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Old Jun 10, 2002, 03:11 PM
CrashTest Dummy
Forney, Texas
Joined May 2002
86 Posts
Homebrew Bat Pack question



Newbie to this electric flight. Just finished a Zagi 400x. Hope to fly tonight. My question concerns building battery packs. Specifically, what are the pics and pans to using the different sizes of batteries to make a pack, other than size, configuration and weight? Re-stated, are their any gains making a 1600 mah pack from a 4/5 or sub C pack rather than say using AA's?

AA batteries seem to be cheaper per cell. So if I have 1600 mah AA's or 4/5 C (or sub C) cells to choose from, and pack configuration is not an issue........

thanks

gavin hill
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Old Jun 10, 2002, 03:33 PM
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tekochip's Avatar
West Dundee, IL, USA
Joined Jul 2001
845 Posts
Welcome to the most humbling hobby you'll ever be involved in!


The battery choice is another classic trade off.

Heavier cells tend to have larger capacities and lower internal resistance, while the lighter cells have a lower capacity and higher internal resistance.

Capacity is easy to understand, it's even in an easy to understand measurement, milliAmps per hour. Unless you're an engineer (in a previous thread it was determined that the bulk of us E pilots are) you may not understand resistance.

A battery with high internal resistance has a difficult time delivering large amounts of current. The battery delivers a lower voltage to the motor and just generates alot of heat instead of turning the prop. Sub C cells have very low internal resistance and can deliver plenty of current. Most of the batteries energy gets to the motor and turns the prop instead of generating heat for global warming.

So a bigger cell will give you more punch, but then it weighs more and you need more punch. So you have to balance weight, power, performance.

Battery chemistries have different capabilities too. NiCd cells have very low internal resistance but low capacity. NiMh cells have great capacity, but high internal resistance.

Anyway, for the Zagi, you won't want to use those NiMh AA cells because that motor will pull alot of current.
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Last edited by tekochip; Jun 10, 2002 at 03:37 PM.
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Old Jun 10, 2002, 03:58 PM
CrashTest Dummy
Forney, Texas
Joined May 2002
86 Posts
Thanks for the reply. I'm not a 'train driver' (engineer) but was studying for it. Got within 5 classes of my Aerospace Engineering degree but work and family got too complicated. Take my advice kiddies, do the school thing and then get a family/big job thing working......
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Old Jun 11, 2002, 08:47 AM
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tekochip's Avatar
West Dundee, IL, USA
Joined Jul 2001
845 Posts
No kidding, it took 10 years to get my degree going to school at night and trying to do my physics labs while chasing after a toddler. I'm the one that needed an afternoon nap.
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Old Jun 11, 2002, 10:05 AM
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Stregone's Avatar
Manassas, VA, USA
Joined Feb 2002
651 Posts
Actualy, Ah is Ampere hour. The rating is the current the battery can provide for one hour. A 3000mah (milliampere hour) battery can provide 3000 milliamps (3 amps) for one hour, a 1000mah battery can provice 1000 milliamps (1 amp) for one hour, and so on.
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