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Old Jun 22, 2011, 12:37 AM
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New lipo - cells not discharging evenly?

I have been running a Savage Flux truck and just got a pair of 3s 4000mAh lipos to try out. (I had been running it on a pair of 2s 5000 previously).

I have never seen this on any of my lipos, but after running, one of the cells in each battery was .1V off from the others. I am a little concerned that they are not draining exactly evenly like all my other lipos.

Is this something to be concerned about at all? Is there something wrong with the batts, or are they fine to use like this? I will see what happens when I balance charge them tomorrow.

Thanks for the info.
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Old Jun 22, 2011, 10:40 AM
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Ontario
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I have two 4s 4500mah packs, and one cell in one of the packs was usually 0.2V or so lower than the others at the end of a run but they still balance charged fine. I didn't keep an eye on the pack over winter and this year it's worse - really is my mistake, I should've kept an eye on it as that cell self discharges faster than the others in the pack. I can still run the pack, but it gets more out of balance. Last run the bad cell was at 2.97V while the others were around 3.6V or so :S - so I'm going to increase the voltage cutoff a bit so that cell doesn't get too low. But it is taking longer for the charger to balance now. I'm not too worried about it though - just keep an eye on things and increase the cutoff voltage if it starts getting too out of balance. My guess is that the cell was bad to begin with since it started getting out of balance pretty quickly after I bought it and wouldn't keep charge as well as the others - Turnigy pack by the way. Cheap batteries though that get the job done for me
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Old Jun 22, 2011, 11:10 PM
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Quote:
Originally Posted by stona View Post
I have two 4s 4500mah packs, and one cell in one of the packs was usually 0.2V or so lower than the others at the end of a run but they still balance charged fine. I didn't keep an eye on the pack over winter and this year it's worse - really is my mistake, I should've kept an eye on it as that cell self discharges faster than the others in the pack. I can still run the pack, but it gets more out of balance. Last run the bad cell was at 2.97V while the others were around 3.6V or so :S - so I'm going to increase the voltage cutoff a bit so that cell doesn't get too low. But it is taking longer for the charger to balance now. I'm not too worried about it though - just keep an eye on things and increase the cutoff voltage if it starts getting too out of balance. My guess is that the cell was bad to begin with since it started getting out of balance pretty quickly after I bought it and wouldn't keep charge as well as the others - Turnigy pack by the way. Cheap batteries though that get the job done for me
Thanks for the info. I am charging them up now and they seem to be back in balance. I'll make sure to keep a closer eye on them during the winter when they are sitting idle. Thanks for the tip!
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Old Jun 23, 2011, 09:50 PM
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Texas
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Thats a fair amount of cell imbalance. As long as they balance while charging, it becomes a matter of making sure that one cell doesn't go too low given the imbalance. Typically you'd set lvc higher to make sure that the low voltage cell(s) doesn't go too low.


Running those in a SAV Flux, you're below Castle's minimum lipo requirement of 5000mah and 25C. The amp demand the Flux is putting on them may be contributing to the imbalance. This other thing that can contribute to cell imbalance is running them down more than 80% of capacity - deep discharges tend to increase cell imbalance issues.
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Old Jun 24, 2011, 02:05 AM
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Quote:
Originally Posted by Duster_360 View Post
Thats a fair amount of cell imbalance. As long as they balance while charging, it becomes a matter of making sure that one cell doesn't go too low given the imbalance. Typically you'd set lvc higher to make sure that the low voltage cell(s) doesn't go too low.


Running those in a SAV Flux, you're below Castle's minimum lipo requirement of 5000mah and 25C. The amp demand the Flux is putting on them may be contributing to the imbalance. This other thing that can contribute to cell imbalance is running them down more than 80% of capacity - deep discharges tend to increase cell imbalance issues.
I am still going on the assumption that it is the battery, as they were a little out of balance before I even ran them in the Flux. I think they should be fine in the Flux, as they are 30c Batts, so very close amp supply to my 25c 5000s.
I guess we'll just run them and see what happens. I have 3 cycles through them, and they seem to be doing OK so far. Still about .1 off on a couple cells, but well above safe lipo cutoff.

Thanks!
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Old Jun 24, 2011, 05:34 PM
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Your cells are simply a normal case of "capacity imbalance"
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Old Mar 07, 2014, 02:54 PM
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yeap have the same issue with 6s 4000 mah turnigys , they balance once they charge but after 2 days sitting all the cells are at 4.16 and this one is at 3.9 , is this dangerous to be used? im flying helis
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Old Mar 07, 2014, 03:44 PM
Did you check the FAQ already?
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That's a big difference. Sounds like one cell is going bad. If you are confident with lipos and now how to safely work on these, you can opt for removing the bad cell, and keep it as a lower S pack, but only if you are sure of what you are doing. Otherwise just retire the pack.
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Old Mar 07, 2014, 07:57 PM
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yeap , question , what if i keep using them? how the cut off works? the esc checks all the cells of the battery? or it cutoff by counting the total voltage of the battery?

forgot to say i have a 12s setup
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Old Mar 08, 2014, 02:23 AM
Did you check the FAQ already?
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The ESC only checks for total battery voltage, as it's not connected to the balancing port of the battery, or is it? So if one cell goes down south, but total batttery voltage is still good and above LVC level, the ESC will not shut down. With 2S setup the ESC will shut down as you will be missing 50% of total voltage, but with 12S the impact is less.

With something flying, and considering that a 12S heli must be a big one, I would not take the risk of taking to the air with a dodgy lipo. Sounds like an accident waiting to happen...
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Old Mar 08, 2014, 06:09 PM
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thanks for the reply solo , any good 6s batteries to recommend? something between 3500-4000 mah?

thank your again for the info you providing
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Old Mar 08, 2014, 06:57 PM
Did you check the FAQ already?
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Gen's Ace are good ones, to name just a brand. I know someone using these in his heli, and he did some extensive testing as well, checking performance with telemetry, and hooking the charger up to the PC. His findings were that performance was very steady over a longer period of use.
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Old Mar 09, 2014, 04:32 PM
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i used to charge my batteries on storage and keep them in a room at the house , some ppl suggest to have them on the frige when not flying so they preserve much better, do you know if that is correct?

can you ask your friend how he storing them when hes not using them?

thank you in advance
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