topic Re: SOC calculation using Coulomb Count method in S32K

SOC calculation using Coulomb Count method

thailivenkatesh8 — Wed, 22 Dec 2021 05:55:00 GMT

Hi,
I am working on calculation of SOC using coulomb count method using MC33771C Driver code below are the test results for coulomb counting for 6Ah Battery.

-----------------------------------------------
| Measurement | value |
-----------------------------------------------
| Cell 1 Voltage | 3521 mV |
| Cell 2 Voltage | 3377 mV |
| Cell 3 Voltage | 3375 mV |
| Cell 4 Voltage | 3377 mV |
| Cell 5 Voltage | 3374 mV |
| Cell 6 Voltage | 3374 mV |
| Cell 7 Voltage | 3376 mV |
| Cell 8 Voltage | 3374 mV |
| Cell 9 Voltage | 3373 mV |
| Cell 10 Voltage | 3376 mV |
| Cell 11 Voltage | 3374 mV |
| Cell 12 Voltage | 3383 mV |
| IC Temperature | 42 degC |
| Coulomb Count | 22373 |
| Current | 1074 mA |
| StackVoltage | 40602 mV |
| BAT Temperature | 25 degC |
|
|------------------End------------------------

using datasheet information we calculated as
coulomb count=coulomb count/ccsamples;

Coulomb Count =22373uv
Rshunt=12500

I=22373uv/12500uv=1.78984uA.
But in datasheet there we don't have any information regarding SOC and we need support to calculate the SOC or any example code or any related document information.

Re: SOC calculation using Coulomb Count method

JozefKozon — Wed, 22 Dec 2021 11:00:34 GMT

Hi Venkatesh Vhaili,

the SOC means Start Of Conversion. There is no formula/calculation of the SOC. Please refer to the section 9 in the MC33771C datasheet.

On-demand measurement: this means the bank of ADCs perform a sequence when
triggered by a SOC command, where SOC means start of conversion. Typically, the
user periodically sends a SOC command followed by the reading of the measured
values of the most important channels, namely all cell voltages, temperatures and
current.

The MC33771C performs on-demand differential measurements of external inputs and
internal measurements using three ADC converters for measurement, calibration, and
diagnostics. Once the device is initialized, on-demand conversions are initiated by writing
to the ADC_CFG [SOC] convert register or a GPIO2 input trigger.

With Best Regards,

Jozef

Re: SOC calculation using Coulomb Count method

thailivenkatesh8 — Wed, 22 Dec 2021 11:49:41 GMT

Hi JozefKozon,

Thanks for reply but we need Algorithm for SOC & SOH state (battery).

Re: SOC calculation using Coulomb Count method

JozefKozon — Wed, 22 Dec 2021 13:06:30 GMT

Hi Venkatesh Vhaili,

I am not sure if we mean the same thing. Could you please explain the meaning of the SOC and SOH abbreviations?

The SOC should be Start Of Conversion. Is that correct? Please see below an answer from an application engineer regarding the coulomb counting and SOC.

With Best Regards,

Jozef

Re: SOC calculation using Coulomb Count method

thailivenkatesh8 — Thu, 23 Dec 2021 04:16:37 GMT

Hi JozefKozon,

Thanks for the reply I know SOC(start of conversion) used in ADC .But we need support for the SOC(state of charge) is calculated using coulomb count to find the battery status like depth of discharge(DOD),state of health(SOH).

Re: SOC calculation using Coulomb Count method

JozefKozon — Thu, 23 Dec 2021 09:21:15 GMT

Hi Venkatesh Vhaili,

I see. Please read the following sections in the MC33771C datasheet.

9.4.2 Measurement sequence,

9.4.2.1 Voltage averaging

9.5 Cell terminal voltage measurement

9.6 Current measurement

9.8 GPIOx port control and diagnostics

All these sections describes algorithms how to obtain SOC and SOH data about monitored Cells. Please note, that these information are confidential and please make sure you share it only with third parties who have an NDA (Non Disclosure Agreement) signed with NXP.

With Best Regards,

Jozef