diy solar

diy solar

1 BMS or 2?

Hi all,
Old thread but very relevant to me right now.
2P4S (1 bms)or 4S2P (2bms) dilemma has got me obsessing.
I want to do the latter as I can shut half the bank down for what ever reason
and continue with half capacity and not rely on switching over to my isolated start battery.
The "difficulties with parallel strings" chapter at https://www.orionbms.com/manuals/pdf/parallel_strings.pdf
seem to make what seems a simple design with redundancy fraught with potential pitfalls.
I will have 8x cell voltage monitoring (visual) plus LV HV cutoff via BMS's on each -Ve leg.
Top balanced and equalised before paralleling, with appropriate fusing.
Is this marketing via fear, or valid?

Quote: Important Note: Due to the risks of parallel strings, additional external safety systems must be used in conjunction with the BMS when the Orion BMS or Orion Jr. BMS are used with parallel strings. Electrical engineering is required to use the Orion BMS or Orion Jr. BMS with parallel strings, and this work must be performed by an electrical engineer who is trained in working with and understands the risks of paralleled lithium ion batteries. Do not attempt to use parallel strings without proper training.
 

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as I can shut half the bank down for what ever reason
Then that is a good reason to do 4S2P. If you are using an Orion BMS like I am then the cost of another BMS is not worth it. Remember the context in which that article by Orion was written. It is for the EV conversion segment where pack balancing may be more important than the advantage of redundancy.
 
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