# Pros and cons of BMS



## EVfun (Mar 14, 2010)

Now there is a subject we've thoroughly beaten to death. I would suggest you pick any thread in this forum with "BMS" in the subject line and take a swing at it.


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## peggus (Feb 18, 2008)

Nooooooooo, not another one!!!!


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## nimblemotors (Oct 1, 2010)

The pros are paid to sell BMS, they are professionals.
The cons are put in cells, they are convicts. 



ascomm74 said:


> What are the pros and cons of BMS?
> I'm planning to build an microcontroller based BMS which have individual cell based voltage monitoring and central controller which reads all individual BMS clients data.
> Total of 16 LiFePo4 cells of 40 to 60 Ah.
> 
> -AM-


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## ascomm74 (Feb 16, 2011)

nimblemotors said:


> The pros are paid to sell BMS, they are professionals.
> The cons are put in cells, they are convicts.


I'm sorry but I don't follow. Do you mean that BMS does some harm to individual cells or why cons are on cells side?

-AM-


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## nimblemotors (Oct 1, 2010)

ascomm74 said:


> I'm sorry but I don't follow. Do you mean that BMS does some harm to individual cells or why cons are on cells side?
> 
> -AM-


If you don't put a con in a cell, they will escape and create havoc,
and are very expensive to locate.


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## EVfun (Mar 14, 2010)

ascomm74 said:


> I'm sorry but I don't follow. Do you mean that BMS does some harm to individual cells or why cons are on cells side?


He's making a little joke there. Professionals are often called pros for short and criminals are often referred to as cons, short for convicts. I guess if the USA variant of English is not your first language the bit of humor would read more like nonsense.


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## ascomm74 (Feb 16, 2011)

EVfun said:


> He's making a little joke there. Professionals are often called pros for short and criminals are often referred to as cons, short for convicts. I guess if the USA variant of English is not your first language the bit of humor would read more like nonsense.


Oh, I see. That's why I didn't understand that. My mistake. I'm sorry.


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## ascomm74 (Feb 16, 2011)

Has anyone come by with a schematics of an uC based BMS's? Care to throw a link maybe?
Otherwise it's pretty straighforward but the communications between individual cells are little bit a problem? How others have implemented that? Obviously the common ground is not an option so a somekind of an galvanic separation is a necessity.


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## Jan (Oct 5, 2009)

ascomm74 said:


> Has anyone come by with a schematics of an uC based BMS's? Care to throw a link maybe?
> Otherwise it's pretty straighforward but the communications between individual cells are little bit a problem? How others have implemented that? Obviously the common ground is not an option so a somekind of an galvanic separation is a necessity.


optocouplers.


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## ascomm74 (Feb 16, 2011)

Jan said:


> optocouplers.


You are joking, right?  Of course it's optocouplers.
The question here was how should I implement the communication between cells.
- Can I use RS232 serial bus?
- How to manage the clients so that they will not try to send simultaneously?
- How the master uC can query individual clients or shoud it make "an broadcast query" to all clients at once?
- By how the clients can then reply back to master?

These kind of an questions are in my mind for now.


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## DawidvC (Feb 14, 2010)

Search for 'minibms' on this and other related forums. There is a lot of material available. The way you are thinking (if I am correct) seems to be close to what the minibms digital system is doing. It is worth checking it out and then coming back with some questions.

Regards
Dawid


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## ascomm74 (Feb 16, 2011)

DawidvC said:


> Search for 'minibms' on this and other related forums. There is a lot of material available. The way you are thinking (if I am correct) seems to be close to what the minibms digital system is doing. It is worth checking it out and then coming back with some questions.
> Regards
> Dawid


Actually MiniBMS has nothing to do with digital BMS, if I have read the correct MiniBMS documents. Doesn't it just indicate if something is wrong with one of the cells (not even exact cell)?

My goal here is to create BMS which can read voltages of all individual cells and report that data to master unit by some sort of serial data bus. This way the driver (rider in this case) can easily know which cell has the problem and the master unit can keep an "eye" on that cell and report it to be bad if it continuously has "someting wrong". Also this way the master unit can reduce the motor current to save the cells and squeeze all the available juice from the battery pack within the healthy zone.


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## MN Driver (Sep 29, 2009)

If I recall correctly, I think the MiniBMS will trigger by opening the NC signal wire but the unit on the particular cell that triggered it will have a fault light lit. I don't think you need to hunt for the problem cell.


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## ascomm74 (Feb 16, 2011)

MN Driver said:


> If I recall correctly, I think the MiniBMS will trigger by opening the NC signal wire but the unit on the particular cell that triggered it will have a fault light lit.


Yes, you are right. That's how it work. 



MN Driver said:


> I don't think you need to hunt for the problem cell.


This is more likely a "nice to have" feature rather than necessity. Although the problem cell watchguard would be usefull as the individual cells in this case can not be easily observed.

-AM-


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