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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Looking for turn-key BMS system
Date: Thu, 3 Oct 2024 03:20:49 +1000
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On 3/10/2024 12:58 am, john larkin wrote:
> On Wed, 2 Oct 2024 15:12:22 +0200, Klaus Vestergaard Kragelund
> <klauskvik@hotmail.com> wrote:
> 
>> Hi
>>
>> One of my clients is looking for replacing existing HW, 2 200Wh battery
>> modules, which each has a BMS controller, that monitors and balances 12
>> lithium ion cells (4 series connection of 3 parallel cells). Each of the
>> modules has SOC output in the form of LEDs.
>>
>> Beyond that, the overall system has a BMS controller that is powered
>>from either 24VDC (grid connected) or from the batteries. This BMS 
>> controller also has SOC, with a connected display.
>>
>> The client would like a turn-key solution, so minimal NRE due to low volume.
>>
>> I am looking for a supplier of finished batteries with BMS and also BMS
>> controller. Perhaps one of you guys has worked with this? (need a stable
>> supplier)
>>
>> Client is based in the EU.
>>
>> Thanks
>>
>> Klaus
> 
> I have a list of future projects which includes a battery monitor. I
> figure it might have a wire per cell (+1 at the end of the string) and
> snoop voltage, ripple, and estimate cell impedance, something like
> that. Measuring string current would help.

Measuring the core battery temperature is a good idea. Measuring surface 
temperature of the battery is useful additional information.

Battery output voltage depends on temperature and the state of charge 
(not to mention the current flowing through the internal resistance).

It you have enough current flowing through the battery to create thermal 
gradients, life can get complicated and you'd need to do a bit of 
thermal modelling on the fly.

I got asked that question at a job interview - I didn't get the job. 
Maybe the interviewer thought that I was over-complicating the task.

-- 
Bill Sloman, Sydney