Can I allow the Multiplus II to charge the batteries as well?

[Sergio Veltri]

Hi guys,

I have some kind of hybrid system where I have an SBMS120  connected to 12 270W solar panels and also a 400A LifePo battery with a Multi and an Ongrid Solax Inverter.

Im having a hard time having the best configuration. Should I allow the Ongrid inverter to charge the battery as well using ESS in the Multi when there is excess solar? Not sure if ESS assistant can co exist with the 2 Signal BMS Support, especially if the instruction is to Disable Charger. SMBS120 has also an external shunt that know if energy is coming in from another source other than the panels. Please see image below. I also wished the Multi could talk to the SBMS and have more accurate info. Thanks

Sergio

[Dacian Todea (electrodacus)]

Sergio,

The 12 x 270W panels are already at the limit of what a 400Ah battery can handle if you want long battery life.

The two signal BMS will allow the Multiplus to charge the battery as long as battery is not fully charged but it will be to much current for your 400Ah battery.

The way your system seems to be setup the Multiplus acts as an UPS so unless the grid gets disconnected the Essential Loads will be powered by the grid and not battery.

I'm fairly certain that the 12x 270W panels will fully charge the battery everyday no matter how discharged the battery is.  I do not even know how the battery will get discharged.

[Sergio Veltri]

Yes, the Multi is more UPS so I wanted to change that and have it at least contribute all it can to the house say until battery goes down to 50% for example and when there is light the 12 panels can also help. Specially in winter this could be a good contribution. I could see if Victron can limit charging current.

Yes the 12 panels look like a bit much but they are in a west-east setup so I havent seen them outputting their max.

Thinking of how I can integrate SBMS with Victron more...I have a smart shunt but its measurement differ from the SBMS usually shows.  Sometimes the smart shunt will go to 100% and SBMS says 70%. 

I guess I would be happy if the system did the following:

- Always send first Ongrid solar to house loads.

- Have the 12 panels + SBMS + Victron contribute all they can to the Loads up untill 50% of battery capacity.

- Remaining 50% left as UPS mode.

-In Winter or cloudy days Ongrid solar ideally could help charge battery if 12 panels are struggling

-If Multi could talk to SBMS I will touch the sky ;-)

Thanks! 

[Dacian Todea (electrodacus)]

I guess you already know hoe the Multiplus needs to be setup and connected to SBMS120 if not check this document https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

The charge limit can be reduced on the Multiplus but it will not be smooth just a PWM type control so peak current will still be very high generating a lot of electromagnetic noise.

 

The Smart shunt can not know when battery is full and only guess at best.

- Always send first Ongrid solar to house loads.

This is done by default due to the nature of the setup.

- Have the 12 panels + SBMS + Victron contribute all they can to the Loads up untill 50% of battery capacity.

I do not think that is possible from Victron software as the Victron can only work as charger or as inverter (there is no separate hardware) and if there is an AC input then it will just bypass that to the Essential loads. There may be some function to supplement the AC input if that is limited to some set current but not sure what are those set limits and if it will help in any way in your case.

- Remaining 50% left as UPS mode.

You can setup the SBMS120 EXT IO4 as type 3 and set the limit at 50% SOC then charging will be requested from the Victron only when battery SOC is below 50%

-In Winter or cloudy days Ongrid solar ideally could help charge battery if 12 panels are struggling

Essential load is powered by the 18 panels so is the rest of the house thus if the 12 panes are struggling the 18 panels will not do much better and likely not produce enough to both power all your AC loads and have extra to charge the battery.

-If Multi could talk to SBMS I will touch the sky ;-)

SBMS is master only and will not take any input from any device.

What could Multiplus communicate to SBMS120 that SBMS120 not already knows ?

The only thing Multiplus needs to know from SBMS120 is provided by the two wires EXT IO4 allows battery charging from grid and ECT IO3 allows battery discharge.

SBMS120 knows all about individual cell voltages and battery current. I can not imagine what you think Victron multiplus can provide to SBMS120 that will be useful.

When it is sunny there is more than enough energy from 12 panels to fully charge the battery and likely there will also be excess energy that can not be used unless you have some place to dump that excess energy like a thermal storage.

When it is cloudy most likely you will need to use grid energy to power your house as likely your consumption is higher than what panels produce and the small amount of battery stored energy.

You could have connected all PV panels to grid that way all PV panels energy can be exported to grid when there is excess. Then battery will have been charged only from Victron multiplus using PV energy or if that is not available then grid.

[Sergio Veltri]

Thank you for your time in writing all of it. It gives me things to think about!

As to the communications between SBMS120 and the Multi I was thinking if the Multi was able to read the exact SOC from the SBMS then it would be way more accurate than the SmartShunt and then it could be setup correctly for the 50% SOC...but you gave me the idea of IO4 AS TYPE 3...will give that a try.

 I think I have to keep thinking that the SMBS is running the show and just see the Multi as a plain inverter.

If I wanted a full Victron install I should have gone all victron gear and a basic bms, but I like the sbms too much. :-) As an example during the mornings the Ongrid takes longer to start generating power any day of the year, whereas the panels that are connected to the SBMS are the first to start working and last to finish!

Thanks for all the ideas.

Saludos

Sergio