Pylontech Battery Fault

[Mendoza]

Sometimes all the lights flash and the battery beeps continuously. The manual says "high voltage protection", "cell voltage higher than 4V or module voltage higher than 55.5V". Usually happens with battery discharging and at a middle ish state of charge.

Manuals says turn off for 15 mins and then back on. That works, however causes a power cut for one second when turning off and on, and the issue will then happen again a day later or a week later. So far 12 times in 6 weeks.

The bottom, slave battery which is always the only one with the fault sometimes discharges slower and the batteries can get out of sync. For example at the moment the bottom battery has 4 green lights and the top has 3 lights (lower state of charge). This may or may not be causing the problem simply because there seems to be a correlation. EDIT June 2022: As far as I can guess at the moment, this was probably not what the problem was.

Thank you if you can help. Any ideas?

EDIT June 2022: Most or all of the discussion in posts 2-18 was not relevant to the eventual solution. Consider skipping to post 19.

 

[sunshine_eggo]

Sounds like imbalance at the top.

Is this a 15S or 16S battery?

Try lowering your absorption voltage in 0.2V increments until it goes away.

 

[Mendoza]

When you say imbalance would you guess imbalance between the two batteries can cause this (since they do sometimes display different SOC) or do you mean within the faulty battery an imbalance of cells within just the faulty battery.

I currently have the following settings in the inverter. I don't see a setting for absorption, should I reduce one or both of those? I'd wondering if the float would more likely be the problem, since the fault tends to occur during slow discharging and not during charging, but I don't know enough about this to be sure. I have a fairly poor understanding of the terms "bulk", "float" and "absorption".

26. Bulk charging voltage: 52.5V

27 Floating charging voltage: 52.5V

 

[sunshine_eggo]

Referring to cell imbalance within one of the batteries.

Please provide a picture of how your battery bank is configured including the main connections to the inverter. If you're getting an imbalance between the battery themselves, you likely have an improperly configured bank.

Bulk, boost and absorption all generally refer to the same voltage.

Given those numbers, I'm assuming a 15S battery.

52.5V is way too high for a float voltage.

Recommend you set:
Bulk: 51.75V
Float: 51.0V

 

[Mendoza]

Thanks for your help.

I have seen it discussed that Pylontech batteries are 15 cell rather than 16 cell several times on forums, and no-one has ever contradicted it or claimed otherwise. So let's say 90% sure it is 15 cell as I've never seen this in official Pylontech material. I assume when you say 15S that is the same as 15 cell. Apologies for forgetting to respond to that point of your message.

Pylontech specifically told me to set to 52.5V in email discussion, although they also told me it could be lower. Here is the discussion:

PYLONTECH: "please set the following parameters that are on the battery side.........:
Bulk charge voltage 52.5V.
Float charge voltage 52.5V."

ME:"If float charging voltage of 52.5V is OK, then I guess a lower float voltage 51.0V or 52.0V might be OK for charging to less than 100%. But never >52.5V. Do you agree?"

PYLONTECH: "That's correct! Because sometimes the voltage sensors on the inverter terminals are not very accurate, the full battery voltage is around 53.2V(smaller than 54V). So 52.5V is a charge voltage value that has been limited in a safe range! You do not need to worry about this. "

If I set to the voltages you specify, it is likely I lose a significant amount of the capacity (e.g. batteries might only charge to 90% and then stop) or do you think it will still charge to the max or very close? In any case, if it prevents the errors it's probably worth it but would be good to know.

Re the photos, I will try and get to that soon.

 

[Mendoza]

Dips are a bit hard to see in photos but the top battery has Dip 1 set to 1 and Dips 2,3 and 4 to zero. The bottom battery has them all at zero.
Keep in mind that the current cable positions going into the battery were done on April 13th. Before that, the configuration was different. I changed them on April 13th incase one particular connection socket could be a problem. In the two days since, no errors yet.
The cable positions going into the inverter have not been changed since the system was installed on February 22nd.

 

[sunshine_eggo]

Okay. Was looking to confirm that the main (-) is on one battery and the main (+) is on the other. That looks to be the case.

From the label, 48V nominal and 53.5V peak charge voltage confirm 15S.

At my recommended 51.75V, you should get to 98%+ SoC.
At a float of 51V, you should float at or above 95% SoC.

51.75V will require a long absorption period - allow for up to 6 hours.

 

[Mendoza]

When the batteries were installed on February 22nd, both the long cables were installed to the same battery. That can be seen in the picture of post 28 here: https://diysolarforum.com/threads/pylontech-the-right-buy-for-me.34002/page-2 However I was then informed of this mistake and it was changed on February 23rd or 24th if I recall. Hopefully this couldn't have caused damage? On February 24th I changed to the cable positions shown in the photo attached to this post. The battery fault I described in my original post in this thread then occurred in this position.

 

[Mendoza]

Okay. Was looking to confirm that the main (-) is on one battery and the main (+) is on the other. That looks to be the case.

