Good day to all. I need some advice, please. I have a Must PV18-3024VPM inverter. I replaced my lead acid batteries with a Nenergy 24v 100Ah battery and need to know what settings to use on my inverter. I have changed the battery type in the menu, but unsure about the float, bulk, and cut-off values. The battery has limited info on the label, it only shows the charging current as 20A, discharge current as 50A, and voltage range as 21.6v - 29.2v Any advice would be appreciated.

First thing is to set BATT type to Li then bulk to 29V float to 27.6

These are the settings I've used on a similar LifeP04 battery. 

Because your battery is a 0.5C you should use a breaker on the inverter output that will not allow the inverter to pull more than

0.5x2560W = 1280W

1280W/230V =5.5A so I sugest a 6A breaker

Please note that in order to set the voltages, you need to be on USE battery type, not LI !

See the comment in the manual for USE battery type.

Otherwise the inverter will use predefined voltages, which might not be optimal.

The inverter has a sticker on the side of it saying one should use Li setting with a Lithium battery. 

It says the charge voltage will go to float(18) first before going to bulk(17) which follows the Lithium charging algorithm shown later in the manual. 

In Li mode I am able to set float, bulk and cutoff voltages

Well, that's confusing...

It contradicts what the manual says:

Does the manual for your model state something else?

On 2023/06/03 at 5:54 AM, MiG said:

First thing is to set BATT type to Li then bulk to 29V float to 27.6

These are the settings I've used on a similar LifeP04 battery. 

Because your battery is a 0.5C you should use a breaker on the inverter output that will not allow the inverter to pull more than

0.5x2560W = 1280W

1280W/230V =5.5A so I sugest a 6A breaker

 0,5c how did you come up with that....im really intrested in that and also when you said inverter output breaker 5,5A, does that limit the user to a load of 1280W

 

@MiG mentioned 0.5c, because you battery has 100Ah capacity, but can only be discharged with half of that (50A), according to the writing on the battery.

I would say he is correct that you should limit the output power with such a limited battery.

On 2023/06/11 at 8:23 AM, MiG said:

In Li mode I am able to set float, bulk and cutoff voltages

As I mentioned, this is counter-intuitive to the manual, but you're correct, it does work with LI settings.

It appears that the MUST inverter is also plagued with the premature float bug. Mine simply won't go into absorption voltage, no matter what I tried, when using USE battery type setting. However, when I changed to LI, it indeed goes into absorption voltage. But now a new problem arises: When battery is full, it will let it discharge a bit (around 2v less than absorption,  which in my case is still pretty full), but then charges up again to the absorption voltage.

So while the LI setting works around the premature float bug, it seems to micro-cycle the battery alot. I would expect it to let the battery go down to "back to grid" voltage, but it doesn't.

This happens when using UTI mode, and Utility First charging mode. I don't have solar connected yet to the inverter, so I don't know if it behaves differently with solar charging.

On 2023/08/17 at 8:38 PM, meetyg said:

As I mentioned, this is counter-intuitive to the manual, but you're correct, it does work with LI settings.

It appears that the MUST inverter is also plagued with the premature float bug. Mine simply won't go into absorption voltage, no matter what I tried, when using USE battery type setting. However, when I changed to LI, it indeed goes into absorption voltage. But now a new problem arises: When battery is full, it will let it discharge a bit (around 2v less than absorption,  which in my case is still pretty full), but then charges up again to the absorption voltage.

So while the LI setting works around the premature float bug, it seems to micro-cycle the battery alot. I would expect it to let the battery go down to "back to grid" voltage, but it doesn't.

This happens when using UTI mode, and Utility First charging mode. I don't have solar connected yet to the inverter, so I don't know if it behaves differently with solar charging.

@meetyg So glad I found this thread! I have pretty much the exact same inverter, it's just an Esener which is a rebranded Must in my opinion, model number is pretty much the same, ES-3024VPM.

I am experiencing the exact same thing after moving to a LifePO4 battery when my lead acids died. I am indeed also using the Li battery type as instructed by the sticker on the inverter, and I am also seeing what you describe with the Utility/mains charger. After discharging the battery and putting in back into charge, the voltage will eventually go to the float voltage(mine is set to 27.2V) and will sit there for a while before moving up to the bulk voltage, mine set at 28.4V for now(I'm still toying with the voltages, more on that later) The issue, mine just seems to sit at the bulk voltage when reached, when charging with Utility. It does not come back down to the float/resting voltage. I don't know if this is by design, as the battery's bms will stop charging when the battery is full, but my concern is leaving the battery at that voltage? Also not sure if the battery's bms internally will perhaps go a resting voltage, which if so, I guess it's ok? Because once the battery is fully charged from Utility, and when measuring the voltage at the terminals with a multimeter, I only see fluctuations of small voltages constantly jumping around all over the place, i.e, 1.2, 0.6, 3.4 etc.. . I would hazard a guess as to say that's probably the BMS being shut off from charging and perhaps just balancing the cells? If I drop the bulk voltage lower to say 27.2V, I get a static voltage reading at the terminals.

BUT, with PV, it seems to be charging as expected. When discharging and letting it recharge, it will again reach the float voltage first as pointed out earlier in this thread, will sit there for a while, move on to bulk voltage, and eventually comes back down to the resting voltage(float voltage setting) of 27.2V. My inverter readings versus actual at the terminals also differs by 0.4v on Utility, and about 0.2v-0.3v on PV, i.e. inverter at 28.0V actually means 27.6V at the battery and so on. So you can see what a tricky balance it is to reach a compromise with the charge voltages when charging from Utility vs charging from PV..

Other people who do not have the Li battery type on slightly older Axpert inverters for example, are happily using the USE mode with float and bulk set to the same i.e. 27.6 with no issues. (Thanks @Flouw and @GMAC)

I just want to understand why this behaviour occurs with the LI battery type mode, when charging with Utility where the battery voltage stays in the Bulk setting and not coming down to the float value.. (I've even left overnight and was the same the next morning until PV takes over.)

On 2023/10/20 at 12:22 PM, Ed S said:

I just want to understand why this behaviour occurs with the LI battery type mode, when charging with Utility where the battery voltage stays in the Bulk setting and not coming down to the float value..

They seem to have a bug, where the entire charging cycle will not "reset" untill the battery is discharged enough.

As you mentioned, it seems the PV charger doesn't have this bug, but the utility charger does.

Some Axperts have this bug with PV too.