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Pylon US2000B alarm again


Elbow

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8 minutes ago, Jaco de Jongh said:

For interest sake, is it the master? Had a call from a friend yesterday with the same issue. Stack of 5, master shows alarm even after resetting them. also US2000, installed in December.

Yep - all fine again when I turned it off and on.

i think there is some sort of log you can read on the console - I’ll go digging.

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3 minutes ago, DeepBass9 said:

So what happens when the alarm goes, does it disconnect the battery? 

Yes, it does.

The second battery was blinking its light and I think would have worked, but last time they both had an alarm.

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2 hours ago, DeepBass9 said:

I think I am glad I didn't go this route when I replaced my batteries with AGMs recently. Next time I'll go with Lithiums. The range of operating conditions seems quite narrow and I'm not sure they would take off grid abuse too well. 

I think the BMS does limit operation outside the parameters of the cells.  I don't have a problem with that especially where you have an inverter that can take the data feed from the BMS and respect what it asks for.

In principle that means that you can't kill your batteries.

Dumb batteries of course will let you do what you want and if it kills your batteries so be it.

In my opinion I didn't do anything to my batteries that should have triggered a fault, so I am interested to see what it is unhappy about since nuisance alarms where the battery goes offline aren't welcome.  My monitoring will need to make an alarm since otherwise it is quite possible I won't notice.

 

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I connected up the RS485 monitoring.

Here's what the two batteries are saying right now:

Master battery (address 2):
Send {
  "time":1551332544,
  "VoltageUpperLimit":53.25,
  "VoltageLowerLimit":47.0,
  "MaxChargeAmps":10.0,
  "MaxDischargeAmps":-25.0,
  "BatteryCycles":3,
  "BatteryVoltage":51.987,
  "BatteryAmps":0.0,
  "BatteryWatts":0.0,
  "BatterySOC":100.0, 
  "RemainingAh":50.0, 
  "RemainingWh":2497, 
  "MinutesToRun":9999, 
  "CellMaxVoltage":3.7, 
  "CellLowVoltage":3.05, 
  "CellUnderVoltage":2.9, 
  "cellVoltage0":3.461, 
  "cellVoltage1":3.463,
  "cellVoltage2":3.457,
  "cellVoltage3":3.456,
  "cellVoltage4":3.461,
  "cellVoltage5":3.448,
  "cellVoltage6":3.461,
  "cellVoltage7":3.463,
  "cellVoltage8":3.474,
  "cellVoltage9":3.473,
  "cellVoltage10":3.474,
  "cellVoltage11":3.474,
  "cellVoltage12":3.475,
  "cellVoltage13":3.474,
  "cellVoltage14":3.473,
  "highestCellVoltage":3.475,
  "lowestCellVoltage":3.448, 
  "cellImbalancePct":0.7, 
  "temp0":27.0,
  "temp1":25.0, 
  "temp2":25.0,
  "temp3":25.0,
  "temp4":25.0,
  "highestTemp":27.0, 
  "lowestTemp":25.0
}

Slave Battery (address 3):

Send { 
  "time":1551332476,
  "VoltageUpperLimit":53.25,
  "VoltageLowerLimit":47.0,
  "MaxChargeAmps":10.0,
  "MaxDischargeAmps":-25.0, 
  "BatteryCycles":3,
  "BatteryVoltage":52.012, 
  "BatteryAmps":0.0,
  "BatteryWatts":0.0, 
  "BatterySOC":100.0,
  "RemainingAh":50.0, 
  "RemainingWh":2497, 
  "MinutesToRun":9999,
  "CellMaxVoltage":3.7, 
  "CellLowVoltage":3.05,
  "CellUnderVoltage":2.9,
  "cellVoltage0":3.468, 
  "cellVoltage1":3.468, 
  "cellVoltage2":3.468, 
  "cellVoltage3":3.444, 
  "cellVoltage4":3.469,
  "cellVoltage5":3.47,
  "cellVoltage6":3.47,
  "cellVoltage7":3.47, 
  "cellVoltage8":3.468,
  "cellVoltage9":3.468,
  "cellVoltage10":3.469,
  "cellVoltage11":3.471,
  "cellVoltage12":3.469,
  "cellVoltage13":3.469,
  "cellVoltage14":3.471,
  "highestCellVoltage":3.471,
  "lowestCellVoltage":3.444,
  "cellImbalancePct":0.7,
  "temp0":27.0,
  "temp1":25.0, 
  "temp2":25.0,
  "temp3":25.0, 
  "temp4":25.0,
  "highestTemp":27.0,
  "lowestTemp":25.0
}

 

That's after floating them a long time at 52V.

The figures look healthy to me.   Cell voltages are well in range.  Balance is <1% out. Temps are fine.

I will look in the docs to see if I can find anything else I can query over the RS485 (Modbus?) interface.

I suppose the inverter may have misread the battery voltage and switched out of constant voltage.  I'll leave the monitoring on and see if I can capture another event.

