cracy idea: can I install 2 SBMS in paralell on one bank, one does charge the other load management

[Chris R8]

Hi all,

i am missing 3 EXT IO to actually manage my whole system as I figured I already need 3 EXT IO for all my charging gear thats from Victron.

As I have 2 SBMS (one was spare) why not install both, like this I have 8 EXT IO?

Could I actually install 2 SBMS in parallel and connect and set all parameter identical. So both should ge the same from the 5 sensing wires to cells (12V/4s) and from AC/PV shunts. keep ribon cable and cat 6 cable the exact same length.

One SBMS does charge side 3 EXT IO would be set to Type 1 charge, 1 type 5

2nd SBMS does all load,  2 EXT type 2 load and 2 on different SOC

don't see anything that interferes...

possible?

[Chris R8]

Can the cell balancing be turn off on SBMS.

That is the only thing that could possibly interfere. If I keep load to one and charge to the 2nd sbms nothing should happen.

[Patrik K]

Cell balancing should be able to be turned off on one of the SBMS0's, see this link

https://01319721522019860390.googlegroups.com/attach/58c6ffd88e9e8/Beginner's%20Guide%20Defaults.pdf?part=0.2&view=1&vt=ANaJVrFFkak7CeO2SfnsaavdOe9Lhfy1iWJS5n7FfR-5do39t8Syj7Lv0baEjoybNIp7iRSQUh0ZLsrNHZg81EEY4ZdYvdWXtCb3TT0mNJm15hdUHY4HQdU

I guess you should try your idea, since you already have 2 of them.

But WATCH them closely over time as you may have interference in the ribbon cables due sensing errors from resistance/capacitance in the wiring.

Have no idea how sensitive the SBMS0 is tho this, but Dacian doesn't recommend changing the length of the ribbon cable.

At a loss of power to one of them, you may also experience discrepancies between them, like temperature settings, so be sure to check settings from time to time until you are sure it works.

// Patrik

[Dacian Todea]

You could install multiple SBMS0 on the same battery but normally each will have his own shunt and control different charge sources and loads.

What you say should work (not tested) but seems wasteful to do that just to get 4 extra IOx.  You can use external optoisolators to control as many charge sources and loads as you want with a single SBMS0.

[Chris R8]

thank you Dacian. I have a marine install on an offshore offgrid catamaran that will go around the world and also to very remote places. Eg. I have life dependent gear like navigation, autopilot, Navigation lights, bilge pumps...that need to be transfered to an emergency backup battery short before a shutsown type 5 of the lithum house will happen, one for a near LVC and one for near HVC event and thats already 2 EXTIO of the 4 avaliable blocked. That means I have more different parameters and use cases/security backups then in an offgrid-on land install.

I simply need more EXTio to support this use and security cases and could get an SBMS v02 used for 80$....compared to the total invest of around 12000Euro the 2nd SBMS is peanuts and well invested money ( just needed to rework the electric setup from 2005 with eg no main fuse present :-(, cleanup of the electric rats nest (made by spanish/UK newbee installers :-)) on the catamaran and lifepo4+electric galley install)

The passive balancer in both SBMS won't interfere each other?

Why use different shunts? I will have 2x500A/50mA shunts in parallel (as I already have them and cannot get the 1000A here) and could just connect each SBMS to one of the parallel shunts, with the PV shunts I could do the same and install 2x 300A/100mA parallel PV shunts.

I would connect both SBMS to the same shunts, all sensing wires cells and shunts are connected in parallel so they get the exactly the same data.

Use cases

You have just 4 EXTIO but I wanna use/need already 4 for just for load side: one as type 2, three as type 4 with 10% (warning LVC shut off soon and switch "must have loads busbar" to emergency backup battery) 30% (switch off big loads inverters and watermaker) and 40% SOC set point (switch off hot water heater).

charge side needs 3 EXTIO charge too plus one Type 5 desaster shut down: one type 1, two type 3 with 80% SOC (switch on Hot water heater and inverters) and SOC 98%/3,6V( warning charge shut off failed and switch "must have loads busbar" to emergency battery) and one type 5.

You could switch the life dependent stuff in a type 5 event but I prefer to have more time to act/troubleshoot and get warnings before the shutdown will happen plus have the life dependent gear isolated from the house while troubleshooting it.

Eg manually switch the charge sources off by pulling the charge bus main fuse in an HVC event when shut off fails....

[Chris R8]

thanks Patrik for the shutoff link, thats what i was looking for.

Yes I will do it and install 2 SBMS...

good point if one SBMS gets shut down, need a type 5 EXTIO on both SBMS in case one fails due to any reason...

I could just cut both ribbon cables so two have the max length of one. but cables are in parallel, so half resistance in theory...but I will check and monitor closely in the first phase.

temp sensor will be put one on each SMBS and if there are little discrepancies I don't care if it shut the house down because one shows a lower temp then the other. better one time more false alarm then if the house gets destroyed in the middle of the ocean....