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I am putting together a new Lithium system and plan to use a REC MBS due to the close integration with both Victron and Wakespeed.
Initially, I am unsure of the battery configuration, it will be a 12v system and I originally wanted 3 paralleled banks of 4 in series - Does the REC BMS allow for this? I have asked REC directly b ut struggling with speed of communication at the moment.
I have seen in the manual that 3p4s is possible, but then each cell isn't monitored, but is this a problem?
Hi,
paralleling cells is fine - the MBS doesn't see each cell as such, but treats them as a single cell with 3x capacity. The over voltage and under voltage are taken care of as the 3 cells will be identical voltage. Make sure you use substantial bus bars for each parallel connection when you assemble the battery.
I run 8p on my REC BMS. (48V system)
Hi Ceriw, really appreciate you getting back to me.
Just to be sure that is the Active BMS system that you are using.
I think I may have been over thinking things. I was planning go 4s3p so that I could isolate each bank in case of a problem with 1 cell in a bank, I could isolate it and still have 2 banks running. But it seems most have all cells in just one bank. Maybe the redundancy is not required?
Thanks for the tip on the bus bars, I guess I will have to make them myself.
Hi, as I'm on a 48V system, I use this one http://www.rec-bms.com/BMSSMA.html as the active one only supports 4S, but the principle is the same.
To do what you suggest is possible in theory, although to get any benefit from it, it is likely to add a significant cost.
You would in effect need 3x BMS systems (controller, current sense, contactor, soft start etc), one for each paralleled battery, then a master unit to communicate with the 3 sub units (presuming the REC BMS MASTER UNIT 9M works, allowing parallel connections with the Active BMS - although I've not had any experience of that one so would need to check with REC first), reporting back to the Victron system the max charge/ discharge current etc. Then there would be the decisions of what to do if say, 1 string went over current - what do you do? If the answer is to shut down the inverter, than you haven't gained anything over a simpler setup.
In summery, on a DIY battery, I personally don't think it is worth the extra cost and complications to try and guard against a rare event. In fact, with the added complexities of the system, there is every chance that the overall reliability may go down.
Just my thoughts :)
There is some good stuff here. As I understand it the Victron Cerbo will only recognize one DC source so if you want a redundant 12V system you will need to use 2 or more 12V Q Series REC BMSs with a Master. The Master then handles and aggregates your DC sources into a single DC source on the VE.CAN network.
Due to the nature of active balancing, you can not parallel multiple systems because of interaction issues.
Here is a draft diagram which shows how this comes together.
