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Uneven cells in lipos

Old 07-05-2015, 06:46 PM
  #1  
apprentice
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Default Uneven cells in lipos

Hey guys, pretty new to rc planes and lipos, as well as forums, so ive got an apprentice s and bought three 11.1v 3s 3200mah 20c e-flight lipos, one of which only has about 7 total volts the lowest cell being like 1.8v the other two lipos have cells that read 3.73 3.84 and 3.85v 11.42 total after flying - can anyone tell me why one of the cells in each of these two lipos is lower and if that is normal or should i try returning the batteries, any help would be awesome as i am so new to useing lipos and not sure what too think. Thanks - apprentice
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Old 07-05-2015, 07:38 PM
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fhhuber
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Kind of normal for it to go out of balance under heavy load... No cell is in the danger zone so you are fine.

Note that the E-Flite chargers that come in RTF packages tend to not balance quite right.

Watch the pack.

Balance charge.

Don't buy E-Flite LiPos for one reason: You can get better for cheaper. Generally the E-Flite LiPos meet their label ratings and do Ok.
SkyLipo (Nitroplanes.com) 20C do better often for half the price and their 30C are better than that and still lower than the E-Flite.
Big problem with Nitroplanes is you have to watch the site and pounce on anything in stock you want because they stay out of stock for months.
Other vendors have good deals too. I'm trying out some LiPos from ChinaHobbyLine.com Good so far.
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Old 07-05-2015, 07:50 PM
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1.8V is too low, you will probably find that your charger refuses to charge it. It could be that you flew too long or left it connected after flying and over discharged the battery, or it could be a faulty battery. Either way 1.8V is effectively a dead cell (they can sometimes be recovered but if it's new return it if you can)

Originally Posted by fhhuber View Post
Kind of normal for it to go out of balance under heavy load... No cell is in the danger zone so you are fine.
Sorry but i'm going to disagree with you there. 7V total for a 3s LiPo with one cell at 1.8V is grossly over-discharged and well below the 'danger zone'... probably too low to be recharged in fact.
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Old 07-05-2015, 07:55 PM
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Like alluded to previously, it's not uncommon for a lipo to drop a few + .10v per cell over time and use...........start to worry and replace when the balance re-charger rate becomes unpredictable and will not fully charge all cells consistently within a .20 to .30 range........by then it will be to late to save and become a hazard........
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Old 07-05-2015, 07:56 PM
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Yep... misread it... the 1.8 is way bad.
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Old 07-05-2015, 08:23 PM
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Originally Posted by fhhuber View Post
Kind of normal for it to go out of balance under heavy load... No cell is in the danger zone so you are fine.

Note that the E-Flite chargers that come in RTF packages tend to not balance quite right.

Watch the pack.

Balance charge.

Don't buy E-Flite LiPos for one reason: You can get better for cheaper. Generally the E-Flite LiPos meet their label ratings and do Ok.
SkyLipo (Nitroplanes.com) 20C do better often for half the price and their 30C are better than that and still lower than the E-Flite.
Big problem with Nitroplanes is you have to watch the site and pounce on anything in stock you want because they stay out of stock for months.
Other vendors have good deals too. I'm trying out some LiPos from ChinaHobbyLine.com Good so far.
Hey fhhuber, thanks for the info, so ive got the dynamite sport plus charger and the dynamite volt checker and discharger, ill try n stay away from the e flight lipos and try some others, one of the three lipos i have from e flight came new with all three cells under 2.5v. Blahh. -apprentice.
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Old 07-05-2015, 08:33 PM
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Originally Posted by JetPlaneFlyer View Post
1.8V is too low, you will probably find that your charger refuses to charge it. It could be that you flew too long or left it connected after flying and over discharged the battery, or it could be a faulty battery. Either way 1.8V is effectively a dead cell (they can sometimes be recovered but if it's new return it if you can)


Sorry but i'm going to disagree with you there. 7V total for a 3s LiPo with one cell at 1.8V is grossly over-discharged and well below the 'danger zone'... probably too low to be recharged in fact.
hey guys, i probly should of made the post little clearer srry, i have three brand new 3s 3200mah 20c lipos from e flight, i tested volts before i used any of them and on 2 of the lipos 1 cell from each lipo was off by about .10 is that okay for a new unused battery and the third lipo was way under, none of the cells were over 2.5 and i never used it, ill try to return that one but what should i do w the other 2 lipos which each have 1 cell about .10 lower, just keep slow charging and balancing, im taking it easy on my flights trying to get the cells to balance. -apprentice
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Old 07-05-2015, 10:27 PM
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Originally Posted by apprentice View Post
one of the three lipos i have from e flight came new with all three cells under 2.5v. Blahh. -apprentice.
They should NEVER arrive new below 3.5v/cell. Should be 3.7 to 3.9v/cell when you get them.
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Old 07-06-2015, 06:28 AM
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Storage charged as they should be when you were supplied often has 0.1v differences in cells. Its a fact of sitting on shelf etc.
After flights its common as well based on different cell resistances.

Balance charge the packs EXCEPT for the very low one. Get that one back to shop and get a refund or replacement. 2.5v is disaster levels for lipo's.

Nigel
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Old 07-08-2015, 04:43 PM
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Rockin Robbins
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I watched a video last night about why our chargers take so long balancing packs and how to speed it up greatly while eliminating overcharge problems caused by our chargers' balancing strategy. This is for bringing up a low cell that's more than a few tenths of a volt below the other two.

