question

Marco Nijholt avatar image
Marco Nijholt asked

Smart battery 200-a 25v Wrongly calibrated voltage sensors

Hi all,

I have the victron LFP 200-a 25v batteries in my system. Recently I've gotten 4 more batteries to add 20kwh to the system.

It seems however that these 4 batteries display the wrong voltages. At first, I thought I was maybe a bad connection, as these 4 batteries (2 sets) added to a new distributor. However, after manually measuring all the batteries, they are all at the same voltage, which is only 0.05v off from the reported voltage of the "old" batch. Even if completely disconnected from each other and the system at rest, this voltage discrepancy exists.

The new batch reports 0.25V lower than what I measure at the battery poles, why the old batch reports only 0.05v lower than what I measure at the poles.

Below, you find a picture of the batteries at 98% SoC. All connected to the same bus bar.

The top 2 batteries are of the "new" batch, and the bottom 2 are of the "old" batch.

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I imagine these batteries on their own could be "unsafe" as the cell overvoltage protection would not work correctly (unless I manually set them to a lower max voltage threshold inside the battery settings). But I can also imagine this creating problems with cell balancing, as the cell balancing gets triggered at a certain voltage.

But because the internal sensing of cell voltage is off, this balancing starts far too late and when the charge cycle ends, and it drops back to "float" state, it no longer will be balancing.

As you can see in the screenshot it is right now also balancing, it's just about always balancing when I check because it never has enough time to balance I feel like. Might have to increase the absorption time just to make sure these batteries manage to balance. Might also be that for example in the 2nd picture. cell 8 is actually 3.53V but measures as 3.45V but due to the wrong voltage sense on it, it never actually manages to "balance" it since it's in reality at 3.53v already.

Of course, they always recommend matching batteries and that adding batteries later into the lifetime of a system should be well-thought-out. However, all the batteries are less than 18 months old. The degradation on them is minimal, and the only issue is that the measured voltage internally does not match up with the actual measured voltage at the poles.

Would it be possible to calibrate the cell voltage sensing? Are these just "broken"?


What would you guys recommend?

Lithium Battery
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2 Answers
Justin Cook avatar image
Justin Cook answered ·

Are all units running the (matching) latest stable firmware release? As specified in the manual, this is a critical first step to commissioning the batteries.

Did you fully charge each battery at a low charge rate -particularly the new ones- before adding them into the system? This too is an important step; otherwise it could take ages for the system to balance itself out since the new batteries will be at varying states of charge out of the box.

Even charging them individually, note that (as mentioned in the manual) it can take multiple "charge>BMS stops allowing charging>balancing board balances>BMS allows charging>charge>BMS stops allowing charging>etc" cycles to fully balance each battery; then, once the battery is charged and balanced it can be commissioned into the system.

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Marco Nijholt avatar image Marco Nijholt commented ·
Hi Justin,


They are all running the same latest firmware, as is the Lynx BMS.

Everything got synchronized to 100% State of Charge, the system (old batch) by the multiplusses and the new batteries via a victron smart charger.

It indeed had multiple start/stops and also did cell balancing. I'm not quite sure if cell balancing fully completed during that first charge, but that also is not necessary per manual.

Regardless, the system with the extra set of batteries has been up since October 2022 and any cell imbalance should have disappeared by now given normal operation of the system.

Also, none of this would explain why the measured voltage, for example, is 28.02-28.04V for all batteries (even when completely disconnected from each other and rested for hours) but the new batch batteries show 27.78v-27.79v in the victron app, while the "old" batch shows 27.96v-27.98v




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jengi avatar image jengi Marco Nijholt commented ·

I see they also have the HQ2217 series like mine.

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jengi avatar image
jengi answered ·
Good evening 
On June 21st, 2023 I got my new Lithium Battery Smart 25.6/200-a.
Installed the latest firmware, after loading I noticed the same thing about my batteries. 
Battery voltage at the poles is 0.2 volt higher as indicated by the BMS. This difference is 
still present even after loading several times

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Marco Nijholt avatar image Marco Nijholt commented ·
Interesting, i've ordered 6 new batteries to increase the capacity of my bank even more. Soon i should be able to measure those too.
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Marco Nijholt avatar image Marco Nijholt Marco Nijholt commented ·
All the 6 new batteries show the same behavior, only the oldest 6 (out of 16) are accurate when it comes to what they internally report, and measured at the poles.
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