Can I use DSSR20 at a DC Battery Disconnect (see attached diagram)

[MR in VA]

Dear Dacian Todea,

I was introduced to ElectroDacus SBMS0 by watching Will Prowse as I was learning about solar systems.  Thank you for sharing your knowledge, expertise, and system (hardware) with us.

I have assembled a portable, hand truck, Solar Generator built around the SBMS0, BYD used 24V 3Kwh battery, and MPP LV2424 Inverter/Charger.  I have connected the SBMS0 to turn off the MPP LV2424 for LVD using EXT IO3 to control.  The LV2424 charge parameters handle the Main Battery HVD and will also keep the batteries at nearly full SOC.  The LV2424 has an automatic transfer to battery if an outage occurs on the AC (grid).  I am using the system to power my refrigerator and freezer all the time (AC Bypass) and if the grid fails the load is transferred to the batteries.  Future upgrades will include Solar Panels controlled by the LV2424.

My setup does not draw more than 19 Amps from the battery at any time.

I have 2 (two) more BYD battery modules identical to the portable system and plan to have a separate SBMS0 on each of them.  These two batteries are not part of the portable system and will be disconnected if the system needs to be moved elsewhere temporarily.

Concerns:  The BYD are used LiFePo chemistry.  The modules had been in controlled storage for a while (2+yrs?) and the cells were out of balance.  I placed an active balancer on the system while I waited for my first SBMS0 to arrive. The cells were bottom balanced when I activated the SBMS0 and remained mostly in balance through the charge/discharge cycles.  Each module has a cell that is either lagging or leading the other 7 cells at the top or bottom of the charge cycle.

I am learning about SSRelays and my questions are:

1.       I am unsure if I should first parallel connect the 2 (two) stationary Aux battery modules (due to their used condition) before I connect them to the Main Busses.

 

2.       Can I use the DSSR20 as shown in the diagram?  NOTE: UNABLE TO ATTACH DIAGRAM

a.       One connected to the Main Positive Bus and use it at a LVD to protect the two Aux Batteries?  And should I use one DSSR20 for LVD for both batteries or have two (one for each battery)? [using EXT IO4 to control]

b.       One connected to the Main Negative Bus and use it at a HVD to protect the two Aux Batteries?  And should I use one DSSR20 for HVD for both batteries or have two (one for each battery)? [using EXT IO5 to control]

 

3.       Alternatively, would you recommend placing the two BYD Batteries in Parallel first and then using one DSSR20 on the Positive for LVD and one DSSR20 on the Negative for HVD as they connect to Main Buses?

If what I am proposing is outside the limits of the DSSR20, can your recommend a relay that will accomplish my goal using the SBMS0 as the control?

Thank you very much for your assistance. I pray these questions are helpful to others building systems with ElectroDacus.

[Dacian Todea]

The charging needs to be controlled by the SBMS0 else you risk overcharging your battery (guaranteed with an 8s battery that will happen).  So LV2424 can only be used as an inverter or you need to add a SSR on the AC input side to allow SBMS0 to stop the charging but that way it will no longer work as an UPS.

The only inverter/charger combo that I know has proper separate controls for inverter and charger is the Victron Multiplus and Multigrid (multi grid seems to be lower cost option and not sure why there is such large difference as they have basically the same functionality).  The document showing how the settings is done is this https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

Same with solar just get the DSSR20 as the build in solar charger in the LV2424 has no remote ON/OFF so can not be used.

You are not allowed to parallel Lithium batteries despite the fact that you may have seen this done in many DIY installations it is a bad idea thus you will not see this in any commercial application. Like you will never see a EV that offers extra range battery by adding another battery in parallel. If there are options for batteries the larger battery will have extra cells in series for higher voltage.

Those used BYD batteries are the most abused batteries I seen with a huge degradation basically already at the end of their usable life and should be recycled.

1. As mentioned above you should just not parallel Lithium batteries.

2. The DSSR20 is for solar PV charging only can not have a battery as the input just constant current limited sources like a PV panel or a constant current limited power supply.

3. As mentioned on point 2 the DSSR20 is not designed for what you mention here.

I can not recommend anything as you should just not parallel batteries. To use both batteries in the same system you will need something like an inverter on each battery and then AC output of the inverter paralleled assuming those inverters support parallel connection.

[MR in VA]

Thanks for setting me straight.