Author Topic: Struggling to find a simple BMS Solution  (Read 1017 times)

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Offline BoscoeTopic starter

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Struggling to find a simple BMS Solution
« on: June 08, 2020, 08:57:00 am »
Hi all,

I wonder if someone could help me.

I'm looking for a simple, low cost BMS solution for two series li ion cells. All I want is over voltage, over current and under voltage protection. When there's a fault, the MOSFETs get switched off. TI don't seem to do over current and if they do the IC is horrendously complex for what I need. I've looked through Digikey and the usual suspects but nothing. I'm currently looking at designing something discrete which I really don't want to do for something safety critical.

Thanks
Boscoe
« Last Edit: June 08, 2020, 09:58:47 am by Boscoe »
 

Offline TimNJ

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Re: Struggling to find a simple BMS Solution
« Reply #1 on: June 08, 2020, 04:50:53 pm »
Will this be installed mass-produced equipment? Or just personal? If it's mass produced, I'd highly recommend using an industry trusted lithium-ion protection IC. At least here in the US, people are getting sued left and right for improper lithium-ion deployment...regardless of which party is actually at fault. Voltage sensing I feel is easy to do correctly with discretes, but over-current (over-discharge), maybe a little more challenging to prove you have a robust solution. Typically those use a timers and delays to check for recovery conditions, etc.
 

Offline nctnico

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Re: Struggling to find a simple BMS Solution
« Reply #2 on: June 08, 2020, 05:06:06 pm »
Hi all,

I wonder if someone could help me.

I'm looking for a simple, low cost BMS solution for two series li ion cells. All I want is over voltage, over current and under voltage protection. When there's a fault, the MOSFETs get switched off. TI don't seem to do over current and if they do the IC is horrendously complex for what I need. I've looked through Digikey and the usual suspects but nothing. I'm currently looking at designing something discrete which I really don't want to do for something safety critical.
How about using a readily made Li-ion battery pack? That is a much better solution; but make sure it has the right certifications.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline BoscoeTopic starter

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Re: Struggling to find a simple BMS Solution
« Reply #3 on: June 12, 2020, 10:28:59 am »
Thank you for the replies and yes it's going to be implemented in a mass produced product. My other problem is that I can't use a dual MOSFET switch was the body diode drop is far too high at the currents it will be used at (~15A), I see drops of up to 1V in typical devices whereas I need something like 10mV!

We have been looking into custom packs but our manufacturer does not provide BMS solutions.

Currently I'm using a voltage monitor and a current trip sensor (INA300) to form HW interlocks with the rest of the circuitry. It seems solid to me but I've got a nagging feeling I'm doing something stupid. The interlocks will cut the charging source and any loads reducing the consumption on the battery to uAs from the MCU and glue.
 

Offline bin_liu

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Re: Struggling to find a simple BMS Solution
« Reply #4 on: June 13, 2020, 03:37:32 am »
It is best to provide detailed electrical parameters, such as the most important operating current.
Generally, small current (such as 1A、2A) can use S-8232 of SII.
https://www.ablic.com/cn/doc/datasheet/battery_protection/S8252_C.pdf
 

Offline Lomax

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Re: Struggling to find a simple BMS Solution
« Reply #5 on: June 13, 2020, 12:36:57 pm »
Maybe you've already looked, but for something like this I would turn to Linear Technology's datasheet search. You don't specify the capacity of your cells, or the desired input voltage, but I'm pretty sure you'll find a suitable chip in the LTC space. Perhaps something like the LTC4020 is a good fit?
 


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