From the label, 48V nominal and 53.5V peak charge voltage confirm 15S.

At my recommended 51.75V, you should get to 98%+ SoC.
At a float of 51V, you should float at or above 95% SoC.

51.75V will require a long absorption period - allow for up to 6 hours.

Allow for up to 6 hours always or just the first time after changing settings?
In layman's terms, does an absorption period of 6 hours mean to leave the batteries charging for 6 hours?

 

[sunshine_eggo]

When the batteries were installed on February 22nd, both the long cables were installed to the same battery. That can be seen in the picture of post 28 here: https://diysolarforum.com/threads/pylontech-the-right-buy-for-me.34002/page-2 However I was then informed of this mistake and it was changed on February 23rd or 24th if I recall. Hopefully this couldn't have caused damage? On February 24th I changed to the cable positions shown in the photo attached to this post. The battery fault I described in my original post in this thread then occurred in this position.

No damage, but could have caused some initial imbalance between the two batteries.

Allow for up to 6 hours always or just the first time after changing settings?

Always. While you can achieve very high states of charge at that voltage, it will not allow as much current to flow at that voltage, so it takes longer to charge.

In layman's terms, does an absorption period of 6 hours mean to leave the batteries charging for 6 hours?

It means the charger must maintain 51.75V for 6 hours prior to dropping to float.

 

[Mendoza]

I'm assuming that if I fail to get 6 hours absorption for whatever reason (high energy use, clouds etc) the only issue will be my battery isn't fully charged. If that's the case, I can probably be Ok with that, or at least try it out and see how we go.

I will likely reduce the voltage settings. I will just wait a day or two to hear if anyone else has any suggestions on the exact value to reduce to. Also, I am checking on another forum.

I'm also somewhat tempted not to change the voltage settings until the next time the error occurs. If I change it now I won't know if it's stopped happening because of the cables being changed on April 13th, or due to the change to the voltage settings.

The battery balancing doesn't seem to be the fix, as it occurs again after battery balancing, and also because the batteries seem to balance themselves during charging phase and end up perfectly balanced, but then a few days later they are out of balance again in discharging phase. This would make sense with your comment that the error is within one battery not due to imbalance between them.

 

[Mendoza]

The same error happened so I changed the voltage settings as you suggested:
26 Bulk charging voltage to 51.8V and
27 Floating charging voltage to 51.0V
However the same error occurred again a few hours later

 

[Mendoza]

The error is happening more frequently now, 4 times in last 48 hours with 3 of those since I changed to bulk charging voltage 51.8V, Floating charging voltage 51.0V. Not sure whether to set the voltage back to the Pylontech recommended 52.5V or should I try what you said and reduce by 0.2V every time this happens and see if the error repeats. However, guessing quite likely none of that will work: my guess is there is NOT a mismatch of several volts between the inverter and the battery because the voltage shown when discharging at low load is consistent with what you would expect for a given state of charge shown on the battery.

I think I may disconnect the one battery and run the system off one battery, at least for a while, if this keeps happening. So what I am thinking is connect the long cables to the master battery, presumably same dip position, remove short cables and other battery. Probably reduce max charging amps, other settings the same. Does that seem reasonable for just one battery?

Would it make sense to switch over the master and slave positions- I can´t think why it would work, but maybe worth a try. Or maybe I´m just getting desperate at this point.

Would it make sense to leave the faulty battery disconnected for a longer time? Several days or a week turned off rather than switching it back on after minutes or hours. Not sure if that would give voltage levels a chance to settle down and smooth out?

Pylontech suggests I buy a RJ45-DB9-USB cable to download the logs(event data and cycle data) and send it them and then they can do a diagnostic on the battery problem. I can try it if I can find anywhere to buy the cable, although it looks complicated.

It could be a faulty cell, a faulty battery, or some fundamental problem caused by the lack of communication between inverter and battery.

On the other hand sometimes when you are just about ready to go for the nuclear option there appears some extremely simple solution that you´ve overlooked...

 

[sunshine_eggo]

At this point it sounds like a faulty battery.

Can you read the individual cell voltages?

 

[Mendoza]

I can´t do that no, or I don´t know how.

 

[Mendoza]

At this point it sounds like a faulty battery.

Can you read the individual cell voltages?

Sunshine Eggo,

Can I turn off just the faulty battery when the fault occurs (this would be for minutes, hours, or 1-2 days at max). This would leave one battery turned on and still connected to the inverter via the orange cable.

Can it still work by passing current through the switched off battery to get to the black cable? Is it safe to leave one operating in this configuration and the other off?

Might it be the case that the top battery could still function to charge but not discharge? Or vice versa?

 

[sunshine_eggo]

Sunshine Eggo,

Can I turn off just the faulty battery when the fault occurs (this would be for minutes, hours, or 1-2 days at max). This would leave one battery turned on and still connected to the inverter via the orange cable.

