Ideas? Multiple Dumb BMS VS single smart for 950AH LifePo4's

[Prffsreric]

I am building a battery for my 48' Sun Deck Trawler. I am stuck on BMS options. The following are the items that I have currently.

The question: Should I go with dumb BMS on every 4 cells or parallel cells into 16 (4s, 4p) or 20 (4s, 5p) and use fewer smart BMS? The price is about the same and I see more protection on the cells with the dumb BMS. What do you think?

System, This is the house battery, 12 volt. I am set with this as everything on the boat is 12V. Electronics, winch, lights, ACC, and charging system.

Battery: 152, 3.4V, 25AH Navitas LifePo4 cells. New.

Inverter: 2500W 12v Sine Wave w/100 amp charger.

House power: 8KW Onan diesel generator. 2 55Amp alternators on main engines.

Solar: Future purchase. 5 panels on hard top. Approximately.

Looking forward to your input!!!

Brett

 

[John Frum]

If the BMS is fet based and in the current path you need to determine your max surge and continuous draws.
The will likely have an influence on your choice.

 

[Samcat]

I would advise on BMS that don't use mosfet and have independent modules, one for monitoring, one for balancing, fast-acting Class-T fuses ,relays. Probably 5A or more active balancer. I have successfully run 1000 Ah parallel battery cells in 16S battery banks. Definitely possible but safety should be your #1 priority when designing this type of battery monster. You should not be confused with ratings what some hardware makers are posting about max Ah ratings for balancing . And for your project i would go with multiple safety in rush kill devices ( fast-acting Class-T fuses and shunt breaker with high in rush ratings for DC power that can handle charge and discharge). If using 2 or more monster banks in parallel i would make sure that shunt trip breaker can handle in rush both ways for DC at max ratings. This could be over kill but it is your choice.

 

[Prffsreric]

Yes. good point. I did finish the post in a hurry!

My basic calculations (meaning that I have not measured them) are:
Maximum amps on the inverter are 190A calculated. Max house current, Lights, VHF radios, anchor windlass and dinghy winch are 50 amps. I like to round up. So lets say 250 Amps max draw. My main usage for the inverter is to run the apartment size refrigerator that the previous owner installed brand new. Instead of replacing it with a 12volt version I opted to put that money into a larger battery. Aside note, I was pleased to plug in my KillAWatt and find that it only draws 100 watts in the Florida summer! Over a 3 week period it only ran 50% of the time. Also intermittent use common household appliances like, microwave, induction cook top, convection oven, Vacuum cleaner.

Samcat. I agree with everything! I have only recently learned of contactor BMS (the QUCC)! Do you have suggestions for a better model?
Also, thank you for bringing my attention to shunt trip breakers. We use them all the time in 3 phase AC work. I never thought bout it for DC!
I am familiar with active balancing. What do you suggest for monitoring 152 cells?

I am still torn about paralleling cells. I know that the factory 100AH do it. Is there a way to monitor and protect 38 individual 4S packs?

Thanks for the input!

Brett

 

[Samcat]

If you have tight tolerance for resistance and have tested for benchtop energy each cell it would be easy to make group of parallel cells to make very safe battery banks with multiple parallel cells. Close attention will be needed for bus bars. I personally use flexible bus bars that are now available for aftermarket solutions. They are not cheap but they are extremely important for tight and solid connections with only 5Nm torque. And try to employ BMS that keeps history on charging and discharging over time. Make notes of all parallel cells for resistance when idle....when under load....when charging....and use this as starting point.
Temperature will have to be taken in to consideration before pointing fingers on parallel cells issue. I have not dealt with aftermarket solutions for BMS. I have been working with Batrium bms for short time ( like the design and individual modules) .Regarding flexible cooper bus bars they are now easily available on Amazon. They are top notch quality and engineering design. To make better control use temperature sensor for each cells in parallel. Example 4 cells in row i use 2 sensors for each parallel cells. And connect to bms and if any of parallel cells start going to 50°C + have system powering down and going out of service for inspection. If setup properly you can live with aftermarket bms...and have inverter and other components to stop before limit is reached for BMS or BMS hardware.