Impedance Track Battery Charging Question

Nicholas Alunni

Other Parts Discussed in Thread: BQ20Z65

Hello,

I have a question about charging the batteries for the first step of the bqEasy "5. Cycle" process. I am using a 2s1p cell with two 4.2V 4400mAh batteries.

1) Should I charge the batteries while connected to the bq20z65EVM while the Impedance track is "Initialized" (QEN is High)

2) How should I charge the batteries? Will the bq20z65EVM automatically cell balance at this stage? I see that my options are:

A) Connect 8.4V @ Charge Current to the 1N and 2P terminal to charge the batteries in series.

B) Connect 8.4V @ Charge Current to the Pack+ and Pack- Terminals and open the CHGFET. I believe that this will charge the batteries in series and not perform cell balancing.

C) Connect 4.2V @ Charge Current to the 1N and 1P terminal as well as another 4.2V @ Charge Current to the 1P and 2P terminals to charge the batteries individually.

D) It does not matter charge them however I would like.

Any help from an App Eng or anyone who has gone through this Cycle process with good results would be greatly appreciated.

over 14 years ago

0 Viktoriya Sherman over 14 years ago

TI__Intellectual 930 points

1) Yes, you should initialize IT for the learning cycle.

2) Yes, the bq20z65EVM has a continuous auto cell balancing feature but it is best to use a balanced pack for the learning cycle.

B) You should charge your batteries through pack+/-.

Regards,

Viktoriya

0 Alexandre Cherpillod over 12 years ago in reply to Viktoriya Sherman

Intellectual 425 points

Hi,

I have an other question relative to the voltage applied to pack+ and pack- for the learning cycle.
I have 3 cells, then I have to apply 12.6 Volt.
But do I have to apply 12.6 constantly during all the charge time (until having 'full charge' set) with a common power supply ? Will the bq20z65 set the different appropriate current for the charge ?
Because I have still no smart charger and I have to do the learning cycles.

Thanks,

Alex

0 Jason Gin over 12 years ago in reply to Alexandre Cherpillod

Genius 3970 points

Doing a learning cycle consists of two charging phases, and a relax period:

Charge at constant current until the battery sees 4.2 volts per cell (for a 3S pack this will mean 12.6 volts). Many bench-top power supplies have a current limiting option.
Charge at constant voltage until current drops by C/10 down to C/10 and the Flags[FC] bit is set. Once FC is cleared set, disconnection of power is important so that the gas gauge can properly take a battery open-circuit-voltage reading.
Disconnect the power supply and do not discharge the battery until ControlStatus[VOK] is cleared. This will usually take over an hour.

More troubleshooting help is in this TI document, "Achieving the Successful Learning Cycle" at http://www.ti.com.cn/cn/lit/an/slua597/slua597.pdf

EDIT: Whoops, step 2 I meant current dropping to C/10, not by C/10. Also, FC should be set, not cleared.

0 Alexandre Cherpillod over 12 years ago in reply to Jason Gin

Intellectual 425 points

Thanks Jason, your answer is very helpfull!

But for the point 2. of your answer, I think you mean: Charge at constant voltage in order to obtain C/10 and as soon as the bit FC is set, disconnect the power supply.

Is that right ?

0 Onyx Ahiakwo over 12 years ago in reply to Alexandre Cherpillod

TI__Guru* 76230 points

yes that's right. charge at constant voltage till current drops to C/10 and FC bit is set, then disconnect power supply.

0 Jason Gin over 12 years ago in reply to Alexandre Cherpillod

Genius 3970 points

Ah yes, thanks for pointing that out! I've fixed the wording in Step 2 now.

0 Onyx Ahiakwo over 12 years ago in reply to Jason Gin

TI__Guru* 76230 points

You missed correcting FC cleared. It should be fc set :)

0 Jason Gin over 12 years ago in reply to Onyx Ahiakwo

Genius 3970 points

Oh my, looks like I need another cup of coffee today! Fixed that bit as well.

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Impedance Track Battery Charging Question