So I got the batteries US2000C x 2 and currently scheduled to be installed Friday. Will be installed with Axpert MKS II 5kW and 3.25kWP Risen panels (10 panels) as discussed previously: https://powerforum.co.za/topic/11261-are-pylontech-up5000-and-us3000c-compatible-with-axpert-mks-ii-5kw/

Here are some of the settings as they currently are (majority of the rest are at default setting):

EDIT March 17th: Keep in mind I have a 15 cell Pylontech battery rather than the more common 16 cells. That means that for most other people with 16 cell batteries some/all the voltage settings are not right.

1. Output Source Priority: SOL EDIT 3rd March: Changed to SBU after installation was completed.

2. Maximum charging current: 30A

5. Battery Type: USE

11. Maximum utility charging current: 30A

12. Setting voltage point back to utility: 48V EDIT March 3rd: Changed to 47V to stop it using grid electricity in the morning. EDIT March 28th: Changed to 46V to stop it using grid electricity when the batter still has 2/6 SOC lights on.

13. Setting voltage point back to battery mode: 51V EDIT March 3rd: Changed to 48V to make it switch back to solar more quickly after it switches to grid. (Unclear if 48V is sensible for most people however, but hopefully will work for me.)

16. Charger source priority: OSO (Only solar)

26. Bulk charging voltage: 52.5V

27 Floating charging voltage: 52.5V EDIT 26th December, 2024. Changed to 51.8V.

29 Low DC cut-off voltage: 47V  EDIT March 2nd: Changed to 46V to stop an alarm going off, but for most people 47V may still be most secure. See discussion from February 28th onwards. EDIT March 28th. Changed to 45.7V later. See discussion from March 28th onwards.

The ones in bold are from an email with Jeff at Pylontech as discussed in the other thread.

12 and 13 is from Coulomb´s January 16th post in the other thread. I guess these two selections are less critical than with lead acid.

16 set to OSO is just my personal preference not to waste utility to charge the battery. However I will probably override this and occasionally charge the battery with utility to ensure battery stays topped up in cloudy winter days incase of power cut. But mostly I would leave as OSO.

 

Do these settings look OK? My main focus at the moment is to have the system work smoothly in its initial days with the new battery with no power cuts, and to chose safe settings that can´t damage or degrade the battery, inverter, or anything else.

 

Let me know if you have any ideas on the settings or other things to do to ensure a smooth installation or initial days.

 

I may try and use limited energy on the first or second day if possible as I suppose it´s beneficial to get the battery charged to 100% in that time.

Edited December 26, 2024Dec 26 by Green Power
Updating new settings, edits marked as such.

37 minutes ago, Green Power said:

26. Bulk charging voltage: 52.5V

27 Floating charging voltage: 52.5V

I would of course choose 51.8 V for the float voltage, to prolong the life of the battery.

Interesting that at least someone from Pylontech is moderating their usual recommendation of 53.2 V for the bulk/absorb setting.

Edited February 17, 20223 yr by Coulomb

4 hours ago, Coulomb said:

I would of course choose 51.8 V for the float voltage, to prolong the life of the battery.

Coulomb, sorry for the possibly silly question, but what exactly is "float voltage", and how does this have an effect on battery life? I have my float voltage set at 51.5V and bulk at 51.6?

1 hour ago, brburger said:

what exactly is "float voltage", and how does this have an effect on battery life?

After the battery is charged, you want to keep the battery "full", despite loads. So the inverter targets a lower constant battery voltage, this is the float voltage. When the battery voltage dips below the float voltage, current flows back into the battery to keep the battery full. Most of it will actually flow to the load.

In summer, the battery will reach full charge in a few hours. So for perhaps 9-10 hours, it will be sitting at the float voltage. Cell voltage, like cell temperature, is the enemy of cell life. The higher the voltage, higher the chance that some particle will have enough energy to overcome the natural barrier and cause a destructive reaction to occur. So it's best for the life of the cell to have the float voltage about 3% lower than the absorb/bulk voltage. You need the bulk/absorb voltage to fully charge the battery in a reasonable period of time, so that high voltage can't be helped. But for the rest of the day, the cell voltage can relax back to a slightly lower voltage, losing perhaps half of one percent of SoC, but extending the life of the battery as a result.

