HELP PLEASE I think I may have some bad cells

[Gazoo]

@Moltensurf in light of the issue that @Gazoo has brought forward I suggest you do some testing to validate the function of your bms.
1. independently verify the voltage with a dvom for each balance lead.
2. test both the high and low battery and cell level triggers.
Make sure to use safe values(in the flat part of the curve) for the 4 triggers.

Agreed. My pack overvoltage is set to 29.2 volts or 3.65 volts per cell. It never gets to 29.2 because of the 100mv delta. This has me thinking the OP could set his pack to 28 volts which would be 3.5 volts per cell and try it. I am still surprised the BMS did not disconnect when the highest cell reached 3.65 volts and concur with you voltages need to be verified.

 

[Baserati]

Rightfully so.

Stop everything you're doing. Don't touch a cell or a charger. Go here:

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

Click the orange download button, save the PDF, open it and read it. If you don't understand something, ask questions.

Hi Snoobler, downloaded and read your PDF. Great resource. Just two questions:
On page 2 Note 3.1 - You state that you should short the leads together. Just want to clarify that this is the power supply leads and the purpose of this is to allow some current flow so as to gauge the lowest setting, correct?
Secondly I intend to follow the step and pause approach to top balancing. Is there any reason I can't do this in increments, like over 4 weekends? Not sure I can set aside enough continuous hours to do it all at once

 

[Dzl]

Hi Snoobler, downloaded and read your PDF. Great resource. Just two questions:

Note of clarification (credit where credit is due) this guide (as well as much of the other content in the resources section) was written by @FilterGuy

Secondly I intend to follow the step and pause approach to top balancing. Is there any reason I can't do this in increments, like over 4 weekends? Not sure I can set aside enough continuous hours to do it all at once

The lions share of the time is taken up by the first step(s), the final step(s) are comparatively quick. But yes, some people have split the process up over multiple weekends. Its likely if you do it this way, it will be the first step that gets split over multiple weekends.

 

[Just John]

Note of clarification (credit where credit is due) this guide (as well as much of the other content in the resources section) was written by @FilterGuy


The lions share of the time is taken up by the first step(s), the final step(s) are comparatively quick. But yes, some people have split the process up over multiple weekends. Its likely if you do it this way, it will be the first step that gets split over multiple weekends.

Yes, you can easily split it up into a couple of weekends.

 

[FilterGuy]

On page 2 Note 3.1 - You state that you should short the leads together. Just want to clarify that this is the power supply leads and the purpose of this is to allow some current flow so as to gauge the lowest setting, correct?

Yes, You short the power supply leads together to set the max current you want to allow into the cell(s). However, on the low cost 10A-30V CC/CV supplies, the 10A will be less than the max for the cells so it is an unnecessary step. I only added that step to cover the case where in case someone has a really high current supply.

Secondly I intend to follow the step and pause approach to top balancing. Is there any reason I can't do this in increments, like over 4 weekends? Not sure I can set aside enough continuous hours to do it all at once

I see no reason why you could not do it over several weekends. However, if you do the pre-charge, you might find that the step-and-pause approach still goes pretty quickly.

 

[Baserati]

Yes, You short the power supply leads together to set the max current you want to allow into the cell(s). However, on the low cost 10A-30V CC/CV supplies, the 10A will be less than the max for the cells so it is an unnecessary step. I only added that step to cover the case where in case someone has a really high current supply.


I see no reason why you could not do it over several weekends. However, if you do the pre-charge, you might find that the step-and-pause approach still goes pretty quickly.

Actually I'm doing a test build of 6000mah cylindricals for an ebike to prove out my design and as learning exercise (so far has taught me a lot) so limiting the amperage on balancing is probably a good idea. Im intending to balance 48 of them in parallel. If my math is right that's about 30amps

 

[FilterGuy]

Actually I'm doing a test build of 6000mah cylindricals for an ebike to prove out my design and as learning exercise (so far has taught me a lot) so limiting the amperage on balancing is probably a good idea. Im intending to balance 48 of them in parallel. If my math is right that's about 30amps

6000mAh=6Ah
You definitely want to limit the current per cell to something like 1.2A (.2C) or less for top balance. (BTW: What is the recommended C rate for charging those cells?)

If you have 48 cells in parallel:
6Ah/cell x 48 cells= 288Ah. In that case, .2C is 57.6A so a 10A CC-CV would never get high enough to worry about.

 

[Baserati]

6000mAh=6Ah
You definitely want to limit the current per cell to something like 1.2A (.2C) or less for top balance. (BTW: What is the recommended C rate for charging those cells?)

If you have 48 cells in parallel:
6Ah/cell x 48 cells= 288Ah. In that case, .2C is 57.6A so a 10A CC-CV would never get high enough to worry about.

C rate for charge is 1C. Thanks for the help and advice

 

[Moltensurf]

file:///var/mobile/Library/SMS/Attachments/43/03/CAD19CF4-5BC5-4891-B5A0-B4F30E838251/IMG_1344.mov

 

[Moltensurf]

 

[Moltensurf]

 

[Moltensurf]

After what seems like forever, finally making some progress on my van. I have a max air fan installed. Been dreaming about making this lift bed for a long time