800mAh 7 Cell 5/4 AAA packs good for messing around? - RC Groups
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Nov 17, 2002, 04:01 AM
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Sloper Mario's Avatar

800mAh 7 Cell 5/4 AAA packs good for messing around?


This may be a really stupid question so bear with me for a moment. I'm getting my VIP together and was thinking about battery combos. From my lurking/reading I've pretty much decided on 7 cell Hecell packs for most of my flying. However I have a stack of Wattage 7 cell 800mAh 5/4 AAA packs that I use in my Hawk. They weigh ~3.75oz and work fine in my Wattage Hawk w/sp400. I was wondering if these would be suitable for use in the VIP as well? Obviously they have lower output so I won't be setting any speed records but I'm thinking maybe their lighter weight would compensate and perhaps allow decent flying at a more relaxed pace. Am I way off base with this? Let me know.

Thanks,
Mario
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Nov 17, 2002, 10:08 AM
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Re: 800mAh 7 Cell 5/4 AAA packs good for messing around?


Quote:
Originally posted by Sloper Mario
Obviously they have lower output so I won't be setting any speed records
Cell capacity has nothing to do with the amps a cell can put out or the power that is delivered by a motor attached to different cells. The motor will take the current it needs until the cells are discharged. The only difference will be that the duration of flight with the lower capacity cells will be less than with the HECells.

So yes. The smaller cells will work fine in the VIP and will probably give you a better overall performance because they're lighter.
Nov 17, 2002, 02:26 PM
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Sloper Mario's Avatar
Thanks for the reply Dave. I guess I didn't use correct terminology. I understand that mAh rating has nothing to do with cell resistance. By output I was referring to the motor's ability to draw power from the battery without performance degradation. Also, what do you mean by "better overall performance"? Most of the pylon folks in here define performance in terms of speed and retention of speed in turns. Certainly lighter wing loading has its advantages but speed usually isn't one of them is it?

Thanks,
Mario
Nov 17, 2002, 06:17 PM
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davidfee's Avatar
The internal resistance of a cell can make a BIG difference in the output of the motor, since V=IR. With a motor drawing I current, if R gets bigger, the voltage drop V gets bigger to compensate. A large voltage drop across the battery means less voltage available for the motor. Small V at the motor=slower speed, since it's voltage that drives the motor.

Unlike slope soaring, where gravity is your source of acceleration, e-pylon uses only the propeller for acceleration. Therefore, heavy means slow, not fast. This is because the heavier the model, the more energy is wasted just to get it moving. Furthermore, matters are made worse when you want to turn. The heavier the model, the higher the lift coefficient required to make the turn. The higher the lift coefficient, the higher the drag... and the more speed is lost.

So if you can find two batteries capable of delivering the current you need at the voltage you want... then the lighter of the two will result in the faster airplane.

good luck,
-David
Last edited by davidfee; Nov 17, 2002 at 06:22 PM.
Nov 18, 2002, 01:22 AM
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Sloper Mario's Avatar
OK so I'm a sloper boat anchor! Thanks for the good explanation David!

Mario
Nov 19, 2002, 09:55 PM
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I read somewhere in ezone that these cells may go as high as 10 amp? am I correct here?
Nov 21, 2002, 02:00 AM
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Sloper Mario's Avatar
I don't really know Tim. Actually my friend has an ampmeter. I suppose I could do a static test to see what they'll do. I'll post the results.

Mario