2 hours ago, brburger said:

I have my float voltage set at 51.5V and bulk at 51.6?

Those are low voltages, although I use the equivalent of 50.3 V myself. I think to fully charge the battery in a reasonable time, you need to increase the bulk/absorb voltage to about 52.5 V. Those figures are assuming 15S LFP, e.g. Pylontech.

6 minutes ago, Coulomb said:

After the battery is charged, you want to keep the battery "full", despite loads. So the inverter targets a lower constant battery voltage, this is the float voltage. When the battery voltage dips below the float voltage, current flows back into the battery to keep the battery full. Most of it will actually flow to the load.

In summer, the battery will reach full charge in a few hours. So for perhaps 9-10 hours, it will be sitting at the float voltage. Cell voltage, like cell temperature, is the enemy of cell life. The higher the voltage, higher the chance that some particle will have enough energy to overcome the natural barrier and cause a destructive reaction to occur. So it's best for the life of the cell to have the float voltage about 3% lower than the absorb/bulk voltage. You need the bulk/absorb voltage to fully charge the battery in a reasonable period of time, so that high voltage can't be helped. But for the rest of the day, the cell voltage can relax back to a slightly lower voltage, losing perhaps half of one percent of SoC, but extending the life of the battery as a result.

Those are low voltages, although I use the equivalent of 50.3 V myself. I think to fully charge the battery in a reasonable time, you need to increase the bulk/absorb voltage to about 52.5 V. Those figures are assuming 15S LFP, e.g. Pylontech.

@Coulomb I've heard so many people saying that one should not float LFP  batteries, yet I also see that some people say it's ok as long as you float at lower voltage than the absorb/bulk voltage. what is your opinion?

59 minutes ago, Antonio de Sa said:

I've heard so many people saying that one should not float LFP  batteries

To keep the battery near to fully charged, you need a constant voltage target for the inverter's charger. That voltage is called the "float" voltage, for historical lead-acid reasons. Perhaps you don't "need" it for chemical reasons as you might for lead-acid, but really it's the same situation, so why not call it the float voltage.

Yes, I believe that the float voltage for LFP should be around 3.36 to 3.45 VPC, or 50.3 to 51.8 for 15S. The lower (within that range) the better for battery longevity.

Should I sign up here?

https://en.pylontech.com.cn/service/support

Is the reason to do it to make sure your 5 years warranty starts from the day you start using it, and not the day it left the factory

Not completely clear if filling this in on installation is necessary to maintain warranty or not

Do people do this? Experiences?

Maybe I'm being lazy, but I started doing it, and there was a bunch of questions and it looks like you are required to upload photos, so not sure if it's worth it

 

Edited February 18, 20223 yr by Green Power

16 minutes ago, Green Power said:

Should I sign up here?

https://en.pylontech.com.cn/service/support

Is the reason to do it to make sure your 5 years warranty starts from the day you start using it, and not the day it left the factory

Not completely clear if filling this in on installation is necessary to maintain warranty or not

Do people do this? Experiences?

Maybe I'm being lazy, but I started doing it, and there was a bunch of questions and it looks like you are required to upload photos, so not sure if it's worth it

 

I registered mine just to get an extended warranty period, from 7 to 10 years if I remember well.

 

Battery was just installed and was charging up. As soon, as we went into discharging rather than charging mode (when the oven was switched on and we had 1800W load vs few hundred W solar) immediately the inverter starting beeping with a low battery warning and the inverter showing one bar out of four (indicating 0%-24% battery).

However the batteries were at that time showing 4 green lights, one flashing light, and one green light off. Which I assume indicates a high state of charge. Possibly four lights and a flashing fifth out of 6 might indicate more than 4/6 and less than 5/6 charge.

So the inverter and the batteries seemed to be in disagreement about the state of charge.

I'm slightly inclined to believe the battery more, because a) I guess (?) it would make sense that the batteries were delivered at a mid state of charge rather than kept at low and b) the batteries were charging for a while after installation and ought to have been charged up by about 0.5kWH-1KWH already (i.e. 0.25kWH-0.5kWH each)

There was not a power cut, but after several minutes of beeping I switched to utility mode (Option 1-UTL in inverter).

