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"Floating" Pylontechs?


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25 minutes ago, Youda said:

Why 52.5V? Because the internal balancers kick-in at 3.480V per cell which translates to 52.2V. The 0.3V difference is the space that allows balancers to operate safely.
If you charge to 52V only (3.466V per cell) then the balancers won't start and the pack will become ubalanced over a long period of time.
If you will charge to 53.5V, then the balancers will have to burn much more energy and the temperature of the pack will rise. But still okay.
If you will charge to 53.6V, then the internal overvoltage protection will throw an error and the battery will disconnect itself.

A bit too much messing around with comma nuthinks of a volt for my liking.

Calibration drift between equipment and cable losses under varying currents would seem to make this unworkable.

Edited by phil.g00
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@Ironman i'm with on this one. I stuck between this to where i need to the-side because i want to go lithium and this will be Pylontech, but i'm running Microcare MPPT's and they can only go between 13.2v to 14.5v x 4 for Float and 13.5 and 16v x 4 Boost voltage. What will happen if you charge the Pylontech at 54v because the min Boost Voltage of the Microcare mppt is 54V . Float will be ok  because min of Float on the MPPT is 52.8v.

The question is what is the max and safe charge parameters of the Pylontech Lithium batteries. Some brands like BlueNova max is 56.2v. 

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5 minutes ago, Gerlach said:

What will happen if you charge the Pylontech at 54v because the min Boost Voltage of the Microcare mppt is 54V

Don't do it.
The internal MOSFET in the Pylontech will start to throttle the charging current once the voltage will be too high in order to protect the battery.Balencers will burn all the excessive energy and produce heat. But since microcare won't stop charging, the battery will disconnect.

 

5 minutes ago, Gerlach said:

The question is what is the max and safe charge parameters of the Pylontech Lithium batteries.

53.5V

Edited by Youda
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10 minutes ago, phil.g00 said:

A bit too much messing around with comma nuthinks of a volt for my liking.

Just set 52.5V and you're okay.

I wanted to explain what's behind all these numbers therefore it looks a bit complicated.
BTW, speaking of "." vs "," I have "." on my numeric keypad, therefore I stick to it.

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50 minutes ago, Youda said:

By the way, these spikes of power are the reason why in the past you've experienced 100% SOC even when charging to 52V only.

Previously his Pylons were charged at 53.2 volts. Last weekend his inverter was replaced and reconfigured using the new 52volt charge setting indicated on the most recent Victron document. Since then the Pylons never reached 100% anymore. 

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26 minutes ago, phil.g00 said:

Calibration drift between equipment and cable losses under varying currents would seem to make this unworkable.

Not really:

- You can set your CC voltage anywhere between 52.5V and 53.5V The lower value is better, as I explained above. This gives you nice window to calibrate the C.C. according to the accuracy of your charger, resistance of the cables etc.

- The BMS measures the voltages directly on the internal side of the battery terminals of each brick and then directly on each cell. Therefore a voltage drop on the battery cable, caused by a huge load, does not mess with the measurements.

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2 minutes ago, Youda said:

The BMS measures the voltages directly on the internal side of the battery terminals of each brick and then directly on each cell. Therefore a voltage drop on the battery cable, caused by a huge load, does not mess with the measurements.

If it is purely a feedback control loop that says raise or lower your output to the CC's?

That does alleviate cable losses and cross-equipment calibration drift.

However what about the BMS's own calibration drift?

When I use a voltmeter to check if a circuit is live I don't care about calibration, if it says 235vac or 225Vac, I have my answer.

However, if these battery BMS measuring systems have to be that accurate to distinguish that 53.5V is OK and 53.6V needs the OV protection to kick in, in my experience of test equipment, they'll need regular calibration.

 

 

 

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So I changed the charging settings to from Absorption 52V/Float 51V to Absorption 52.5V/Float 52V about 10 minutes ago. Uploaded new settings to MP II, downloaded again to confirm that the new settings are active.    The remote console is still showing 52V - with no increase in charging current?

49812038_Annotation2019-11-17114115.thumb.png.f282307d4c04a78d5fe8d18f9ff4c009.png

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2 hours ago, Youda said:

Why 52.5V? Because the internal balancers kick-in at 3.480V per cell which translates to 52.2V.

Hi Youda

How do you know this?  Did you get inside information, or did you take a Pylontech apart? It seems like nobody else seems to really know the inside of these batteries.

Also - battery balancing is not an instant thing?  As in - the balancers basically waste energy as heat by drawing current from cells that are higher than other cells - and this will take some time to balance?  So how long should it be kept at a "balancing" voltage?  

 

Edited by Ironman
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And now this happens:  The Venus display of the Pylontech battery shows 99%:

1304927962_Annotation2019-11-17115533.png.f00bb2e9f17a350ec17918b48676031d.png

While the overview graphic animation shows the battery at 83%:

1945651293_Annotation2019-11-17115532.png.20b3acbaa33d544b91e5a4e610bc2b08.png

The voltage is still 52.0V.

