Top balancing question

[tsunami3775]

Just want to urgently reiterate something mentioned earlier, because it sounds like there may have been potential for a mistake amidst the confusion:

Set the power supply to 3.65V with the power supply DISCONNECTED from the batteries. Then connect it and DO NOT touch the voltage again.

If you adjust the voltage while the PS is pegged at 10A, you're increasing the max voltage the PS will provide but it won't show up on the screen and you have no way of knowing what it is. If it happens to exceed the max voltage of the cells, then when the cells get full the PS will just keep going and damage the cells.

Oh man you saved my butt. I just attached them and raised it up to the max. For the past 10 min. Hopefully it isn’t damaged. I measured it and it only showed 3.42 on the multimeter while it was connected so hopefully it’s good. I checked them without the connections and they were 3.36. Now 3.42 again with the bench power supply set at 3.65 before connecting. Now it shows 3.6v going in at 10.4amps

 

[Blackhat]

Oh man you saved my butt. I just attached them and raised it up to the max. For the past 10 min. Hopefully it isn’t damaged. I measured it and it only showed 3.42 on the multimeter while it was connected so hopefully it’s good. I checked them without the connections and they were 3.36. Now 3.42 again with the bench power supply set at 3.65 before connecting. Now it shows 3.6v going in at 10.4amps

Yeah, you caught it in time and they're completely fine. As far as the cells are concerned nothing ever happened because they never saw high voltage. Sounds like the top balance is progressing as expected now.

 

[tsunami3775]

Yeah, you caught it in time and they're completely fine. As far as the cells are concerned nothing ever happened because they never saw high voltage. Sounds like the top balance is progressing as expected now.

Awesome thank you

 

[tsunami3775]

Merry Christmas!
Finished top balancing all cells to 3.65 . I have one cell that loses .001 charge every 10 seconds or so. It now reads 3.604 while other 3 cells read 3.640z. So I’m assuming I need to buy a new cell for replace this one. Is it normal to lose voltage this fast? Is it normal for the good cells to go to 3.64v just 15 min after it was 3.65? If you’re have any other insight please advise. Thank you!

 

[time2roll]

Normal. See where they settle in 24-48 hours. Probably drop to maybe 3.45

 

[sunshine_eggo]

Normal. See where they settle in 24-48 hours. Probably drop to maybe 3.45

+1

The drop really appears to be related to brand, size and individual cells, but outliers are definitely a concern.

Example: if 1 cell settles to 3.40 in 24 hours, and all the rest are at 3.50, expect that the 3.40 cell may cause you issues if you store the battery for as little as a week.

 

[tsunami3775]

+1

The drop really appears to be related to brand, size and individual cells, but outliers are definitely a concern.

Example: if 1 cell settles to 3.40 in 24 hours, and all the rest are at 3.50, expect that the 3.40 cell may cause you issues if you store the battery for as little as a week.

Noted thank you

 

[tsunami3775]

Now it’s 3.4 and all other cells are 3.6 about 12 hours later

 

[Sback]

This is a set that I just got done top ballacing . They have been resting for about 36 hrs. You can see the voltage drops

 

[tsunami3775]

Are

This is a set that I just got done top ballacing . They have been resting for about 36 hrs. You can see the voltage drops

Are yours still attached in parallel? I disconnected mine and just checking each individual cell

 

[Sback]

No. They are in series with the bms hooked up.. you should put them in series with the bms and let them rest. If there is a ballance issue the bms will help. Depending on what bms you have.

 

[sunshine_eggo]

Now it’s 3.4 and all other cells are 3.6 about 12 hours later

3.4 is a concern. Recommend you recharge this cell individually to 3.65V and see how it behaves. The charge shouldn't take long at all.

Are yours still attached in parallel? I disconnected mine and just checking each individual cell

This is valid. Had you left them in parallel, that would have masked the individual cell behaviors.

No. They are in series with the bms hooked up.. you should put them in series with the bms and let them rest. If there is a ballance issue the bms will help. Depending on what bms you have.

No. That is not valid. He has taken all of his cells to 3.65V in parallel, so he already knows there's not a balance issue, and doing as you recommend would MASK any issue, not fix it.

 

[tsunami3775]

3.4 is a concern. Recommend you recharge this cell individually to 3.65V and see how it behaves. The charge shouldn't take long at all.



This is valid. Had you left them in parallel, that would have masked the individual cell behaviors.



No. That is not valid. He has taken all of his cells to 3.65V in parallel, so he already knows there's not a balance issue, and doing as you recommend would MASK any issue, not fix it.

Yah its a bad cell.. not holding the same voltage as others.. dropping exponentially faster... I'll take the loss on this one and order another. :/

 

[John Frum]

Yah its a bad cell.. not holding the same voltage as others.. dropping exponentially faster... I'll take the loss on this one and order another. :/

Just for fun can you leave it to settle on its own until/unless the vendor asked for it to be sent back.
I'm really curious to see if it keeps on dropping over time.
Ideally I would like to see what happens over the course of a month.
I'm curious to see if the self discharge slows down and at what voltage that might happen.

Consider it a service to the community.

 

[tsunami3775]

Just for fun can you leave it to settle on its own until/unless the vendor asked for it to be sent back.
I'm really curious to see if it keeps on dropping over time.
Ideally I would like to see what happens over the course of a month.
I'm curious to see if the self discharge slows down and at what voltage that might happen.

Consider it a service to the community.

Yah I can, I doubt I could even get a refund from Ali express at this time because I bought them several months ago. Also interesting to see that Will isn’t endorsing these anymore and advises against buying cells from AliExpress. I think that’s a good call. Hopefully I can buy 1 cell from his American distributor.

 

[Sback]

Now seeing where you purchased your batteries you might want to do a capacity test on the batteries. You might find that none of them meet capacity.

 

[Sback]

No. That is not valid. He has taken all of his cells to 3.65V in parallel, so he already knows there's not a balance issue, and doing as you recommend would MASK any issue, not fix it.

Agree. But it could also fix a problem that was created during top ballance. Your suggestion to charge the one cell to 3.65 is a good idea.

 

[John Frum]

But it could also fix a problem that was created during top ballance.

What problem would this fix?

 

[Yurtdweller]

I'm going to relate the story of charging my second built pack. I am off-grid, 100% solar. After finding my cells had very well matched voltages, I decided to just build my pack (12v 280ah) with BMS, and charge it with my scc to a high state of charge, then, if necessary, proceed with balancing at high soc. This worked well with my first pack, so I assumed it was effective. First pack is still very well top balanced, and was balanced entirely by the jbd bms. At mid voltage, pack two was well balanced, as well. Until the sun finally came out. I charged pack two with my power supply for a full day. Once each cell approached 3.6+, the pack went out of balance. So far out of balance that the BMS was incapable of bringing it back. At that point, I took everything apart, paralleled the cells, and applied my 10amp btps. The pack came into balance in just a few hours, and I put it back into series in it's milk crate, and all is good So, balanced at 50 or 75% soc does not mean it's balanced at 100% SOC, regardless of voltmeter readings. But you can bulk it up first, and then do the top balance procedure, and you will save a lot of time.

 

[Yurtdweller]

This is a set that I just got done top ballacing . They have been resting for about 36 hrs. You can see the voltage drops

Quick note. This readout is from his BMS app. This info comes from his BMS. A BMS can only be connected when the battery pack is in series, 12v, configuration. Do not attempt to connect a BMS in parallel configuration. That would probably be bad.