Edited February 22, 20223 yr by Green Power

Also, the two batteries are touching each other, stacked one on top of the other, as there wasn't enough cable to install them side by side. At some point I'll get the proper bracket I think to stack them better with space between them. The installer thought this wasn't ideal due to heat build up but isn't a problem for some days (note batteries will be sat in a temperature of about 15C-28C mostly in this area for now).

Any comments on this. Is this OK for a) a short time like days or weeks b) indefinitely - leave them stacked for years c) not OK even for one day

Looks like the low battery warning on the inverter is just not correct. It will say low battery and then the battery goes on providing energy for hours and hours and gives another 2kWH maybe in total. So I just turned off the alarm sound and ignored it.

Apart from that, everything working smoothly.

There is an undocumented interaction between the battery low cutoff voltage setting and the warning going off. For unpatched firmware like yours, it will be 2.0 V. This is acceptable for lead-acid batteries, but makes little sense for LFP with their relatively flat voltage versus SoC curve. Hence "just not correct".

Since you have a BMS to save your battery anyway, you could also just reduce the low DC cutoff voltage setting until it goes off only at a sensible voltage. Then you can keep the beeper on in case of any actual warnings.

7 hours ago, Coulomb said:

Since you have a BMS to save your battery anyway, you could also just reduce the low DC cutoff voltage setting until it goes off only at a sensible voltage. Then you can keep the beeper on in case of any actual warnings. SOC).

Agree!  The datasheet of my LFP batteries says that the BMS cuts off at 40.5V (0% SOC). So I set the inverter low voltage cut off to 42V. "Back to utility bypass" at 47V, however 48V if load shedding looms. It worked well so far. It cut out once at night when load shedding came as a surprise and the geyser heating remained on. It happened 10 minutes before power came back.

LFP batteries seem to be less vulnerable to deep discharge than lead batteries.

Edited March 1, 20223 yr by Beat

13 hours ago, Coulomb said:

There is an undocumented interaction between the battery low cutoff voltage setting and the warning going off. For unpatched firmware like yours, it will be 2.0 V. This is acceptable for lead-acid batteries, but makes little sense for LFP with their relatively flat voltage versus SoC curve. Hence "just not correct".

Since you have a BMS to save your battery anyway, you could also just reduce the low DC cutoff voltage setting until it goes off only at a sensible voltage. Then you can keep the beeper on in case of any actual warnings.

Are you talking about in my Axpert option 29 Low DC cut-off voltage:? And reduce it from current level of 47V - is there any safe limit here - perhaps 44V, 42V or 40V under which I should not go?

5 hours ago, Beat said:

Agree!  The datasheet of my LFP batteries says that the BMS cuts off at 40.5V (0% SOC). So I set the inverter low voltage cut off to 42V. "Back to utility bypass" at 47V, however 48V if load shedding looms. It worked well so far. It cut out once at night when load shedding came as a surprise and the geyser heating remained on. It happened 10 minutes before power came back.

LFP batteries seem to be less vulnerable to deep discharge than lead batteries.

When you say "inverter low voltage cut off" would that be in my Axpert or option 29 "Low DC cut-off voltage

When you say "Back to utility bypass" would that be in my Axpert option 12: "Setting voltage point back to utility."

 

If either of you can explain the difference between options 12 and 29, or point me to a source, that might be helpful. I do understand option 12 and often used and changed it with the old battery. I don't really understand option 29 and what it does.

12. Setting voltage point back to utility

29 Low DC cut-off voltage:

 

Thanks again for your help.

Option 12 is for a specific level to stop discharging the battery and go back to the grid(bypass) . During a power outing there is no grid to go to so discharge will continue until you reach setting 29 where the inverter switches off. This level can be a bit above the BMS cut out as per the battery specs.

 

8 hours ago, Green Power said:

Are you talking about in my Axpert option 29 Low DC cut-off voltage:? And reduce it from current level of 47V - is there any safe limit here - perhaps 44V, 42V or 40V under which I should not go?

Yes, setting 29.

But I didn't realise that your BMS would let your battery go to such low voltages. So I would not go below 46V, which is just over 3.06VPC. That forces a minimum of 48.0V for back to utility, which is a reasonable point for that. I use much the same voltage myself. Then you can still increase setting 12 above 48V if you want to keep your battery SoC high for coming load shedding. 

