Built My Pack, Cause for Concern?

[fsu1tm]

OK. I just finished my pack built off of the specifications in Sergio's Generic Chinese BMS write-up (https://www.buggiesgonewild.com/showthread.php?t=160302). I followed his directions to the letter ordering the same parts.

When I got my Leaf Modules from TechDirect, I measured all of the voltages as such.

Negative to Positive = Total Module
Negative to Center Post = Cell 1
Center Post to Positive = Cell 2

The voltages I measured are in Pic 1 (top).

I then manually balanced the pack by connecting all negatives together, all center posts together, and all positives together. I did this using 14 AWG wire. After the manual balance, I remeasured the voltages using the method above and got the voltages in Pic 1 (bottom).

I had already received the parts for the BMS/Relay box so I started with that build. The charger had not yet arrived. I kept all of the BMS to Pack wires the same length and tinned all of those ring terminals rather than crimping. You can see the built pack and BMS/relay box in Pics 2 and 3.

A few days after completing the pack the charger came in so I adjusted the voltage on it to 58.1V. I don't have regen on this series cart so my voltage is set a little higher than Sergio's. I also set the BMS parameters as shown in Pic 4.

Next I plugged in the configuration and the charger immediately came on as expected. I use the word "configuration" because Sergio has a 120V relay in his design that is connected to the same AC source as the charger. The charger charged the pack and shut off approximately as expected. The BMS reports the pack charge to be 57.59V while my DVM reports it to be 57.87V. A little lower than the 58.1 I had expected but pretty close.

My concern with all of this is that now the cells seem to be way out of balance with the difference between the highest and lowest over 0.1V (Pic 5). This is as measured by the BMS. I haven't taken manual readings since the pack is now fully enclosed.

My questions are:

1. Is this a concern?
2. Is there something I should go back and check?

Thanks. I decided to start my own thread since I had already bombed Sergio's thread enough.

[Sergio]

I think you are fine, what you are seeing is likely difference in capacity between cells and it should resolve as you top balance them.

This old post I did may help explain why getting your cells to 3.81v does not mean they will stay at the same voltage at 4.10v:

https://www.buggiesgonewild.com/show...3&postcount=17

Lower your "Balance turn-on voltage" to 4.05V and use the system like that for a few charge cycles until the voltages get closer and then raise it again to 4.10v.

[Volt_Ampere]

I agree with Sergio. I always check my balance after charging when the cells are all over 4 Volts. I am sold on Top Balancing. My Leaf cells stay in pretty good balance. I only balance them every couple months or so and even then they are pretty close to start with. My home built BMS has great balance capability and I have it set up to do it only when I ask it to.

[WalterM6]

In case you missed it here's what the manufacturer has to say about balancing.

About balance setting :
About the consistency of the battery system , if user does not have the professional test
instruments , we can make judgment based on below simply conditions .
1. when makes the battery package , each single cell voltage difference should be less
than 0.03V
2. After 10 times aging cycles . after fully charge of the battery , voltage difference are
less than 0.03v , it will indicate the battery capacity consistency is good .
3. With one month rest , voltage difference is less than 0.03V , it indicates the battery
inner resistance consistency is good .
4. when there is no electricity with the battery , and big voltage difference will be normal ,
it has no relation with battery consistency .
Application of Balance function：
1、 Charge battery : balance will start works when the voltage reached the value of
balance start voltage also the voltage difference is bigger than the voltage
difference you have set during charge process .
2、 Static balance : when reaches balance condition during rest time . the balance will
start work .
3、 When the battery has good consistency , we recommend to use charge balance
function . as for the static balance it works more effectively when the battery
voltage difference is big .
4、 Do not set the voltage difference with below of 0.02V , our default value 0.03V will
be good .
SHEN ZHEN LLT ELECTRNIC TECHONLOGY CO,.LTD WWW.lithiumbatterypcb.com
5、 When the battery consistency is good , you can set the balance start voltage with
higher value

[fsu1tm]

Thanks for all the info, Guys. The cart this will go in should be ready for the pack in a couple of weeks and I'll be able to see how things progress.