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11 minutes ago, SolarNoob said:

Just my 2 cents but the cells are out of balance. I suggest you increase your float voltage to at least 53.2V as per the SOP supplied by voltronic for their inverters.

When the cells are properly balanced they are usually a few millivolts difference between the cells.

Thats my experience on my US2000B's

I suspect they balance a lot faster if you take the voltage higher. They should still balance at 52V, but probably just take much longer.

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18 hours ago, plonkster said:

I suspect they balance a lot faster if you take the voltage higher. They should still balance at 52V, but probably just take much longer.

Hi @plonkster,

My evidence is different.  (Though I haven't got that much data yet).

I've been running with a float voltage of 52v since 11th Feb.

In that time the battery wasn't discharged. The battery has been reporting a current flow of 0A (charger says about 0.4A is flowing.  BMV says 0.00A

Over that time the cell balance has got worse - when I was cycling the battery lightly - say 5% DOD - then the battery was between 0 and 0.1% out of balance.

It's now 0.8% out of balance, so its got worse over that time, not better.  It's one cell in each battery that is low.

So it looks like 52v is not enough to allow the battery to balance cells.

I'm actually going to put my load over to battery now and I think as the battery discharges the cells will come into balance.

(I still don't know if my alarm is related to the balance of the batteries.  Since the last alarm the battery balance is no better and I didn't get another alarm).

 

 

 

Edited by Elbow
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1 hour ago, Elbow said:

So it looks like 52v is not enough to allow the battery to balance cells.

I hope this isn't true, but if it is, then I will have to revisit the DVCC decision on that...

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1 hour ago, plonkster said:

I hope this isn't true, but if it is, then I will have to revisit the DVCC decision on that...

Here's what happened when I turned off the mains side and put load on the battery:

 

image.thumb.png.a9992ba83db16f302d64be82a122736f.png

 

It happened almost immediately:

image.thumb.png.ab577acfae5384a1be3996e7a520bc1f.png

 

I'm not sure that this means, but I guess I must try the 53.2V again.

 

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So when you put load on the battery, the cells come into balance? Am I reading that correctly? Is the 'imbalance' caused if there is no load and only tiny current going in or out of the batteries, you will get  large but insignificant voltage variations?

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4 minutes ago, DeepBass9 said:

So when you put load on the battery, the cells come into balance? Am I reading that correctly? Is the 'imbalance' caused if there is no load and only tiny current going in or out of the batteries, you will get  large but insignificant voltage variations?

Yes (no?), there was no load on the battery.

And according to the batteries data and my BMV the battery was not drawing any power.

 

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20 minutes ago, Elbow said:

Yes (no?), there was no load on the battery.

And according to the batteries data and my BMV the battery was not drawing any power.

 

"Here's what happened when I turned off the mains side and put load on the battery:" ?

 

What I have noticed with my batteries is under 'normal' operating conditions, i.e charging or discharging but nothing funny going on, my battery midpoint is zero. If you apply a large load or varying charging current (like sun in and out of clouds) then the batteries go out of balance up to 0.3% and then settle down again to zero. When the batteries go to float I also see an 0.1-0.2% out of balance condition, once the sun goes down and a load is applied again, the go back into balance.

Edited by DeepBass9
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23 hours ago, DeepBass9 said:

So when you put load on the battery, the cells come into balance? Am I reading that correctly? Is the 'imbalance' caused if there is no load and only tiny current going in or out of the batteries, you will get  large but insignificant voltage variations?

Here is one of my batteries recharging:

B4C24B6A-776B-4BD8-8FA3-8B03519F80C1.thumb.jpeg.91ee517be5e1003a494a239d695c9393.jpeg

Basically the cells discharge in very close balance.  They charge in very close balance. It is only right at the end that the imbalance appears.

This is with charging at 52v.  52/15=3.4667 which is pretty much where the cells ended up, only slightly imbalanced.  I think I switched to constant voltage float a little too soon.

I’ll redo this test using 53.2v and see how these curves look.

Edited by Elbow
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On 2019/03/01 at 7:33 AM, plonkster said:

I hope this isn't true, but if it is, then I will have to revisit the DVCC decision on that...

Can you give a bit more detail @ plonkster... I'm keen to hear why you say this... and DVCC?? (i'm slow this morning ;))

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7 minutes ago, Mark said:

DVCC

Distributed Voltage and Current Control. Victron loves acronyms. Victron loves acronyms. It's the feature where the BMS controls the voltage and current levels of the solar chargers and the inverter.

Because the Pylontech has a very narrow band (charge at 53.2V, overvoltage at 54V, so a mere 0.8V to work with), and because above 3.55V per cell you tend to get very fast voltage rises, and because of the way the excess PV is detected and fed in (by applying an 0.4V overvoltage), we lowered the charge voltage to 52V (ie, quite literally, if it detects a Pylontech battery, it lowers the voltage automatically). Now if 52V is too low... then this needs revisiting. But I think the later results, that show the imbalance actually appear higher up... that means the jury is still out.

