrong with the settings on the charge controller, inverter, or batteries.

 

[Pim57]

Check the settings in the MPPT to make sure these are still correct.

Maybe the accidental switching of the inverter caused some glitch in the MPPT.

 

[AgroVenturesPeru]

Check the settings in the MPPT to make sure these are still correct.

Maybe the accidental switching of the inverter caused some glitch in the MPPT.

I just went through VE configure and re-entered all the values in the Victron-Pylontech compatibility manual. That didn't fix it.

 

[Bobert]

What voltage are your batteries at at 88%?

 

[AgroVenturesPeru]

51.49 -51.5v

I don't really want to tamper around with the limits in VEconfigure due to warranty reasons.
Victron limits the voltage even further beyond what the Pylontechs request:

When DVCC is enabled, the battery (via the CAN-bms) is responsible for the charge voltage. The Pylontech battery requests a charge voltage of 53.2V. We have however found that in practice this is too high. The Pylontech battery has 15 cells in series, so 53.2V equates to 3.55V per cell. This is very highly charged and makes the system prone to go overvoltage. It should also be noted that a LiFePO4 cell stores very little additional energy above 3.45V. For this reason we opted to override the BMS and cap the voltage at 52.4V. This sacrifices almost none of the capacity and greatly improves the stability of the system.

 

[Bobert]

51.49 -51.5v

I don't really want to tamper around with the limits in VEconfigure due to warranty reasons.
Victron limits the voltage even further beyond what the Pylontechs request:

I’m no expert on victron stuff but my opinion is that your smart shunt is out of calibration as others have suggested.

 

[AgroVenturesPeru]

Based on a discussion on the victron community, it sounds like the problem has to do with cell imbalances in the batteries, but I didn't read a solution:

Pylontech UP5000 not charging to 100% - Victron Community

community.victronenergy.com

 

[Bobert]

Based on a discussion on the victron community, it sounds like the problem has to do with cell imbalances in the batteries, but I didn't read a solution:

Pylontech UP5000 not charging to 100% - Victron Community

community.victronenergy.com

Sounds to me that you must periodically charge the batteries to polytechs recommended voltage or else the cells will not equalize and eventually go out of balance. It would probably be best if victron didn’t second guess the recommendations of the battery manufacturer.

 

[Pim57]

Sounds to me that you must periodically charge the batteries to polytechs recommended voltage or else the cells will not equalize and eventually go out of balance. It would probably be best if victron didn’t second guess the recommendations of the battery manufacturer.

I agree that the battery is out of balance. You could verify that yourself by looking at the cell min-max voltages.

Victron themselves advise a cell voltage of 3.55 V for their Lithium batteries and keep it there for 2 hours in order to give the battery a chance tot balance the cells. Victron starts balancing above 3.3 V and has a balance current of 1.8 A and so can shift 3.6 Ah over different cells in that two hour timeframe.

I don’t know the balance settings and current of the polytech, but you could give it a try with the Victron settings.
And 3.55 V is still a safe voltage.

 

[AgroVenturesPeru]

Sounds to me that you must periodically charge the batteries to polytechs recommended voltage or else the cells will not equalize and eventually go out of balance. It would probably be best if victron didn’t second guess the recommendations of the battery manufacturer.

How can I charge at that voltage if victron "overrides the bms and caps the voltage"? I guess I can augment the parameter in VEconfigure, to see if I can override the override.

A couple days ago, on the more highly charged battery, I got an alarm message stating Low Temperature Warning, which kicked in at about 23 Celsius. This alarm stayed on all night, but the next day it stopped and has not recurred. Full sun day today, the battery bank has reached 87% and is now stuck there.

The answer on the victron community from Ned of Pylontech (battery manufacturer) was saying the equalization kicks in above 89%. Which for the those of us with this problem is not a helpful response because we are all stuck below 89%

 

[Bobert]

I’m unfamiliar with setup of victron equipment. Perhaps you can set the charge parameters manualy to manufacturers’ specs. Perhaps someone with victron experience will chime in.

 

[HRTKD]

How can I charge at that voltage if victron "overrides the bms and caps the voltage"? I guess I can augment the parameter in VEconfigure, to see if I can override the override.

A couple days ago, on the more highly charged battery, I got an alarm message stating Low Temperature Warning, which kicked in at about 23 Celsius. This alarm stayed on all night, but the next day it stopped and has not recurred. Full sun day today, the battery bank has reached 87% and is now stuck there.

The answer on the victron community from Ned of Pylontech (battery manufacturer) was saying the equalization kicks in above 89%. Which for the those of us with this problem is not a helpful response because we are all stuck below 89%

A low temperature "warning" on my BMS would shut off charging if the warning was trying to tell me that the temperature had fallen below 32°F. If the temperature sensor becomes unplugged from my BMS then the BMS assumes a temperature of something like -40°F. This has been posted about here on the forum.

My JBD BMS does not communicate with my Victron Multiplus or any other of my Victron equipment. I've had no issues with the lack of communication. My Victron MPPT uses somewhat conservative charging numbers (14.2 volts bulk and 13.5 float). The cells in the batteries are well balanced.

Have you tried disconnecting the BMS communication from the rest of the system?

Have you verified that all four batteries are at the exact same voltage and state of charge?

 

[AgroVenturesPeru]

Pylontech says I need to buy a special debugging cable to hook up my laptop to the battery and run BatteryView software.

Assuming that's just going to show me a cell or two that are out of balance, I'm worried about what they will have me do since they're under warranty. I hope I don't have to send them in to the distributor or something. Otherwise I'll be out of power for a while.

 

[AgroVenturesPeru]

A low temperature "warning" on my BMS would shut off charging if the warning was trying to tell me that the temperature had fallen below 32°F. If the temperature sensor becomes unplugged from my BMS then the BMS assumes a temperature of something like -40°F. This has been posted about here on the forum.

My JBD BMS does not communicate with my Victron Multiplus or any other of my Victron equipment. I've had no issues with the lack of communication. My Victron MPPT uses somewhat conservative charging numbers (14.2 volts bulk and 13.5 float). The cells in the batteries are well balanced.

Have you tried disconnecting the BMS communication from the rest of the system?

Have you verified that all four batteries are at the exact same voltage and state of charge?

My batteries were 20-24 Centigrade when that alarm came on.

 

[HRTKD]

My batteries were 20-24 Centigrade when that alarm came on.

Bad temperature sensor?

 

[AgroVenturesPeru]

Bad temperature sensor?

It only happened twice over the course of a month, and why would such a thing cause the entire battery stack to limit capacity down to first 88 percent and slowly now only 85%?

 

[HRTKD]

I thought about this thread overnight and the only thing I can come up with is what I stated already: Disconnect communication between the BMS and the rest of the system and see what happens.