AA's vs Sub-C's ?

[BrianG]

OK, another update. I got a hold of a brand new un-zapped GP3300 sub-C cell. I charged the GP cell at 3.5A. I then charged the Duracell 2300mAh AA cell at 2.5A. Both cells were charged on a Superbrain959 and allowed to cool before the following test.

I made a resistor load network comprised of five 0.33 ohm resistors for a total load of 0.066ohms to test the AA cell at approximately 15A. I then made another network to put in parallel to create a load of 0.033ohms to test the sub-C cell at approximately 30A.

Each test was run for 10 seconds before measurement was taken to allow the cell voltage to even out somewhat to get the results are below:

	Test Load	Theoretical	Measured Cell	Measured	Calculated Internal
	Resistance	Amps @ 1.2v	Voltage		Amperage	Resistance

AA	Unloaded	NA		1.351v		NA		NA
	0.330 ohms	03.636A		1.175v		03.561A		0.04943 ohms
	0.066 ohms	18.182A		0.870v		13.182A		0.03649 ohms

Sub-C	Unloaded	NA		1.315v		NA		NA
	0.330 ohms	03.636A		1.250v		03.788A		0.02666 ohms
	0.066 ohms	18.182A		1.120v		16.970A		0.01361 ohms
	0.033 ohms	36.364A		0.980v		29.697A		0.01249 ohms

This test proved:

- An un-zapped GP cell will not maintain even 1v under a 30A load unless it is a hand-picked cell, or you are lucky. I would be curious to see how a zapped GP cell truly does under a 30A load despite websites that claim a certain voltage under this load.

- Using two AA cells in parallel comes really close to providing the same voltage and current as a sub-C under the same load, at least up to 30A. I don't have enough .33ohm resistors to take the load much lower to test higher currents.

At a later date, I plan to test the Ah rating of a sub-C cell at 10A and a AA cell at 5A prolonged loads. Judging by the increased capacity of the AA cell of 2300mAh, I expect about a 35% longer runtime on the AA cell until the cell voltage lowers to 0.9v.