26650 A123 vs. Enerland 4350's Ri

[zeropointbug]

I have been testing all my packs and the individual cells in them for the last few days and have found an odd result that doesn't make any sense to me. First of all I tested each and every one of my 26650 A123 cells by tapping the cells with power clips and balance tap (for accurate voltage monitoring), doing several D/C cycles on a 720i charger before taking an average Ri reading. Here is what I found:

Hyperion Enerland VX 4350mah cells: 7-10 mOhm Ri /cell (unkown rated Ri)

A123 26650 (2200mah): 7-8 mOhm Ri /cell (8 mOhm rated)

Hyperion G3 VX 4200mah: all 1.6 mOhm/cell (1.33 mOhm rated)

What makes sense is the G3 and A123 cell Ri's, as they are within 1 mOhm of rated impedance, but the Enerland cells is where this seems to me that the 720i is not accurate at all? I know for a fact that the Enerland based packs have ALOT more power than the A123 cells obviously in the real world, so why would they have a higher reported Ri? I haven't ran them in over 6 months, and it has been my first year using LiPo, so do they wake up once you start using them again with a higher load than a 720i discharge can offer?

I am still waiting for an RX8 to arrive from Mike so I cannot test them in R/C at this moment.

Any input would be extremely helpful in solving this mystery.

[snellemin]

Hey zpb, have you measured the resistance on the A123 at 140F?

[zeropointbug]

Yup. Wait, 170F actually, put them in the oven for 30 mins.... the Ri went down to 5-6 mOhm. I also froze them at -28 C (-18F) and did a discharge, IIRC, they were like 30 mOhm /cell? Off the start at least, decreased as it warmed up.


Also, at the pack level, a 4s1p A123 pack has an impedance of ~29 mOhm, and a 6s HP Enerland reads out at 69 mOhm. Make any sense?

BTW, if anyone knows how to read individual cells Ri on a 720i NET? I have seen 'Everydayflyer' over at RCGroups forum post cell Ri... unless the NET 3 can do this, and NET cannot?