# BMS and PCM, are they the same?



## Siwastaja (Aug 1, 2012)

Both of the terms can mean anything. The only way to know is to see what the _actual_ features are. PCM may mean a weak top balancer circuit which tries to ensure that the cells come up full at the same time so that by carefully controlling the charging voltage, no overcharging takes place. BMS may mean that in addition, there is cell-level monitoring that automatically cuts charger power if any cell gets full before others, and cuts the load if any of the cells gets empty before others. These features are hard to integrate into a monolithic block, especially if these blocks are going to be connected in series.


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## Elithion (Oct 6, 2009)

A PCM is a BMS for a small battery (one cell or few cells) that includes a bidirectional protection switch and is mounted directly to the cells.

It means "Protection Circuit Module". (Not terribly descriptive, I know.)

BMS is a general term, which encompasses (by my count) 8 different types of BMSs.


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## E30_Dave (Apr 19, 2012)

Davide,

Great link - Many thanks !


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## Ziggythewiz (May 16, 2010)

Elithion said:


> BMS is a general term, which encompasses (by my count) 8 different types of BMSs.


Does that include Kanto's Battery Mutilation System?


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## Siwastaja (Aug 1, 2012)

Ziggythewiz said:


> Does that include Kanto's Battery Mutilation System?


Any type can optionally be _mutilative_. For example: übercomplex, distributive, super advanced mutilative battery management system.

BMS's are funny, because the whole field of design is so _trivial_. So everyone wants to design a BMS. It's a funny little project. I was into it a while ago, designing nice distributive advanced systems, but got bored quickly.

Also, because it is so trivial, many want to make it as complex as possible to make their system look "advanced". OTOH, to make it really reliable and safe and cheap, a lot of engineering skills are of course needed, even if it looks so trivial on the surface. This is where the problem lies; (1) obfuscating the simplicity to make one (company, or design engineer) look like advanced professional, more than they really are, and then (2) underestimating the real design challenges.


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## jumpjack (Sep 9, 2012)

Elithion said:


> A PCM is a BMS for a small battery (one cell or few cells) that includes a bidirectional protection switch and is mounted directly to the cells.
> 
> It means "Printed Circuit Module". (Not terribly descriptive, I know.)


Aren't you confusing with PCB (Printed Circuit Board)? I think PCM is related to power...


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## Siwastaja (Aug 1, 2012)

jumpjack said:


> Aren't you confusing with PCB (Printed Circuit Board)? I think PCM is related to power...


I think the term "Printed Circuit Module" comes from small cylindrical cells that are standard size such as AA or 18650 (compatible with non-protected ones) and have very small round PCB that has the protection electronics. An example: http://i00.i.aliimg.com/photo/v0/637258558/Protected_18650_2600mAh_3_7V_Li_ion.jpg


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## Siwastaja (Aug 1, 2012)

And, sometimes PCM = simple top-balancer.

It boils down to the fact that any term can mean anything. Just make sure that the specific system you are buying does what you want it to do.


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