[GerhardRP]

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090023862_2009023573.pdf
Here is some interesting reading on Lithium Ion batteries for space flight.
Gerhard
PS. cell level management is included. grp

 

[tomofreno]

PS. cell level management is included. grp

Well, not quite. More like some here have said: packs with significant capacity margin can afford some imbalance and operate fine. Packs with no margin require management:

Applications with large capacity margins may be able to charge and discharge to the weakest cell limits without requiring cell-level control. For applications with long cycle life requirements or little capacity margin, it is more likely that cell-level monitoring and end-of-charge or discharge control will be required for reliable battery performance and safety.

Thanks for the reference!

 

[icec0o1]

NASA couldn't have made it more clear and some people are still pushing the idea that BMS's are an absolute requirement... sheesh

 

[T1 Terry]

NASA couldn't have made it more clear and some people are still pushing the idea that BMS's are an absolute requirement... sheesh

Ummm..... Did you read the same article I did?

NASA Engineering and Safety Center
Technical Report​

Document #:​

RP-08-75​

Version:​

1.0​

Title​

​

​

​

:​

NASA Aerospace Flight Battery Program​

Page #:​

9 ​

​

of 49​

Discharging multi-cell series-connected batteries must be controlled​

to prevent safety problems that might arise from mismatched or unbalanced cells. When operated in a series string, the voltage must be controlled to prevent the lowest voltage cell from being driven into voltage reversal possibly resulting in cell venting or rupture.​

and all of section 5 sound very much like the requirement of a Battery Management System to me.

T1 Terry

 

[GerhardRP]

Ummm..... Did you read the same article I did?
and all of section 5 sound very much like the requirement of a Battery Management System to me.
T1 Terry

It doesn't seem to be required, but must work and not fail if fitted. There is also mention of 1/2 pack monitoring.
Gerhard

 

[icec0o1]

Discharging multi-cell series-connected batteries must be controlled​

to prevent safety problems that might arise from mismatched or unbalanced cells. When operated in a series string, the voltage must be controlled to prevent the lowest voltage cell from being driven into voltage reversal possibly resulting in cell venting or rupture.​

Ummm..... Did you read the same article I did?
and all of section 5 sound very much like the requirement of a Battery Management System to me.

T1 Terry

It would be controlled. Not electronically with a BMS for each cell, but by good design. That's why you bottom balance and charge up to a voltage where the weakest cell hits HVC. It never states that each cell's voltage must be monitored, but the string's voltage should be.

 

[EVfun]

From page 11:

Applications with large capacity margins may be able to charge and discharge to the weakest cell limits without requiring cell-level control. For applications with long cycle life requirements or little capacity margin, it is more likely that cell-level monitoring and end-of-charge or discharge control will be required for reliable battery performance and safety.

They seem to think it's advised if you want to safely use up the batteries cycle life. Remember though, that if you are in the air when $#!& goes wrong cannot just pull over to stop and fix it. Their safety requirements tend to be greater.

I see a possible explantion for why some cells have been reported to just go dead with rather low impedance. This is on page 13 just one sentence before they mention mid-string monitoring:

Overdischarge conditions lead to the electrodeposition of copper on the cathode causing the formation of a short circuit condition when the cell is subsequently charged. In most cases, overdischarge is benign and results in a dead cell.