BQ40Z80: Abnormal output data from RemainingCapacity() and RunTimeToEmpty()

faqian huang

Prodigy 100 points

Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO

Dear guys,

Our BMS is based on TI BQ40Z80. Below is configuration:

Load Mode = 1 (constant power)

Load Select = 2 (Current() × Voltage())

CAPM = 1 (cWh)

if more configuration information are needed, I will paste here later.

The questions are:

1. RemainingCapacity keeps 7760 [cWh] for 63 seconds and then starts to decrease. Why not decrease from the beginning?

2. RemainDischargeTime=2 [min] only keeps 6 [s] and RemainDischargeTime=1 [min] also keeps 6 [s]. It should be 60[s] or close to. Could you please give some explanation? (RemainDischargeTime is the return value of RunTimeToEmpty())

3. RemainDischargeTime=0 [min] keeps 27 [s] before reach under voltage condition, Why RunTimeToEmpty() does not take the extra 27s into account?

Any feedback and comments are welcome. Thanks in advance.

over 5 years ago

0 Andy Liu (BMS) over 5 years ago

TI__Guru 52115 points

Can you share your log with us so that we can take a close look at it? Thanks.

0 faqian huang over 5 years ago in reply to Andy Liu (BMS)

Prodigy 100 points

Gauging.xlsx

0 Andy Liu (BMS) over 5 years ago in reply to faqian huang

TI__Guru 52115 points

Hi Faqian,

I took a quick look at your log file. It seems like that log file was created by yourself. Do you have any log file that was created by bqStudio. I'm asking because I don't see much info in your log file. If the bqStudio is used, I can see many useful detaills, which will make it much easier to find out the cause.

In addition, could you share with us your gg file and srec file. Please make sure you the srec file is already unsealed. Thanks.

Andy

0 faqian huang over 5 years ago in reply to Andy Liu (BMS)

Prodigy 100 points

Hi Andy,

The battery pack is designed by 3rd party, we cannot use bqstudio to get log directly. Also no gg or srec file to share with you. Maybe the battery pack factory has. The BMS and main control board exchange information with UART communication and all log data in Gauging.xlsx are captured from communication packet.

0 Kang Kang over 5 years ago in reply to faqian huang

TI__Mastermind 24870 points

Hello Faqian,

We really need repeated bqStudio data for this particular type of issue. Without it, debugging this is just guess work as the battery has a lot of information. Let us know if you can work with the factory to get this data for us.

0 faqian huang over 5 years ago in reply to Kang Kang

Prodigy 100 points

Hi Kang,

Please see attachment for bqStudio log data.

discharge test 20200113.xlsx

Note my question #1 and #3 are reproduced from the log data, but not for question #2. We are trying to reproduce #2 with bqStudio, and get back to you when we reproduce it.

By the way, please give us your Email address or send an Email to huangfaqian@roborock.com, I'll send you the gg and srec files. Thanks.

0 faqian huang over 5 years ago in reply to faqian huang

Prodigy 100 points

For question #2:

discharge test 20200114.xlsx

0 Andy Liu (BMS) over 5 years ago in reply to faqian huang

TI__Guru 52115 points

I already sent an email to you.

0 faqian huang over 5 years ago in reply to Andy Liu (BMS)

Prodigy 100 points

More test log files:

3# 50W discharge test 20200114.xlsx

4# 50W discharge test 20200114.xlsx

and please see my reply email for gg and srec files. look forward to your feedback.

0 Andy Liu (BMS) over 5 years ago in reply to faqian huang

TI__Guru 52115 points

See my comments on your first.

I have looked into this file discharge test 20200113.xlsx.

First of all, I see that the RSOC remains 99% before the discharge begins. It seems like a VCT (Valid Charge Termination) has not ever occurred. I don't see any data for the charge. I would suggest you check again and see if all the conditions for the VCT can be met.

If a VCT doesn't occur, 100% RSOC will never show up and more importantly, the true remaining capacity will keep accumulating. In your log file, the true remaining capacity is higher than the true FCC. To gauge, it looks like the batteries are overcharged (Note that the gauge only reports 100% RSOC as the maximum even though this situation happens). That's why the RemainingCapacity() stays for 63 seconds after the discharge starts. Basically, the gauge is waiting for the remaining capacity to be lower than the true FCC.

Once a VCT occurs, 100% RSOC will be reported and also that issue will be gone.

0 Andy Liu (BMS) over 5 years ago in reply to faqian huang

TI__Guru 52115 points

I would need some more time to dig into the other two issues.

0 user6259906 over 5 years ago in reply to Andy Liu (BMS)

Prodigy 10 points

Hi andy：

The VCT has occurred,the tapper current set 250mA,the end off charge current is 100mA

Gauge is controled by MCU,Gauge will into shutdown mode, while gauge wakeing up ,the SOC is re-calculated

0 Andy Liu (BMS) over 5 years ago

TI__Guru 52115 points

The RunTimeToEmpty() depends on the remaining capacity. Basically, RunTimeToEmpty = the remaining capacity / the present rate of discharge.

A simulation will update the remaining capacity and then lead to an update of RunTimeToEmpty(). The following conditions can have the remaining capacity updated.

Here is an example. See the two highlighted rows below.

The T_sim goes from 25.4C to 30.5C, which means a simulation has occurred. The conditions to trigger it is that the temperature changes over 5C.

0 Kang Kang over 5 years ago in reply to Andy Liu (BMS)

TI__Mastermind 24870 points

Hello User,

We took a look at your log file. Can you include the VCT bit setting during charge and also discharge.

The accuracy is okay for this gauge. I would recommend running this with fast scaling disabled.

Power management

Power management forum

BQ40Z80: Abnormal output data from RemainingCapacity() and RunTimeToEmpty()