16 hours ago, Scorp007 said:

Option 12 is for a specific level to stop discharging the battery and go back to the grid(bypass) . During a power outing there is no grid to go to so discharge will continue until you reach setting 29 where the inverter switches off. This level can be a bit above the BMS cut out as per the battery specs.

 

OK, thanks. That seems clear but just to be sure....

So option 12 is saying "once this voltage is reached, changed from battery to grid provided that grid is available, otherwise continue with battery".

Whereas option 29 is in effect saying "once this voltage is reached, stop using battery even if there is no grid and the system will shut down".

That would mean that if there was a functioning grid connection option 29 would be irrelevant, and never used (assuming it's set lower voltage than option 12).

And when you (Coulomb) say "I would not go below 46V" you are in effect saying it's better to have a power outage than go below 46V. Although I do understand that once you reach 46V you are pretty close to a power outage anyway.

Let me know if any of the above is not correct.

I just changed option 29 from 47V to 46V and you were correct, the error message went away, great knowledge! The battery is currently half full or less so I'm guessing that message is gone for good, or will appear far less now.

I am still going to write to Jeff at Pylontech since he advised me of 47V to see if he is OK with 46V. I suspect he will be. I can't imagine it makes much difference. In the manual it says "When the battery discharges to 44.5V or less, battery protection will turn on." Does that suggest having option 12 maybe even at something like 45.0V or even 44.6V - giving you two chances to protect the battery - one from the inverter, and one from the battery itself? However I will leave it at 46V Coulomb for now unless you or Jeff says otherwise.

I am not sure if the battery voltages are displayed correctly on my inverter. A quick google of the relationship between voltage and state of charge for lithium batteries suggests that for much of the battery range (excluding low charge and 100%) the voltage should be around 52V-57V (sources differ a bit) whereas mine shows a battery voltage of about 49V or between 49V and 50V on the inverter display - for a state of charge of half or above half. Does that seem normal? Maybe I'm getting confused between float, absorption or other type of voltages? I don't have any meters to measure it, although my friend has some and lends them to me or comes over occasionally.

I suppose I could also set option 12 to 49V on a rainy or windy day (we often have power cuts in those days) especially if the battery is already depleted to half by the evening. And that would cause a switch to grid and if the power cut does happen then it would switch back to the battery power that has been kept in reserve.

Pylontech already replied to my email about reducing option 29 low DC cut-off voltage and said:

"You can try to set low voltage cut-off at 46V (no less than this value pls), but in this case I'm afraid you cannot set your batteries in idle for a long time. Otherwise it maybe over discharged since the inverter power is also supplied from the batteries."

EDIT: I asked the contact at Pylontech whether by long time he means days, weeks or months and he replied "A long time means around 10 hours. We need to consider the most critical conditions and make sure the batteries will be fine in this condition."

 

Edited March 2, 20223 yr by Green Power

Taking all what is said it seems 46V is what you should aim for. We know your inverter is know for not always measuring true values. Thus min as in inverter shut down set at 46V gives some margin to the absolute min of 44.5V.

The reason why you get a range of values provided for 48V lithium is Pylontech use 15 cells while most others use 16 cells. This then give you about 3V lower on the discharged side.

The 46V is then about in line with the value @Coulomb

mentioned. I have found that my Axpert would at times display the same Watt value and VA for inductive loads which is wrong. Just accept it.

3 hours ago, Green Power said:

I am still going to write to Jeff at Pylontech since he advised me of 47V to see if he is OK with 46V. I suspect he will be. I can't imagine it makes much difference. In the manual it says "When the battery discharges to 44.5V or less, battery protection will turn on." Does that suggest having option 12 maybe even at something like 45.0V or even 44.6V - giving you two chances to protect the battery - one from the inverter, and one from the battery itself? However I will leave it at 46V Coulomb for now unless you or Jeff says otherwise.

I am not sure if the battery voltages are displayed correctly on my inverter. A quick google of the relationship between voltage and state of charge for lithium batteries suggests that for much of the battery range (excluding low charge and 100%) the voltage should be around 52V-57V (sources differ a bit) whereas mine shows a battery voltage of about 49V or between 49V and 50V on the inverter display - for a state of charge of half or above half. Does that seem normal? Maybe I'm getting confused between float, absorption or other type of voltages? I don't have any meters to measure it, although my friend has some and lends them to me or comes over occasionally.

