One cell always higher

larrylwill

New Member
Joined
Aug 22, 2021
Messages
70
Yes your right. I got to 3.6 in another hour.
Now can you please tell me the best settings for my BMS?
Here is only a few default settings.
Overvoltage = 6.3v I set this.
under voltage = 2.5v
Pack over voltage = 14.6
Pack under voltage = 10v
Balance turn on voltage = 3.2v
Balance precision = 0.03v
Single full voltage = 3.6v
Single cut off voltage = 2.8v
Self discharge rate 0.2%
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,380
Yes your right. I got to 3.6 in another hour.
Now can you please tell me the best settings for my BMS?
Here is only a few default settings.
Overvoltage = 6.3v I set this.
under voltage = 2.5v
Pack over voltage = 14.6
Pack under voltage = 10v
Balance turn on voltage = 3.2v
Balance precision = 0.03v
Single full voltage = 3.6v
Single cut off voltage = 2.8v
Self discharge rate 0.2%

Hopefully overvoltage is 3.6?

Balance turn on, set to 3.4v. Below that it is self defeating, you don't want it to come on until you get to the steep part of the curve. If you balance before then, you are actually UN-balancing your pack.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,182
From 3.1 to 3.4 there should be such small variations between cells that balancing will not happen anyway.
Many seem to worry about active balancers in the same way. Balancing really shuts off in the middle voltages.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
70
I finally got the cells balanced and hooked everything up. I started my engine and watched the current go from 100a to 0 in about 5 min. I then put my small 10A charger on and it ran for a few minuets before shutting off. Everything was working perfectly.
Then the problem, I had 2 small battery cables to B- and bought a bigger one and I swapped that out about 1/2 hour ago. Now the BMS has shut down. I get full voltage across B+ and B- but C- is about 2v. If I put the 10a charger on B+ and C- I get lights and the battery is charging again but If I remove the charger it shuts down. I tried disconnecting each cable and reconnecting them, no luck. I had the same problem yesterday when installing it but it suddenly came on. Now it wont. I do not see any problems with any cell or any parameters. Nothing should be shutting it down. All cells are within parameters and the total Voltage is also. The temp is 27c.
Any Ideas?
 

MisterSandals

Participation Medalist
Joined
Nov 5, 2019
Messages
4,786
Location
Silicon Valley
I am a little late here but I cannot tell if everybody is on the same page with the battery type.

4 lipo4 280a
“lipo4” is a gibberish cross between lipo (lithium polymer) and LiFePO4 (lithium iron phosphate). Pretty different battery types!

Are all the different voltages being thrown around because chemistries, equipment and settings are mixed/confused? The charger probably has different charge profiles for each.

I would have thought the Lipo charger/balancer
My guess would be that 280Ah cells (common) would be LiFePO4 but if OP really has a lipo BMS and lipo charger, it might explain some of these oddities.

Just a thought.
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,333
A before and after pic of the battery cable with the dual before and the larger after would be nice.

DOes the BMS keep track of cutoffs and type?

Do you have a charger and what are the settings. I found that an absorption of 3.45 volts per cell or slightly less works for my SCC and battery. For my Float, I set it to the 24 hour resting voltage of my battery.
==========
The exact type of battery is important. When I saw 4.1 and BMS attached earlier, I started thinking there was a Lithium Ion BMS installed, which has higher parameters than a LiFePO4.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
70
The battery is charging through the C- terminal but it wont allow a load through it. It was earlier today working perfectly.
 

MisterSandals

Participation Medalist
Joined
Nov 5, 2019
Messages
4,786
Location
Silicon Valley
The exact type of battery is important. When I saw 4.1 and BMS attached earlier, I started thinking there was a Lithium Ion BMS installed, which has higher parameters than a LiFePO4.
Yea, those hobby chargers are usually really good with charging cells within their range when proper battery type selected and using balance leads.
The BMS looks compatible with different lithium types.

The BMS is 3 terminal B+, B-, C-,
Sounds like it’s wired properly. And the balance leads are connected too?

Happen to have pics of batt/BMS wiring (extra eyes find issue all the time here) and of your charger and BMS settings?

Something in those pics should explain how you got a cell to 4.1V.
 

larrylwill

New Member
Joined
Aug 22, 2021
Messages
70
the 4.1 was before I balanced them. Also before I set up the parameters.
I will take picts but again, I did NOTHING except change out 2 small wires n the B- for a larger one.
 
Top