Molicel P42a cycle test

[goatman]

i thought endothermal/exothermal
maybe software
even though the numbers are off, cycle after cycle its relative, charge and discharge are consistent
docware mentioned he wrecked one of his testers by constantly calibrating

then i thought maybe its the battery temperature

in winter ill lose 15% of capacity compared to summer

i could try 0.5 capacity discharge and charge to see what happens to the numbers

 

[Pajda]

Before entering the field of enthalpy and electrochemistry which is also welcome it should be note that this results are in most cases caused by the lowcost tester, particularly the accuracy of current measurement. In particular, the problem is that in CC discharging mode you measure a constant current all the time, while in CC-CV charging mode the current changes significantly, usually from 0.5C in CC phase down to 0.05C (100 mA for ZKE Testers) at the end of the CV phase. ZKE testers have only one current range and it is practically impossible to calibrate them for both ends of its range simultaneously (from 20A to 100mA).

EDIT: I completely forgot to point out another problem associated with current measurement in CC-CV mode. Lowcost testers like ZKE have a low sampling rate, which again does not bother so much in constant current measurement, but causes a problem when measuring a variable current.

The conclusion is that for measuring of coulombic efficiency you need a high precision tester with temperature chamber. But on the other side for cycle life ageing you only need the long term consistency of current/voltage measurement which is satisfactory for ZKE testers.

 

[bigboy061293]

I am thinking about the voltage response

Do you have experience about this aspect, comparing Lion and Lipo?
I mean I would love to know how much delay the P42A will take. Can you set up experiement to measure this?

 

[goatman]

im not a battery guy :lol:
try asking pajda over in this thread
https://endless-sphere.com/forums/viewtopic.php?f=14&t=103092&start=550#p1675227

 

[Pajda]

I am thinking about the voltage response...

Do you have experience about this aspect, comparing Lion and Lipo?
I mean I would love to know how much delay the P42A will take. Can you set up experiement to measure this?

It can be done, but I don't understand in what exactly do you interested? The figure shows the common method for measuring DCIR, specifically one-step method. I use this method and refer to it as "DCIR 10s". A measurement conditions must be defined for comparison between cell samples. Conditions which I am using are: SoC (50%), Temperature (25°C), t2-t1 (10s), Current (0.5C).

You are interested in the course of load / relaxation voltage? I can measure/plot it with 10ms sample rate at best.

 

[bigboy061293]

Hi, thanks for your response.
I am trying to figuring out the reason why li-po is prefered to use in multicopters instead of li-ion.
By comparing the C rate and energy density, this P42A is a good candidate. Actually, we have build the P42A package (12S6P) for using in my drone but the response of the drone was not so good (compared to the similar one which used li-po battery).
This makes me think about the "response" of li-ion vs li-po.

 

[Pajda]

in my opinion, DCIR has the biggest influence. Batteries that are called li-po in the RC model/drone industry means "a cell that is designed to deliver maximum power at the expense of other features". So both electrochemical and electromechanical design are subject to this. The electromechanical design is especially important, because the pouch cell format today allows the best electrical connection of cell electrodes/current collectors to the output terminals. On the other hand, the cylindrical format still suffers from a narrow neck in the design of connection between the cell electrodes and the cell output terminals by something which is so-called tabs. Some manufacturers (Tesla) are aware of this and are trying to solve this problem of cylindrical format by a tabless electrode design.

The second issue is the quality of electrical connection between the cell terminals. The pouch cell format also benefits from the fact that the cells are mostly connected into the batteries directly in the production (ie only a few individuals build batteries from bare pouch cells), where more expensive technologies can be used (ie laser welding) which have a lower current path resistance than DIY spot welded nickel strips.

This all leads to the situation, that pouch cell batteries (li-po) can easily have up to 10 times lower DCIR than industrial cylindrical cell based battery.

 

[Hillhater]

Hi, thanks for your response.
I am trying to figuring out the reason why li-po is prefered to use in multicopters instead of li-ion.
By comparing the C rate and energy density, this P42A is a good candidate. Actually, we have build the P42A package (12S6P) for using in my drone but the response of the drone was not so good (compared to the similar one which used li-po battery).
This makes me think about the "response" of li-ion vs li-po.

There is no commercial 18650/21700 li-ion cell that can compare with even the common 65C lipo RC pouch packs,...let alone the more intense 100-200c lipo.
Of course there are compromises, cost, cycle life, energy density, etc being some, but if outright performance (response ?) is the objective, then lipo is the obvious choice for non military use.