Internal resistance

[grsboats]

What it's a good IR for a new Lipo pack? I've been checking out my IR packs after one year of use and found out that this number raised almost the triple from the first charge but still working good with little puffs.My new A-spec packs(65C) 6S have 17 mohs against 31 mohs of my new 45C batts.Would be interesting to have experts chime in! Gill

[kevinpratt823]

I asked about individual cell resistance recently, here is the threadhttp://forums.offshoreelectrics.com/...ell-resistance
You may be better off posting and searching the battery specific forum.

[martin]

Gill I see on your web site you now have an iCharger, I recently started using one also & what a great charger they are. I have a pair of new A Specs 3s 65c 4500mah,IR is 3-3-2 on both packs, I also checked 6 Dinogy 3s 65c 4000mah & all were 2-2-1. I also checked some smaller used Nanos 3s 45c 2200mah & got 14-13-11 on one & 14-45-12 (this pack is finished) as its has low voltage on 1 cell. Martin.

[jetnfast]

I think it all depends on the C rating. I have a 60-120C Gens Ace pack that has IR of about 1 or 2 per cell and has held that way for over a year. I also have packs that are 25C rated for use with planes, etc that have IR of 10-15 per cell. I would say an IR per cell of less than 10 is ideal. Keep in mind this number will depend on when you measure it. To get an accurate assessment, check your IR immediately after charging. In your case, your IR has gone up quite a bit over time compared to new, I would consider some new packs. I am a huge fan of Gens Ace and China Hobby Line. I never had good luck with HK stuff!

[RaceMechaniX]

Gill,

Keep in mind temperature has a significant impact on IR when you measure it. True measurement of IR is not straightforward either and takes some specialty equipment. The very best cells I have seen are around or below 5mOhm.

TG

[785boats]

Gill.
As a matter of course, I always write down the IR of a new pack on its first charge. The Hyperion 720i Duo 3 charger displays the individual cell IR in one of the menus during & at the end of each charge.
I know the actual values may not be exact but I'm more interested in the difference between the cells in each pack.
I also check at the end of future charges, now & then, to see if a cell is starting to develop a higher resistance than the other cells. Especially if it seems to be lacking power or coming in a bit hotter than it should. Or if the cell checker shows a lower voltage &/or capacity in one cell after a run.

Here's some actual values of some packs on the initial charge. These represent an average of a number of packs of the same makes & sizes.

Haiyin 40C 5000mah 4s................2.3--2.3--2.1--2.2
Haiyin 40C 5000mah 6s................2.8--2.5--2.9--2.4--2.5--2.6
China Hobbyline 60C 5000mah 4s...2.6--2.5--2.5--2.5
China Hobbyline 50C 5000mah 3s...2.5--2.5--2.5
Zippy 45C 5000mah 6s.................2.8--2.3--2.4--2.3--2.3--2.2

Bear in mind that those values do drop slightly after a few cycles.

If anyone has some similar measurements of packs like TP, Hyperion, Gens Ace, Dinogy, etc. It would be good to see.

[RaceMechaniX]

As previously mentioned a charger is probably not the most accurate, but it is repeatable for A to B comparisons. Wayne Giles did develop a specific ESR meter to measure Lipo IR values. http://electriflyer.co.uk/esr-meter/. The meter's configuration is now a little behind on measuring the IR of very good cells which should fall below the meters range. Wayne is working on a new meter with lower range for high C, high capacity batteries.

TG