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Old 07-08-2015, 04:54 PM
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Turnigy 420 charger balances by charging at up to 2 amp rate.
Fastest automatic 4 cell balancer I know of.
It handles each cell individually instead of pushing current through the whole pack.

and its cheap.
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Old 07-08-2015, 05:10 PM
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Originally Posted by Rockin Robbins View Post
I watched a video last night about why our chargers take so long balancing packs and how to speed it up greatly while eliminating overcharge problems caused by our chargers' balancing strategy. This is for bringing up a low cell that's more than a few tenths of a volt below the other two.

RR I was just going to sugest the same video. Good info I have not tried his "jumper cable" yet but do intend to build one. Idea is great in my opinion
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Old 07-08-2015, 05:26 PM
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Hey guys I just want to say that I had the same situation with a 3 cell lipo and 1 cell was down to 1.8 and my charger which is a Hi -Tec multi charger AC X-1. It kept saying that it was too low a voltage to charge. A buddy of mine came along and we set the lipo to charge with NMH chemistry for about 15 minutes on a 0.1 charge
Then switched the charger to LIPO on a 0.1 charge and along with the balance plug and the lipo came right back to life. I don't know if I just got lucky with this Batt. or will that sequence work all the time with an almost dead batt.??
My buddy calls it TRICKING A LIPO :O)) fdnyjery
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Old 07-08-2015, 05:36 PM
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Originally Posted by fdnyjery View Post
Hey guys I just want to say that I had the same situation with a 3 cell lipo and 1 cell was down to 1.8 and my charger which is a Hi -Tec multi charger AC X-1. It kept saying that it was too low a voltage to charge. A buddy of mine came along and we set the lipo to charge with NMH chemistry for about 15 minutes on a 0.1 charge
Then switched the charger to LIPO on a 0.1 charge and along with the balance plug and the lipo came right back to life. I don't know if I just got lucky with this Batt. or will that sequence work all the time with an almost dead batt.??
My buddy calls it TRICKING A LIPO :O)) fdnyjery
I have done this as well. I learned via youtube however each one said perform at your own risk. A cell can quickly overcharge which causes a lipo fire. When doing it you need to keep an eye on it. Safety Safety Safety
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Old 07-08-2015, 05:53 PM
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Any time a LiPo is below 3.0 V / cell its damaged. It might recover and be useful but its life has been reduced.
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Old 07-08-2015, 06:46 PM
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Originally Posted by fhhuber View Post
Any time a LiPo is below 3.0 V / cell its damaged. It might recover and be useful but its life has been reduced.
I ran a couple of 3s 2200mAh batteries down to dead flat by inadvertently leaving them plugged into a plane for a day (two separate incidents a few weeks apart).

After unplugging for a while they self-recovered to a fraction of a volt per cell. I then recharged using the NiMh charger setting followed by a standard LiPo charge. After recovery these batteries performed exactly as the others from the same batch. This was over two years ago and both batteries continue to perform exactly as the others, in fact i no longer know which ones suffered the over-discharge but they all work the same and none of them have any puffing or any outward signs of distress. IR as measured on my iCharger also showed no change on the over-discharged packs.

I did also have a smaller LiPo that was left connected up for several days. I attempted recovery on that one too but one cell on that one didn't come back, so you don't win them all. On my small sample it seems to me that if they do come back then they can be 'as good as new', or at least so close that you cant tell the difference.
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Old 07-08-2015, 07:03 PM
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Originally Posted by Rockin Robbins View Post
I watched a video last night about why our chargers take so long balancing packs
My icharger doesn't work that way. It balances and charges simultaneously, it pushes current in while simultaneously draining the higher cells. The balance drain current is over 1amp rather than the 0.1A mentioned in the video.

So balancing takes no time at all. Time-outs are a thing of the past even when parallel charging multiple large batteries.
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Old 07-08-2015, 07:16 PM
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The extremely rare cases of the batteries recovering and appearing to be normal don't change the fact that more often you can expect to get about 3 cycles then they die after being drained flat and then recharged using some way to fool the charger's safety systems.
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Old 07-08-2015, 08:19 PM
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I can only speak from experience. As i explained, out of the three batteries I've attempted recovery from extreme over-discharge two have gone on to work perfectly normally over a two year period and at least 100 cycles. One that had been connected and drained for days did not recover, a cell just refused to charge so that one went straight in the trash.

So my success rate is 66.6%, possibly i just got really lucky (twice) but if so I've heard of many others having similar luck.


Of course, if the battery came over-discharged as new I'd be the last one to recommend attempting recovery, just send it back for refund. But if you over discharge due to your own fault like i did, then it's worth a go at recovery based on my experience.
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Old 07-08-2015, 08:38 PM
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I sit with JPF as well having recovered packs .... some good some bad.

Nigel
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Old 07-08-2015, 08:53 PM
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Originally Posted by JetPlaneFlyer View Post
My icharger doesn't work that way. It balances and charges simultaneously, it pushes current in while simultaneously draining the higher cells. The balance drain current is over 1amp rather than the 0.1A mentioned in the video.

So balancing takes no time at all. Time-outs are a thing of the past even when parallel charging multiple large batteries.
Some people wonder what they get when they spend $100 for a charger instead of $30 for a Hobby King Accucell. Well actually what you buy is three or four separate chargers that handle their individual cell.

As explained in the video, the cheaper chargers actually overcharge the cell by a hundredth of a volt. Then it stops and discharges the overcharged cell(s) until they're not overcharged, the charges the whole pack again until one overcharges. Around the circle until they're all fully charged. It can take time. In this case time is money, $70 to be pretty precise.

Is it worth it? If you're field charging and need balanced packs fast then probably yes. If time isn't the essence and you build one of those jumper cables for severely mismatched batteries then you can save the money.
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