# 144 volt battery pack bms?



## Antoine (Nov 2, 2020)

Hi!
I am wondering where to find a BMS for a 144v pack. I am using 40 cells in series, so I need to monitor every cell right? Do I need a BMS with 40 inputs? I am fairly new to battery management systems and I am wondering how to make my battery pack safe and reliable. 
Thanks!!!


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## brian_ (Feb 7, 2017)

Antoine said:


> I am wondering where to find a BMS for a 144v pack. I am using 40 cells in series, so I need to monitor every cell right? Do I need a BMS with 40 inputs?


Yes, 40 inputs. BMS usually come with inputs in sets such as 8 or 16, so you get the one with at least 40 channels and leave the extras unused.

There are debates about how necessary cell-level monitoring is, but every production EV does it, which I think is a strong hint. 

You also need the BMS to be set up for the specific voltages for your cells (LiFePO4 voltages are significantly lower than other lithium-ion chemistries, for instance).


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## john61ct (Feb 25, 2017)

brian_ said:


> There are debates about how necessary cell-level monitoring is, but every production EV does it


Really? Name one


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## brian_ (Feb 7, 2017)

brian_ said:


> There are debates about how necessary cell-level monitoring is, but every production EV does it...





john61ct said:


> Really? Name one


Every production EV has a BMS which monitors the lowest level of parallel cell group - that's why they have a BMS tap wire to each group, typically connected to BMS slaves through a multi-pin connector on each module. To name one, just name any EV. Is this just a misunderstanding because you think that I meant something else?

I should note that a group of cells connected in parallel (not in series) are effectively a single cell, so cell-level monitoring means one monitor point for that group. And I'm referring to voltage monitoring, not temperature (which is normally monitored at only one or two locations per module).

If you were asking me to name a debate... the forum has had lots of them. A search for just BMS will usually dredge up some threads in which someone says they happily run without a BMS or that a BattBridge is the best solution.


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