Originally Posted by jj604
Aero, the numbers you are showing look fairly logical to me.
1) The ESR/IR meter shows a max IR of 9.12 for a 2600 cell. This comes out at a recommended current draw of 41 but that's a conservative number and for average current. You say these packs are peaking at between 47 and 60 Amps (guestimate). So the average current draw is likely to be 40Amps or under - unless you drive around with the throttle wide open all the time which you clealy don't. The fact the packs deliver adequate power and come down mildly warm confirms this.
2) My PL8 always gives lower IR than the meter. It measures IR during a very brief resting pulse and we do not know what correction algorithm FMA have used to allow for voltage settling. So I would not expect the two methods to agree since they are measuring IR in different ways. My guess is that the PL8 is also more sensitive to variations in settling time between cells because of the very brief measurement window and a bit of variation in IR and inconsistancy is not really a surprise. I'm assuming the PL6 works the same.
Bottom line is don't get stressed about it but ignorance is not bliss.
The IR meter will accurately and consistantly track the decline of these packs and show up any potential problems arising. Don't sweat the absolute value it's the relative numbers over time and between cells that really matters. The LiPo tool is intended as an emperical guide, that's all.
You have the critical piece of information - these packs fly the plane just fine and do not get excessively hot. Just keep monitoring their health with the IR meter and observing flight performance.
I'm guessing given their age and your recorded 3.5V under load that they are actually average quality "20/25C" packs that are gradually increasing in IR as they get older. Probably good for quite a while yet, especially in your 700 Watt plane. 900 Watts is probably pushing them a bit.
Thanks for the detailed response John. Your conclusion is especially helpful.
This was a bit of an odd situation since the packs had sat on the shelf for almost 2 years, I wasn't sure how much they had pre-aged before I got my first IR measurement and first flights with them. It will be very interesting to see what the IR is on the two new identical packs I ordered turns out to be.