Multiplus II and LiFePO4 parameters (free talk)

DIY
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1

Hi,

There is too much information, sometimes discrepant, about setting up the right parameters of a Multiplus II 48V with LiFePO4 batteries. So, I set my values as below and I would like to start a free discussion about why it could be good and get your feedback telling us why it could not be good. My setup is:

Inverter tab:
DC input low shut-down : 44.8V (2.80V on cells)
DC input low restart: 47.0V (2.93V on cells)
DC input low pre-alarm: 47.0V (same as low restart)

Charger tab:
Absorption voltage: 56.0V
Float voltage: 52.8V

ESS:
Sustain: 47.0V
Dynamic Cut off: 44.8V (2.8V on cells)
Restart offset: 3.0V (2.9V on cells)
Voltage to restart PV: 46.4V (2.9V on cells)

Would you do the same? If not, why?

2

I set my Quattro to shutdown at 48 volts. On the odd chance that my battery gets that low, I will likely need to use power on the DC side to troubleshoot. My battery has never seen voltage below 50 volts, so 48 volts is pretty low.

I am not in an ESS environment. My equipment is deployed in an RV, so your mileage may vary.

3

My understanding of “shutdown” is that this is the limit to prevent damaging the batteries. This said, you can tailor what you really want by setting a minimum SoC in ESS (that I use). In this case, the minimum SoC is the deepest the system will go unless if the system is off-grid. I “guess” that if in off-grid for some reason (e.g.: grid is down), then the “shutdown” will be the limit.

4

Look:

image
image2834×1126 185 KB

5

To bad the discussion is so short here as I would like to have some more details about this as well.

2.8V is still a bit high. You limit the SOC (unless grid falls) to 10%
But in your situation , let’s say you do not go below 5% which is perfect

Otherwise if you want to go really low, I ‘guess’ a value of 2.7 * 16 = 43.2V is the minimum?

I don’t understand your restart voltage of 3V, it seems a bit high…

And you sustain voltage seems a bit low (compared to the (i thought) default of 50.0)

6

Are you charging / discharging fully every day ?

Are your settings within manufacturers specifications?

If you answer yes to the above, chances are manufacturers cycle life expectations will exceed around 10yrs.

In 10yrs i would guess your cells will be derogating from age more than use.