EG4 Wall Mount Pros (Optimal Settings for Optimal Performance and longevity

The nature of these lithium based batteries do not provide for a very consistent SOC vs voltage curve like with lead acid batteries.  I have seen some of my batteries report a low SOC while the voltage still looks "high", just like your screen shots. 

While I have not worked specifically with these wall mount units, I would think the BMS would be very similar to the LL units.  When using multiple batteries in a cluster it is good to give the cluster a full cycle every now and then; what I mean by that is take it down to 20'ish% SOC then charge all the way up to 100% SOC in the same day if possible.  This will help to get the BMS of each battery back into sync.   I have my system setup/scripted to do this every 30 days.  I have tried going longer but the SOC drift/variation from battery to battery seems to get even more out of sync and starts to throw off the overall SOC calculations (36 batteries/BMSs involved with this particular setup).

Even with the BMS SOC variation from battery to battery, I would still trust the reported SOC over the reported volts as a basis for actual SOC. 

Here is the charge/discharge curve from one of the 48v-LL battery manuals. The voltage will "level out" through a very wide range of SOC then very quickly spike up or down depending on if you are charging or discharging.  I believe the wall mount units are using a 280ah cell vs the 100ah in the LL units, but the battery/cell chemistry should be the same so the charge/discharge curves should be relevant.

Note how the voltage reports higher while charging, and lower while discharging.  This would also throw off any voltage based SOC tracking.

J

Here is an example of my system today while it is performing the monthly top up / SOC sync. (using Schneider inverters and charge controllers)

My wife is doing some laundry so the amps are all over the place, but you can see that as each BMS "synced up" the reported voltage and SOC spiked very quickly even though the charge amps was going down.  I actually battle this voltage spike vs SOC with my system because the inverters and charge controllers can't properly work with the SOC data even though the system as a whole knows what the SOC is.  For me this is ONLY an issue when the battery cluster is reaching 100% SOC as the inverters and charge controllers can only charge based on voltage levels, not SOC.  The very quick voltage spike will send my charge controllers into float mode even though the SOC is not actually at 100%.

In general use SOC whenever possible. Voltage can be used for the fringe 0-5% and 95-100% SOC situations but it will not be 100% accurate.  For longevity, these cells are best kept at, and cycled daily in the 30-80% SOC range.  If you need that extra power then use the 20-100% range which these batteries are warrantied for, but you could get even longer life out of them using the 30-80% range and you wouldn't be so reliant on tracking the voltage as is fluctuates very little while in that range.

J

SomeJ this is very very useful information and these curves is exactly what I am experiencing 50 to 54 is like bulk of the range 10% to 90%  46 to 50V is range of 10% and 54 to 56.3 is also a range of the upper 10%. The sweet spot is to stay 50 to 54. Thanks again for your post! 

No problem!!  Glad to help!  Just remember that the voltage while charging will be higher than the voltage while discharging even though the BMS will report the same SOC.  Sounds like you have a good upper charge voltage and lower discharge voltage range. 

Keep in mind charging with higher amps will present a higher voltage vs SOC, and same with discharging amps and lower voltage vs SOC.  If you have a trickle draw at night the voltage will appear higher longer while the SOC drops.

Cheers!

J

Here are SOC vs Voltage... I was taking the battery down to 46v based on setting one of the EG4 tech guys ..but that is too low. so wanted to see taking the battery down to 50v. So as of now changed the SOC low to 5% and it is depleting down to 5% and will see what the corresponding voltage be. I am getting my 3 battery replacement today so excited to add it to the system as 3 batteries should last me the night. They are charging up to 56v on the high side and that is corresponding to 100%. I want to see to changing that to 90 or 95% max. and low 5% to 10%. Now with third battery I dont think I will get even to 10% by morning.