Jakob N's Cell Change Thread

[MickeyS70]

I had the idea to have the car running with the heater on, until it shuts down.

Yes, that’s the easiest way to use the battery function in Hobdrive as the battery voltage needs to be below a certain level (can’t remember what exactly).

 

[Jakob N]

Yeah, I think that this is the Problem on my car.
Calculated SOC is not alligning with the cells voltage.
So I tried to get the car as empty as possible, but a low SOC might not be enough for the procedure to start.
Can I damage Something, like the car not accepting charging anymore when i let the heater run until it is empty and shuts down?

I will take a Screenshot of the voltages as soon as I get home from work tomorrow.
today it was at 51,8% an I wanted to try a second trip to work.i plugged the car in for literally two minutes, and now it is sitting at 71%.
I think the BMS is confused because the cells do not work as they used to.
Voltages are now at 4,012V and 0,01V difference

 

[MickeyS70]

Can I damage Something, like the car not accepting charging anymore when i let the heater run until it is empty and shuts down?

No, the low voltage protection will keep the cells in the ‘green’

I think the BMS is confused because the cells do not work as they used to.
Voltages are now at 4,012V and 0,01V difference

Correct, the BMU calculates with the old battery’s capacity which doesn’t match the new one’s voltage levels

 

[Jakob N]

I made two boards for mounting the AD202KY
One mounts horizontally to the existing holes on the main PCB, the other one is mounted vertically, and will need so glue for preventing damage due to vibrations.
As my inverter is already running in the car again I can not test it now, but maybe someone will find this usefull in the future.
PCBs were drawn in eagle (Fusion electronics) If needed I can export the Gerber- files.

On the vertical version 90 degree angled pinheaders need to be used;
Alternatively standard- pinheaders can be soldered to the board like SMD- parts.



On the horizontal PCB special care needs to be taken that the pins of the AD202 don't cause a short- circuit on the Main PCB, as the replacement board is bigger than the original ISA- board!



As I have not tested the boards the manufacturing and usage of these boards is done on ones own responisbility!
Only attempt this repair if you know what you are doing!

BR

 

[hjdlsnbc]

Awesome! This is the sort of content i would love to see all over this forum!
You have also put it as a backup on github and made PR possible?

 

[Jakob N]

Not yet; I don't have a github account; But I can do this too, so it will not be lost for those who need the files.

 

[Jakob N]

I just finished discharging the traction battery.
I let the car running until it shut down the heater, and then let it run until it stopped moving.
This is the state of the cells:



I think the state of the cells is pretty good; the voltages are all pretty close together.
What do you think?

The old cells have been much further appart different (665mV!) which shows that some of them are in really bad shape - which was the reason for me to change them.



So the end of discharge is 324V or 3,681V per cell on both batteries.

I am now charging the car, and hoping that it will give me the true capacity from now on;
But from what I have read the BMS will only allow around 2Ah changerate per charge, so this could still take some time.

I still couldn't get the capacity measure featur on HobDrive to work.

BR

 

[MickeyS70]

I still couldn't get the capacity measure featur on HobDrive to work.

Your voltages are still too high for Hobdrive, SoC 0% with your old cells is around 3V. Because of the capacity mismatch SoC 0% of the new cell is @ 3.7V, which won’t work.

Drain the battery to 0% SoC again then turn off the car. Disconnect the 12V aux for a minute and reconnect, this should force the BMU to do a voltage based SoC calculation and you will see the fuel gauge going up again.

Turn on the heater and repeat the process until the cell voltages are just below 3V (someone went as low as 2.8V iirc)

Try HobDrive again as the ‘native’ calibration is very conservative when it comes to changing the capacity value. Someone actually tried this, no matter how many times he repeated the calibration, a change of 2Ah per month is all he got?!

 

[Jakob N]

This was the bit of information that I needed, thank you!
I will repeat this process and deplete them down to below 3V.
I didn't think of disconnection the 12V, but it is a great idea!
No wonder theBMS is still behaving strangely:



But I must say that these small electric vehicles are a great way to get into EVs and learn about all the parts, as they are built in a really understandable and modular way!