18650 4S Battery management system

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Hi

I'm working on a design for a handheld scientific instrument which will be  
a low-volume production item (<200 units/yr). Its power supply is four 1865
0 Lithium Ion cells in series. The device will draw approximately three amp
s in short (< three second) bursts during its active time and <200 mA durin
g its on time (between measurements). The charging source will be a 19V ext
ernal supply (ubiquitous laptop charger).

I have seen many circuits for managing charging, many for "fuel gauging" an
d many for "protection". Also, there is cell balancing, which I don't think
 I need.  

What I haven't seen is any sort of integrated solution, or even a suggestio
n on how these parts fit together.  

So far, I have more-or-less narrowed it down to:

  ABLIC S-8254A for protection (mostly because I have boards here left over
 from another project that I can use for building a model)

  LTC2943 for fuel gauge

  LTC4162 for charging

Do these seem like reasonable choices? Has anyone here done something simil
ar? Are there any more integrated solutions? There's a fair amount of dupli
cation in the three circuits - voltage and current measurements, for instan
ce. Any gotchas?

Thanks

18650 4S Battery management system
The gotcha maybe in assuming you don't need cell balancing.
M

Re: 18650 4S Battery management system
snipped-for-privacy@gmail.com wrote in news:69967bc1-4fc1-4cf2-903b-
snipped-for-privacy@googlegroups.com:

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These batteries should definitely be individually charge managed.
Not knowing what that means is also a fail.

  With that much energy, even the in-use on time (and series adding  
of the voltages) might perhaps be better managed by an individual  
discreet FET switch on each.

  Turn this part of your circuit into a "battery module" where the  
output terminals are attached to your circuit, and the input  
terminals are for the re-charge power input.  In that battery module  
you manage the application of loading at the output terminals and  
you also manage the charging of each 'cell' in your custom designed  
battery module.
You'll lose a tiny bit in final output voltage but gain battery  
module and system safety.  The separate module can even be sealed  
against catastrophic failure causing damage to the main circuit  
module.

Re: 18650 4S Battery management system
On Thursday, February 14, 2019 at 10:12:38 AM UTC-5, rangerssuck wrote:
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e a low-volume production item (<200 units/yr). Its power supply is four 18
650 Lithium Ion cells in series. The device will draw approximately three a
mps in short (< three second) bursts during its active time and <200 mA dur
ing its on time (between measurements). The charging source will be a 19V e
xternal supply (ubiquitous laptop charger).
Quoted text here. Click to load it
and many for "protection". Also, there is cell balancing, which I don't thi
nk I need.  
Quoted text here. Click to load it
ion on how these parts fit together.  
Quoted text here. Click to load it
er from another project that I can use for building a model)
Quoted text here. Click to load it
ilar? Are there any more integrated solutions? There's a fair amount of dup
lication in the three circuits - voltage and current measurements, for inst
ance. Any gotchas?
Quoted text here. Click to load it

Have you looked for a battery pack from a reputable source with the chargin
g built in, which provides a voltage you can then transform into the voltag
es you need?  

Rick C.

Re: 18650 4S Battery management system
On 14/02/2019 15:12, rangerssuck wrote:
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I'm sure there's chips that will handle 4 x lithium charging including  
ballancing...can't remember what I saw in the past...

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Re: 18650 4S Battery management system
On 15/2/19 2:12 am, rangerssuck wrote:
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You'd be wrong, there. Whichever cell has the highest cycle losses will  
end up under-charged and will get damaged, pulling the whole string down.

See if you can adapt a USB power-pack. You don't need to use the 5V  
output side if you find one that has four cells in series.

Clifford Heath.

Re: 18650 4S Battery management system
On Thursday, February 14, 2019 at 10:12:38 AM UTC-5, rangerssuck wrote:
Quoted text here. Click to load it
e a low-volume production item (<200 units/yr). Its power supply is four 18
650 Lithium Ion cells in series. The device will draw approximately three a
mps in short (< three second) bursts during its active time and <200 mA dur
ing its on time (between measurements). The charging source will be a 19V e
xternal supply (ubiquitous laptop charger).
Quoted text here. Click to load it
and many for "protection". Also, there is cell balancing, which I don't thi
nk I need.  
Quoted text here. Click to load it
ion on how these parts fit together.  
Quoted text here. Click to load it
er from another project that I can use for building a model)
Quoted text here. Click to load it
ilar? Are there any more integrated solutions? There's a fair amount of dup
lication in the three circuits - voltage and current measurements, for inst
ance. Any gotchas?
Quoted text here. Click to load it

Another user here responded to me in private mail and suggested BQ76920. I  
don't know why that chip didn't turn up in my searches (including on the TI
 web site), but it does pretty much everything I need, including balancing.
 I will order the evaluation kit (ridiculously expensive) on Monday.

Re: 18650 4S Battery management system

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I forgot to mention that BQ TI chips have reduced cells voltage accuracy  
(about few +-10mV per cell) so this may be insufficient for scientific  
measurement purpose.

Re: 18650 4S Battery management system
So what is inside the typical 17V laptop battery.

Is there cell balancing in there?

m


Re: 18650 4S Battery management system

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Li-Ion Voltage = 3.6V typ (4.15V max)
17V uhmm ... Probably a pack of 5S Li-Ion cells
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Balancing is mandatory during charging process of the cells in series,  
don't know how the battery pack of laptop are designed, hope a fully  
functional BMS is embedded ... hope for us.

Designing a real BMS is my funny job at the moment. I spent a month  
comparing AD, LT, TI, ... solutions and finally it seems AD7284 is great  
chip for large batteries ; no tricky SMB/SPI protocols, no obfuscated  
documentation.
Prototypes are almost fully functional after a week of basic  
software/hardware recette ... AD is definitively my favorite.
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Habib


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