Maybe the battery voltage "spiked" to 52.5V quickly, and now the battery is in float, which is still at 52V. But then why does the Venus state the mode as "absorption"?

 

 

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5 hours ago, Ironman said:

Hi Youda

How do you know this?  Did you get inside information, or did you take a Pylontech apart? It seems like nobody else seems to really know the inside of these batteries.

Also - battery balancing is not an instant thing?  As in - the balancers basically waste energy as heat by drawing current from cells that are higher than other cells - and this will take some time to balance?  So how long should it be kept at a "balancing" voltage?  

 

Once you connect to the battery via CLI, you can get a LOT of information on how it works internally. For example, a portion of this BMS is built around Texas Instruments bq34z100 chip, which is a nice piece of HW, I would say:

https://www.ti.com/lit/ds/symlink/bq34z100.pdf
https://www.ti.com/lit/ug/sluu904a/sluu904a.pdf

 

5 hours ago, Ironman said:

Also - battery balancing is not an instant thing?  As in - the balancers basically waste energy as heat by drawing current from cells that are higher than other cells - and this will take some time to balance?  So how long should it be kept at a "balancing" voltage?  

One have to ensure that all the cells reached the balancing voltage, in order to be equalized. Once the voltage of the Pylontech battery reaches 52.5V all the balancers should be working already. So you don't need to keep that voltage up for longer than couple of minutes normally. And that is what inverters usually do. AFAIK, no inverter stops supplying current immediatelly when he reaches to the C.V. voltage, but he wants to see steady C.V. voltage for a minute or two, at least.

Some smart inverters with BMS communication, might stop charging as soon as BMS would report 100% SOC. But since SOC is being calculated (estimated) by amphours, it's never 100% accurate. Therefore Pylontech BMS stops reporting SOC increments at roughly 88% despite the fact that bq34z100 is still counting amphours. Once all the cells reach balancing voltage, the Pylontech BMS starts to simulate a gradual increase of SOC from 88 to 100%.

image.thumb.png.dd9d0be8ba2dd91ac5cd2e915f670526.png

With some other, not-so-smart batteries and their BMS'es you will experience a similar step at the end of the charging, but it will be just one big clear jump, no smooth increments. Basically all of this is just a reset of BMS AmpHours counter.  In short, when the cells reach their balancing voltage too quickly, most BMS'es will wait for 2 minutes and then reset their AmpHour counter and update the battery SOC value directly to 100% even if AmpHours counter did not reached the nominal capacity yet. For most of the LFP batteries, it jumps from 90 to 100% and it's okay.

But if the above jump is huge, like from 50% to 100%, it actually means that the battery capacity is much lower (degraded) than what BMS was programmed for. Or, that AmpHours meter is seriously uncalibrated.

 

So, charge Pylontech to 52.5V, maybe to 52.6V or so,  watch for jumps and you will be okay :)

 

Edited by Youda
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my Pylontech batteries are currently communicating with the axpert king inverter and it uses a charge and float voltage of 53.2V which cannot be altered unless one disables the PLY 05 setting and go for the USER option. I hope this is not an issue going by your recommended 52.5V?

for the Jump, I have noticed that my batteries usually ideals at 89% SOC for some hours before it gradually moves to 100% within 5 minutes or less

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Yes, this is a well-know behavior of Axpert when set to 05 PYL. Don't worry, the balancers will produce a bit more heat, but AFAIK nobody with Axpert set to 05 PYL experienced overvoltage alarm yet.

On the other hand, I've seen cases where Axpert (with enabled RS485 communication to the Pylontech BMS) switched back to the grid too early during a discharge - once the battery was at 48V. So, just test your setup, how deep it will allow you to discharge the batteries. It should work till 45V or 10% SOC, whatever will come first. Then the Axpert should switch to grid.

BTW: If you will force the Axpert to continue discharging the batteries, they will go into "sleep mode" once they will get down to 8% SOC and will be kept there for at least 10mins.

 

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11 hours ago, Ironman said:

 Agreed.  According to the Pylontech sheet, the voltage can be higher. Thanks. 

I don't know how this happened exactly, how this was missed (the 52V decision was pretty much mine... believe it or not... but I did discuss it with someone at Pylontech). Now that I see the 52.5V number on the spec sheet, I think that is enough justification to raise it a bit. 52.5V is exactly 3.5V per cell. It also leaves a goo 0.1V per cell room at the top to avoid overvoltage issues.

10 hours ago, Youda said:

Because the internal balancers kick-in at 3.480V per cell which translates to 52.2V.

Again, the info I have is different. I was told the balancers kick in as low as 51.8V.

In any case @Ironman, I had forgotten about this today (I'm sorry, Sundays are always a bit busy with Church and the family braai), but I note that something happened at your site today. Around 13:30 the charge current limit was lowered and the SOC suddenly started climbing, almost as if some imbalance was finally resolved? At least it proves that 52V is sufficient... although perhaps not optimal.

Still, I logged into your system and raised the charge voltage. It will now charge to 52.5V.

