Enginer replacement battery balancing

Hi Daox,
Sure I can help you through this process. I think you have my Private Email and phone if you need to contact me that way.

First we need to be talking with the same terminology. I assume you have a 4kwhr system with Buddy cells and 2 DB8s. Label one DB8 as U for upper and the other as L for lower. Then L1 is the voltage that come up as 1 on the L DB8. Do this with the Black cable from the charger and converter connected to L1 and the Red cable going to U8.

Now, Which cells did you replace? Have you done a full charge yet? Did you get a charging alarm? What are all the voltages (at rest) on both DB8s?

Thanks,
Dan

 

Hi Daox,
Go ahead and put some charge on it. Plug it in and watch the voltages. When you get one of the cells up to 3.5v then record all cell voltages with the charger still on. Then unplug the Charger and Post those voltages so that I can see them.

Thanks,
Dan

 

Hi Dan
I just found this thread and am very interested in this process. Has Daox responded (offline maybe?), It would be of interest to me and possibly others as I am learning more of how this system works. I also have installed the 4k system. The beep that signals the high voltage limit of 3.7 is very faint and I have found that a baby monitoring gadget works well. After a short drive, it sounds like it best not to plug it in immediately. Electricity is not my strong point,

 

Hi Eximage,
The point here is that we relay do not know the SOC from an "at rest" voltage. We get better information while charging as we approach the high limit and while discharging as we approach the low limit. So we are waiting for that information from Doax so that we can do the next step.

Also realize that new cells will change a little as they "break-in", so the process may take a few cycles.

Finally you always need to understand your BMS. In this case the DB8s only drain power from the highest cells. So if the new cells are at a low SOC then they will pull that whole bank down and then the 2 banks of cells can be out of balance from each other.

Yes, I agree that the DB8 alarms can not be heard. I have installed CellLogs with Radio Shack Sirens (part 272-079) These are very loud and allow me to hear a charging alarm when I am in the house with the car in the garage.

The key is to have the system balanced. After driving, a wait will allow the system to balance a little. You would not need to worry so much about this if you were sure that you would hear all the alarms. I do plug-in right after a drive. But if there is a balance issue I get an alarm at the end of the charge and unplug. Then after waiting some time I can do a topoff charge. As my system balances better I do not get that alarm very often.

Thanks,
Dan

 

what's the thinking behind not just go ahead and drain them all down to reach the bottom ?? then charge them all back up ? is it to un-stiffen the new cells ?

Pb

 

The main reason for not doing as you suggest is that it is a lot of work and time. I did this on one set of cells and it took several days. You need to disassemble the whole pack, then go through the discharge process. Then you need to reassemble the pack. Then after all of that the new cells may change a little after several charge discharge cycles.

I think Daox is fine with the process he is using.

Thanks,
Dan Lander

 

My system (4KWH version) can not be charged since yesterday. I've checked the individual cell voltage via the one balancer, the voltage of cell 7 is 4.84H with very small alarm sound. I assume the voltage should be 4.84 with high voltage warning. The other cells are looks normal with 3.3 V.

I've been advised by Jack

1. To swap another balancer to check whether the balance 1 is dead as it may leads the false reading as well.
2. Check the voltage of cell 7 by volt meter.

I do hope the balancer is dead instead of cell 7!