Can the 3000VA Multiplus Low Voltage Cutoff be set below 21.5V?
Is it a Tesla battery module?
most Lithium ion batteries can be safely discharged to 3,3 V per cell, some even have energy left at 3,2 V
Tesla cells are pretty much empty below 3,3 V so 20V is a good setting, cells that have energy to 3,2V I use 19,2 V lower cutoff
The inverter works down to 18 V but in ESS mode might stop earlier.
(these values are at low C discharge rates, say 0,25-0,35 C)
The 6S is for sure not LiFePO4 and when using other chemistry you get problems for 12 V and 24 V installations. One problem is low voltage for inverter and some other high loads. Another much bigger problem is if connecting 24 V standard charger (i.e. 28.8 V) at 6S NMC battery, which must be charged at max of about 25 V. That's the reason why recommendation is to use 8S LiFePO4 if custom for 24 V system and no problem to hook on Victron 24 V inverter.
Yes, low voltage cut-off can be reprogrammed. But you should be aware of the RESTART issue below 21.8V. Even though you can operate the inverter below 21.8v (down to 19v), it will not re-start unless the power goes back up to 21.8v (assuming you turned it off).
Although many customers are requesting a fix, it appears that Victron is not going to fix this issue. The reason given is hardware limitation and software is not easy to change.
See the post Tesla 50% SOC:
BTW, there is nothing magic about '6S" or "8S". You can have lithium or non-lithium at 6S, 7S, 8S, or whatever. You will just have to know the V-I characteristics from the manufacture of the battery.
Hey all; some replies:
> The idea there is a hw limitation (see the official response) is interestingly worded. I have spoken to someone on-line who tells me he was given a patched one that works. Apparently, the whole test voltage on restart was disabled. It works fine. He refuses to tell me who he worked with at the company for fear he will get the employee in trouble, now that there has been an official answer from the top.
It sounds rather unlikely for such firmware to exist; but I can assure you that no-one will get in trouble. Its not thát easy to get into trouble here. :-).
> Can't see why there should be a hardware limitiation when the inverter can work fine all the way down to 37.2V on a 48V model.
There is a hardware limitation in the 12V models: its internal power supply can't start up below ~10.9V. Once running; it can remain operational down to the ~9.3V. Back in the days; the choice was made to keep the ratio between the 12/24/48 V the same. For simplicity. Even though the hardware of the 24V and 48V doesn't need that high a voltage to start up.
There is another limitation, relating to transformer ratios (is that the right english?). At too low voltages, the inverter/charger won't be able to make a true sine any more: it can't reach the required peak to peak voltage.
Which is also the answer to the other question, written by @lassestu:
> It also seems like there is alot of undocumented features that I see many folks havent got answered, like why 48v inverters start using grid power at 41V when theres plenty of battery juice left.
The answer is that below 41V, the inverter can't make a true sine any more, and because of that it stops PowerAssist, GridAssist, Feedin; or how ever you call it ;-). Reason being that to continue feeding in at those low voltages would create 3rd harmonics in the current and other issues.
All together, there is indeed possible some room for improvement by changing the software. Why do I write 'possibly'? because it needs looking into to make sure that there are not more issues when lowering those thresholds. And all that together, plus some other projects that I've judged has higher priority are the reason we are not looking into this now. Hopefully/probably later there is more possible.
I do see the importance (and commercial value) of second-life batteries. But we can't do all always now. And, in some cases, adding feature on feature on feature is nice for someone; but then bad in total because also our distributors & support teams need to keep up. Being worthwhile to sell, support and install, as well as being a swiss army knife; can be a difficult balance at times.
Hope this clears it up; and sorry to not make it all work now.
ps, @lassestu, you wrote:
> Theres so many things that I would love to get answered, but I'm afraid I wont get it clearly explained.
If you can find me someone that is able to work answers into the documentation properly; while keeping it readable for a novice as well as having all the answers at the right place for the expert; I'll be here to help find them!
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