Lynx smart bms charging behavior

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solseekerssolar asked May 19, '22

Lynx smart bms charging behavior

I 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 charging BMS

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Answer 1 · 2022-05-19T18:11:00Z

Stefanie (Victron Energy Staff) answered · May 19, 2022 at 06:11 PM

@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 commented · May 19, 2022 at 07:51 PM

@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?

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Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented · May 19, 2022 at 08:30 PM

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 Stefanie (Victron Energy Staff) ♦♦ commented · May 20, 2022 at 04:27 PM

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 Stefanie (Victron Energy Staff) ♦♦ commented · May 22, 2022 at 04:29 PM

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

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.

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) ♦♦ solseekerssolar commented · May 22, 2022 at 06:29 PM

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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solseekerssolar Stefanie (Victron Energy Staff) ♦♦ commented · May 23, 2022 at 03:13 PM

It is entirely possible I am confusing something. Is there any way to understand how CVL is managed? The little information I have gleaned from the manual and other sources, my understanding is that it charges to 56v for a 2hr absorption period and then floats at 54v. This unit doesn't do that, therefore my confusion.

I am also increasingly concerned about the battery voltage reported by the Lynx BMS is quite a bit higher than the CVL, this seems like it shouldn't be the case.

The system is 2x 48/3000 Quattro's in split phase with 4x 200ah 25.6 Smart lithiums in series/parallel. There is also a Smart Solar 150/60, it is connected to the Cerbo and showing external control. There are no other chargers in the system.

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Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented · May 23, 2022 at 04:22 PM

Nice and clean installation!

It's 56.8V for 2 hours (depending on set absorption time). There is not much more behind it to understand. That little bit in the manual has all the necessary info.

Even if you have double checked everything, please do it again, especially the Quattro settings.

What are the firmware versions for your Quattros, GX device and the Lynx Smart BMS?

My expert contact is currently not in the office. Might take a few more days.

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solseekerssolar Stefanie (Victron Energy Staff) ♦♦ commented · May 23, 2022 at 06:22 PM

Thank you very much!

It seems simple and straightforward. Just doesn't seem to be doing it. Please let me know if you find anything out or need additional info. Thanks again for your continued help.

Here are the Quattro settings:

Firmware versions:

Quattros 494

Lynx BMS v1.04

Cerbo GX v2.85

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Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented · May 23, 2022 at 06:35 PM

Thanks. Looks like firmware are up to date.

Not sure if it makes a difference, but can you please change absorption time in both Quattros to 2 hours instead of 8 hours?

Normally this is controlled by DVCC and the Absorption time setting in the Lynx Smart BMS. Just to rule out that they interact with each other. 2 hours is the recommended maximum absorption time for Victron Lithium Smart batteries.

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Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented · May 30, 2022 at 11:35 AM

@solseekerssolar

How is it going, have you made any progress?

In the meantime, I talked to my contact and we agreed that it looks like the Quattros are not listening to the BMS and therefore the charging process was not started by the BMS. Although CVL (in the widget) sometimes looks like it set CVL itself, it just follows the battery voltage. This is an expected behavior and can be observed, for example, when a non-DVCC charger starts charging. Assuming the Quattros weren't recognized as DVCC compatible for an yet unknown reason, that would also explain the behavior.

Can you please make sure that DVCC is enabled in your GX device? It should be forced on, but just to be sure. If it is enabled, please restart the GX device and see if that solves the problem.

Please keep us updated.

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solseekerssolar Stefanie (Victron Energy Staff) ♦♦ commented · May 30, 2022 at 03:16 PM

Hello, thank you for following up. Nothing new to report. Behavior hasn't changed. DVCC is enabled (forced on). The setting "limit managed battery charge voltage" is not active. I turned it on and set it to 56.8v, I will keep an eye on it and see if this changes anything.

I will be onsite with this installation tomorrow. I prefer to be there when the GX device gets restarted.

Also, I'm still concerned about the significant difference between the charge/discharge limits and the actual voltage reported by the bms. Is this something to be concerned with?

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Stefanie (Victron Energy Staff) ♦♦ solseekerssolar commented · May 30, 2022 at 05:52 PM

Limit managed battery charge voltage should be off.

This is really only intended for when to set a specific voltage on heavily unbalanced batteries and should not be used to control a common charge voltage.

No reason to be concerned with the differences between CVL and actual voltage reported. It's definitely not correct, but still within limits.

Please let us know about your experience after the reboot.

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