SBMS0 & MPPSolar PIP-LV-MK all in one

[GLASHINC Developments]

I have been looking at the MPPSolar PIP-LV-MK series (specifically the 2024LV-MK: http://www.mppsolar.com/v3/catalogs/PIP-LV-MK.pdf).  The ability to do 0ms transfer between battery mode and AC mode in the event of inverter overload would really help in scenarios where inrush currents are higher than what the inverter(s) can manage.

My questions are:

• Can this all in one system be used with the SMBS0 and DSSR20 such that both the 2024LV-MK and the DSSR20 have solar panels attached to them and charge the same same battery?
• If that setup cannot work does it make sense to use this all in one system for the other components (AC charger, automatic transfer switch, inverter)?

[Dacian Todea]

The MPP Solar can be used as an inverter only as there is only remote ON/OFF control for the inverter no separate remote ON/OFF for the charger (neither the grid charger or the build in charger).

So the 2024LV-MK can be used only as an inverter when used with Lithium.

[GLASHINC Developments]

Questions on diagram:

1. Would the PV panels specified be compatible with the DSSR20 or do lower wattage PV panels need to be used?
2. If the Heat+ terminal of multiple DSSR20 are tied together to feed a common output do diodes need to be installed on each Heat+ to prevent reverse current flow? 

Could this configuration work?

• SBMS0 would be the primary means of charging the battery via the DSSR20s. All the regular settings for LiFePO4 would be used
  • Charge to 100% SOC at start of day
  • Max SOC set to 90%
  • Under Voltage set to 2.80V
  • Over Voltage set to 3.55V
• When the DSSR20s are not charging the battery they would divert the PV to the solar input of the 2024LV-MK
• The 2024LV-MK has a maximum PV input of 2000W which would limit the number of PV panels specified to 5
• 2024LV-MK is setup as follows
  • Solar energy provides power to the loads as first priority. If solar energy is not sufficient to power all connected loads, battery energy will supply power to the loads at the same time. 
  • Utility provides power to the loads only when at least one of the following is true:
    • solar and battery is not sufficient
      
    • battery voltage drops to programmed level to engage utility as source (24.0V or 3.00V/cell avg)
    • battery voltage drops to low-level warning voltage (22.0V or 2.75V/cell avg)
  • Battery provides power to the load when the voltage reaches 28.0V or 3.50V/cell avg
  • Solar energy provides power to the load first and the utility is allowed to charge battery.
    
  • Charging settings(same for solar and utility charging):
    
    • Bulk charging voltage set to 28.1V or 3.51V/cell avg
    • Floating charging voltage set to 27.0V or 3.38V/cell avg
    • Max charging current set to 60A (~0.2C)
    • Equalization disabled
  • Low DC cut-off set at 21.0V or 2.63V/cell avg (inverter shuts off at this point)
    

With the configuration and settings above the following should be the mode of operation:

• At start of day DSSR20s are used to charge the battery until 100% SOC is achieved (highest cell at 3.53V)
• After 100% SOC the DSSR20s go into divert and supply solar power to the 2024LV-MK
• As the battery at that point is above the float voltage the 2024LV-MK sees the battery as being fully charged and applies a float charge voltage of 27.0V or 3.38V/cell avg which in effect does not charge the battery
• As load is applied the 2024LV-MK supplies the load from solar power first. It draws on battery as needed if solar is not sufficient.
• When power drawn from the battery reduces its SOC to 87% (90% - 3%) the DSSR20s will be used to attempt to charge the battery back up to 90% SOC
  • During this time the solar input is not available to the 2024LV-MK  and so it supplies the load from battery
  • If the rate at which the DSSR20s can charge the battery is higher than the rate at which the 2024LV-MK  is discharging the battery then the SOC will return to 90% and the PV will be diverted back to the 2024LV-MK
    
  • If the rate at which the DSSR20s can charge the battery is lower than the rate at which the 2024LV-MK is discharging the battery the SOC will continue to fall
• If the depletion in SOC results in the battery voltage falling to 24V or 3.00V/cell avg the 2024LV-MK switches to utility to power the load (this should happen infrequently)
  • Switching to utility stops the 2024LV-MK from discharging the battery (except for the self consumption discharge)
  • The utility charger will now switch on and will charge the battery using a bulk charge followed by an absorb charge
  • When battery reaches 28.0V or 3.50V/cell avg the 2024LV-MK switches back to battery to supply the load
  • During the period that the 2024LV-MK is charging  the battery the DSSR20s would also be charging the battery (until 90% SOC is achieved at which point the DSSR20s switch to diversion)
• If the battery voltage falls to the Under Voltage setting level of the SBMS0 (lowest cell voltage <2.80V for more than 1s),  EXTIO3 will be used to turn off the 2024LV-MK
• If for some reason the SBMS0 fails to turn off the 2024LV-MK based on the Under Voltage setting then when the battery reaches the Low DC cut-off ( 21.0V or 2.63V/cell avg) the 2024LV-MK will shut itself down

[Dacian Todea]

1.  While the panels are compatible and they will work they are 72 cell panels so a bit of a waste as the extra 12 cells will not do anything unless you have very long PV cables and then it will help with the voltage drop on cables or maybe it looks like you want to use the MPPT inside the MPPSolar then it should be fine tho not sure if that MPPSolar can handle that many panels.

