Recently got a MultiPlus 24/2000/50-50 120V and the documentation says nothing about Lithium batteries at all (LiFePO4 is the desired use-case).
Firstly, given the serial number, etc. is there a way to tell the hardware version? (I read about “v3”, etc). I’m assuming there are firmware updates if it has not been recently updated?
Thanks!
Usually there is adequate range of the Voltage setting parameters for using these devices with Lithium batteries, as Lithium’s have a smaller operating voltage range than lead acid. It is usually the low end - cut off voltage setting that has to be raised.
The firmware version can be accessed if you have a Mk3 adapter, this is needed anyway to configure the Multiplus. The firmware can usually be updated using the Mk3 and Victron connect, however, if the firmware is really old, then there is a different procedure, the new firmware needs to be installed with the flash program (never needed to do this!!). The software can all be downloaded form the Victron web site. (VE-bus tools, Victron connect).
Thanks!
It seems the manual talks about “trickle” and other things that are not relevant (or desired!) with lithium batteries. With the MK3-USB dongle, I assume you can select Lithium cell types and things like charging CV/CC crossover, termination voltage, etc?
P.S. What is the meaning of the word “absorption” in the manual. A weird word to use… Does it mean overall cell/pack capacity (typically Ah, or mAh)? EDIT: seems to mean the CC/CV crossover voltage, which is something that varies between cell manufacturers and should be researched or empirically tested.
Yes, the current firmware has LiFePO4 battery type presets, also you can ‘trim’ these voltage settings afterwards.
With Lithiums, the critical thing is to prevent cell undervoltage, then next is cell overvoltage. However, to do this, you do need a BMS communicating with the charger, as it is NOT possible to detect cell events just be measuring the pack voltage.
The firmware for the Multi’s has had 2 wire BMS ‘assistants’ for some time now.
The Absoption voltage: this is the maximum voltage that the charger will put out - in Lead acid battery terms, it marks the transition from CC to CV - this is still relevant to Li battery packs, and usually I set this to about 3.55V per cell - or about 100mV per cell less than the manufacturer’s stated max. Likewise the Min cell voltage should be limited to about 2.75V - there is very little energy stored between this voltage and the typical 2.5V per cell voltage. However, in calculating the cut off voltage, you need to allow for one cell only to be at 2.75V, the remainder are likely to be at or above 3.0V!! (i.e 7*3.0+2.75).
Yep, intimately aware with Li-Ion pack regimes and pack-building. The idea of explicitly declaring an “absorption voltage” is odd since the particular cell’s CC/CV regime itself will determine the crossover voltage (typically, it’s the fully-charged voltage state, per-cell) and the charger should shift into CV mode and track the current to a set cut-off.
FYI, I’m really just going to use the MultiPlus as a “better-quality” short-duration emergency UPS (allow proper shutdown of PC’s, etc, in a power failure), not any kind of long-term or daily use.
I have some original(!) A123 M1 cells that I’m going to make customs packs of and they can support continuous discharge rates (70A!) that drop the voltage below 2.5V for the duration of the discharge, so setting the cutoff to 2.75V/cell would trip really early! I have been grading and matching individual cells (ugh!), so the packs should be very well balanced and M1 cells are highly resistant to drift.
I just want to be confident that the charger in the MultiPlus is not doing -anything- once the cells are fully-charged!
Also, since I’m making custom packs, I’m hoping I can bump the cell-count to 9 cells (probably 9S2P @ 32.4V max, fully-charged, which is below the 33V max of the specs) to increase the efficiency and drop the current draw a little.
Lots to experiment with! 
I think that the Lithium’s do have an absorption phase - if held at 3.5V, a cell will gradually charge to 100%, and the current will tail to <1%C.
I have also used compact multi’s as UPS - on large solar system monitoring and SCADA systems, where they do work fine.
Regardless of drift and matching, I would still not operate a lithium pack without a BMS of some sort.
Yep, a BMS is important in a critical-use regime, but if it’s a home-based temporary-use backup and the cells you are using are phenomenally stable and essentially fireproof, the worst that’s going to happen is that it simply doesn’t work when called-upon! 
Even at 24V, a “dead” or weak cell would trip the LVC long before you’re going to drive the cell negative. BMS’s are extremely important on large arrays, like an EV, where a weak/dead cell could be driven strongly negative and have minimal impact on the current delivery, creating a very possible fire-hazard.
On the demo page in victron connect, it shows a “lithium batteries” setting under charger settings that can be enabled.
It also shows a link to what that does.
Thanks!
I just flashed the latest firmware and there seems to be a lot more fine-grained detail in the settings now!
The critical answer I found that that, yes, you can completely switch-off charging. (if it’s a requirement/preference for a given situation…)
It’s an impressive piece of kit, but it’s still a bit annoying that they use archaic, and irrelevant, terminology like: bulk, absorption, float when using Li-Ion cells.