I've been observing a behavior of my inverter for some time. I used to have 2xus5000 and now 3xus5000, which should in principle be capable of instant 300A discharging. The battery is protected with an 167A MPR fuse, which has not burned yet. Anyway, the inverted is capable of 120A discharge. The inverter should be able to handle 5.6kW constant and higher instant. However, if two large appliances overlap (HVAC and microwave in case below) the inverter instantly switches to grid power (always connected) which continues to be used for a while until the consumption settles down. In the event below the HVAC was on and the microwave was switched on. I have the same behavior with the dishwasher when the water pump kicks in, but in that event I would believe the surge of the pump motor is non negligeable.

At the time of the event, the battery was nearly full (96%). My settings are SOL, SBU, PYL, Back to grid 47V, Back to discharge 49V. 

Am I putting to much load on the inverter in case of these events? If I water the lawn, and there are no other big loads, the water pump starts and stops, this behavior does not take place. If events like these would be seldom, there is no issue, the grid consumption would be small anyway, however I do notice that the inverter sometimes remains with the grid side connected. I am not feeding to the grid. 

It feels like the instant power demand is too high and the battery BMS denies it, so the inverter takes some from the grid, while still taking some from the battery (15-20A). I have no proof in this, just observation.

If I break the AC-in, the inverter "survives" such an event without an issue. It compensates the load from the battery at higher discharge current, 40-50A, depending on the case. After the big load demand has passed, the inverter continues to make a clicking sound, like that of a relay, like it's trying to restart one source. However, this seems to happen in dusk conditions (with low PV input) even if AC-in is connected.

The inverter has the capacitor mod implemented (display artifacts solved) and it's in service for almost 1y now, 3.2MWh have passed from PV-in. 
 

Maybe something else worth mentioning: if I disconnect the battery communication cable, there is the 61 warning alternating with the date display on the LCD screen of the inverter. With each change of the bottom line, one clicking sound takes place. Could it be a deffective RJ45 cable, hence the inverter losing communication with the BMS in such high load scenarios? The cable is UTP5 and it passes along AC-in/out cables. I know these HF inverters are notorius to induct in the PV side at least.

 

 

Edited October 2, 20232 yr by onobeka

If your microwave oven is not an inverter type, then it has a large 50Hz transformer which has a substantial magnetising current. So at switch on, depending on where the AC sine wave is in its cycle, it can be similar to a motor's start-up in-rush current. So there could be an instantaneous overload for a fraction of a second if there is a background load.

The other thing is that factory firmware doesn't take into consideration the internal resistance of the battery. So a sudden high load can cause the uncompensated battery voltage to trigger a change to bypass mode. Factory firmware also stays in bypass mode for at least 10 minutes, which I feel is far too long. Unfortunately, patched firmware that overcomes this problem to a large degree is not available for your model. 

Edited October 3, 20232 yr by Coulomb

Thanks @Coulomb! That makes sense.

Maybe something that I should have mentioned as well, the battery is connected to a busbar, then the inverter. On the busbar there is an additional MPPT that has no communication with the battery. It has a small number of panels, if that would matter, compared to the inverter. That MPPT has sun in the evening, while the panels that are connected to the inverter tend to have shadows, so the MPPT is feeding both the battery (as much as the BMS would accept) and the inverter, appearing as "battery" to it, however without any communication between the two units. Just 30 mins ago, I've noticed that the inverter seems to loose connection to the battery and regain it every 5-10s. This happens only in the evening.

 

This takes place now. The battery state is read by Solar Assistant directly from the battery (not through the inverter).

OTOH, the master Pylontech is new, 2cycles today and so far I am thinking of sending it back. It had from new quite a cell imbalance, when first being full, one cell went to 3.64V, while one stayed at 3.39V. The BMS temperature was high (47C). I understood this is normal for a brand new module. The imbalance dropped today to less than 0.2%. 

Edited October 3, 20232 yr by onobeka

I think I've found the reason for this behavior. For some reason, the back to grid voltage is changed to 51.2V (higher than back to battery voltage). Why this happens, I have no idea.

I've restored the setting to original 47V. Also maximum charge current 60A seems arbitrary ... it was 80A.

The inverter has internet connection and it's communicating with the cloud. I use SolarPower or WatchPower to check it from time to time, but normally I only use Solar Assitant (for which I have not activated the power settings).

Sorry for the many posts, this will be the last one, I'll wait for some replies. While searching I've found this.

It may be that I've had the two settings at 48V (back to grid) and 49V (back to discharge). Unfortunately I cannot use .5V settings. Now they are 47V, 49V and cutoff 45V.

 

Maybe something that I should have mentioned as well, the battery is connected to a busbar, then the inverter. On the busbar there is an additional MPPT that has no communication with the battery... 

I have no experience with batteries that have a built-in factory BMS. It seems to me that there would be potential for the BMS to get confused by the additional MPPT. But my guess is that there should be no problem as long as the additional MPPT bulk battery voltage setting is low compared to what the BMS wants. It can be tricky because you can't know if there happens to be a big imbalance right now and the BMS wants little to no charging. Perhaps with the new master battery module needing a lot of balancing, you might need to reduce that voltage or even disconnect the additional MPPT for a few days. I guess you will have to monitor the situation and try various things. 

