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Daniemj

Pylontech uneven discharge

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Since the newer ICC software (2.4.3 and 2.4.4) has been used,  each Pylontech battery values could be read independently.

I have noticed the last 2 days (using the batteries every night) that batteries number 1, 2 and 3 discharge almost at the same rate, but that battery number 4 is discharced at least 20% more than the other 3.  Is that normal and is there something I can do about it?

I will try and take a picture tomorrow when it is discharged to a SOC of between 35% and 40%. The current picture indicates fully charged batteries.

This is how they are set up at the moment.

 

IMG_6998 (3).jpg

IMG_7003 (3).jpg

IMG_7033.jpg

Edited by Daniemj
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Try this

The other thing I have noticed is that if you mix firmware types for the Pylontech you end with some errors in reporting. My units report a collective SOH of 51% but individually they report 100%.

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2 hours ago, Daniemj said:

I have noticed the last 2 days (using the batteries every night) that batteries number 1, 2 and 3 discharge almost at the same rate, but that battery number 4 is discharced at least 20% more than the other 3.  Is that normal and is there something I can do about it?

Note that battery 4's temperature is lower too. It might very well have something to do with it. It is common for the different cells to not have quite the same capacity. The battery is empty when the lowest cell drops too low. The battery is full when the highest cell is too high. The balancing circuitry will over time get them closer together. The balancer tends to create some heat. Also, the one with the higher cells might in fact run a bit cooler and might therefore be tasked with providing a bit more power.

In other words, this might be normal. Don't know for sure though.

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3 hours ago, Daniemj said:

Since the newer ICC software (2.4.3 and 2.4.4) has been used,  each Pylontech battery values could be read independently.

I have noticed the last 2 days (using the batteries every night) that batteries number 1, 2 and 3 discharge almost at the same rate, but that battery number 4 is discharced at least 20% more than the other 3.  Is that normal and is there something I can do about it?

I will try and take a picture tomorrow when it is discharged to a SOC of between 35% and 40%. The current picture indicates fully charged batteries.

This is how they are set up at the moment.

 

IMG_6998 (3).jpg

IMG_7003 (3).jpg

IMG_7033.jpg

In a DC circuit, during a discharge, electrons flow from negative to positive, hence causing what you observe here. 

When being recharged, electrons flow from positive to negative. 

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2 hours ago, Chris Hobson said:

Try this

The other thing I have noticed is that if you mix firmware types for the Pylontech you end with some errors in reporting. My units report a collective SOH of 51% but individually they report 100%.

Thank you. This makes sense to me since I have added a new battery to 3 fully charged batteries that has been in use for about 2 weeks.

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4 minutes ago, Daniemj said:

I have added a new battery to 3 fully charged batteries

The battery with the better capacity will provide more current during discharge. This is natural and happens for other chemistries too (including lead acid). The trouble is usually on recharge, but for Lithium batteries (where their impedance increase significantly as they become full) there is also more of a natural split of charge current.

In short... they just need a bit of time to "find each other".

Some batteries even have a specific procedure that has to be used. I know that with both LG and BYD, you can't just throw another module into the rack without doing this. I am not sure what the procedure is though.

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As you could see, the SOC of the first 3 batteries range between 36% and 37%, but battery number 4 have a SOC of only 21%.  20% SOC is the minimum what the batteries want, so this difference is huge. I have tried the battery balancing tonight, so I will see what happens tomorrow. The initial picture showed that the SOC was 100% on all 4 batteries before they have been used through the night. They also powered the geyser (2000W element ) for 35 minutes between 23H55 and 00H30.

 

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I have not balanced mine and noticed that the SOC difference is much smaller after 2 weeks. Now at 6:41 this morning  SOC is 69, 69, 68, 70. The last two are the older modules.

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15 minutes ago, Chris Hobson said:

difference is much smaller after 2 weeks

According to the information I have, these batteries also balance at the top end. The way to get them fully balanced will be to hold them at something above 52V for a long time (like more than a day) to give the balancers time to work. The balancer usually transfers really small amounts of current, so this takes time.

Or as Chris says, just forget about it and give them time. They will balance a little bit every day, getting closer by the day when you recharge and eventually arrive fully in sync.

My Victron batteries did something similar. For the first week or two, the 12.8V module on the right was warmer than the one on the left, and the bluetooth app showed the cell voltages were higher. It evened out in the end.

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