The connection is wrong if that is what you want to do and the Batt+ will connect to Solar+ on the MPPSolar while the Heat+ will remain unconnected.

2. You will not sue the Heat+ in the way you show in that diagram and that is even assuming you got the division version of the DSSR20 as else the Heat+ is not even connected to anything inside the simple DSSR20.

When the DSSR20s are not charging the battery they would divert the PV to the solar input of the 2024LV-MK

I see now what your intention was but doing so you will overcharge the battery as the 2024LV-MK has no idea when to stop the charging and will damage your battery.

While DSSR20 charges the battery the Load will use the PV energy first and if there is extra that will go to battery (that is the case with any charger including DSSR20).

battery voltage drops to low-level warning voltage (22.0V or 2.75V/cell avg)

Bulk charging voltage set to 28.1V or 3.51V/cell avg

No charger or Load can protect the battery if is not controlled by the BMS.

So for example the 22V under voltage will be guaranteed to damage your battery as there is always a cell with just slightly lower capacity even if is a fraction of a percent then all cells will be at around 3V (almost empty) and that one lower cell will be at 3V x 7 = 21V so remaining cell will be at 1V that is why a BMS is needed and the only one able to protect the battery by turning off all loads when any cell is below 2.8V

So in order to protect the battery the SBMS0 will need to have remote ON/OFF control over all charge sources and separate remote ON/OFF over all loads.

[GLASHINC Developments]

Thank you for the answers.  In terms of cost the 72 cell panels cost less per watt than the 60 cell panels but if I end up not being able to use those watts then it would be bad economics to buy them.  I will have to investigate other panel options.

I will be using the the DSSR20D units (the ones with diversion).  

Reading your answers and also reading this thread I get a better understanding of the danger of using any control that is based on the aggregate battery voltage: 

https://groups.google.com/g/electrodacus/c/h9tpaRnpNRM/m/1Q6pN2rsBgAJ

So essentially I will need to remove input to the Solar+ of the 2024LV-MK (effectively disabling the solar charger). This means that battery and utility will be the only 2 source available to provide power to the load.  Given, however, as you said, the DSSR20s would be charging the battery, PV power would be shared with the 2024LV-MK on its battery input. I figured it would have been more efficient (MPPT optimization) and less stressful (less cycles) on the battery to have the 2024LV-MK feed power to the load without involving the battery when the SOC is in the region between 100% and 90%.

If I leave the utility charger enabled I would need to shut down the 2024LV-MK on both the Under Voltage (EXTIO3) condition and a high cell voltage condition.  I am thinking that the OVLK condition could be used for this and setting it to 3.60Vpc triggering EXTIO5.    Is this possible?

[Dacian Todea]

Cycles are not relevant for LiFePO4 there will be no degradation (insignificant) based on that. Utility charger can also not be enabled.

When battery is fully charged any cell gets to 3.55V all chargers need to be disabled so load will work on battery until SOC drops enough so that charging can be re enabled.

The MPPSolar was just not designed to work with Lithium batteries so it has no proper controlls for an external BMS like the Victron multiplus for example see this paper to understand better how that works https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

That one has separate remote ON/OFF for inverter and separate remote ON/OFF for grid charger so inverter can work while charger is disabled and also works as an UPS so as long as grid is available the Load will be supplied from grid.

[GLASHINC Developments]

Back to the matter of panels...would I be able to put 2 of these on a DSSR20:

Maximum Power at STC (Pmax) 450W
Voltage at Pmax (Vmp) 34.67V
Current at Pmax (Imp) 12.98A
Open-Circuit Voltage (Voc) 41.25V
Short-circuit Current (Isc) 13.89A
Cells Mono 6*20

[Dacian Todea]

Yes DSSR20 should be able to handle two of those if you have a small fan helping with cooling as those panels will put out 13 to 15A each so up to 30A from two panels and those type of new panels is one of the reasons why I work on the DSSR50 that will handle 4 of those panels groups of two on two separate inputs.

Do you have a link to those panels ? Guessing they are quite a bit larger than standard 60 cell panels.

[GLASHINC Developments]

https://www.alibaba.com/product-detail/2021-best-selling-450w-cheap-price_1600220394925.html

[Dacian Todea]

Yes those panels are significantly larger as typical 60 cells or 120 half cut cells are about 1.65m x 1m = 1.65m^2 while those panels are 1.91m x 1.13m = 2.16m^2 that is a 31% increase in surface area so about same cell efficiency used in typical 340W panels will also be present in those larger 450W panels.

But are you considering getting panels for alibaba ? It just seems that when you add the large shipping cost and the import taxes it will not be much if any saving.