recoverable

[Guest]

Hi question for you i have eight 6 cell lipos i use in my t rex500 but lately 4 of them aint been performing too well they aint puffy but when flying under full throttle the heli revs up and down as if they cannot deliver a full constant voltage output.
They are only a year or so old but were very cheap off hobby king.
In anyone's opinion does it sound like a voltage output issue and if so can they somehow be recovered or are they done for.
Thanks for any input.

[waveydavey]

Its to do with the ability to supply current. This is mainly down to the IR of the pack which goes up as they get older, as the packs aren't old have you ran them down to 0, not stored them at 50% or so. Your charger should be able to give you an idea of the IR.

https://sites.google.com/site/tjingu...os/lipo-issues

[Guest]

just done a resistance check 18/27/36/34/18/26 on a bad one and 29/15/16/16/22/11 on a one that still works

[Grumpy]

Assuming they are around 3000mAh size batteries then those IR's are all sky high, plus the big range between cells points to some cells failing badly. Looks like they are probably all toast, unless it's a measurement error.. what did you use to measure IR with?.

You haven't been storing them while fully charged by any chance?

[mahbouni]

Dunno what he's using to check the IR's but my PL8 is a random number generator. The last cell is always ridiculously high, even with brand new batteries. My two 10XP's seem to give more believable numbers but I'm none the wiser. I hear the Wayne Giles meter is the most accurate

[Grumpy]

Yeah, the Powerlabs arent the best for IR because they try to measure discharge IR by measuring resistance during charging. IR measurements from Powerlabs are often half of what you get from other means of measurement. You get more accurate results by measuring IR during discharge which is what Ichargers and the Wayne Giles meter does.

[Guest]

I used my turnigy reaktor 300w 20amp charger to test the IR.
I guess the high and uneven IR levels are whats causing the t rex to rev up and down at full throttle.
Also i may be guilty of leaving them fully charged.

[Grumpy]

Yes, the high resistance causes big voltage sag under load which in turn activates the low voltage cutoff (LVC) in the ESC.

There is no way to fix the damage. The batteries may be still ok for low demand applications like maybe powering your charger for field charging, but for flying your heli with IR like you have measured they are no use.

[Guest]

Thanks grumpy that explains the up and down revving just got back from flying and after some pack testing out of my 8 packs four are shot with IR up to 44 on some cells the other four are ok but i can tell there is quite a bit of speed difference between them in flight speed.
I will invest in 6 new packs next year as i dont get much flying done in the winter my hands cannot handle the cold and i get clunky in my flying from frozen fingers.
I will also only charge on the day i go flying no more packs sat around on charge.
One last question am i ok after flying just to leave the packs until i next go flying then charge them.
Thanks

[Grumpy]

Providing the resting cell voltage is in the range 3.7-3.9V I just leave the packs as they come off the heli.

[_tj_]

I used my turnigy reaktor 300w 20amp charger to test the IR.
I guess the high and uneven IR levels are whats causing the t rex to rev up and down at full throttle.
Also i may be guilty of leaving them fully charged.

I have just checked a couple of lipo's of mine.
one is about 2 years old, the other a couple of months old.

Both are Zippy 6s 5000mah 30C lipos.
Ir resistance of them measured with the Turnigy Reaktor 300w charger.

New 3-2-3-3-1-1
Old 3-2-2-2-1-1

Tested a couple of times and the batteries cell ir either increases a 1 or 2 cells by 1 at the most.

Fwiw,
I always balance charge my lipo's after a days flying.
And leave them fully charged until my next outing to the field.

I have another 6 of the same lipos, might give them a check also.
There are another 2 new ones, and the rest are a couple of years old.

[Guest]

I always normally leave mine fully charged until next flying session but these lipos are only a year old they were those hobbyking scratch dent at ten quid each for a 6cell 2650mah.
I never checked the ir when i got them they may of been high when i got them but aint buying no more of them going to get some zippy 3000mah for next year.
I suppose i always left them charged as i had ten of them and just liked them sat there ready to go

[Grumpy]

I cant comment on the remarkably low IR or tj's older batteries but it generally recognised both in the RC community and in other applications that use Lithium ion batteries that they should spend as little time as possible at fully charged state. Some do seem to cope better than others but it's still good practice not to leave them above about 3.9V for long if it can be avoided. Temperature is another major factor, batteries should be kept cool when in storage.

The best source of authoritative info I've found on battery care is here: How to Prolong Lithium-based Batteries - Battery University

PS....bear in mind that you cant directly compare IR batteries of different capacities. Large batteries have lower IR than small ones, for instance all things being equal you would expect a 2500mAh battery to have double the IR of a 5000mAh. The temperature of the battery also has a big effect, a cold battery will have much higher IR than a warm one. You also get a significant reduction in IR if the battery has just been charged or discharged (presumably because it warms up?).