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Rechargable Battery Circuit Advice


#1

I would like to add a rechargeable battery circuit to my G80 controlled device. I need the battery pack to be able to run the main 5V line. Total 60 mA current draw. I intend to link two of these 3.7V / 2.2Ah Lithium-Ion batteries in series to give me 7.4V. Thinking of charging this off a 9V AC/DC wall adapter but am having trouble finding an IC for this cell voltage + battery pack voltage…maybe I am just misunderstanding what the IC specs are referring to by “Battery Pack Voltage.” Does that voltage have to be an exact match or can an IC rated for 12V charge a lower voltage battery pack? It also seems most IC’s are for charging cells above 4V

Is the 3.7V rating of the cells I am looking at just the average voltage? Will they work with a charging IC rated 4V per cell?


#2

If its just a one off then try searching eBay etc for “Intelligent Balance Charging Protection Board 2S”

They’re a couple of quid from China and the one I got seems OK


#3

@monoculture Thank you but I need an IC that I can add to one of my own PCB’s rather than a module as this is for mass production. I am a bit confused by the technical specs of the charging ICs though…


#4

zoom in on any of those battery balancing chargers and you’ll see what IC they use. Pick that.

3.7V is nominal single cell voltage for a LiIon battery, and they have a max voltage of 4.1 or so. Read up on battery chemistry and charging, make a circuit with the reference schematic the vendor you choose supplies, and spin a board. What’s the worst that can happen? oh yeah, that’s right, fire.


#5

@hwalker_MIWV - I’ve just tried to read the number off the board for you but it’s been scrubbed off.

I wonder if something like this might work: http://www.ti.com/lit/ds/symlink/bq2057w.pdf

[edited] wrong link [/edit]


#6

Do you need to power the device at the same time as charging? You will likely need to use a Power Path charging IC if you do. Most circuits, like the IC link by monculture, are designed to charge the battery away from the device it is powering.


#7

find a vendor who makes a module that meets your requirements and supports open source. buy the module and test it. if it works, then use their schematic for your design. I found one in 30 seconds.


#8

Thanks for the input everyone. I actually looked at that IC that monoculture posted…went through quite a few of those datasheets. I have studied a bit about battery chemistry and the different charging states…i.e. completely dead, topping off, etc. I am just a bit overwhelmed with the circuitry.

@Dave_McLaughlin the device should be able to be used while charging. Thank you for pointing that out, definitely was not aware of that. Do you have any recommendations? This did not seem to be clearly emphasized in any of the data sheets.


#9

TI do a number of power path IC’s and depends on your current requirements but not sure they have dual cell options.


#10

Ah I see…they are like hybrids between the two types of IC’s I saw…the battery chargers and the power management IC’s. Current requirement is about 60 mA discharging.


#11

Only one I can find so far is:

http://www.analog.com/media/en/technical-documentation/data-sheets/4012fa.pdf

It says it is a charger+powerpath control for dual cell lithium ion, 6-28V but appears to require a micro controller to “fully implement the charging algorithm”…guess that means it doesn’t top off/charge from completely dead?

…struggling to find IC’s that do both charging and power path control for more than 1 cell


#12

@Brett Trial by fire is the story of my career haha


#13

http://www.ti.com/product/bq24133


#14

@hwalker_MIWV - Having the power-path built in is just a convenience. You can get it as a separate IC or implement your own custom circuit. Maybe try googling for terms like “Power Prioritisation”, “Powerpath Controller”, and “Power Multiplexer”

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Also maybe investigate if you really need two 18650’s - They have a huge maximum continuous discharge rate so you should be able to get 5v / 60 ma out of just one of them and maybe you only really need 3.3v anyway.


#15

:slight_smile:

But that’s different to trial WITH fire, that’s definitely something nobody wants !


#16

@hwalker_MIWV - @Justin suggestion looks pretty good - It’s not ridiculously priced and there is an evaluation board available for it http://www.ti.com/tool/BQ24133EVM-715-15V - Might even use that myself! :slight_smile:


#17

NIce! That IC is exactly what I am looking for…saw the BQ24123 but not the BW24133. Should that IC use an AC power supply? Saw one mention where it said AC or DC but am not 100% sure.


#18

“The bq24133 charges the battery from a DC source as high as 17V”
“requires a regulated supply approximately 1V minimum above the regulated voltage of the battery pack”

I’d buy the evaluation board, check that everything works as expected and then just lift the design as @MikeLab suggested earlier.


#19

Thanks, I missed the “other,” in “The total input current from an AC adapter or other DC sources…”

Probably will get the eval board


#20

My favourite design option right now is to use a bridge rectifier on the power input so that I don’t have to deal with wrong wiring and can take 24Vac or 24Vdc of any polarity. After suffering from system damages due to negligent installation engineers, this has worked well and everything since doing so is still working :slight_smile: