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Reviving an undercharged BYD 11kWh pack

Dala

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Jun 6, 2021
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Hi forum!
So I am in the middle of reviving a "broken" BYD 11kWh battery pack, that will be used with a Fronius Solar inverter.

Backstory, the pack was left at 0%SOC at -25C and not really wanting to work after that, tripping main breaker. So I dismantled the pack and most cells range between 2.6V and 2.9V. This to me looks like a possible undervoltage situation, which trips the BMS to not undercharge the cells further. Normally they shouldn't be discharged to 2.6V AFAIK?

bCJOR7L.png


So now I'm charging up the cells individually before attempting to restart the battery. I set my LiPo charger to 3.3V programme to save time. Due to the flat nature of the LiFePo4 chemistry, will this be OK, or should I go for higher voltage? Really new on this chemistry, been mostly using LMO. Any tips at all appreciated :)

oaEo80V.png
 
Go for a bit higher. Up to 3.65v...

Here is a good curve chart I keep in my favorites (even download a copy)...

For top balance you typically can parallel all cells, charge to 3.65v (or slightly lower if you want) but to stay above the knee in the SoC curve (maybe 3.45v-3.65v)...


Most agree you shouldn't always go right up to 3.65v (during normal charge/discharge cycling), but it doesn't hurt to do it once during a top-balance procedure.

Typically, people say for longest life, during normal charge and discharge cycling they will just stay between 20%-90% (in the green band on the chart).

1639862814962.png
 
Hi @Samsonite , thanks for that excellent chart. Since I do not know the limits of the BYD BMS, and can only assume it will be very conservative, I don't want to go over the max voltage that the BMS calls for. Imagine spending all the time to balance the pack to 3.65V and then have the BMS go into overvoltage protection mode! I will be cautious here :)

That is why I'd like to target a lower SOC that is in the green area somewhere. Since the curve is so incredibly flat, I think I will target 3.1xV for now.

I will also experiment with a bench power supply, this will be a long project to get all 64 cells to the same voltage ?
 
Lowest cell was 2.5V, highest 3.0V

I charged all cells up to 3.1V. I made a video on the pack:

Now, it still doesn't turn on. SOC% shows as 0% in the app.
qiCBTR7.jpg


Any ideas on what to try next? I will try to get Modbus going so I can read the fault registers. The application just says "Breaker tripped unexpectedly".
 
nice pack
but why not charge 1 pack at 48 v (skip the bms) in stead of charging the individual cells
now you have unbalanced the pack and you need to top balance the pack again.

i think the packs are fine even if they have bin in a really low sate of charge 2.8 v

the fuse is a short just replace
 
While I was connecting the modbus cables yesterday, I noticed the LED on the side is blinking in a pattern. I read the manual, and supposedly the BMU has this issue:
WFcwvJX.png


So, thinking about opening it up and inspecting the precharge circuit...
 
Status update, we are getting closer:

Still having issues, the solar inverter doesn't detect the battery, the battery just blinks the EC111 error code. Ideas?
 
It finally works !


Now I need good tips on passive modbus RTU sniffing...
 
Good luck with it. My Symo is the previous generation and not a hybrid so no connecting battery to it for me (DIY for grid tied not permitted here anyway). I find your project interesting nonetheless.
 
Great progress on the Gen24BYD reverse engineering, we now have Tesla Model 3 packs hooked up to the Gen24 natively!
 
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