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What is considered normal/acceptable Delta V ?

Mountainlion

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Jul 10, 2020
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I have EVE 280 Ah cells that I bought on AliExpress.

Did top balance the cells @ 3.65V.

I charge them to 3.475 (13.9V) with 2 hours of absorbtion.

Delta V goes to 55 mV.

The Daly BMS is the only balancing that take place.

My question:

What is considered an acceptable Delta V for matched grade A cells?
 
As long as nothing goes over volt at top charge I would call it good and put in service.
Keep some notes on what cells have what voltages at top charge and compare again in 3 to 6 months.

I don't think there is any warranty adjustment or indication of bad or weak cells at this point.

Who was the seller?
 
I have EVE 230 AH cells in a 16s pack. Right now they're at 54.43 volts and the delta is .009. I was extremely meticulous about cleaning the contact surfaces on the mounting studs and bus bars.
 
As long as nothing goes over volt at top charge I would call it good and put in service.
Keep some notes on what cells have what voltages at top charge and compare again in 3 to 6 months.

I don't think there is any warranty adjustment or indication of bad or weak cells at this point.

Who was the seller?
They are in service since a year. Have no problems. My question is more academic in order to understand what you can expect if buing matched Grade A cells. I think the seller was Varicore.
 
Last edited:
Acceptable DeltaV will depend on how accurate your bms is in reading voltage.
When you know this that will give margin of error +/- (example BMS is accurate down to 6 mV) . How fast you charging and discharging scenario will change how DeltaV across cells. Grade A +++ will stay between 2-8 mV considering that you have all bus bars without any gaps or loose bars. Flexible bus bars are usually needed because even if you have high quality cells they are different between each other ..... you can use non conductive level and put it across all cell terminals. If any of cell terminals have gap this will be place where if you use rigid type of bus bars that will cause resistance raises under load, heating, imbalance during charging and discharging. All of the cell terminals should be even all across without any gaps. If you have worked or watched engine builders checking block or heads for warping it applies same way when assembling the battery pack. Once you master this step when assembling a pack it will help you eliminate many problems that a lot of people facing on this forum.
Good luck and try to keep attention to the details.
 
Welded bus bars are cheap alternative to overcome this issue and many good quality Chinese makers are switching to this. This is not right solution but band aid ( by eliminating screws and nuts making more profits). Up to certain degree it is better than rigid bus bars with screws. I will call any of the future pack builders to put flat non conducting bar across all cells terminals and try to use gap Guage to see if all terminals are flat and have no gaps at all. If someone get lucky and have 16 cells so good i will download his picture and post it on my wall so i can provide evidence that Chinese prismatic cells indeed have perfect tolerances.
So please challenge me and i will be happy to see with my own eyes something I'm dreaming ever since I started playing with Chinese prismatic cells.
 
How you compare with calibrated volt meter your deltaV?
Definitely good build and cells
It compares reasonable well with by Fluke. I will let the 3P16 configuratation and the Heltec balancer take the credit. Although I did polish cell tops and bus bar and imediately apply NoAlox to both surfaces before each step of assembly.
 
It compares reasonable well with by Fluke. I will let the 3P16 configuratation and the Heltec balancer take the credit. Although I did polish cell tops and bus bar and imediately apply NoAlox to both surfaces before each step of assembly.
How you tried to check for gaps using flat non conductive bar across all cell terminals. This is very important for long life battery pack. If you use flexible cooper bus bars please scratch my post.
And if you don't mind can you post pictures of your 3P16S I'm interested on terminal bus bars zoom in.
 
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