I would expect so.

Can it still work by passing current through the switched off battery to get to the black cable? Is it safe to leave one operating in this configuration and the other off?

I would expect so.

Might it be the case that the top battery could still function to charge but not discharge? Or vice versa?

Without knowing the cause or getting more specific data, like cell voltages, I can't say.

 

[Mendoza]

Summary: If you don't have time to read all this the bottom line is I decided to run the system off one battery until issue is fixed later. It looks like you were right Sunshine Eggo, but see below for further detail.


(comment is about 900 words, 2 minutes to read)


The fault has been regularly occurring still. If I turn off the battery and then turn it back on again only minutes later, and do nothing else, the fault never instantly reappears, but will reliably recur minutes or hours later, at the most the next day.


Batteries tend to be out of balance after the fault, especially if I detect the fault at 6am or 7am which means it could have been in the faulty condition for hours as the alarm is not quite loud enough to wake me to the other end of the house. This unbalance (which happened a few times in the last weeks) suggests that when the battery is in the fault condition it is probably not discharging. In some cases when this happened I then disconnected the batteries and did a partial or full rebalancing before connecting. When I did this, then the fault will not recur as soon, but will still recur after perhaps a few days or a week.


There is insufficient data to draw a conclusion with high probability, but my gut feeling is that the benefit of battery balancing is to give the battery time to rest and recover from heavy demand situations, rather than because of the actual balancing benefit itself. To test this theory I just turned the batteries off for over a day recently and it was 2 days later that the fault occurred. Similar to when I do battery balancing.


Last night I tried turning the one faulty battery off and back on again after only 30 minutes, but the error repeated within a few hours. I then left just one battery off overnight. The single battery was still able to handle a 2000W load. However after turning off the faulty battery a red fault light (no flashing, nothing audible) was displayed on the master battery, and the 6 LED lights on the master battery showing SOC did not display. However it still worked - during steady discharge at low load for maybe 10 hours. I turned the bottom battery back on this morning so I didn't get to test charging with the one battery turned off. When I turned the bottom, faulty battery back on the red fault light disappeared immediately and the SOC lights immediately returned also.


Interestingly, when I turned the batteries back on they were heavily unbalanced with one showing one light and the other four, however, impressively, the two batteries then balanced each other out over a few hours. At one point one of the batteries was actually charging even though the whole system was discharging (i.e. loads > PV input). So all the times I disconnected the batteries to balance them in isolation from the inverter and the rest of the system may not have even been necessary.


I am able to turn the faulty battery off and on again without causing a power cut if I don't turn off the other battery. This is the only way I've found to reliably create a short term fix to the error without a power cut. However, given the fault light and the non-display of SOC, this makes me uncomfortable as there may be a possibility, however slight, that I could damage the top battery in this arrangement of passing circuit through the turned off battery.


I therefore now completely disconnected (and turned off) the faulty battery for now and connected both long cables to the top battery. I have not changed the dip positions. I have reduced the charging current from 30A to 20A but kept other inverter settings the same. I attach a photo with the current cable connections if anyone wants to check it. I currently plan to only connect it if necessary to do so as part of an attempt to solve the problem or if we had a grid power cut and it's the only power we have left. I am storing the battery at 50% charge level, by the way, and if it gets cold out there (nearer to zero degrees than ten) I will move the battery into another storage location in the house. Given this, it seems like that should be OK to store it for months turned off if necessary (according to a few articles I just read including some graphs).


I'm too busy to properly solve this this week. It looks like the issue needs software diagnostic with Pylontech at this point and failing success with that to try and get the battery replaced or repaired. I will try and get to that within May and then provide an update.


It looks at the moment less likely that the error is caused by communication issues or current flow from the faulty battery to the inverter or the other battery. And perhaps more likely that there is an internal issue with one of the faulty batteries.


I am concerned about running the system with one battery as it is quite undersized for the evening demand. 2000W evening demand will work but is above the recommendation and could affect lifetime. I don't know what happens with 4000W or so demand in the evening, but hopefully would default to grid. However, this seems to be the best solution for now. I may also try this is a permanent solution if I can't get the battery repaired or replaced under warranty.

 

[Mendoza]

Update: Pylontech told me to buy a RJ45-DB9-USB cable and rewire it to their instruction. I got a computer shop to do that. This then enabled me to, via a software program and some instructions they sent me, take the logs of data out of the battery and send them to Pylontech, who told me that "I think the problem is on the battery BMS board" so they are going to send me a new board.

 

[Mendoza]

The battery BMS board (tarjeta de control in Spanish) has been replaced and the battery returned to me and the system is now working again with the two batteries.

Since the error previously occurred occasionally in the past with gaps of days or weeks in between we won't know for sure if this BMS board replacement was the correct solution to stop the error until some time has passed - maybe a month or two.

This also confirms that the guarantee's vaidity has been accepted in spite of using the battery with an inverter with no communication. I was not charged for the replacement.