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e-Electric General Discussion > LiPo, Balance, PinOut
 
 
tricid
Heliman
Location: Sherman, TX USA

I'm new to electric models, and lipo batteries. I understand that balance is a major concern. My battery, an Impulse Power 3s 2100mah, has a pinout for a balancer. It has 4 wires, one of them red. From checking the voltage, keeping one plug on the red, then switching among the blacks, it seems to multiply (hope that makes sense). One red one black can be 3, then moving over one back could be 6, move over one more and it would be 9.

So, question time:

1. Am I checking the voltages of each cell properly? Right now I get

3.53
7.11
10.26

So by my math that means

Cell one: 3.53v
Cell two: 3.58v
Cell 3 : 3.15

2. If so, it appears to me they're out of balance. How far out of balance is allowed? With this kind of pinout how can I discharge only one cell to bring them to balance. It seems the second/third wire is 2-3 cells in parallel. So to discharge the third cell, I'd be on the pins that make the volts 10.26.

Thanks for any help you can give.
06-02-2008 05:51 AM
 
 
Rob_T
Elite Veteran
Location: Tualatin, OR - USA

Your math and technique for caculating the cell voltages are right, except for one detail... You'd be better off doing the measurement with the battery near full not near empty. It's balance at full charge that makes the difference in burning your house down or not (it's the overcharging that comes with being out of balance that is the biggest problem). When the battery is near empty, your measurement is influenced by variations in capacity between cells, which is normal and not an immediate problem. (Although differences in capacity do tend to increase over time which can lead to problems later, which is why manufacturers try to match the cells).

Near fully charged, 0.1V spread between the highest and lowest cell is about the most you should tolerate. Most balancers can bring this down to better than 0.02V spread.

You can also measure between adjacent pins on the balance connector (be careful - spacing is close together) this will give you the cell voltages directly. You can then connect a load directly to the high cells using the same pins.


Rob
Eco8, Piccolo Fun, Shogun, HB Elite CP, Trex 450XL CDE, Swift
06-02-2008 06:25 AM
 
 
tricid
Heliman
Location: Sherman, TX USA

I'm charging now and I'll check again. I plan on purchasing a balancer soon as well.

Assuming one is out of balance, without a balancer, what is a good method to discharge just one cell? Using the second or third wire, with the volts being 2-3 cells added together, would that discharge just the one cell?
06-02-2008 06:35 AM
 
 
tricid
Heliman
Location: Sherman, TX USA

nevermind my last post, didn't see the last part of yours.

Thanks tons!
06-02-2008 06:37 AM
 
 
tricid
Heliman
Location: Sherman, TX USA

near fully charged, there's only a .01 difference with two of them, and a .04 difference on the third, so it does get a lot better.

Thanks again!
06-02-2008 08:05 AM
 
 
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MTA Hobbies . Model Rectifier Corp . RCHover

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e-Electric General Discussion > LiPo, Balance, PinOut
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