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Lipo Balancing - how close do they need to be

Lipo Balancing - how close do they need to be

Old 06-24-2010, 09:18 PM
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Default Lipo Balancing - how close do they need to be

I am a lipo newb. I just charged my first one using this charger. I selected the Balance Charge and it went on it's way however when it was done and I looked at the results it showed Cell 1 @ 4.9 and Cell 2 @ 4.11. The balance plug was plugged in and the charger detected the battery as a 2S which is what the battery was. The battery was a 35c 5000mah 2S Turnigy. Should this be a concern?
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Old 06-24-2010, 10:54 PM
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Definitely a major concern here.
If one cell is truly at 4.9V, then you could have a dangerous pack in your hands. 4.2V is maximum voltage for any lipo cell. I would check with a voltmeter first before condemning your pack as toast, sometimes the balance connectors have poor connections and can read funny. If you actually have 4.9V on one cell you should be very careful and do not use the pack again.

After typing this I figured maybe you meant to type 3.9, and 4.11, in which case this is reasonable. Next cycle balance charge at 0.2A, it will take a while, but should balance the pack perfectly.
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Old 06-24-2010, 10:59 PM
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may he have meant 4.09???
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Old 06-24-2010, 11:23 PM
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For his sake I hope so!
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Old 06-25-2010, 05:03 AM
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Thanks guys, I am pretty sure the charger said 4.09 and 4.11 sorry for the typo there. On a related note how do I check the voltage of each cell? Through the balance plug?
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Old 06-25-2010, 05:54 AM
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Yes, you were prob looking at 4.09 - max lipo cell voltage is 4.2v and 4.9 is such a serious overcharge. If it was 4.9v, your charger would have been doing a horrible job letting it overcharge like that!

You can use a dvm/MM and check the voltage of the pack and each cell through the balance plug. Touch the metal that shows on the bacl with your test leads. The outer two balance wires should give you pac voltage. Checking across a pair of the wires shuld give you cell voltages.

BTW, your orig question - 4.09v vs 4.11v is close enough to consider them balanced. I'd be a little concerned why they are not closer to 4.2 than they are. Doe sthis lipo have a lot of cycles on it? Do you remember the 1st voltage you saw when you put it on teh charger - in other words, how low (voltage) did you discharge the lipo?
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Old 06-25-2010, 07:45 AM
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Originally Posted by Duster_360
Yes, you were prob looking at 4.09 - max lipo cell voltage is 4.2v and 4.9 is such a serious overcharge. If it was 4.9v, your charger would have been doing a horrible job letting it overcharge like that!

You can use a dvm/MM and check the voltage of the pack and each cell through the balance plug. Touch the metal that shows on the bacl with your test leads. The outer two balance wires should give you pac voltage. Checking across a pair of the wires shuld give you cell voltages.

BTW, your orig question - 4.09v vs 4.11v is close enough to consider them balanced. I'd be a little concerned why they are not closer to 4.2 than they are. Doe sthis lipo have a lot of cycles on it? Do you remember the 1st voltage you saw when you put it on teh charger - in other words, how low (voltage) did you discharge the lipo?
I just checked and total pack voltage is 8.07 and cells are 4.050 and 4.005. This pack is brand new and this is its first charge. I did notice what the voltage was when I plugged it in to the charger. After I got the pack, before charging it, it was ran for about 20-30 minutes. Power was the same all the way through and my VXL-3S never kicked off the LVC and I did verify it was in LIPO mode. Another concern I have is that the charger showed it put 5000mAh into battery. Wouldn't the battery have to be totally drained for that to happen on a 5000mAh battery?
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Old 06-25-2010, 08:03 AM
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The batt should have been 3.7-3.8v (50-60-65% capacity) when you got it new, they are only partially charged before they're shipped. Part of the prob is that the pack should have been charged before you ran it -that is SOP with lipo - charge it fully before you run a new one. I suspect what you're seeing cell balance wise may be related to running it first rather than charging it first. This cell imbalance and low voltage should go away after a few cycles.

Chargers like yours are pretty accurate usually, dbl check your esc settings and be sure its on lipo and that the lvc is set. I'm not familar with the esc, but if you can set it to 3.2v/cell (6.4v for a 2S) it will provide some safetly cushion. Running lipo to lvc at 3v/cell is tough on them and you won't get the life from them versus not running to lvc everytime or using a higher lvc.

Go ahead and run it again from where it is and then re-charge it and see if charger numbers make better sense. Lipos can be overrated - I've read of 5000mah rated lipos that routinely charge to 6000+mah, so you may have really put 5000mah back in and run the voltage down pretty low.
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Old 06-25-2010, 07:11 PM
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A couple of charging cycles should balance it out fine.
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Old 06-26-2010, 01:04 PM
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batteries generally also bleed some charge will charging. if you cycle a battery a few times on a charger that has a discharge function you should see that it almost always chargers more mAh into the battery then what comes out of them. lipos are way better about this than nickel based batteries but still do it. dont ask me where those extra electrons go though

but on the original point. a good balancer should get the cells to be within one hundredth of a volt (.01) of each other. the biggest concern is that no cell goes beyond its voltage range (about 3-4.2v). so when your speed control hits LVC, for the first few runs double check the individual cells with a digital voltmeter and make sure non of them are below 3.0v per cell (worst allowable scenario is if one is under 3.0v but gradually rising to above 3.0v in a matter of seconds). the charger, if its doing its job, should have a safety to keep any cell from going over voltage. unfortunately the VXL speed control does not have adjustable voltage cutoff so as the pack ages you may want to eventually make sure to stop running before you hit the LVC just to protect any weaker cells.

Last edited by benben10; 06-26-2010 at 01:15 PM.
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