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Old Jan 05, 2013, 12:33 PM
mrforsyth is online now
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Originally Posted by junsi View Post
For example: Charge Lipo with Vstd, set Balance Over charge to Vboc,the cells internal resistance detected is Ri, when the charge current is Ia, the actual CV value of cells is Va
IF Ri*Ia > Vboc THEN
Va = Vstd + Vboc
Va = Vstd+Ri*Ia

For example: one cell Vstd is 4.2V, Ri is 4 mohm, Vboc is 5mV, when the battery enters CV status, if the current Ia is 10A, then the voltage drop on the internal resistance is 10A*4 mohm>Vboc, and the actual CV value of cells is Va=4.2V+Vboc=4.25V;
if Ia drops to 1A, then it should be 1A*4 mohm<Vboc, the Va=4.2V+4mV=4.24V;
Similarly Ia drops to 0.2A, the Va=4.2V+0.8mV=4.208V.
As I understand the logic diagram of this feature, selecting this feature and setting a value above 0 may actually result in increased charge times as Balance Over is only engaged when Vboc is less than Ri*Ia. If Vboc is greater than Ri*Ia, the charger defaults to Va = Vstd+Ri*Ia. Since Vstd+Ri*Ia is greater than Vstd + Vboc, the charge cycle will be faster without enabling this 'feature'.

There's some bad units in the above calculations as well. 4mV = .004V, not .04V. Likewise, 4mOhm = .004 Ohm, not .04 Ohm

Something's fishy or I need a cup of coffee, or both. Somebody help me out here.

As an aside, I have accomplished what you're seeking by using John Julian's cutoff circuit in conjunction with a constant current charge setting to create custom charge cycles with virtually no CV stage for charging my 18650 cells. One simply needs to know that internal resistance of individual cell being charged as well as the charge current to set a custom interrupt. I set it on the low side as IR decreases during charge.

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