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I was wondering 2 things:

1. Is the PT's voltage range valid (specifically the max) 

2. if not, is there a need for a firmware change to the PT (something like @Coulomb) has done for the Axpert.

Any thoughts...

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54 minutes ago, Mark said:

I was wondering 2 things:

1. Is the PT's voltage range valid (specifically the max) 

2. if not, is there a need for a firmware change to the PT (something like @Coulomb) has done for the Axpert.

Any thoughts...

54v is 3.6v per cell.  The absolute maximum a Lifepo4 cell can "survive" is 4.2v, but it damages the cell.

The Pylontech are following a sensible figure no doubt trying to maintain the life of their battery.  

53.2v is 3.547v per cell - and to stop charging when the cell voltage is 3.5-3.6 is good practice - they’ve split that almost exactly down the middle;

So I don’t think hacking this in the firmware is a good idea.  This chemistry does have a very flat voltage curve so different from Lead acid where voltage maps quite linear to SOC.

52v is 3.4667v so a little less than 100% charged.

To play fair with Pylon I will charge per their application note at 53.2v and see how it goes as a test.

I tested 51v and that gives 90% SOC which actually might be a good figure for a long life, but I went to 52v following the advice of the master, @plonkster.

My observation in other tests is that there is almost no energy stored in those final 10ths of a volt.

I don’t think my alarm light has to do with this, though.

Edited by Elbow
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3 hours ago, Elbow said:

To play fair with Pylon I will charge per their application note at 53.2v and see how it goes as a test.

I'll tell you one sort of story of how 53.2V could be an issue. OK, I will tell you two. Neither applies to you, because your system is much simpler than these two.

The first was with older firmware. Victron inverters have a bulk offset, that is to say, while it is in bulk mode the charge voltage is raised above the configured absorption voltage and then as soon as the battery voltage reaches absorption it removes the bulk offset. It does this to ensure that you aim high enough so that any voltage drops on cables are overcome. Otherwise you might well end up in a situation where the battery is lower than absorption (because of a voltage drop on the cable) but the solar charger doesn't go any higher because on its end it sees the right voltage. Roll on a few years, and small lithium packs is now popular. The charge voltage syncs between the various devices every 3 seconds. So in theory, you have as much as 6 seconds where absorption was reached, but some of your solar chargers don't know it yet and they still apply the offset.

We discovered that a Pylontech battery can go from 52V right across to 54V and switch off in the space of 6 seconds.

So this was fixed in later firmware, where the bulk offset is removed completely when there is a BMS in the system (aka... we're dealing with Lithium). But I retell the story so others can learn from it... 🙂

The second story was with a PV-inverter on the output of the inverter, running off-grid. This is throttled using frequency shifting, but as always it takes a while for the downstream equipment to pull back after you rise the frequency. So again there is this little window of time within which the excess energy has nowhere to go but into the battery. If you constantly run it past the elbow-point where it is prone to rise sharply... then you have no margin to work with.

On top of all that, your battery lives longer if you leave a bit of space.

The Victron batteries switch off at 4V per cell, for interest sake. I found out by accident. I was messing around with a BMS simulation script (one I use that pretends to be a BMS, for testing other components), and accidentally had the voltage set to 24V... on a 12V system. The Multi promptly charged the batteries to above 16V and the BMS kicked out 🙂

 

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7 hours ago, Elbow said:

Basically the cells discharge in very close balance.  They charge in very close balance. It is only right at the end that the imbalance appears.

All LFP cells look close when the cell voltage is at the 3.33 V plateau. It's mainly at the high and low ends that you can see an SOC difference as a significant difference in voltage. So your cells might not be as close as you think.

I'm not saying you do this, but it's a classic beginners mistake to say "Wow! My cells are really well balanced! They're all within a millivolt of 3.333 V! It must have been my awesome balancing technique." <_<

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Hi,

I discharged my batteries to about 95% and then charged using 53.2v as the bulk and float voltage per the recommendations for a Voltronic.

it does seem to make much difference - again, when the cells get near full a voltage difference creeps in - currently at 0.7%.

Here’s the big picture chart:

92C13A68-97B3-41DF-8507-69E6465E4A08.thumb.jpeg.88afff5291d0be905c386468f2951ef8.jpeg

Left scale is cell voltage - blue and orange - and right scale is actual charge amps - red - and "max charge" as signalled by the battery on the rs485 interface - green.

You can see that I charged at the 53.2v and the cells did get higher, but overall the balance was about the same.

Zoomed in:

B76A80AA-3693-4616-95D6-5FB70197E699.thumb.jpeg.e958ded148712d13848f09ff1d155b28.jpeg

 

You can see that the cells did rebalance somewhat as the charge current dropped.  But only so far.

Here is the very detailed chart:47B514A6-B53C-4617-AF42-2D6F5DF14553.thumb.jpeg.4a9d49aaa5c69a390a49636a1e4a2731.jpeg

 

I think I’m going to stop worrying about this, though.

 

 

 

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