gringosailingexpeditions avatar image
gringosailingexpeditions asked

Lynx BMS - GX Not going into float ( kinda)

Hello ,

My set up , i have just finished my install and have run into a few bugs/ settings i cant figure out . I

3 x 200 li smart

Lynx smart BMS,

multiplus 5 kw

several lynx distro's and smart battery protects.

Firmware on all devices is currentI have read all the manuals both the GX and Lynx bms. DVCC is forced on .

The BMS is working well, I was super impressed it balanced the batteries on the first charge. when you start charging the GX displays as it should , bulk then goes to Absorbtion at the correct voltages. What is weird is that it will go to a float voltage of 27.2 and float but not indicated float on the GX or the lights on teh multi.


the GX is showing the status of the Mulit not what the status of whet the BMS is doing.

Have i missed something here?


cerbo gxBMSmultiple inverters
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3 Answers
bathnm avatar image
bathnm answered ·

The reason is that the Multi is not actually running any charge algorithm, the DVCC from the Lynx BMS is controlling things. If you take a look at the DVCC section of the Cerbo/VenusOS manual it explains this.

It would be great ion the MultiPlus could display Ext.Control like the MPPTs do, and maybe at some stage that will happen.

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sv-drumbeat avatar image
sv-drumbeat answered ·

I am having the exact same issue, though with a 12v system. I understand it says so in the DVCC section of the manual, and do understand why the LEDs on the front of the Multi can't change when under remote control, but please explain why the GX Touch is not able to display 'Float' status from the Cerbo. Surely this information is - or can be made - available on the bus and is only a firmware/software issue.

After spending literally several tens of thousands of dollars on a premium Victron-only system to prevent precisely this kind of weirdness, I find this extremely disappointing, and hope this can be easily rectified, and soon. Unlike the rock-soid VE.Bus BMS we just took out which provided a simple to understand status, I am shocked to find out that the WAY more expensive Lynx/Cerbo combo we replaced it with is providing different and misleading information to the crew and now I'm not sure how to trust it as the vessel's master. It's not just the money I'm concerned with, it's safety and peace of mind both alongside on shore power, and at anchor. How do I know there's a problem if it only says absorption as the final state?

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@Bathnm explained this quite well.

Additionally, bulk, absorption and float describe charge phases that are important for lead-acid chemistry but not for LiFePo4. It's all about voltage and current limits (CVL and CCL) that keep a lithium charged and under control, not bulk, absorption and float. And the Cerbo is displaying those limits (as well as a VRM widget).

Maybe you can explain a bit more why you think this is misleading and why you don't trust it?
What exactly are the benefits of continuing to show bulk, absorption, and float?

BTW, chargers that are not controlled by DVCC will still show the old 3-phase wording.

I personally see no reason to stick with words that are no longer relevant to the chemistry being used.

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

Hi @Stefanie I fully agree and think you summarised the key issue with these words

“I personally see no reason to stick with words that are no longer relevant to the chemistry being used”

The Cerbo is using words that are no longer relevant and not being applied when the MultiPlus/Quatro is being controlled by the BMS. At least there is a change logged and to be worked that will change the label on the MultiPlus/Quatro to be Ext. Control like the MPPTs. That way at least from the VenusOS people will know what the MultiPlus/Quatro is doing and if it is externally controlled or following legacy change stages.

Maybe a Victron can even find a LED combination to display on the device itself.

But all of this is not a reason to not trust the system. As we both say, voltage is king and that is what needs to be checked.

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sv-drumbeat avatar image sv-drumbeat bathnm commented ·
Hi @Stefanie and @bathnm, thanks so much for your feedback and word of a logged change and firmware update. This is excellent news. I do understand everything you said and I am NOT disagreeing with you. I understand it's about CVL and CCL, and that the terminology of previous chemistries doesn't "really" apply any longer in the same way; we are all getting to the crux of the matter here though, that there is perhaps a need for some new standard nomenclature or indicators (at least within the Victron suite of products when the same battery chemistries are employed).

My thoughts about it being misleading... I will need to carefully synthesize something offline when I've had a chance to think about it fully and I'm not "distracted" by work. :-)

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bathnm avatar image bathnm commented ·

Victron will be addressing through a firmeware update so that at least the Cerbo will report external control for the the MultiPlus/Quattro in the sma e way the MPPTs do. The LEDs will be unlikely be changed, but with the device hidden away who actually uses them in a day to day basis.

What you need to consider is two things. (1) what phase of charge is the MultiPlus/Quattro in to maintain the charge voltage the Lynx BMS is calling for. In order to maintain the 13.5v that we all assume to be a float voltage, the internal algorithm the MultiPlus/Quattro might be in is absorption and not float, so technically the label is correct as the device has not internally swapped to a float phase, but has restricted its output as requested by the BMS (2) what the voltage is, as that is more important than a label that has been used to denote a mode.

It will all be addressed in a firmware upgrade of I suspect the MultiPlus/Quattro and the VenusOS.

if you really want to know what is going on you need to look in the Lynx BMS menu page parameters and see what the CVL is calling for.

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Jmarc avatar image
Jmarc answered ·

1) More than one answer mentioned the DVCC Manual section. It does describe how the DVCC uses the CVL and CCL but I do not seem to find what section explain the Charging States implication.screenshot-2024-02-15-133742.png
2) Yes the Overview now does show "Ext-Control" which is good. But in the Device status and on VRM, the unit is either in Bulk or Absorption as I can see for a Lithium battery system. It never switch to float.
Is this important: Not in my mind since effectively for Lithium Battery there are no distinction of absorption and float. It is either Current controlled or Voltage Control which both Bulk and Absortion respectively are. But for many people used to the Lead acid type, they look for the Float to tell them it is done charging... Which never happens... Disconcerting at first

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