Lipo resistance figures

[tonydevon]

I just got myself a decent charger for the first time ever.

Pulsar touch conpetition.

Anyway it displays a resistance figure.

What figures should i expect to see and what does a high or low reading mean?

[jayst]

ive been cycling some saddles that are 3yrs but new. there started off at 35m@ and done 2 cycles and there comin down. now at 15m@

[neallewis]

It will vary from charger to charger. I've tried measuring IR figures on difference charger platforms, and the same pack will give different readings on different chargers. You can't therefore use the actual values measured on one pack as good or bad. In theory a lower IR value is better, but I've taken a pack with a value reading of 7-8mOhms one one charger, and it come back with 20-30mOhms on another. The higher value is a consistent measurement on that charger and lead set, not wrong.

Measure your packs and look for consistent figures (or significant changes), not what the actual value is, as it doesn't really matter. Knows what's good and whats not by measuring your known good packs and keeping note of the values.
Some chargers measure the pack as a whole, others measure each cell in the pack, which can be useful in detecting a failed or failing cell.

Edit: Additionally a low reading is a low internal resistance, which is desirable. A higher reading is worse. if you are getting 5-50mOhms measurements on your charger, then i'd not be worried. if they were consistently reading say 8-15mOhms, and then you suddenly got readings of 1Ohm, i'd say it was duff or failing, or very out of balance.
As was mentioned above cycling packs can help with measured IR figures. If a pack has rested for some time, your first charge may give a high(ish) reading, but after a few charge, race/discharge cycles, it will drop to its typical lower value.
Just observe what you normally get, and look for the times when it's off that typical reading.

[5tone]

you also have to pay attention to the charge leads, clean the inner battery plugs and check the clearance of the male plugs.
this way you can get a coherent value to compare time after time.
some chargers really measure the IR others calculate it.

in my experience, with my charger (a D200), I can't point the most powerfull pack with the IR measurment, only a dying one.
the charging curve seems to be more revealing of it.
(in my case, the goal is 5mn without lost of power)

[tonydevon]

Ok thanks for replies will try to read and understand better later on.

I run 5 shorty packs. 1 per heat and a final.

All bought at same time. And all showing 15.1 to 15.3 on that charger.

So they all similar. Guess thats good news.

I need to read up more on storage etc as i came back to buggy racing after a long gap. Nicads were my power lol

[mark christopher]

Lower ir. Means more punch,

The biggest factor when measuring ir is cell temp, a warm cell will have lower ir, so when comparing chargers your Lipo should be same temp.

I can get my 1s packs around 1ohm, by discharging and charging at 40amp. Only really need low ir in stock racing, off road with mod motors batteries are not the limiting factor

[tonydevon]

will keep an eye on them, but Ive never felt them even get faintly warm.. LOL

im running 2wd buggy and never had to put more than 1200mah back in after a run

I plug the balance lead in every time and they always been charged at 5A

I run the pack then after the heat/final I put it away, was told to do this as it leaves the lipo partly charged, and never to leave them the fortnight gap fully charged

am I doing anything proper wrong???

[neallewis]

Originally Posted by mark christopher

Lower ir. Means more punch,

The biggest factor when measuring ir is cell temp, a warm cell will have lower ir, so when comparing chargers your Lipo should be same temp.

I can get my 1s packs around 1ohm, by discharging and charging at 40amp. Only really need low ir in stock racing, off road with mod motors batteries are not the limiting factor

Are you using an iCharger Mark? Typical pack IR values from my various chargers are in the milliOhm range, not Ohms. However the value does depend on the charger and the IR measurement/calculation process (no industry standard), which is my original point about the actual measured values are a bit meaningless, or not comparable between chargers. You are looking for consistency through the packs life on your charger. When you see the values creeping up, time to replace it.

I think the points above by 5tone are right, charge lead (condition) is important, and battery terminal condition is certainly important influence on the total internal resistance of the system as a whole, both for measurement (consistency) and actual charging.

And most chargers do calculate the IR figures, not measure, which is a complex process to do accurately. The process of trying to measure will change the actual values. Also the "cheaper" chargers do the pack as a whole, not the individual cells within the pack.

And Mark mentions pack temperature is also a fair point. One can play a game of getting the lowest IR of a pack by changing the variables, but it's generally a waste of time and effort, as for a given pack the IR is what it is.

[neallewis]

Originally Posted by tonydevon

will keep an eye on them, but Ive never felt them even get faintly warm.. LOL

im running 2wd buggy and never had to put more than 1200mah back in after a run

I plug the balance lead in every time and they always been charged at 5A

I run the pack then after the heat/final I put it away, was told to do this as it leaves the lipo partly charged, and never to leave them the fortnight gap fully charged

am I doing anything proper wrong???

No you are not doing anything wrong at all. That's fairly typical for buggy racing. I typically run one car on 2-3 packs per race meeting, so they get charged a few times each.

Warm cells after a run are when there has been a huge discharge load, so in say 4wd outdoors, or 12th scale 1S onroad circuit racing. It's not something you'll typically see if club racing 2wd buggy. To be fair I get it after 2wd racing on high grip carpet, but using hot modified motors and racing fairly hard for the 5mins, everything seems to come off warm then.

[mark christopher]

Originally Posted by neallewis

Are you using an iCharger Mark?.

And Mark mentions pack temperature is also a fair point. One can play a game of getting the lowest IR of a pack by changing the variables, but it's generally a waste of time and effort, as for a given pack the IR is what it is.

yes using icharger
its also not a waste of time , as i said in blinkey racing it can make a big difference.
icharger measures each cell, and if you use the seperate IR check function on icharger measure the same pack cold , or warm thats been cycled, the difference is huge