Hi
I'm working on a design for a handheld scientific instrument which will be a low-volume production item (
Hi
I'm working on a design for a handheld scientific instrument which will be a low-volume production item (
The gotcha maybe in assuming you don't need cell balancing. M
snipped-for-privacy@gmail.com wrote in news:69967bc1-4fc1-4cf2-903b- snipped-for-privacy@googlegroups.com:
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.
e a low-volume production item ( I have seen many circuits for managing charging, many for "fuel gauging" and many for "protection". Also, there is cell balancing, which I don't thi nk I need.
ion on how these parts fit together.
er from another project that I can use for building a model)
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?
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.
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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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.
e a low-volume production item ( I have seen many circuits for managing charging, many for "fuel gauging" and many for "protection". Also, there is cell balancing, which I don't thi nk I need.
ion on how these parts fit together.
er from another project that I can use for building a model)
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?
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.
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.
So what is inside the typical 17V laptop battery.
Is there cell balancing in there?
m
Li-Ion Voltage = 3.6V typ (4.15V max)
17V uhmm ... Probably a pack of 5S Li-Ion cellsBalancing 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.
Habib
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