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-   -   AA's vs Sub-C's ? (https://www.rc-monster.com/forum/showthread.php?t=1888)

BrianG 12.27.2005 09:01 PM

Quote:

Originally posted by Dafni
BrainG, thank you for this info!

Looks like you are a pretty knowledgeable person yourself! :D

I'd like to think so, but knowledge isn't experience. Who better to ask than the people here who have both? :)

I actually have an electronics background, so building small circuits and number crunching formulas is fun to me. I'm actually in the process of designing a circuit that will take the varying 1ms to 3ms, 50Hz square wave pulses from any channel output (1,2, or 3) of a receiver and converting it to a 6v or 0v DC signal to use for triggering lights, solenoids, whatever. I plan to make it so it can be used in parallel with whatever the channel is currently used for. Something like turning on reverse lights when putting a BL motor in reverse or something like that. :)

BrianG 12.29.2005 12:04 AM

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:

Code:

        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.


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