Charge rate

[BrianG]

Originally Posted by zeropointbug

...You don't actually get a linear decrease in charging time per charge rate, it is merely the MAX charge rate during charge, the higher the C rate you set the charger at, you will hit CV phase after CC phase exponentially sooner, thus making the very top end of the C rate spectrum, the benefit seems to drop off a bit. I have found 4C is only a few minutes longer than 5C, and definitely not 25% longer, which it would be in theory.

That makes sense. Cell resistance plays a definite role in this. The higher current you charge, the higher voltage it will take to generate that current, and so hits the 4.2v/cell threshold faster.

[zeropointbug]

Yah, precisely. Ideally, if you could increase the max charge voltage as you increase C rate. You can do this with A123's however, I usually use 3.7v/cell for charging 5 amps/cell for a 2p pack, and then 3.8v/cell, sometimes even 3.9v/cell at 10 amps for a 1p pack.

I would be interested in finding out how a G3 cell would handle a 4.3v/cell charge threshold at 5C rate. I could only do this using my programmable power supply however.

As resistance decreases in lipo cells even further, 4.2v/cell should be sufficient for 5C or more charging to get the benefit. Like you said, it is mostly limited by the cells Ri.