The difference between settings 12 and 29 has been well explained, so I don't have to repeat it. However you must consider this: BMS and inverters have each their own independent measuring systems. Those have naturally their inherent measuring inaccuracy, same as multimeters have. The range of their inaccuracy may be 0.5 to 1V. The display of more than 3 digits therefor is nonsense if already the third digit is doubtful. For you that means that setting of 29 just 0.1V above the value stated for your BMS cutout is most likely not gonna work even if your logic is correct. I suggest to take a margin of at least 1V.

Another concern is that battery voltage is also strongly dependent on battery current due to battery inherent resistance. In particular the discharge current lowers that voltage, the so called kettle effect. That means that under heavy load the battery voltage will reach the limits of settings 12 and 29 earlier than with little load.

Edited March 2, 20223 yr by Beat

Just to add what @Beat

Just explained around discharge voltage the same applied when you say charge the batteries from grid or PV. During this phase the reading will be about the same margin higher. Should there be cloud the voltage will quickly drop by 0.3 or more.

I still like these cheap meters($2 or less)where you can see the voltage by just passing the inverter.

 

 

Edited March 2, 20223 yr by Scorp007

Yes, well argued both of you, so I won't set 44.6V or 45V for the reasons you gave, makes perfect sense. I should have thought of that.

Another question about the settings for either of you or anyone else (and @Coulomb might be able to help as well): a couple of times I've noticed the inverter/the system using grid electricity for all the load, even though the load was less than the available solar power. I left it for a while and in both cases it was still using grid for the load even a half hour or an hour later when I came back to check.

It may or may not have made sense to switch to grid in the first place. Perhaps there was a very high load for a short time which reduced the voltage to 48V or below and passed to grid as specified in option 12 setting, or some other reason. But surely it shouldn't be running on grid indefinitely like that.

What I did eventually in both cases was changed option 13 (setting voltage point back to battery mode) to 50V instead of 51V, and it then immediately switched back to using solar instead of grid. However in both cases I then set it back to 51V once it was running normally again.

Would it be OK if I always set option 13 at 50V rather than 51V?

 

Edited March 2, 20223 yr by Green Power

4 hours ago, Green Power said:

What I did eventually in both cases was changed option 13 (setting voltage point back to battery mode) to 50V instead of 51V, and it then immediately switched back to using solar instead of grid. However in both cases I then set it back to 51V once it was running normally again.

Would it be OK if I always set option 13 at 50V rather than 51V?

Yes, you finally found the way it is working. There are some factors to consider. With my setting 16 to CSO "charge priority solar first" the charging current from PV in the morning is normally low, it will take long to reach the 13 "back to battery mode" level. Therefor I set 13 to 49V during daylight. On the other hand with setting utility charge current (11) to 1/10 of battery Ah, during absence of PV input and after having reached setting 12 limit it will recharge reasonably fast from utility. Therefor I set 13 to 50V during night. I found these settings convenient for the way I want to run the system, that is use solar energy as much as possible.

@Green Power

Without knowing what the voltage was when grid was used while a lot of PV available or if the load was high it all is just guessing as to why the grid was used.

Settings affecting it 01  12  13  16.

When you get it again try to change 16 to charge from PV only and see if it changes.

For setting 16, I use OSO, only solar, otherwise grid energy seems to be  used needlessly (from experience with previous lead acid battery). I may manually change that on some cloudy days in mid winter or stormy/rainy/windy days with the possibility of power cuts. However it is OSO for now (and was when the issue occurred), and it will probably be on OSO 95% of the time in the future as well.

I just rechecked Coulomb's January 16th post in the thread "Are Pylontech UP5000 and US3000C compatible with Axpert MKS II 5kW?" and it did recommend 51V for option 13 which is why I set it but now I check again it also says 50V OK for less utility use. And Coulomb says these settings have been agreed with some other users of the forum.

So I just changed option 13 to 50V.

Beat, my main two goals are to avoid power outages of any sort and use minimal grid. I am also interested in extending battery life, but that is a bit below the other two goals. Do you have to manually change from 49V to 50V every day or is programmed to do that in the inverter with a timer? Can settings 12 and 13 be 48V and 49V - 1V apart - or might that cause the inverter to constantly flick between solar and grid? What do you have setting 12 on when you have setting 13 at 49V?

Edited March 3, 20223 yr by Green Power