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Lynx smart bms charging behavior

screenshot-2022-05-17-at-71717-pm.jpegscreen-shot-2022-05-19-at-92555-am.pngI am using the Lynx Smart BMS for the first time and need some help understanding its behavior. The system is installed in an RV and consists of 2x 48/5000 Quattros configured in split phase, along with 4x 25.6 200ah Smart lithium batteries in a 48v arrangement.

The Lynx BMS has the following settings:

Charged voltage: 56.8v

Tail current: 4%

Charged detection time: 3 minutes

Absorption time: 2 hours

SoC threshold: 70%


When connected to shore power and the batteries full, the BMS will frequently call for bringing the voltage up to the charged voltage of 56.8v. It will remain there for roughly 20 minutes and then return to float voltage. The timing of this appears to be random, but it seems to occur at least twice per day. Would this be considered normal? What triggers this to occur? I haven't been able to find published information regarding the BMS charging strategy.


When this occurs there is a momentary power outage within the coach. VRM data doesn't show any interruption in input or output power. Logging interval is set to 1 minute, so it may not be fast enough to capture this momentary power loss.


battery chargingBMS
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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

@solseekerssolar

The first thought that comes to my mind is that there may be a problem in the split phase configuration and one of the two quattro's is not controlled by the BMS and instead acts independently.
I'm no expert in parallel or split phase configuration. But this is where I would look at. You could check the GX settings for your Quattros and also make sure they are both controlled by your GX device.
You have not described the other system components. Perhaps there is another charger that is not controlled by the BMS via DVCC and therefore acts by its own charge algorithm. This would also explain this behavior.

There is no particular charging strategy. In a properly configured system, the Lynx Smart BMS, together with the GX device, takes control of CVL (charge voltage limit) and CCL (charge current limit) of your DVCC compatible devices (Quattro in your case), setting CVL to 56.8V when the SoC is becomes lower than the threshold of 70%.

When this voltage is reached, it remains at this level for 2 hours to give the cells time to balance. Then CVL is set to 54.0V. Only when the voltage falls below the SoC threshold again, the whole process is repeated. Until then CVL remains at this level. The batteries then take what they can get from your charger.



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solseekerssolar avatar image solseekerssolar commented ·

@Stefanie


Thank you for your response. I have double checked the system settings, everything looks correct. We have commissioned a number of split phase systems, the only difference with this system is the addition of the Lynx BMS.


The BMS does have control of the Quattros. Every change in battery voltage corresponds with a change in the CVL. It seems to be ignoring the SoC threshold and keeping the batteries at 100%. It also seems odd that the BMS is currently requesting 54.3v. Any idea why it would choose this seemingly arbitrary number?screen-shot-2022-05-19-at-124113-pm.pngscreen-shot-2022-05-19-at-124800-pm.png

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented ·
I just noticed that the charged voltage setting is at 56.8V, which for my taste is a bit too high and means that the SoC syncs a bit too late (actually at "absorption" voltage"). Not sure if it makes a difference, but you can try 56.0V, which corresponds to 14.0V in a 12V system.

It normally should only affect SoC synchronization, but who knows. I will ask at a higher level and come back to you.

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solseekerssolar avatar image solseekerssolar Stefanie (Victron Energy Staff) ♦♦ commented ·

I'm not with this install at the moment. I will try to have the charged voltage set to 56v today. It continued this odd behavior through the night, and is currently calling for 54.3v again. Any further information we can gather would be greatly appreciated.

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solseekerssolar avatar image solseekerssolar Stefanie (Victron Energy Staff) ♦♦ commented ·

Still confused about the Lynx BMS behavior. The previously noted behavior has not changed, and just now it is doing this:

screen-shot-2022-05-22-at-92314-am.png


I'm also seeing a significant difference between the CVL and the actual battery voltage the Lynx BMS is reporting. It seems to me this would indicate an issue with the BMS.

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Lastly, the manual for the Smart Lithium battery recommends an absorption voltage of 28.4v, this is why charged voltage is set to 56.8v. It certainly seems like this wouldn't cause the issue we're experiencing. I'm inclined to leave this voltage as is.

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented ·

Hi,

You are probably confusing something. The charged voltage setting is a setting for the battery monitor of the Lynx Smart BMS and has nothing to do with CVL. See also the Lynx Smart BMS manual sections 6.3.3 and 6.3.4 The CVL is automatically managed based on the detected battery system voltage and cannot be changed by the user.

Can you please provide us with a system diagram and/or images of your installation? What other chargers are in the system? Without more details it is extremely difficult to give further assistance.

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