Originally Posted by Wayne Giles
I have carried out the IR v Charge state measurements and the plot is attached. I chose a well used Loong Max 3S1000 20C pack which shows a nominal cell IR of about 15 milliohms at 25deg.C.
The pack was charged and left to settle in a temperature controlled chamber at 25C for several hours and then discharged at 1C (ie 1A) with measurements of the IR of Cell 1 being taken at 50mAh intervals.
The pack was discharged down to 3V/cell ie fully discharged.
The process was then reversed with the pack being charged at 1.2A (no 1A setting on charger) with readings again taken at 50mAh intervals, this time of Cell 2 so as not to confuse the graph.
Note that at about 2/3 charged I thought that the charge rate was too high and heating the pack causing the IR to fall so I reduced it to 0.7A. This caused the IR to start rising slightly which you can see on the lower plot, which confirmed my suspicions; I should have used a lower charge rate throughout.
You can see that allowing for the slight heating caused by the charge and discharge currents that the IR of the pack is essential independant of state of charge, certainly in the area where you are working ie between fully charged and 80% discharged.
So in answer to your question, and confirming what Charles has said in his post above, yes, whoever from Hyperion told you it varies is quite wrong. The reason a fully discharged pack gets hotter at the end of discharge is that the extra total heat produced has got to the surface of the pack.
The problem with getting technical information from suppliers (apart from their prejudice) is that invariably you are talking to a salesman who has no technical understanding and is therefore talking through the wrong orifice.
If only we could get to the engineers at Hyperion et al, we might get some sense!
BTW you should get your IR Meter next week; perhaps you would be good enough to measure some of the lipos you have listed in you original table. If you could post the results it would be helpful to us all. (You MUST use the same temperature when comparing packs.)
Thanks Wayne for the result.
How did you measure every 50mah the IR while charging/discharging ? , can you do it with the ESR/IR meter while charging/discharging ?
" the IR of the pack is essential independant of state of charge" what we can see in your graph.
Software of Hyperion stores every second all measured values in a database during charge/discharge.
So you can see afterwards the charge/discharge results in a graph.
Attached graph is during a 3S 3Amp 35C lipo charge, charged with 3A
TCS = terminal capacity state in % ( 100%= fully charged)
the Lipo was discharged to 34% level before charge.
And Ri dropped from 27 to 13mOhm.
Charging with (1C) 3Amp will the lipo being heated up inside ( i dont feel the pack is getting warm at all) that much so the Ri drops from 27 to 13mOhm ?
Yes I will measure with IR meter my lipo's and compare with my report, and i will report it.
Getting info from Hyperion engineers is very difficult or secret.
i asked for the table where i can see the cell voltage values with indicated rest capacity in %.
They could not give it to me , its secret they told me