BMS Master Controller

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BMS Master Controller

Electric Vehicle Discussion List mailing list
For a BMS of a large battery pack for an automotive application can I have
all my slave boards connected to the cells and part of the pack and a master
controller outside the battery pack where I can integrate some other control
functionality as well ?

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Re: BMS Master Controller

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Sure, as long as the communication to the slave boards is isolated,
preferably on the slave board itself.
That way you just bring 12v plus communication bus to each slave. Almost
every commercial bms works this way. OEM bms typically uses CAN bus.
Cor.

On Wed, Aug 8, 2018, 12:38 AM bvgandhi via EV <[hidden email]> wrote:

> For a BMS of a large battery pack for an automotive application can I have
> all my slave boards connected to the cells and part of the pack and a
> master
> controller outside the battery pack where I can integrate some other
> control
> functionality as well ?
>
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> Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com/
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Re: BMS Master Controller

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bvgandhi via EV <[hidden email]> wrote:
 >> For a BMS of a large battery pack for an automotive application can
 >> I have all my slave boards connected to the cells and part of the
 >> pack and a master controller outside the battery pack where I can
 >> integrate some other control functionality as well?

Cor van de Water via EV wrote:
> Sure, as long as the communication to the slave boards is isolated,
> preferably on the slave board itself.
> That way you just bring 12v plus communication bus to each slave. Almost
> every commercial bms works this way. OEM bms typically uses CAN bus.

I took a slightly different approach in my BMS. I route a (fused) wire
from each cell "+" terminal to a cental relay board. The relay board
selects two wires (the + and - of the cell to be monitored), and routes
them to a central controller. The controller has the optical isolation.
That way, only *one* isolator is needed, rather than one per cell.

This is how the Toyota Prius BMS works as well. Just a thin wire from
each cell to the central BMS board. The isolation is done on the central
board.

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little worse and sell a little cheaper. Those who consider price
alone are that person's lawful prey. -- John Ruskin
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Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: BMS Master Controller

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Thanks for sharing that Lee, I was trying to understand from the perspective
of a heavy duty application something like a class 5 truck. I was wondering
, for a pure EV application will an OEM use a Master Controller and expand
it to encompass some of the major VCU functions or would they build a
simpler BMS with a more sophisticated VCU.

I was thinking that a more sophisticated BMS would allow for better control
of the pack and the VCU can perform auxiliary functions.


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Re: BMS Master Controller

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bvgandhi via EV wrote:
> Thanks for sharing that Lee, I was trying to understand from the perspective
> of a heavy duty application something like a class 5 truck. I was wondering
> , for a pure EV application will an OEM use a Master Controller and expand
> it to encompass some of the major VCU functions or would they build a
> simpler BMS with a more sophisticated VCU.
>
> I was thinking that a more sophisticated BMS would allow for better control
> of the pack and the VCU can perform auxiliary functions.

That's true; there are no doubt many functions that might be of some
benefit. Data logging, temperature monitoring and control (fans,
heaters), estimating range and charging time, etc.

But keep in mind that the BMS for lithium is a safety critical function!
It HAS to keep working despite damage, and MUST not fail in an unsafe
manner. It is much harder to design such systems. A classic mistake is
not to consider failures, or their consequences.

My preference is not to use an all-encompassing universal controller,
where a single point of failure takes down the entire system. Also,
avoid complexity; the more parts, the harder it is to make it reliable.

I prefer a KISS design (Keep It Simple, Stupid). Divide up the task
between separate, independent, redundant systems. If one fails, the
others still work; so it fails gracefully. For example, you might lose
the ability to read individual cell voltages when that controller fails;
but the overvoltage and undervoltage systems still work.
--
There is hardly anything in the world that someone cannot make a
little worse and sell a little cheaper. Those who consider price
alone are that person's lawful prey. -- John Ruskin
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: BMS Master Controller

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Hi Lee,

Yes you are right, I was looking at commercially available BMS controllers
such as Elithion and I thought that this is good but can do with more
functionality such as power prediction for better energy management. I did
think about the failure modes. So if you have a M/S topology and
slaves have adequate protection circuitry and fault detection IC's installed
as well as a high functional Master with added protection for cell current
limits wouldn't that make it safety critical. I can then have the slaves as
a part of the pack and the master outside the pack. The BMS essentially
serves as a powertrain controller and interfaces with the VCU. So in that
sense it is not necessarily a universal controller but does serve more
functions. I think the universal controller that you are talking about is
something like what Porsche tried to do :
file:///C:/Users/bgandhi/AppData/Local/Microsoft/Windows/Temporary%20Internet%20Files/Content.Outlook/62KQ3514/Powertrain%20Manager%20for%20Electric%20and%20Hybrid-Electric%20Vehicles.pdf


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