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Old Jul 07, 2014, 08:41 PM
Registered User
Canada, QC, Montreal
Joined Nov 2008
544 Posts
Help!
Battery is unbalanced even though balance charged

Hi,
I have a Zippy Compact 4000mah 3S 25C battery from Hobbyking. It has about 10 cycles on it and lately I notice the battery is unbalanced even though I ALWAYS balance charge it. I use the battery for multirotors only. Currently the cell voltage will be something like 4.21, 4.13 and 4.11. I'm nervous that something bad might happen, any advice on how to proceed from here?
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Old Jul 07, 2014, 08:52 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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What charger?
What charge rate?
How much is the balancing power of your charger?
have you tried doinga slow balanceing charge ?
Wahat are the cell voltages right after a flight?
The deeper the discharge the worse the inbalance is likely to be.

Many chargers have verylittle balancing power and can no cope with a unbalanced / mis matched cells 4000 mAh being charged at 1C (4A).
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Old Jul 07, 2014, 09:21 PM
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Vancouver Intl, Canada
Joined Dec 1996
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Mine - same thing! 1300 3s pack.

Landed and I was at 3.6, 3.6 and 3.11.

Balanced charged it. Ran a slow discharge through it (3 amps) through my simple auto lightbulb discharger, and it was still balanced within 0.01.

Would a higher discharge rate make this happen again (say another flight?)

It also was puffy, and then after it cooled not puffy...
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Old Jul 07, 2014, 09:40 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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battery assembled from poorly matched cells discharged below 3.8 or so per cell are going to be inbalaced most of the time. The deeper they are discharged the worse the inbalaced becomes. Slow discharge to low voltage is likely to cause a greater inbalance than a fast discharge to the same voltage level(s). The reaso I have recomended notusing motre than 80% of the LiPolys capacity for many years now is to help avoid such issues and provide much longer LiPoy service life along with much faster balanced charges.
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Old Jul 07, 2014, 10:07 PM
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Canada, QC, Montreal
Joined Nov 2008
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Quote:
Originally Posted by everydayflyer View Post
What charger?
What charge rate?
How much is the balancing power of your charger?
have you tried doinga slow balanceing charge ?
Wahat are the cell voltages right after a flight?
The deeper the discharge the worse the inbalance is likely to be.

Many chargers have verylittle balancing power and can no cope with a unbalanced / mis matched cells 4000 mAh being charged at 1C (4A).
I have a Hobbyking HKC6 that I have been using for almost 2 years now. It works fine so far and this is the first incident of this kind. For this particular 4000mah 3S I'm charging at 5A so a little over 1C. The balancing power based on the manual is 300mah/cell (i'm not sure if this is the information you're looking for)

What do you mean by slow balance charge? Like at lower current rating? I can definitely try that. Right now I'm discharing the battery at 0.4A and will try to recharge it at slower rate.

I fly a Naza on my multirotors which has low voltage warning and I always land when the voltage is 11.1.
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Old Jul 07, 2014, 10:10 PM
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Canada, QC, Montreal
Joined Nov 2008
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Quote:
Originally Posted by Aviron View Post
Mine - same thing! 1300 3s pack.

Landed and I was at 3.6, 3.6 and 3.11.

Balanced charged it. Ran a slow discharge through it (3 amps) through my simple auto lightbulb discharger, and it was still balanced within 0.01.

Would a higher discharge rate make this happen again (say another flight?)

It also was puffy, and then after it cooled not puffy...
Do you fly multirotors or fix-wings? where do you fly in Vancouver? I'm moving there in 2 months and am wondering if it's safe to fly in public parks around the city
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Old Jul 08, 2014, 05:11 AM
A man with too many toys
United States
Joined Feb 2001
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Quote:
Originally Posted by boycoldface View Post
Hi,
I have a Zippy Compact 4000mah 3S 25C battery from Hobbyking. It has about 10 cycles on it and lately I notice the battery is unbalanced even though I ALWAYS balance charge it. I use the battery for multirotors only. Currently the cell voltage will be something like 4.21, 4.13 and 4.11. I'm nervous that something bad might happen, any advice on how to proceed from here?
Those voltages are definitely not good.

You need a charger with a higher balance current. Power Labs and some other chargers have 1A or higher balance current. That will speed up balancing and even out the voltage between cells. A PL6 would be perfect for your needs.

Also with a better charger you can charge at 2C or 3C. As I recall the ZC.4000.3s.25 batteries are designed to be charged at 5C so anything up to that won’t shorten the battery life.



.
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Old Jul 08, 2014, 06:48 AM
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Canada, QC, Montreal
Joined Nov 2008
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wow that's way out of my price range, any suggestion for chargers in the 30-50 range?
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Old Jul 08, 2014, 08:07 AM
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With that budget limitation, you might be better off making a single cell adapter that allows you charge each cell individually. You can probably make that out of stuff you already have.
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Old Jul 08, 2014, 08:23 AM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
20,699 Posts
Quote:
Originally Posted by boycoldface View Post
wow that's way out of my price range, any suggestion for chargers in the 30-50 range?

Here is
the info for a 2 pin charge cable like Dave suggested.

Use it to charge the low cell to the same level as the high cells after charging the pack.
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Old Jul 08, 2014, 08:34 AM
A man with too many toys
United States
Joined Feb 2001
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Quote:
Originally Posted by boycoldface View Post
wow that's way out of my price range, any suggestion for chargers in the 30-50 range?

If you can't afford a good charger don't waist your money on a 30-50 charger. Hobby king is not that bad. Keep what you have and start saving up for a good charger. You might try a very low balance charge rate and see it will bring the pack into balance.

.
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Old Jul 08, 2014, 09:03 AM
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United States, MN
Joined Feb 2011
4,246 Posts
Just do a low rate charge to solve the imbalance. The problem is obvious when you look at the math. You are charging at 5000mA and your balancer is only 300mA. The charger is going to terminate the charge at C/10 or 500mA. For it to be able to finish balancing the pack the current in needs to be at or less then the balancer current. Only when the rate is at 300mA or below can the charger completely bleed off all current going into the full cell while the other cells continue to charge.
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Old Jul 08, 2014, 09:06 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
12,556 Posts
You can make your own adapter to charge a single cell by making one from a servo extension using the male end which has the .100 thou, spacing to fit your balance connector. Cut one side off to make it into a 2 cell connector. Just make sure you get the polarity right when you plug things in.

Gord..
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Old Jul 08, 2014, 11:09 AM
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Canada, QC, Montreal
Joined Nov 2008
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Please excuse my noob-ness but how do I identify which cell is undercharged? I only have a simple cell checker from hobbyking http://www.hobbyking.com/hobbyking/s...l_checker.html
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Old Jul 08, 2014, 11:11 AM
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Quote:
Originally Posted by grimbeaver View Post
Just do a low rate charge to solve the imbalance. The problem is obvious when you look at the math. You are charging at 5000mA and your balancer is only 300mA. The charger is going to terminate the charge at C/10 or 500mA. For it to be able to finish balancing the pack the current in needs to be at or less then the balancer current. Only when the rate is at 300mA or below can the charger completely bleed off all current going into the full cell while the other cells continue to charge.
Thats what I'm trying to do but when i charge at 3A, around 12.52V the charger stop with a "Capability" error message. Not sure what that means.

Also, would you recommend any of these chargers?
iMax B6AC
Thunder AC6
iCharger 106B+
Turnigy Smart6 80w
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Last edited by nguyen.tran; Jul 08, 2014 at 11:35 AM.
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