Thank you @Coulomb. I will check today again, without much changes, I will first monitor for that ghostly setting of "back to discharge". I suspect it could be the issue here. For some reason it was arbitrary set to 51.2V. In the late afternoon, that battery voltage will will occur frequently, oscillating between charging, idling and discharging (since the battery was full) - hence the clicking relay sound. Looking back at the graphs of yesterday, the battery voltage fluctuates a lot around that 51.2V. This value is impossible to set either in the inverter or through remote apps, as the inverter will only accept integer values, not even half steps between.

My suspicion now goes to the fact that I've set the values to 47V and 48V when I've added the third module (last week), thinking with the extra battery I can lower them a bit. I do not know if this inverter model has to have that 2V difference between the values. 😕. Now, I am back to 47V and 49V.

Edited October 4, 20232 yr by onobeka

 

 😕. Now, I am back to 47V and 49V.

That is an ideal setting for 15 cell LFP battery. However in view of the looming load shedding and in order to always have enough in the batteries to overcome 4 hours of black out, I set it to 48V and 50V. Bulk charge 52V, floating charge 51.5V. Equalizing disabled.

I don't think that the additional MPPT could create any problems.

Thanks @Beat! I do not have that many options when using PYL, actually both Bulk and Float are set automatically (and not changeable) to 53.2V. I can do that if I go in USE mode.

I've disconnected the second MPPT (no panels voltage). 

The battery reached 100% one hour ago, it started then with the clicking sound temporary battery disconnection. The mysterious setting of 51.2V is back :(. All other settings are unaffected. I've connected BatteryView to see if I can find some errors, everything looks in order. No faults, no errors ... and I do not have the disconnection. 

I will check to see if Solar Assistant could be causing this by disconnecting the battery console cable. So frustrating!

 

 I do not have that many options when using PYL, actually both Bulk and Float are set automatically (and not changeable) to 53.2V. I can do that if I go in USE mode.

I strongly recommend to use "User defined" battery in setting 05. That should give you full control over battery charge management. I do not have BMS to inverter coms.

Thanks! I did not want to lose the BMS communication with the inverter so far, one of the reasons for paying extra for Pylontech instead of a DIY battery. Proably that's next.

The 51.2V did not reoccur without the Solar Assistant connection to the battery. Could it be that the communication between Solar Assistant and the battery can cause the battery to disconnect from the inverter and somehow trigger the change of back to discharge to 51.2V? Solar assistant is connected on the Console port of the Pylontech.

 

. Could it be that the communication between Solar Assistant and the battery can cause the battery to disconnect from the inverter and somehow trigger the change of back to discharge to 51.2V? Solar assistant is connected on the Console port of the Pylontech.

You are not the only one in that forum that scratches his head about BMS influences in inverter behavior. I do not trust BMS's much. I observe BMS consistently reporting 100% SoC while the batteries have not yet reached bulk- or floating charge voltage and continue charging. Obviously they do not take internal losses in account. Therefor I refuse to connect BMS with the inverters. The correct settings in the inverters according to the battery manufacturers specs assures the best charge management.

 

 Therefor I refuse to connect BMS with the inverters. The correct settings in the inverters according to the battery manufacturers specs assures the best charge management.

How do you manage a overshoot if a big load is suddenly removed from the inverter that could cause the voltage to spike for a short period. This might be recorded and affect a claim should the battery fail? 

 

 The correct settings in the inverters according to the battery manufacturers specs assures the best charge management.

The thing is that with Pylontech, once connected in PYL mode, the settings are as indicated by Pylontech (on paper they say charge voltage 52.5-53.5V for us5000).

If the battery type is set to PYL and the BMS is connected to the inverter, both float and bulk are set to 53.2V and I cannot change them in the inverter. The battery reaches 100% at arround 52V (sometimes 51.5V), however there will be several topups during the day in the PYL mode, dictated by the BMS, so the battery will reach eventually 53.2V once a day for a short period.

So, the battery manufacturer seems to suggest that 3.54V per cell is the correct value, while the community generally recommends to not exceed 3.45V per cell. It's true that in general for Lifepo4 cells, above 3.4V there is only voltage, not much current so no capacity. Charging with PYL mode, 90-100% SoC is reached in a matter of minutes, which indicates that their cells also comply to that. 

 

23 hours ago, Scorp007 said:

How do you manage a overshoot if a big load is suddenly removed from the inverter that could cause the voltage to spike for a short period. This might be recorded and affect a claim should the battery fail? 

I do not have to manage such, the inverter takes care of it. There is no way of any kind of "overshoot" of battery voltage when a heavy load is removed, since there is no inertia involved. Besides, I cannot imagine how a BMS could react to this.

19 hours ago, onobeka said:

The thing is that with Pylontech, once connected in PYL mode, the settings are as indicated by Pylontech (on paper they say charge voltage 52.5-53.5V for us5000).

