Setting up my 2nd SBMS

[Tom]

Hi Guys, I'm in the UK and have been using a lithium solar rig with an SBMS100 for 7+ years It's a great system so firstly I'd like to say thanks and respect to Dacien at Electrodacus.

I'm setting up a larger rig now with 8x eve 304AH lifepo4 (they are clamped don't worry)

I've had a little trouble with my Multi Plus 24/3000/70 (which were second hand) they are old microchip 1912xxxx type. The control system works to turn off the inverter but it doesn't work to control the charger. There are three terminals. leftmost is "v sense" middle is "TR charge"  and i'm controlling the inverter with the last one; "T sense". Are these actually AUX controllers? I'm reading 26vdc across the TR charge terminal and the SBMS0 can't switch the charger off. Could it be something to do with the firmware? I've got xxxx2xx firmware on it at the moment. Yes I did run the 2 wire bms assistant. 

I know these are older inverter/chargers but there must be a way to control the charger! Thanks!

[Dacian Todea (electrodacus)]

Tom,

I'm not familiar with that old model. In VE. configure if you select Two-Signal BMS support like in the example in the document https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf  What options do you have other than Temperature sense input ?

From a google search I made it seems the TR charge is a trickle charger output for a secondary battery.

Maybe you can use the T sense to control the charging  and then use the main ON/OFF switch for stop discharging but then if the battery will ever be empty the Multiplus will not be able to charge until battery is recharged sufficiently from solar  so that Multiplus is turned back ON.

So use the T sense set to control the charger controlled by EXT IO4 set as type 1

And use the H connector controlled by the EXT IO3 set as type 2 to control inverter/charger ON/OFF so it will fully turn OFF the inverter and charger in case of battery fully discharged and then it will need to wait for solar to charge the battery so that inverter/charger is turned back ON.

[Tom]

Hi Dacien, Thanks for your reply. The VE configure two signal bms assistant gives 3 options Aux1 Aux2 and temperature sense. I like your work around using the H connector but like you say the charger wouldn't then work when I potentially need it the most!

 I don't think I tried Aux1 (presumably the Vsense connnector?) Might that work?

[Helge Flataker]

I also have an older multiplus, and I think we are in the same position here. As far as I know you can not use the 2-wire BMS ESS on these older units.

Probably the easiest option is to connect one (or both) leg of incoming AC supply through an SSR and use that to control charging. Downside is that you loose the automatic transfer switch capabilities of the multiplus

I also suspect you can run battery voltage through a boost converter and feed a higher voltage through the V-sense terminal. (Eg 15V) That should probably kick the multiplus into absortion/float mode (And those voltages can be turned way down effectively stopping all charge). Testing required to establish if this happens quick enough to be sufficient protection. 

The boost converter would need some additional circuitry to feed the multiplus battery voltage normally and then a higher voltage once a type 1 IO opens. I am planning to experiment on that this summer and hopefully design and build this circuitry fall/winter. If anyone else here have build a similar circuit I would be highly interested in looking at it

For now I simply use very conservative charge voltages and current in the multiplus and only use IO type 1 on the H connector. This is on a boat and I have alternate charge sources (Solar and alternator) that fully charges the battery once in a while to reset the SOC counter. This has worked well for me, but you need to make sure your battery stays well balanced

[Dacian Todea (electrodacus)]

Tom and Helge,

Not sure what will be the situation where the H connector will not work.

If you have AC input connected then your loads will be directly supplied by the grid so battery can never get to fully discharged.

If there is no AC available at the inverter/charger input then it is irrelevant that inverter is fully turned OFF as there is no AC charging available anyway and if there is solar then that will charge the battery when sun is available and when battery is sufficiently charged the inverter/charger will be turned ON by the SBMS.

So just use the T sense to control the AC charging  and use the H connector to protect the battery in case the battery is fully discharged.

Helge,  Having Lithium battery in absorption is just not a good idea. As mentioned above I do not see any issue with using the H connector. As long as you have AC input battery can not be discharged as load is supplied by that and if you do not have an AC connection then if battery is discharged the inverter will just be turned OFF.

[Helge Flataker]

Using T-sense to control charge using the 2-wire BMS ESS is only supported on devices with 20XXXX firmware, and its not possible from 19XXXX (or 18XXXX that I have)

[Dacian Todea (electrodacus)]

Helge,

So in assistant there are no two wire BMS options ? Or you can not select T sense for charge ?

If that is the case then the only option seems to be SSR on the AC input but with the limitations you already mentioned.

I had the impression that T sense can be used to either stop charging or discharging and there just is no Aux input.

[Helge Flataker]

Not for me (on 18XXXX), but not sure about the 19XXXX firmware. 

Regarding absorption on LiFePO4 thats not possible to disable either, only adjusted down to 15 minutes and I think i set ny absorption voltage all the way down to 10V or so its effectively disabled as no current should be flowing from the charger to the battery at that voltage

[Dacian Todea (electrodacus)]

If SBMS controls charging either trough T-sense if possible or trough SSR on AC input the absorption float will be disabled as SBMS will stop charging as soon as any cell gets to 3.55V.

[Tom]

Thanks for the input Helge I'm glad I'm in good company! 19122xx firmware on mine allows BMS linked to T sense to control the inverter side.

Using the H connector with a solid state relay between the pins 2+3? to turn it all off when battery is low will be fine normally  I'm just thinking if it's dark and the battery is out I'll start the generator but the battery won't charge. 

I think the V sense mod solution could work to signal charging to stop. The VE configure settings allow you to disable float. I'll try it with the bms connected to Vsense at some point to see if that works and update here.