I have Multi RS Solar that charges 6 lithium batteries (2 in series, 3 in parallel) in a 48V system controlled by a Lynx BMS 500. Now, after reaching absorption voltage (56.8V) battery voltages immediately drop to the 54V float voltage preventing them to balance properly. My absorption time is set to 2h in the BMS that somehow this does not seem to bother the Multi RS.
How I need to configure the Multi RS in order to respect the absorption time set by the BMS?
Configure the float voltage to be 56V (3.5V per cell) and the batteries will balance.
Keeping the pack indefinitively at 3.5V per cell will not stress the batteries.
But beware, that if you have 24V batteries, as from you description 2s3p, you need to balance them additionally in the 24V point, in regard with the 48V point.
Thank you, yes I understand that I can increase the float voltage. However, why would Victron specify 54V if 56V does not stress the batteries at all? I thought that even though LFP are less damaged by high voltages, they still don’t like to stay there. I don’t understand what you mean by balancing them at the 24V point. How would that work? I have never come across this recommendation, could you elaborate please? Thank you.
You have 24V batteries, right?
In order to make 48V, you connect two in series and you’ll have 3 points, i.e. in regard to one end, you’ll have: 0V, 24V, 48V.
So you’ll need a 24V balancer that is making sure the mid point is staying at exactly half of 48V, especially if you have multiple parallel strings.
@alexpescaru Victron lithium Smart batteries controlled by s Lynx BMS do not have the absorption and voltage settings available for user configuration.
Didn’t know that. Every day is a learning day…
In that case, I know that Lynx BMS is connecting in a daisy chain configuration with all batteries, right?
Thanks.
But somehow, somewhere, some parameters are set. Maybe in the Lynx BMS.
Because the BMS is for sure reporting something back to Cerbo and DVCC in order for these to stop charging.
There is even a “quirk” in dvcc for the Lynx BMS where there is a comment like: When the Lynx Smart BMS sends CCL=0, it wants all chargers to stop.
So for sure some limits are defined and communicated at some points.
Strange thing, the Victron is telling left and right that it doesn’t like BMSes that sends CCL=0 when the charging is done and the same Victron BMS is doing this…
Also, maybe this is the reason the Multi RS is dropping to float, because all chargers must stop, implies this.
The Lynx BMS sends CVL, either 14.2V or 13.5V and a CCL>>0 in normal operation. It only sends CCL=0 when there is overvoltage/ low temp etc and charging is definitely not required. If things worsen then it opens the contactor. User can not adjust the 13.5 / 14.2V settings.
What’s the value of CCL, in normal operation, when the CVL is 13.5V ?
I find hard to believe that Victron didn’t realized this problem with the inability to balance their own batteries…
Still, what’s happening here in this case?
OK, so in the Cerbo do you see that DVCC is forced on in the DVCC menu. When the batteries next charge to absorption see what CVL does, does this stay at absorption for 2 hours or does this go to float straight away. You could also plot this in the advanced widgets in VRM.
On the Multi, is this under external control from the Cerbo. If it is doing its own thing could you set a 2 hour absorption time in this.
Finally, according to the Cerbo menu, the Multi RS needs to be firmware v1.08 or higher.
Still, you may look at the original message, where he clearly said:
So, my question was rhetorical, wondering what’s happening here if the Victron, like you’ve said, took every precaution…
PS:
No offense, don’t want to be “difficult”, just curious what is causing this and how this can be solved…
I also own a Multi RS and think about expanding the system with some batteries and I am exploring the SWOTs of various options.
Thank you. In the Cerbo DVCC is forced on. In the Multi RS absorption voltage is set to 56.8V and float voltage to 54V. In the Lynx BMS, absorption time is set to 2h. I still don’t fully understand how these three devices interrelate with absorption settings distributed between the Multi RS and the BMS. Where could I read up on this?
I will charge again to absorption level and see what happens. Then I will report here.
Thank you for your support, helping me to understand the system better!
I think the only option is to read the manuals. The BMS should control the Multi RS through DVCC on the Cerbo. However if the Vetno to Multi RS is not working tjen the Multi will control its own charging, which may be the issue and the Multi RS may not do the 2 hr absorption by default. The manual says
Additionally, the absorption period is also ended when the charge current decreases to less than 2A.
So this may be what is limiting the absorption time. The manual also says that you can swap from adaptive to fixed absorption, that may be something to look into and the tail current function disabled.
Also from the manual
6.4. Solar charger externally controlled
The solar charger can be controlled by an external device. The external device can stop or reduce the charge current to the battery. This is not a fault but expected behaviour.
Managed batteries or an inverter/charger with an external control system like, for example, an ESS system, can control the solar charger via a GX device. The battery dictates if charging is allowed, and when charging is allowed, what charge voltage and currents are used. If external control is active this will be displayed in the VictronConnect app and also on the GX device.
Therefore it is worth checking to see if external control is active.
