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16s cell 9 voltage

km101

New Member
Joined
Jul 7, 2021
Messages
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So i have a standard 16s 280ah setup. I have just received my new set of cells to make second battery. On both new and old batteries cell 9 always seems to be the first cell have a higher cell voltage when charging and a lower voltage when discharging.

What am i missing.
 
Is it always at the same location even when you swap cell #9 with other other cell?
How much higher Voltage is it?
The connections are good?
If you swap the BMS, same issue exist?
Pictures of the setup?
 
Unable to swap as I only have one BMS (seplos)

Connections believe to be good otherwise it would be low all the time (not sure how a bad connection can give you a high voltage)

on charging the cell 9 goes up by 45mv and discharging by 9mv but as mentioned always the highest on charge and lowest on discharge

Yes swapped around cells and different pack now
 
Unable to swap as I only have one BMS (seplos)

Connections believe to be good otherwise it would be low all the time (not sure how a bad connection can give you a high voltage)

on charging the cell 9 goes up by 45mv and discharging by 9mv but as mentioned always the highest on charge and lowest on discharge

Yes swapped around cells and different pack now
I do not understand why you cannot the swap cell #9 location with cell #8 location or #10 location.
Some BMS may show high Voltage reading if it is connected to the cell or have high contact resistance, it may depend on the Voltage measurement circuit topology.
And if you use the Voltmeter, does it show the same reading?
 
I do not understand why you cannot the swap cell #9 location with cell #8 location or #10 location.
Some BMS may show high Voltage reading if it is connected to the cell or have high contact resistance, it may depend on the Voltage measurement circuit topology.
And if you use the Voltmeter, does it show the same reading?
Hi, I have swapped the cell locations and have a completely new battery pack as well.
 
for clarification.
You now have two battery packs indicating the same issue ?
Both are 16S with Seplos BMS ?
Which format of pack did you make ? see below.
Are you 100% Sure the Busbars are on clean contact surfaces and properly tightened down ? Even a simple ridge on the busbar hole CAN make a difference, you'd be surprised how often that is the case. And everyone denies it, till they discover it. (Well trod rabbit hole)
Also have you verified the BMS Sense lead.

1641543211975.png
 
for clarification.
You now have two battery packs indicating the same issue ?
Both are 16S with Seplos BMS ?
Which format of pack did you make ? see below.
Are you 100% Sure the Busbars are on clean contact surfaces and properly tightened down ? Even a simple ridge on the busbar hole CAN make a difference, you'd be surprised how often that is the case. And everyone denies it, till they discover it. (Well trod rabbit hole)
Also have you verified the BMS Sense lead.

View attachment 78675
bottom layout. I know what you are saying but why would it be high on charge and low on discharge it would seem its the cell to me, being a lower capacity but changed around, new cell in place, tried different busbars. etc etc.

I was hoping it was something someone had come across but the high and low voltage and all the changes to ensure it was not the cell, leads,etc etc

what can it be???
 
bottom layout. I know what you are saying but why would it be high on charge and low on discharge it would seem its the cell to me, being a lower capacity but changed around, new cell in place, tried different busbars. etc etc.

I was hoping it was something someone had come across but the high and low voltage and all the changes to ensure it was not the cell, leads,etc etc

what can it be???
What @Steve_S is telling you is that Voltage equals Current times Resistance. 45mV on charge implies only 0.9 milliOhms at 50 Amps charging, or 1.5 milliOhms at 30 Amps.

It doesn't take much resistance at high current to give you a measurable voltage. If your busbars are not all the same and making very good contact with each cell terminal, you will see different voltages at each cell. This is due to slightly different resistances in your connections or busbars. My guess is that your jumper from the 1-8 bank to the 9-16 bank is not identical to the busbars in the rest of the connections.
 
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