Remember that we have to do it again if a new firmware is loaded (I see you are on a candidate release). But for now, I would like to see what it does over the coming days.

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17 minutes ago, plonkster said:

Around 13:30 the charge current limit was lowered and the SOC suddenly started climbing, almost as if some imbalance was finally resolved?

mmm I never saw a SOC higher than 84% today.

1673856488_Annotation2019-11-17204057.thumb.png.1428b8f845658b14154717e9c39679cf.png

And even now there is a large difference in the graphic display of the Venus, and the Pylontech data:

5192575_Annotation2019-11-17204401.png.27d3272d08715f3e08535993aa4e2639.png

1102118761_Annotation2019-11-17204339.png.496c9dee1c390365a644e1b65f06a791.png

The one shows the SOC at 68% and the other at 84%...

Something really weird happening here.

 

 

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Oh, and about "Absorption" and "Float". Ignore that. There is no such thing for LFP batteries. There is only a single charge voltage, though some designs may lower the charge voltage slightly towards the end of charge. "Float" is a lead acid thing.

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10 hours ago, Youda said:

Don't do it.
The internal MOSFET in the Pylontech will start to throttle the charging current once the voltage will be too high in order to protect the battery.Balencers will burn all the excessive energy and produce heat. But since microcare won't stop charging, the battery will disconnect.

 

53.5V

Thanks @Youda

So I guess I need to call Microcare tomorrow , and there service isn't not some of the best. I need to send my MPPT's of to them that they can upgrade the  chips for lover volts settings. 

Edited by Gerlach
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3 minutes ago, Ironman said:

mmm I never saw a SOC higher than 84% today.

I'm sorry. I was looking at old data from 23 October (as part of the support case for swapping the inverter).

Now that I'm looking at today's data, I see what you mean:

Selection_387.thumb.png.1891d531be4365c35629e4352293b3e5.png

Right. Let's see what it does tomorrow. If it resolves, your system becomes THE argument for bumping it.

Let me just explain why we lowered it in the first place. The Pylontechs give you very VERY little space to work with. Charge voltage is 53.2V, but it switches off with no grace period or margin when you hit 54V. So only 0.8V. In that 0.8V we have to fit in any calibration errors, cable losses, and the 0.4V overvoltage that is used to feed excess PV into the grid.

Long story short, 0.8V is way too small a margin. Additionally, at 3.55V per cell, the battery is very prone to voltage swings resulting in overvoltage conditions. The only solution was to lower the charge voltage. So when deciding on the voltage, the question was simple: What's the lowest we can go while still 1) getting to almost 100% SoC, 2) going high enough to activate the balancers. I was told 51.8V is high enough.

The fact that the PTs are 15s batteries with a tight limit of 3.6V per cell... that is really limiting. In a Victron battery the limit is 3.75V per cell (perfectly safe for an LFP). A high voltage disconnect of 56V would have been perfectly doable and would result in much more stable systems.

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20 minutes ago, plonkster said:

Let me just explain why we lowered it in the first place.

Let me also add that it isn't really the DC-tied systems that's causing issues. It's more common in AC-tied systems, where the Multi charges the battery using energy from a PV-inverter. Regulating that system, with a highly charged LFP battery and only 0.8V margin... it works for the most part, but it is just a bit too tight.

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9 hours ago, plonkster said:

Oh, and about "Absorption" and "Float". Ignore that. There is no such thing for LFP batteries... "Float" is a lead acid thing.

It's true that LFP batteries don't charge during "float", and self discharge is very low, but don't you agree that their lifespan will improve by not holding a very high cell voltage after the battery is full?

So why not take advantage of the "float" stage, and reduce the voltage to say 52 V for 15S?

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51 minutes ago, Coulomb said:

their lifespan will improve by not holding a very high cell voltage

Yes. Which is another reason for lowering the charge voltage 🙂

I don't disagree about lowering the charge voltage. I'm pointing out the terminology is not applicable to LFP.

The very best managed LFPs do this automatically in their BMS. They lower the charge voltage slightly as the SOC reaches 100%. The best I have seen was the Discover AES battery. Man.... that is a beast of a battery. It's a pity it's on the expensive side.

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@Ironman, it appears you have sent my on a wild goose chase.

Your batteries are reporting 99% SoC. You had the Multi selected as "battery monitor" instead of leaving it on Auto or selecting the Pylontech as battery monitor.

It was staring me right in the face, as you also have the charts right below each other:

Selection_388.thumb.png.2065a1e7afb170655d9d27e86ffa6ec8.png

So there was nothing wrong, the configuration was just bad.

Nevertheless, let's leave the 52.5V voltage change in place and see what it does. Might as well.

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Thanks for the fix.  I did ask two times earlier in this thread why the graphic representation's battery level differed from the Pylontech's indicated level.

🤦‍♂️

For anybody that has this issue in future: the setting is under system setup:

399766261_Screenshotfrom2019-11-1809-35-35.png.0a320bf12ca224ab6e99fca5a71a7592.png

Mine was set to Multiplus - and somehow the multiplus has a completely different SOC level.

 

Edited by Ironman
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