If the battery type is set to PYL and the BMS is connected to the inverter, both float and bulk are set to 53.2V and I cannot change them in the inverter. The battery reaches 100% at arround 52V (sometimes 51.5V), however there will be several topups during the day in the PYL mode, dictated by the BMS, so the battery will reach eventually 53.2V once a day for a short period.

So, the battery manufacturer seems to suggest that 3.54V per cell is the correct value, while the community generally recommends to not exceed 3.45V per cell. It's true that in general for Lifepo4 cells, above 3.4V there is only voltage, not much current so no capacity. Charging with PYL mode, 90-100% SoC is reached in a matter of minutes, which indicates that their cells also comply to that.

I'm under the sad impression that Pylontech deliberately manages its batteries such as to reduce their live expectancy.

That could be indeed the case.

I've been running in user mode for 2days now and I did not get the behavior I was complaining about initially, no 51.2 setting either.

I've set Bulk to 52V and Float to 51.5V. The batteries are not charging anymore above 96% and I think no balancing takes place either. Elsewhere on this thread I've read that the balancing of Pylontech happens above 3.48V.

Also, my inverter stops charging at float voltage. I thought that first a battery will reach the Bulk voltage setting briefly and then float.

2 hours ago, onobeka said:

That could be indeed the case.

I've been running in user mode for 2days now and I did not get the behavior I was complaining about initially, no 51.2 setting either.

I've set Bulk to 52V and Float to 51.5V. The batteries are not charging anymore above 96% and I think no balancing takes place either. Elsewhere on this thread I've read that the balancing of Pylontech happens above 3.48V.

Also, my inverter stops charging at float voltage. I thought that first a battery will reach the Bulk voltage setting briefly and then float.

As I mentioned before I would not trust the BMS SoC reporting too much. Mine always reports 100% SoC while floating voltage is not yet reached. It looks like yours does the opposite. However it's the chemistry of the battery that determines the battery's full charge voltage. If the BMS does not balance at this voltage, then the BMS programming is lousy, to say the least. Considering all the above, I would think twice before buying Pylontech.

Yes, I would also reconsider having this experience, but it's too late now :).

Yet, maybe my question was not well understood. Normally in the charging of the battery should first reach Bulk, stay there for a while and then get down to floating and maintaining of that voltage.

However, in the case of my inverter, the battery only gets to to floating voltage and NEVER to Bulk. So, if I want equalization to take place, I need to set floating to 52.2V (3.48V per cell) and either set the Bulk to the same value or above. I think this is a bug of the inverter, not the pylontech batteries.

I am in USE mode now (not PYL). So, even if the communication cable between the BMS and the inverter is there, the inverter does not use any values from the BMS, even the state of charge is wrong. The inverter thinks (based on voltage) that the battery is at 64% while the battery is fully charged.

4 hours ago, Beat said:

I do not have to manage such, the inverter takes care of it. There is no way of any kind of "overshoot" of battery voltage when a heavy load is removed, since there is no inertia involved. Besides, I cannot imagine how a BMS could react to this.

Why I asked is some MPPTs can take up to 2 seconds to react to reduce the output they get from the panels. 

I find my lithiums have a definitive battery voltage rise the moment a over say 800W load is removed. 

19 hours ago, Scorp007 said:

Why I asked is some MPPTs can take up to 2 seconds to react to reduce the output they get from the panels. 

I find my lithiums have a definitive battery voltage rise the moment a over say 800W load is removed. 

That may well be. But in no way that voltage rise could be of any problem. Unless you have such a small battery capacity not matched to the inverter and PV sizes, that cannot take such a surge. My inverters are programmed such as to lead all available current from the PVs to the batteries (400Ah). I don't want to lose any energy. They limit the current only when batteries have reached floating voltage level.

On 2023/10/06 at 8:30 PM, onobeka said:

Also, my inverter stops charging at float voltage.

That sounds like the premature float bug to me. Is this on solar charging, or utility charging, or both?

On 2023/10/06 at 8:30 PM, onobeka said:

I thought that first a battery will reach the Bulk voltage setting briefly and then float.

It should reach the bulk voltage, and stay there until the charge current drops to a low level; that's the absorb stage. A bit of a misnomer for lithium batteries, but it's still very important. Without that, the battery won't be reaching 100% SoC.

When you set the battery type to USE, then the battery's BMS is no longer in control, and it's all strictly voltage based.

22 hours ago, Scorp007 said:

Why I asked is some MPPTs can take up to 2 seconds to react to reduce the output they get from the panels. 

On Voltronic MPPTs, it can take tens of seconds to react, I suspect because of integral wind-up. It's frustrating to watch... ok, getting close, time to back off... ok, inverter, back off... BACK OFF! Clunk! Too late; the PV contactors have dropped out to save the battery from over-charging.

@Coulomb, thank you! Indeed I have been reading about the premature float bug! After more observation and changing settings I can absolutely confirm that the batteries will not reach bulk voltage, only float. So, I’ve raised the float to 52.2V which is 3.48V per cell because I’ve read that is where the ballancer kicks in action, and from my observation it’s true. A little lower voltage and the unballanced battery does not raise the BMS temperature at all. Maybe there are other ways to check that the ballancer is working. 
 

I guess there are no firmware upgrades for my model or … I do not know where to look for them.