Since the max. recommended voltage is 54.4V, my current settings under the charger section in VEConfigure are:
Absorption voltage = 55.2V
Float voltage = 54.4
Charge current = 70A (in the VRM app I limited it to 54A)
Repeated absorption time = 1h
Repeated absorption interval = 7 days
Maximum absorption time = 1h
I will say, my (Victron-certified) installer is not very knowledgeable and after some research I’m having second thoughts about these settings. I read that typical charging voltage for 3.2 lifepo4 cells is 3.5-3.65, which means absorption should be 56V? The DC input low shut-down is set to 48V.
What charge/discharge and shut-down settings do you suggest for my pack?
You need to look into the spec in more detail to decide on “absorption” voltage – which for LFP is really only needed for cell balancing. This normally starts at a voltage above the normal float voltage (54.4V in your case), and will continue up to the “maximum recommended voltage” which is usually when the SoC is reset to 100% by the BMS.
From your spec, I’d say you want to spec 57.6V as the “absorption” voltage. 48V is fine as shutdown, 40V is really low and may lead to cell damage since you’re doing top-balancing.
For my battery the “float” voltage (set by the BMS, the Quattro is externally controlled) is 54V, “absorption” voltage = 100% SoC is 57.3V, and it charges to this once a week for 2 hours, then discharges again – usually takes a few hours to drop back to 54V which is 99% SoC (calculated by integrating current).
I’m almost exclusively charging the battery pack with solar. As a result it charges and goes into absorption mode depending on the battery SoC and available solar power. Which in the summer days I presume it will be every day? I don’t know of a different way to manage this, since I’m already filling in all the fields in the Charger tab. I guess if repeated absorption interval is set to 7 days, it makes sense for the inverter to only go back into absorption mode 7 days later and not before. Is that accurate?
As for the voltages then, I will increase my absorption voltage. What is your sustain voltage? should it be like float at 54.4?
Is the dynamic cut-off useful? I’ve read it’s disabled by default since varying loads may lead to temporarily decreased voltage, leading the inverter to shut down inadvertently. The guy who set it up seemed to made up all the voltages in there, leading the inverter into absurd behavior like going into Sustain mode at like 52V (that was like 42% or so) while shutdown was set to 48 (20%). At some point I had enough and set all of them to 48V and now it’s behaving as expected.
the label I posted is ALL the info the manufacturer provided. When I asked them for a user manual or spec sheet, I was basically yelled that the battery should only be installed by authorized personnel. The thing is, the Victron authorized guy who installed the battery shows very little knowledge about these type of installations. So I have to deal with this somehow.
You could set float and absorption to the same voltage. Usually the batteries that recommend 54.4/8v do.
Second thing usually the cut off allows 10% soc reserve on the batteries that use 54.4v float.
The other observation for the same batteries is their balancing is ultra slow (which is probably the reason for the lower voltage recommend for charging to prevent the run away.
The dynamic cut off in the ess assistant overrides the low shut down on the inverter tab. You could set that to 47V for the higher C draws.
And sustain is only triggered if the battery draws under the dynamic cut off. But it would probably bee ok to drop it to 51v.
If you set the float and absorption the same then worrying about longer absorption won’t be a thing. And the battery hasn’t stated a float.
Allegedly from showroom models with “0 km” on them. They should be +98 or 99% SoH.
They’ve just published the Victron recommended setup in the product page (here).
Absorption = 56V
Float = 55.5V
Absorption time=1h
DC input low-shutdown = 45V
DC input low restart = 47V
DC input low pre-alarm=46V
Do these seem reasonable to you guys given the hardware specs? For some reason and despite being the same model, the label on my battery pack has different voltage values for SoC 20% and 80%.
Brand is called second life. If they are second life cells, it is not a terrible thing.
They are using a dally bms. So it is how they programmed it that will be interesting. They don’t have great balancing
Neat go with that. If you experience problems the can be revised down. You have to start somewhere. You will find out soon enough if the bms will allow it.
I would make this one higher if they are second life. But see how you go there.
This is normal as a new company tries to work out the best performance for cells used. Each batch will be different if they are using second life. It will depend on where they were used previously. (If they are their name throws some question marks)
They want them cycled not kept at 100% most second life companies do.
How can I tell if the cells aren’t balanced? I mean, what symptoms should I look out for?
Yeah, the DC-low settings seem very low. Based on the info I find online, 20% SoC corresponds to 3.2V, that’s 51.2V; 2.85V is below 10%, that’s 45.6V. So their settings don’t seem conservative at all to me plus they seem to conflict with their own min. recommended of 20%.
Brand is called second life. If they are second life cells, it is not a terrible thing.